Cambridge Science Year 7 LB Lyp [PDF]

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Cambridge Lower Secondary

Science LEARNER’S BOOK 7

SA M

Mary Jones, Diane Fellowes-Freeman & Michael Smyth

Second edition

Digital access

Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. ISBN_9781108742788.

We are working with Cambridge Assessment International Education towards endorsement of this title.

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Cambridge Lower Secondary

Science LEARNER’S BOOK 7

SA M

Mary Jones, Diane Fellowes-Freeman & Michael Smyth

Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. ISBN_9781108742788.

We are working with Cambridge Assessment International Education towards endorsement of this title.

University Printing House, Cambridge CB2 8BS, United Kingdom One Liberty Plaza, 20th Floor, New York, NY 10006, USA 477 Williamstown Road, Port Melbourne, VIC 3207, Australia 314–321, 3rd Floor, Plot 3, Splendor Forum, Jasola District Centre, New Delhi – 110025, India 79 Anson Road, #06–04/06, Singapore 079906

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Cambridge University Press is part of the University of Cambridge. It furthers the University’s mission by disseminating knowledge in the pursuit of education, learning and research at the highest international levels of excellence. www.cambridge.org Information on this title: www.cambridge.org/9781108742788 © Cambridge University Press 2021

This publication is in copyright. Subject to statutory exception and to the provisions of relevant collective licensing agreements, no reproduction of any part may take place without the written permission of Cambridge University Press. First published 2012 Second edition 2021

20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 Printed in ‘country’ by ‘printer’

A catalogue record for this publication is available from the British Library

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ISBN 978-1-108-74278-8 Paperback ISBN 978-1-108-74279-5 (Digital Learner’s Book) ISBN 978-1-108-74280-1 (eBook)

Additional resources for this publication at www.cambridge.org/delange

Cambridge University Press has no responsibility for the persistence or accuracy of URLs for external or third-party internet websites referred to in this publication, and does not guarantee that any content on such websites is, or will remain, accurate or appropriate. Information regarding prices, travel timetables, and other factual information given in this work is correct at the time of first printing but Cambridge University Press does not guarantee the accuracy of such information thereafter. NOTICE TO TEACHERS IN THE UK It is illegal to reproduce any part of this work in material form (including photocopying and electronic storage) except under the following circumstances: (i) where you are abiding by a licence granted to your school or institution by the Copyright Licensing Agency; (ii) where no such licence exists, or where you wish to exceed the terms of a licence, and you have gained the written permission of Cambridge University Press; (iii) where you are allowed to reproduce without permission under the provisions of Chapter 3 of the Copyright, Designs and Patents Act 1988, which covers, for example, the reproduction of short passages within certain types of educational anthology and reproduction for the purposes of setting examination questions.

Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. ISBN_9781108742788.

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Introduction

Introduction Welcome to Stage 7 of Cambridge International Lower Secondary Science. We hope this book will show you how interesting and exciting science can be. Science is everywhere. Everyone uses science every day. Can you think of examples of science that you have seen or used today?

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Have you ever wondered about any of these questions? •

What am I made of ?

•

Where do all the dead plants, animals and their waste disappear to?

•

Why does frozen water behave differently to liquid water?

•

What happens in a chemical reaction?

•

What is electricity?

•

How did the planets form around the Sun?

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You will work like a scientist to find answers to these questions and more. It is good to talk about science as you investigate and learn. You will share your ideas with classmates to help them understand, and listen to them when you need reassurance. You will reflect on what you did and how you did it, and ask yourself: ‘would I do things differently next time?’ You will practise new skills and techniques, check your progress and challenge yourself to find out more. You will make connections between the different sciences and how they link to maths, English and other subjects. We hope you enjoy thinking and working like a scientist.

Mary Jones, Diane Fellowes-Freeman, Michael Smyth

Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior iii to publication. ISBN_9781108742788.

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Contents

Contents Page Unit

Science strand

Thinking and working scientifically strand

Science in context

Carrying out scientific enquiry Models and representations

Discuss how scientific knowledge is developed through collective understanding and scrutiny over time

1 Cells 1.1 Plant cells 1.2 Animal cells 1.3 Specialised cells 1.4 Cells, tissues and organs

Biology: Structure and Function

21 21 28 34 39 44

Chemistry: Materials and their Structure Earth and Space: Cycles on Earth Earth and Space: Planet Earth

Models and representations Carrying out scientific enquiry Scientific enquiry: analysis, evaluation and conclusions

Discuss how scientific knowledge is developed through collective understanding and scrutiny over time

50 57

2 Materials and their structure 2.1 Solids, liquids and gases 2.2 Changes of state 2.3 Explaining changes of state 2.4 The water cycle 2.5 Atoms, elements and the Periodic Table 2.6 Compounds and formulae 2.7 Compounds and mixtures

68 68 78 84 90 98 104 110

3 Forces and energy 3.1 Gravity, weight and mass 3.2 Formation of the Solar System 3.3 Movement in space 3.4 Tides 3.5 Energy 3.6 Changes in energy 3.7 Where does energy go?

Physics: Forces and Energy

Carrying out scientific enquiry Models and representations

Describe how people develop and use scientific understanding, as individuals and through collaboration, e.g. through peer review

120

4 G  rouping and identifying Biology: Life organisms processes 4.1 Characteristics of living organisms 4.2 Viruses 4.3 What is a species? 4.4 Using keys 4.5 Constructing keys

Models and representations Carrying out scientific enquiry

Evaluate issues which involve and/or require scientific understanding Discuss how science can have a global environmental impact

5 Properties of materials Chemistry: Materials and 5.1 Metals and non-metals 5.2 Comparing metals and non-metals their structure 5.3 Metal mixtures 5.4 Using the properties of materials to separate mixtures 5.5 Acids and alkalis 5.6 Indicators and the pH scale

Carrying out scientific enquiry Models and representations

Describe how science is applied across societies and industries, and in research

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1 1 6 10 15

120 123 127 131 136

144 144 150 154 162 166 172

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Contents

Page Unit

Science strand

Thinking and working scientifically strand

Science in Context

6 Earth physics 6.1 Sound waves 6.2 Reflections of sound 6.3 Structure of the Earth 6.4 Changes in the Earth 6.5 Solar and lunar eclipses

Physics: Light and Sound Earth and Space: Planet Earth

Scientific enquiry: Evaluate issues which purpose and planning involve and/or require Carrying out scientific scientific understanding enquiry Scientific enquiry: analysis, evaluation and conclusions Models and representations

226

7 M  icroorganisms in the environment 7.1 Microorganisms 7.2 Food chains and webs 7.3 Microorganisms and decay 7.4 Microorganisms in food webs

Biology: Structure and Function

Models and representations Scientific enquiry: purpose and planning Carrying out scientific enquiry Scientific enquiry: analysis, evaluation and conclusions

Describe how science is applied across societies and industries, and in research Evaluate issues which involve and/or require scientific understanding Describe how people develop and use scientific understanding, as individuals and through collaboration, e.g. through peer review

Scientific enquiry: purpose and planning Carrying out scientific enquiry Scientific enquiry: analysis, evaluation and conclusions Models and representations

Describe how science is applied across societies and industries, and in research

Scientific enquiry: purpose and planning Scientific enquiry: analysis, evaluation and conclusions Models and representations Carrying out scientific enquiry

Describe how science is applied across societies and industries, and in research

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226 231 237 242

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185 185 195 204 209 215

252 252 261 269 274

8 Changes to materials 8.1 Simple chemical reactions 8.2 Neutralisation 8.3 Investigating acids and alkalis 8.4 Detecting chemical reactions

287 287 292 297 303 310

9 Electricity Physics: Electricity and 9.1 Flow of electricity magnetism 9.2 Electrical circuits 9.3 Measuring the flow of current 9.4 Conductors and insulators 9.5 Adding or removing components

Chemistry: Properties of materials Chemistry: Changes to materials

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How to use this book

How to use this book This book contains lots of different features that will help your learning. These are explained below. This list sets out what you will learn in each topic. You can use these points to identify the important topics for the lesson.

In this topic you will: •

begin to learn about cells

• make a model of a plant cell

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• •

use a microscope to look at plant cells.

Getting started

This contains questions or activities to help find out what you know already about this topic.

Plants and animals are living organisms. They are made of units called cells. With a partner, think about answers to these questions: •

How big do you think a cell is?

•

How can we see cells?

•

Can you describe what a cell looks like?

Be ready to share your ideas with the class.

Key words stain

1.2 Plant cells

Activity 1.3.1

Sap vacuole: This is large, fluid-filled space inside a plant cell. The liquid and function in animal cells inside is a solution of sugarsStructure and other substances dissolved in water. Work with a partner. The solution is called cell sap.

You will have the opportunity to practise and develop the new skills and knowledge that you learn in each topic. Activities will involve answering questions or completing tasks.

Here is the start of a table that you can use to summarise how each kind of specialised

Chloroplast: Plant cells that animal are incell theis sunlight contain adapted tooften carry out its function. chloroplasts. This is where plants make their food. Chloroplasts look cell.substance called chlorophyll. green because they contain ablood green

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Important words are highlighted in the text when they first appear in the book. You will find an explanation of the meaning of these words in the text. You will also find definitions of all these words in the Glossary and Index at the back of this book.

Mitochondrion: All plant cells have mitochondria (singluar: Next, add entries for a neurone and a ciliated cell. Remember to give your table a title. mitochondrion). Inside mitochondria, energy is released from food.

Questions

When you are ready, copy your completed table onto a large sheet of paper, ready to be displayed.

1

of plant cell Function of cell Look at the photograph Name of the cells. What do you Specialised think the structure little green circles inside the cells are? Why are they green? What is their function?

How this helps the cell to carry out its function

2

blood cell has haemoglobin Describe four differencesred between a celltransports wall and a cell membrane.

haemoglobin carries oxygen

oxygen

in its cytoplasm

How have your tried to remember the difference between a cell wall and a cell membrane? How successful do you think you have been? Neurone

Think like a scientist Making a model of a plant cell In this activity, you will make a model to represent a cell. You will then think about the strengths and limitations of your model.

This provides an opportunity for you to practise and develop scientific enquiry skills with a partner or in groups.

Here is a list of materials and objects you could use to make your model. • transparent boxes • cardboard boxes • small and large plastic bags filled with water • green peas or green beads

• cling film (transparent food wrap)

• cardboard boxes of various sizes • empty plastic bags • purple grapes • some green grapes • Plasticine®

In your group, decide how you can use some of these materials and objects to make a model of a plant cell. Then make your model. Be ready to explain your model to others. Questions 1

Compare your model cell with the models made by other groups. Are there are any features of your model that are better than theirs? Are they any features of other groups' models that are better than yours?

2

Discuss how well your model cell represents a real plant cell.

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How to use this book

1 Cells 1 Cells

5

Young plants and animals get bigger. This is called ……………… .

a things scientist: Self-assessment 6 Think All like living break down some of the food they eat, to provide them withhow energy. Think about youThis did happens this task.in a process called ……………… . 7 ForMost things can change theyourself: shape and position of their eachliving of these statements, rate bodies. This is called ………………… .

After completing an activity, this provides you with the opportunity to either assess your own work or another student’s work.

Activity 1.1 Is aif car youalive? think you if you did it quite did it veryshows well, a car. well, or needed The picture with no help some help Here are some facts about cars.

Cars fuel of and I cut ause piece theoxygen. inside layer of onion that was about 1 cm square. Inside the engine of the car, the fuel

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•

if you didn't do it all, or needed a lot of help

• • •

This contains questions that ask you to look back at what you have covered and encourages you to think about your learning.

• ••

and to of make I wasoxygen able toprovide spread energy the piece onion flat in the the dropcar ofmove. water.

The produces waste gases,without getting I putengine the cover slip over the onion including carbon dioxide. These are any air bubbles. given off in the of the car. I saw onion cellsexhaust down the microscope

Some have sensors. For example, they sense • cars Write down one thing that didIreally well in can this I focused the microscope soyou that could see theactivity. cells when it is •dark and turn the light Write down one thing thaton youautomatically. will try to do much better next really clearly

Questions

time. How will you do this?

1 In your group, make a list of similarities between a car and Summary living checklist things. 2

I can name structuresbetween in a plantacell, what Make a listall of the differences car and anddescribe living things.

they do I can make a model of a plant cell, and discuss its strengths and limitations Summary checklist I can use a microscope to look at plant cells I can list the seven characteristics of living things

This list summarises the important material that you have learnt in the topic.

I can describe the meaning of each of these characteristics

1.2 Plant cells

Project: Cells discovery timeline

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At the end of each unit, there is a group project that you can carry out with other students. This will involve using some of the knowledge that you developed during the unit. Your project might involve creating or producing something, or you might all solve a problem together.

This project is about how scientific knowledge gradually develops over time. You are going to work in a group to do research, and then use your findings to help to make a time line. Science never stays still. When one scientist makes a new discovery, this suggests new questions that other scientists can investigate. You are going to help to produce a timeline. The timeline will show how scientists gradually discovered that 4 all living things are made of cells. 10

Here are some of the important steps that occurred. Your teacher will allocate one or two of these steps to your group. You will then help to find out more about these steps, and produce an illustrated account of what happened. Try to include an explanation of how the work of earlier scientists helped this step to take place. 1625 Galileo Galilei builds the first microscope. 1665 Robert Hooke looks at cork (from tree bark) through a microscope, and describes little compartments that he calls cells.

1 1670 Cells Anton van Leeuwenhoek improves the microscope and is able to see

living cells in a drop of pond water.

1833 Robert Brown discovers the nucleus in plant cells

These questions look back at some of the content you learnt in each session in this unit. If you can answer these, you are ready to move on to the next unit.

1838 Matthias Schleiden proposed that all plant tissues are made of cells. Theodor Schwann proposed that is also true of animal cells.

Check your Progress

1845 Carl Heinrich Braun proposed that cells are the basic unit of all life. 1 Different cells have different functions. Rudolf Virchow says all cells only arise from other describes. cells. 1855 Choosing from this list,that name the cell that each function red blood cell

2

root hair cell

palisade cell

a

Moves mucus up through the airways.

b

Absorbs water from the soil.

c

Makes food by photosynthesis.

nerve cell

ciliated cell

[3]

The diagram shows an animal cell. insert new diagram of animal cell; label A to cell membrane, label B to cytoplasm, label C to nucleus, label D to mitochondrion a

Name the parts labelled A, B, C and D.

b

Describe two ways you can tell that this is an animal cell and not a plant cell.

[4]

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1 Cells In this topic you will:

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1.1 Plant cells •

begin to learn about cells

•

find out about the parts of a plant cell, and what they do

•

make a model of a plant cell

•

use a microscope to look at plant cells.

Getting started

Plants and animals are living organisms. They are made of units called cells. With a partner, think about answers to these questions:

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• How big do you think a cell is? • How can we see cells?

• Can you describe what a cell looks like? Be ready to share your ideas with the class.

Key words

cell cell membrane cell wall cellulose chlorophyll chloroplast cytoplasm magnify mitochondria nucleus sap vacuole

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1.1 Plant cells

Cells If you study a plant by observing part of it through a microscope, you will see that it is made up of a very large number of tiny ‘boxes’. These are called cells. All living organisms are made of cells.

Parts of a plant cell

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Cells are so small that you cannot see them with your eyes alone. The photograph of the plant cells was taken through a microscope. The microscope magnifies the view of the cells, so that they look much bigger than they really are.

one cell

Part of a leaf seen through a microscope

The diagram shows a plant cell from a leaf. cell wall Every plant cell has a cell wall. The cell wall is strong and stiff. It holds the plant cell in shape. Plant cell walls are made of a substance called cellulose.

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cell membrane All cells have a cell membrane. The cell membrane is very thin and flexible. It is like the thin skin of a soap bubble. It lies along the inner edge of the cell wall. The cell membrane controls what goes in and out of the cell.

cytoplasm All cells have cytoplasm. Cytoplasm is like clear jelly. Chemical reactions happen inside the cytoplasm. These reactions keep the cell alive.

nucleus Most cells have a nucleus. The nucleus controls the activities of the cell.

sap vacuole This is a large, fluid-filled space inside a plant cell. The liquid inside it is a solution of sugars and other substances dissolved in water. The solution is called cell sap.

chloroplast Plant cells that are in the sunlight often contain chloroplasts. This is where plants make their food. Chloroplasts look green because they contain a green substance called chlorophyll.

mitochondrion All plant cells have mitochondria (singular: mitochondrion). Inside mitochondria, energy is released from food.

Diagram of a leaf cell

Questions 1

Look at the photograph of the plant cells on this page. What do you think the little green circles inside the cells are? Why are they green? What happens inside them?

2

Describe four differences between a cell wall and a cell membrane.

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1 Cells

How have you tried to remember the difference between a cell wall and a cell membrane? How successful do you think you have been? Think like a scientist Making a model of a plant cell

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In this task, you will make a model to represent a plant cell. You will then think about the strengths and limitations (weaknesses) of your model. Here is a list of materials and objects you could use to make your model. • transparent boxes • cardboard boxes

• small and large plastic bags filled with water • green peas, green beads or green grapes • transparent food wrap • empty plastic bags • purple grapes

• coloured modelling material

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In a group of three or four, discuss how you can use some of these materials and objects to make a model of a plant cell. Then make your model. Be ready to explain your model to others. Questions

1 Compare your model cell with the models made by other groups. Are there are any features of your model that are better than those in the other groups’ models? Are there any features of other groups’ models that are better than yours?

2 Discuss how well your model cell represents a real plant cell.

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1.1 Plant cells

Microscopes

eyepiece

Scientists who study living organisms often use microscopes to help them to see very small things.

coarse focussing knob fine focussing knob high-power objective lens medium-power objective lens low power-objective lens microscope stage

The diagram shows a microscope. Look at a real microscope and find all of these parts on it.

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mirror

A microscope

Think like a scientist

Looking at plant cells through a microscope

This task gives you practice in using scientific equipment and doing practical work safely. You will need:

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a microscope, a microscope slide, a cover slip, a piece of onion bulb, tweezers (forceps), a small sharp knife, a dropper pipette, a small container of water 1 Collect a small piece of onion. Cut out a piece about 1 cm square. 2 Use a dropper pipette to put a small drop of water into the middle of a clean microscope slide.

3 Very carefully, peel the thin layer from the inside of your piece of onion. 4 Gently push the layer into the drop of water on the slide. Spread it out as flat as you can. 5 Collect a very thin piece of glass called a cover slip. (Take care – cover slips break very easily!) Gently lower the cover slip over your piece of onion on the slide. Try not to get air bubbles under the cover slip. 6 Turn the objective lenses on the microscope until the smallest one is over the hole in the stage.

7 Put the slide onto the stage of the microscope, with the piece of onion over the hole.

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1 Cells

Continued  8 Look down the eyepiece. Slowly turn the focussing knob to move the lens away from the slide. Stop when the piece of onion comes into focus. 9 Make a drawing of some of the cells you can see. Questions 1 Suggest why the cells from the onion do not look green.

Self-assessment

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2 Describe any difficulties you had with this activity. How did you solve them?

Think about how you did this task.

For each of these statements, rate yourself.

if you think you did it very well, with no help

if you did it quite well, or needed some help

if you didn't do it all, or needed a lot of help

• I cut a piece of the inside layer of onion that was about 1 cm square.

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• I was able to spread the piece of onion flat in the drop of water.

• I put the cover slip over the onion without getting any air bubbles.

• I saw onion cells down the microscope.

• I focussed the microscope so that I could see the cells really clearly.

• Write down one thing that you did really well in this activity. • Write down one thing that you will try to do much better next time. How will you do this? Summary checklist

I can name all the structures in a plant cell, and describe what they do. I can make a model of a plant cell, and discuss its strengths and limitations. I can use a microscope to look at plant cells.

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1.2 Animal cells

1.2 Animal cells In this topic you will: • find out how animal cells differ from plant cells • use a microscope to look at some animal cells. Key words

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Getting started

There are five parts of a plant cell with names beginning with the letter c.

stain

Make a list of these five parts. Think about how you can remember what each of the words means.

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Be ready to share your ideas.

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1 Cells

Parts of an animal cell All animals are made of cells. You are an animal, and your body is made of cells. No one knows exactly how many cells there are in a person. One estimate is about 100 trillion. That is 100 000 000 000 000 cells.

cell membrane cytoplasm mitochondrion nucleus

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Animal cells are similar to plant cells in several ways. They have a cell membrane, cytoplasm and a nucleus.

An animal cell

Think like a scientist

Looking at animal cells through a microscope

This task gives you more practice in using scientific equipment safely. You will need:

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a microscope, a microscope slide, a cover slip, a cotton bud, some methylene blue, a dropper pipette

1 Very gently rub the cotton bud along the inside of your cheek. This will collect some loose cells.

2 Rub the cotton bud on the surface of a clean microscope slide. You will not be able to see the cells yet, because they are so small.

New version of this with Zara's hair tied up was supplied in July. AW_U1_WB_06 is suitable, even though it seems allocated to the Workbook. Tech-Set:- AW_U1_WB_06 is a black and white version of the same artwork! Please advise

3 Use a dropper pipette to add a drop of methylene blue to the cells. Methylene blue is a dye that will stain the cells blue, making them easier to see. 4 Carefully lower a cover slip over the drop of blue stain. 5 Put the smallest objective lens over the stage. 6 Put the slide onto the stage, with the part you want to look at over the hole in the stage. 7 Looking from the side, turn the focussing knob until the lens is close to the slide.

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1.2 Animal cells

Continued 8 Look down the eyepiece. Slowly turn the focussing knob to move the lens upwards. Stop when you can see the cells. 9 Turn the lenses until a larger one is over the stage. Look down the eyepiece. You should be able to see a more magnified view of the cells.

Questions

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10 Make a drawing of one or two of the cells you can see. Label your drawing.

1 The photographs show some cells, seen through a microscope.

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For each photograph, decide whether the cells are plant cells or animal cells. Explain your decision.

2 Think about the model of a plant cell that you made. What would you change to make it into a model of an animal cell?

Activity

Building up pictures of plant and animal cells You will need:

• fifteen cut-out oval pieces of card or paper, each about 1 cm long, five coloured red and ten coloured green • one cut-out circular piece of grey card or paper, about 1 cm in diameter

• long pieces of string or wool • a long piece of wide tape

• glue or double-sided sticky tape • a very large sheet of paper

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1 Cells

Continued 1 In a group of two or three, use the materials to build a picture of a plant cell. It is up to your group to decide exactly how to use the materials to make your picture. You may not want to use all of the materials. 2 Ask your teacher, or other people in your class, to check that you have put all the right pieces in the right places.

Self assessment

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3 Now remove some of the pieces, to change your picture into an animal cell.

Compare your picture with the pictures made by other groups. What differences are there between them?

Now that you have seen the other pictures, is there anything you would like to change in yours?

• What have you done that helps you to remember the differences between animal cells and plant cells?

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• Do you think that you can always decide whether a picture shows an animal cell or a plant cell? What is the most important feature to look for? Summary checklist

I can use a microscope to look at animal cells. I can describe similarities and differences between plant cells and animal cells. I can decide whether a picture of a cell shows an animal cell or a plant cell, and give reasons.

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1.3 Specialised cells

1.3 Specialised cells In this topic you will: • learn about some specialised animal and plant cells

Getting started

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• explain how the structure of these specialised cells helps them to carry out their functions.

With a partner, think of a suitable way to complete each sentence. • Cell membranes … • Cell walls … • A nucleus … • Chloroplasts …

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Be ready to share your ideas with the rest of the class.

Key words

absorb adapted axon capillary cilia ciliated cell dendrite function haemoglobin mucus neurone palisade cell pigment red blood cell root hair cell specialised

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1 Cells

Some specialised animal cells Not all of the cells in your body are the same. There are many different kinds of cell in your body. Each kind of cell has a particular function. The function of a cell is the job that it does, or the role that it plays. Each cell is specialised to carry out its function. This means that it has a structure that helps it to do its function really well. The cell is adapted to carry out its function.

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The diagrams show three kinds of specialised cell in the human body. Red blood cells are smaller than most other cells in the body. This allows them to get through tiny blood capillaries, so they can deliver oxygen to every part of the body.

The cytoplasm contains a red pigment (colour) called haemoglobin. This carries oxygen around the body. The cell has no nucleus. This leaves more space for haemoglobin. Neurones carry electrical signals from one part of the body to another. They help all the different parts of the body to communicate with each other. For example, they can carry signals from the brain to muscles, to make the muscles move.

nucleus

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cytoplasm

Red blood cells

cytoplasm

cell membrane

The axon is a very long strand of cytoplasm. Electrical signals can travel along this very quickly.

Dendrites are short strands of cytoplasm that collect electrical signals from other nearby nerve cells.

cell membrane

dendrite

axon

Neurones

Ciliated cells have tiny threads along one edge, like microscopic hairs. These are called cilia. The cilia can move. One place in the body that contains ciliated cells is the lining of the tubes leading from your mouth to your lungs. Other cells in this lining make a sticky substance called mucus. When you breathe in, the mucus traps dust and bacteria in the air, to stop them going into your lungs. The cilia sweep the mucus up to the back of your mouth and you swallow it.

cilia cell membrane nucleus cytoplasm Ciliated cella

Questions

1 List two things that red blood cells, neurones and ciliated cells have in common. 2 How can you tell that all of these three cells are animal cells, not plant cells?

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1.3 Specialised cells

Activity 1.3.1 Structure and function in animal cells Work with a partner. Here is the start of a table that you can use to summarise how each kind of specialised animal cell is adapted to carry out its function. Copy the start of the table onto a piece of paper. Then complete the entries for the red blood cell.

PL E

You could include a small drawing of a red blood cell underneath its name in the first column. Next, add entries for a neurone and a ciliated cell. Remember to give your table a title. When you are ready, copy your completed table onto a large sheet of paper, ready to be displayed.

Function of cell

Specialised structure

How this helps the cell to carry out its function

red blood cell

transports oxygen

has haemoglobin in its cytoplasm

haemoglobin carries oxygen

SA M

Name of cell

Neurone

Some specialised plant cells

Plants also contain specialised cells. Here are two examples. Root hair cells are found on the outside of plant roots.

Their function is to absorb (soak up) water from the soil. Each cell has a long, thin extension that allows water to move easily from the soil into the cell.

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1 Cells

cell wall

nucleus

cell membrane cytoplasm

A root hair cell

PL E

large vacuole with cell sap

Palisade cells are found in the leaves of plants. Their function is to make food by photosynthesis. They have a lot of chloroplasts containing chlorophyll.

The chlorophyll absorbs energy from sunlight, which is used to help the plant make food. cell wall

cell membrane

SA M

mitochondrion

cytoplasm

chloroplast

nucleus

A palisade cell

Questions

3 Suggest why root hair cells do not contain chloroplasts. 4 Water moves through several parts of the root hair cell, as it goes from the soil into the sap vacuole. List these parts, in order.

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1.3 Specialised cells

Activity 1.3.2 Structure and function in plant cells Make a table to summarise how the structures of the two kinds of specialised plant cell are related to their functions. Peer assessment Exchange your table with a partner.

if you think they did it very well

PL E

For each of these statements, rate your partner’s work.

if they did it quite well, but it if they didn't do it all, or it could be improved needs a lot of improvement.

• They made a clear table with ruled lines.

• They gave the columns in the table headings to make clear what each one shows. • They headed the rows in the table with the names of the two kinds of plant cell. • They wrote short, very clear descriptions of how the cell is specialised.

SA M

• The table is very clear and you can understand it easily. Summary checklist

I can name three kinds of specialised animal cell, and two kinds of specialised plant cell. I can explain how the structure of each kind of specialised cell is related to its function. I can design and construct a table to summarise information.

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1 Cells

1.4 Cells, tissues and organs In this topic you will: • find out about tissues, organs and organ systems in living organisms

Getting started

PL E

• recognise and name human organs that are part of different organ systems.

Draw an outline of a human body.

Sketch and label each of these organs on the outline.

brain  heart  stomach  intestine  lungs Key words

   organ system   organism    palisade layer    spongy layer

tissue upper epidermis

SA M

ciliated epithelium lower epidermis onion epidermis organ

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1.4 Cells, tissues and organs

Tissues Living things, including animals and plants, are called organisms. There are many different kinds of cell in an animal or a plant. Most of them are specialised to carry out a particular activity. Usually, many cells of the same kind are grouped together. A group of similar cells, which all work together to carry out a particular function, is called a tissue.

PL E

The diagrams show a tissue from a plant, and a tissue from an animal. This is a diagram of a tissue from inside an onion. It is called an onion epidermis. This tissue covers the surface of the layers inside the onion.

SA M

Onion epithelium

This is a diagram of ciliated epithelium – the tissue that lines the tubes leading down to our lungs. The cilia all wave together, like grass in the wind. cilia

nucleus

Ciliated epithelium

Questions

1 What is the function of the ciliated epithelium tissue? (Think about the function of a ciliated cell.) 2 The word ‘tissue’ has an everyday meaning and a different scientific meaning. Write two sentences, one using the word ‘tissue’ with its everyday meaning, and one using the word ‘tissue’ with its scientific meaning.

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1 Cells This is part of a leaf, cut open. A leaf is a plant organ,

Organs and organ systems and contains several different kinds of tissue. The bodies of plants and animals contain many different parts, called organs. For example, your organs include your brain, heart and muscles. Plants’ organs include leaves, roots and flowers.

palisade layer

PL E

Each organ is made up of several different kinds of tissue, working together. For example, your brain contains neurones, and also several other kinds of cell. A plant root contains root hair cells, and also several other kinds of cell.

upper epidermis

spongy layer

lower epidermis

This is part of a leaf, cut open. A leaf is a plant organ, and contains several different kinds of tissue.

Organs also work together. A set of organs that all work together to carry out the same function is called an organ system. Activity 1.4.1

SA M

Organs and systems in humans

Your task is to find out the names and functions of the different organs that are part of one system in the human body. Choose from: digestive system, circulatory system, respiratory system or skeletal system. When you have found this information, decide how to display it. Perhaps you could make a presentation, or a large drawing with labels and descriptions.

Question

3 Copy and complete each sentence, using words from the list. organism  tissue  organ  organ system

A group of similar cells is called a

.

An

is a structure made of many different tissues.

An

is a group of organs that carry out a particular function.

An is a living thing. It may contain many different organ systems, organs and tissues.

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1.4 Cells, tissues and organs

Summary checklist I can give examples of tissues and organs in animals and plants. I can explain the meanings of the words tissue, organ and organ system.

Project: Cells discovery timeline

PL E

This project is about how scientific knowledge gradually develops over time. You are going to work in a group to do research, and then use your findings to help to make a timeline.

Science never stays still. When one scientist makes a new discovery, this suggests new questions that other scientists can investigate.

You are going to produce a timeline. The timeline will show how scientists gradually discovered that all living things are made of cells.

The list below shows some of the important steps that occurred. In your group, choose one of these steps to investigate. Make sure that you do not choose the same step as another group.

SA M

Help your group to find out more about this step. Then help to produce an illustrated account of what happened.

This is the type of microscope that Robert Hooke used.

Try to include an explanation of how the work of earlier scientists helped this step to take place. 1625  Galileo Galilei builds the first microscope. 1665 Robert Hooke looks at cork (from tree bark) through a microscope, and describes little compartments that he calls cells. 1670 Anton van Leeuwenhoek improves the microscope and is able to see living cells in a drop of pond water.

1833  Robert Brown discovers the nucleus in plant cells 1838 Matthias Schleiden proposes that all plant tissues are made of cells. Theodor Schwann proposes that is also true of animal cells.

1845  Carl Heinrich Braun proposes that cells are the basic unit of all life. 1855  Rudolf Virchow says that all cells only arise from other cells.

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1 Cells

Check your Progress 1.1 Different cells have different functions. Name the cell that carries out each function. Choose from the list.

PL E

red blood cell  root hair cell  palisade cell  neurone  ciliated cell a

Moves mucus up through the airways.

[1]

b

Absorbs water from the soil.

[1]

c

Makes food by photosynthesis.

[1]

1.2 The diagram shows an animal cell. A B

SA M

C D

a

Name the parts labelled A, B, C and D.

b

Describe two ways you can tell that this is an animal cell and not a plant cell. [2]

[4]

1.3 The diagram shows a plant cell. A

B

C

D

E

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1 Cells

For each letter, A–E, write the name of the cell part and its function. Choose from these lists:

[5]

Names: mitochondrion  cell membrane  nucleus  cell wall  chloroplast Functions:

PL E

holds the cell in shape

controls what goes in and out of the cell where photosynthesis takes place

where energy is released from nutrients controls the activities of the cell

SA M

1.4 The diagram shows a specialised cell from the human body.

a

What is the name of this cell?

[1]

b

What is the function of this cell?

[1]

c

Describe how the cell is adapted to carry out its function.

[1]

d

Name the system in the human body that this cell is part of.

[1]

1.5 These sentences are about the way that cells are grouped together in complex organisms. Copy and complete each sentence. Choose from the list. cell  tissue  organ  organ system

a

In a complex organism, such as a human or a plant, similar cells are grouped . together to form a

b

The stomach is an example of an

c

The heart and blood vessels are all part of the same

[1] [1]

. .

[1]

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2 Materials and their structure In this topic you will:

PL E

2.1 Solids, liquids and gases • sort the states of matter into solids, liquids and gases

• learn about the properties of solids, liquids and gases

• use particle theory to describe the structure of solids, liquids and gases

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• use particle theory to learn about the properties of solids, liquids and gases.

SA M

Getting started

1 Name two solids, two liquids and two gases. 2 Copy and complete the table. Use the substances you listed in Question 1. Discuss your reasons for each decision with your group. Substance

Solid, liquid or gas

Example: tap water liquid

I know this because…

I can pour it.

Key words

compressed flow hypothesis matter particle pour property states of matter theory vacuum vibrate volume

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2.1 Solids, liquids and gases An updated version of this was received in July

Looking at states of matter

Tech-Set:- Please advise as this is version we have received

Everything you can see and feel is called matter. Scientists sort matter into three groups or states called ‘solids’, ‘liquids’ and ‘gases’. These states of matter behave in different ways. The ways they behave are called their properties.

Solids

Liquids

PL E

Solids keep the same shape. Solids take up the same amount of space. Solids keep the same volume. Solids cannot be compressed (squashed) or poured.

Liquids take the shape of the container they are in. Liquids can be poured. Liquids cannot be compressed. Liquids take up the same amount of space, whatever shape their container.

An updated version of this was received in July (He should be wearing safety glasses and a lab coat.)

The volume of a liquid does not change.

SA M

Gases

Gases flow like liquids. They will fill any closed container they are in. Gases are very easy to compress. The volume of a gas can change. Gases weigh very little. Generally, you cannot see or feel gases, but you can sometimes smell them, and you can feel air moving on your face.

Tech-Set:- Please advise as this is version we have received

100cm

50cm

100cm

50cm 0cm

0cm

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2 Materials and their structure

Questions 1 What are the three states of matter? 2 Which state of matter can be compressed (squashed) easily? 3 Which state of matter cannot be poured? 4 List the properties of solids. 5 Name a property of liquids that they do not share with solids.

PL E

6 Name a property of gases that they share with liquids. 7 Name a property of gases that they do not share with solids or liquids.

Scientists look at what matter does

Scientists try to explain what they see. Here are some examples of how matter behaves that scientists have tried to explain. You can smell food cooking in another room.

•

Some substances get bigger when you heat them.

•

Liquids, such as water, change to a gas when you heat them.

•

Substances change from liquid to solid if you cool them.

SA M

•

Scientists think about why these things happen and try to come up with ideas to explain it. They form an hypothesis, which is a suggestion for an explanation. This hypothesis can then be tested by carrying out more investigations. When an hypothesis has been tested and widely accepted as valid by other scientists, it is called a theory. The best theory to explain how matter behaves uses the idea of particles. Particles are tiny portions of matter. This theory says that all matter is made up of tiny particles arranged in different ways.

Particle theory

All matter is made up of tiny particles that are much too small to see. The particles are arranged differently in solids, liquids and gases.

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2.1 Solids, liquids and gases

Solids In solids the particles are arranged in a fixed pattern. The particles are held together strongly and are tightly packed together. This is why solids have a fixed shape. The particles in a solid can vibrate (make small movements) but they stay in the same place.

Liquids

PL E

In solids the particles are packed together and can vibrate. They stay in the same place.

In liquids the particles touch each other. The particles are held together weakly. The particles can move past one another but they still touch each other. Liquids can change shape.

SA M

In liquids the particles touch each other, can move and can change places.

Gases

In gases the particles do not touch each other. They are a long way apart. The particles spread out by themselves. The particles can spread out to fill up the space they are in. Gases can change shape.

In gases the particles are far apart and can move about freely.

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2 Materials and their structure

Think like a scientist Modelling the particles in solids, liquids and gases In this task, you will describe the strengths and weaknesses of a model. Work in a small group. • Arrange yourselves in a pattern, as if you are the particles in a solid. • Now arrange yourselves as if you are the particles in a liquid. Questions

PL E

• Now arrange yourselves as if you are the particles in a gas. 1 With a partner, discuss and describe the ways in which the particles are arranged in the three states of matter. 2 Copy and complete these sentences to describe how particles are arranged in solids, liquids and gases. • In solids, the particles are arranged

• In liquids, the particles are arranged • In gases, the particles are arranged Self-assessment

SA M

In what ways was your group a good model for the particle theory? Think about how well you did for each of the solid, liquid and gas models.

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• Were you in regular rows?

• Were you touching the people around you? • Could you change your position?

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2.1 Solids, liquids and gases

Explaining the properties Matter can only flow (be poured) if the particles can move past one another. Matter can only change volume if the particles in it can spread out or move closer together.

Solids

Liquids

PL E

The particles in a solid are very close together. This makes it difficult for the volume of a solid to be made smaller. Solids have a fixed shape because attractive forces hold the particles together. These forces stop the particles from moving around. The particles can only vibrate. This means that a solid cannot flow.

Solids cannot flow.

SA M

The volume of a liquid cannot be changed. The particles are very close together and cannot be squashed. The particles touch each other but they can move past each other. The attractive forces between the particles are weak enough to allow them to move but strong enough to hold them together.

Liquids can flow.

Gases

Particles in a gas are a long way apart so they can move quickly in all directions. The particles can move easily because there are no attractive forces between them. This means that gas has no fixed shape or volume. When you squash a gas, the particles move closer together and the gas takes up less space.

No particles?

A space where there are no particles at all is called a vacuum. A vacuum contains nothing.

Gases can flow and spread out.

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2 Materials and their structure

Think like a scientist Particle theory Scientists observe the world around them and think carefully about what they see. Development of the particle theory was based on the observations that scientists made about how solids, liquids and gases behave.

Questions

PL E

Scientists saw that most solids cannot be compressed. Can you think of any solids that do not fit the rules of particle theory? Think about the properties of a sponge or a marshmallow. Can a sponge be compressed? 1 Use particle theory to explain how a sponge can be a solid, but it can also be compressed.

2 How well does particle theory explain the properties of solids, liquids and gases? 3 What are the strengths of the particle theory?

4 What are the weaknesses of the particle theory? Activity States of matter

SA M

On a large piece of paper, draw three large squares and label them ‘solid’, ‘liquid’ and ‘gas’, like this. Leave space around them. Solid

Liquid

Gas

In each square, draw how the particles are arranged in that state of matter. In the spaces around the squares, write the properties of the three states of matter.

Summary checklist

I can classify matter as a solid, liquid or gas. I can list the properties of solids, liquids and gases. I can describe the way in which particles are arranged in solids, liquids and gases. I can explain the properties of solids, liquids and gases using particle theory.

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2.2 Changes of state

2.2 Changes of state In this topic you will: • practise measuring the volume and the temperature of a liquid • learn what happens when matter changes state

Getting started

PL E

• investigate the temperature increase when you heat water.

With a partner, draw three diagrams to show the particle structure of a solid, a liquid and a gas.

SA M

Be ready to show the class when you are asked to do so.

Key words

boil boiling point change of state condensation condense evaporation freeze measuring cylinder melt melting point meniscus steam thermometer water vapour

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2 Materials and their structure

Changing state If you leave ice in a warm place it melts and becomes liquid water. The temperature at which a solid melts is called the melting point. Water on the ground will gradually disappear as it changes to water vapour, an invisible gas. This is called evaporation. The warmer the water, the more quickly it evaporates.

PL E

If you heat water until its temperature reaches 100 °C, it will boil. All of the water rapidly changes to steam. Steam is water heated to the point that it turns into a gas. 100 °C is the boiling point of water.

If the water vapour or steam touches something cold, it condenses and changes back to liquid water. This is called condensation. If you put liquid water in the freezer, it freezes and becomes ice. These changes are known as changes of state.

steam

water

melting

SA M

boiling

ice

condensing

freezing

Activity 2.2.1

Which change of state? Work in pairs.

Cut out nine rectangles from a piece of A4 card. Write these words onto the cards: melt, freeze, condense, boil, liquid, gas, solid, from, to. One of you should have the change of state cards (melt, freeze, condense, boil). The other should have the remaining cards (liquid, gas, solid, from, to). Hold up a change of state card. Your partner should then select the correct cards to show which state is changing to which other state. For example: ‘freeze’ would be from ‘liquid to solid’. Swap the sets of cards so that you take turns.

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2.2 Changes of state

Measuring Measuring volume

meniscus

PL E

When you measure the volume of a liquid you use a measuring cylinder. The liquid forms a curve at the top. This is called the meniscus. You measure the volume from the bottom of the meniscus. To do this, you must make sure that your eye is level with the meniscus.

°C

Measuring the volume of water in a measuring cylinder.

Measuring temperature

SA M

When you measure the temperature you use a thermometer. The liquid inside the thermometer expands as it gets hotter, so it rises up inside the thermometer. You read the temperature from the scale. Make sure that your eye is level with the top of the liquid in the thermometer.

A thermometer

Questions

1 Look at the diagram. What is the volume of water in each measuring cylinder? A

B

C

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2 Materials and their structure

2 What are the temperatures shown on the thermometers? B

C

SA M

PL E

A

Think like a scientist

Measuring the temperature when you heat water In this task you will take accurate measurements. You will need:

beaker, Bunsen burner, clamp stand, gauze, measuring cylinder, thermometer, tripod

Safety

Wear safety spectacles. Take care when handling hot water. Work in groups of two or three. Before you start the activity, discuss in your group what other safety measures you will take. Check these with your teacher.

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2.2 Changes of state Updated artwork was supplied in July with the boy wearing a lab coat. However, there are other changes that need to be made. See below.

Continued  safety spectacles

Tech-Set:- Equipment labeling and corrections have been made. Changes to Arun ie wearing a lab coat not actioned as we have not recieved this version of him.

clamp stand with boss beaker

PL E

gauze

bunsen burner

stopwatch

measuring cylinder

tripod

heat-proof mat

SA M

1 Accurately measure of water into a beaker.

2 Place a thermometer with its bulb in the water. Use a clamp stand, as shown in the illustration. This is so that you measure the temperature of the water, not the temperature of the bottom of the beaker.

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3 Measure the temperature.

4 Record this in a table. (Copy and extend the one below.) Time in minutes

Temperature in °C

0 1 2 3 4

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2 Materials and their structure

Continued  5 Heat the water. 6 Use the thermometer to measure the temperature every minute. 7 Repeat until the water is boiling vigorously. Questions

PL E

1 Plot your temperature measurements on a graph. Put the time along the horizontal axis and the temperature on the vertical axis. 2 Describe your graph. You could complete these sentences. • When we heated the water, the temperature • The longer we heated the water, the

the temperature

• The increase in temperature was

You could mention how quickly the temperature increased and if the temperature increased by the same amount each minute. 3 What happened to the temperature of the water when it was boiling? 4 Why do you think this happened?

SA M

5 The thermometer is held in the water so that it does not rest on the bottom of the beaker. Why?

• Describe any problems you had with this investigation. How did you solve them? • Think about how you carried out this investigation. What did you do to keep safe? Could you have made the investigation any safer? Summary checklist

I can name the three states of matter. I can use the correct terms to say how water changes from solid to liquid to gas. I can use a thermometer and a measuring cylinder accurately. I can carry out an investigation safely.

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2.3 Explaining changes of state

2.3 Explaining changes of state In this topic you will:

PL E

• use the particle theory to explain what happens when matter changes between states • use a model to illustrate the particle theory. Getting started

Key words

1 For each process, write down the changes of state. The first one has been started for you. • Melting: solid to • Condensing: • Freezing:

attractive force expand heat energy transferred

SA M

2 For each statement, decide if it applies to a solid, a liquid or a gas. Some may apply to more than one state of matter. particles in regular rows

can be poured

can be compressed

particles spread out

has a fixed volume

can change its shape

cannot be compressed

has a fixed shape

Check with a partner. Are you correct?

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2 Materials and their structure

Changes of state Heating solids When solids are heated they expand (get bigger). The particles in solids are arranged in a fixed pattern. The particles are held together strongly and are tightly packed.

Melting solids

PL E

The particles in the solid vibrate. When the solid is heated, heat energy is transferred to the particles in the solid. The more energy the particles have, the more they vibrate. As the particles vibrate more, they take up more space. The particles are still held in position by the attractive forces between them.

When solids are heated more strongly, they melt. They become liquid. (Heating more strongly means that even more heat energy is transferred to the particles.)

When a solid is heated, the particles vibrate more and take up more space.

SA M

The particles in a solid vibrate more and more as heat energy is transferred to them. The particles vibrate so much that the attractive forces between them are not strong enough to hold them in a fixed pattern. The particles can slide past one another – they can now move, not just vibrate. The forces are still strong enough for the particles to stay in touch with one another. The more the liquid is heated, the more energy is transferred to the particles and the more the particles vibrate and move.

The particles vibrate so much that some escape the strong forces and can move around as a liquid.

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2.3 Explaining changes of state

Boiling liquids When liquids are heated, they evaporate and boil. The particles in liquids touch each other. The particles are held together weakly.

Cooling gases

The particles move so quickly that some escape as a gas.

PL E

The particles move more as heat energy is transferred to them. Some particles have enough energy to break the weak attractive forces holding them together. These particles can move freely and escape as gas particles.

cold surface

The particles in a gas are free to move anywhere and spread out. There are no forces holding them. When a gas gets cooler it condenses to form a liquid. When gas particles reach a cold surface, some of the heat energy from the particles transfers to the surface. The particles move less and get closer together. They form a liquid.

SA M

Freezing liquids

When a liquid freezes it becomes a solid.

The particles in a liquid can move and flow past each other. As heat energy is transferred from the particles to the surroundings, the particles move more slowly and the liquid gets cooler.

The cooler the liquid, the less energy the particles have. The less energy the particles have, the less able they are to move or slide past one another. Eventually, the particles have so little energy they cannot move and flow anymore – they can only vibrate. They become arranged in a fixed pattern to form a solid.

When the particles hit a cold surface, their movement slows down.

Particles in a liquid (left). Particles in a solid (right).

Questions

1 Explain why a solid expands when it is heated.

2 Use particle theory to explain why solids and liquids cannot be compressed (squashed into a smaller volume). 3 Use particle theory to explain why liquids and gases can flow.

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2 Materials and their structure

4 Use particle theory to explain how a liquid changes to a gas. 5 Use particle theory to explain how a liquid changes to become a solid. 6 Use particle theory to explain what happens when steam in the bathroom hits a cold surface, such as a mirror. 7 Copy this flow chart. The arrows represent the processes involved when matter changes state. Add the name for each process, A–D. gas

PL E

liquid

solid

A ……….…....

B ……….…....

liquid

solid

C ……….…....

Think like a scientist

gas

D ……….…....

Modelling changes of state

In this task, your class will model the changes of state by arranging yourselves as particles. You will need a lot of space.

SA M

Solid to liquid

• As a class, arrange yourselves as if you are the particles in a solid. • Imagine the particles are being heated. Move as if you are being heated gently. Move as the particle theory suggests you should.

• Imagine the particles are now being heated strongly, so that the solid melts and becomes a liquid. Remember to behave as the particle theory suggests you should. Question

1 Describe how you had to act to illustrate the behaviour of particles as a solid melts. Think about how you behaved. Was the model a good or a bad model for particle theory? Explain. Liquid to gas

• As a class, arrange yourselves as if you are the particles in a liquid. • Imagine the particles are being heated. Move as if you are being heated gently.

• Imagine the particles are now being heated strongly so that the liquid boils. Remember to behave as the particle theory suggests you should.

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2.3 Explaining changes of state

Continued  Question 2 Describe how you had to act to illustrate the behaviour of particles as a liquid evaporates and then boils. Think about how you behaved. Was the model a good or a bad model for particle theory? Explain. Gas to liquid

PL E

• As a class, arrange yourselves as if you are the particles in a gas.

• Imagine part of the room is a cold surface. As you move near to the surface you must behave as particle theory suggests. You should start to condense to form a liquid. Question

3 Describe the way you had to behave to illustrate the behaviour of particles as a gas condenses. Think about how you behaved. Was the model a good or a bad model for particle theory? Explain. Liquid to solid

• As a class, arrange yourselves as the particles in a liquid. Make sure you move as particle theory suggests.

SA M

• Now imagine the liquid has been placed in a freezer. Behave as particle theory suggests, as you become a solid. Question

4 Describe the way you had to behave to illustrate the behaviour of particles as a liquid freezes to form a solid. Think about how you behaved. Was the model a good or a bad model for particle theory? Explain.

• How did you learn and remember the structure of solids, liquids and gases as states of matter? Summary checklist

I can describe how particles behave, depending on how much energy they have. I can explain that energy can be transferred to or from particles. I can describe the effects of the energy on the forces holding the particles together.

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2 Materials and their structure

2.4 The water cycle In this topic you will: • learn about the water cycle • use scientific words to describe stages of the water cycle. Key words

PL E

Getting started

Spend one minute thinking about where rain comes from. Then spend two minutes discussing your ideas with a partner.

SA M

Now write down your ideas and show them to your teacher.

atmosphere groundwater open water precipitation surface run-off transpiration water cycle water vapour

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2.4 The water cycle

The water cycle Water is vital for all living things. Our bodies are made up of at least 60% water.

PL E

Water on Earth is constantly moving. The water moves between rivers, lakes, oceans, the atmosphere and the land. It is recycled over and over again in a continuous system called the water cycle. You are still using the same water that the ancient Greeks and the Romans used. The Earth has been recycling water for more than four billion years.

condensation

precipitation

SA M

evapotranspiration

evaporation

oceans

streamflow water

groundwater flow

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2 Materials and their structure

What happens during the water cycle? Water moves into the atmosphere

PL E

Energy from the Sun heats the Earth and the temperature of the water in the rivers, lakes and oceans increases. When this happens, some of the liquid water forms water vapour. This is called evaporation. This happens because some of the particles in the liquid water gain enough energy to break free from the forces holding them together and they change to a gas. Water can also evaporate into the atmosphere from plants; this is called transpiration.

Water in the atmosphere cools down

As the water vapour goes up into the atmosphere, it cools and changes back into little droplets of water in the air, forming clouds. This process is called condensation. It happens because the particles in the water vapour lose energy and cannot move so quickly. Air currents high in the atmosphere move the clouds around the world.

SA M

Water falls from clouds

When a lot of water has condensed, the water droplets in the clouds become too heavy for the air to hold them. The droplets fall back to Earth as rain. If the drops become colder they may form snow, hail or sleet. This process is called precipitation.

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2.4 The water cycle

Water falls on the Earth The precipitation that falls then collects in rivers and open water such as large lakes and the oceans. How it is collected depends on where it lands. Some precipitation will fall directly onto the rivers, lakes and oceans and will evaporate, then the cycle starts again.

PL E

If the precipitation falls on plants it may evaporate from the leaves back to the atmosphere or trickle down to the ground. The plant roots in the ground may then take up some of this water.

Water in the ground

Some of the water from precipitation will soak into the soil and rocks as groundwater. Some of this water will stay in the shallow soil layer and will move towards streams and rivers. When groundwater soaks deeper into the soil, it refills underground stores.

SA M

In cold climates the precipitation may build up on land as snow, ice or glaciers. If the temperatures rise, this solid snow and ice will melt into liquid water, which soaks into the ground or flows into rivers or the ocean. Some of the precipitation will soak into the soil and move through the ground until it reaches the rivers or the open water, large lakes and the oceans. Water that reaches the surface of the land may flow directly across the ground into the rivers, lakes and oceans. This water is called surface run-off. When there is a lot of surface run-off, soil can be carried off the land and into the rivers. This can cause them to become silted up and blocked. Activity 2.4.1

Water cycle poster

Make a poster to show the water cycle. Remember to use the scientific terms. You should make your poster as clear and colourful as you can.

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2 Materials and their structure

Continued Peer assessment Swap your poster with someone else in your class. What do you like about their poster? Think of at least two things. How could they improve their poster?

Questions 2 How does rain form?

PL E

1 What are the different types of precipitation?

3 Use particle theory to explain how a pool of water on the road disappears. 4 Where does your drinking water come from?

5 What methods have people used to ensure they always have a supply of water? You may need to do some research. 6 What do we use water for in our bodies? 7 What other things do we use water for?

SA M

8 Think about all the water you used today. Try to work out how much water you use in one day. Summary checklist

I can use scientific vocabulary to describe the water cycle. I can use particle theory to explain what happens in each part of the water cycle.

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2.5 Atoms, elements and the Periodic Table

2.5 Atoms, elements and the Periodic Table In this topic you will: • learn what an atom and an element are

PL E

• find out about different atoms and elements • learn about the Periodic Table

• use symbols to represent the names of elements. Getting started

1 Draw a diagram to show how particles are arranged in a solid and explain how the arrangement of particles changes when the solid melts.

SA M

2 What do you need to do to a solid to make it melt?

Key words

atom element group metals nanotube non-metal period symbol The Periodic Table

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2 Materials and their structure

What are atoms? Over 2000 years ago, a Greek philosopher called Democritus suggested that everything was made up of tiny pieces. Democritus suggested that, if you could keep on cutting up a substance into smaller and smaller pieces, you would end up with a very small piece that could not be cut up any more.

PL E

Democritus called his tiny pieces of matter atoms. Atom means ‘cannot be divided’. We now know that atoms really do exist. Today we can even see some of the large kinds of atom, using special microscopes called scanning tunnelling microscopes. The photograph shows the atoms in some carbon nanotubes. (Nano means ‘very, very small’.)

Nanotubes

Different types of atom

There are many different types of atom. Scientists have discovered 94 different types of atom that occur naturally in the universe. Another 24 kinds of atom have been made in laboratories.

SA M

Some substances are made up of just a single kind of atom. A substance made of just one kind of atom is called an element. For example, carbon is made only of carbon atoms. Gold is made only of gold atoms. Silver is made only of silver atoms. Carbon, gold and silver are examples of elements. Each type of atom has different properties. This is why different elements have different properties.

These rings are made from pure silver.

If you could see some of the atoms in the silver ring, they would look something like this.

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2.5 Atoms, elements and the Periodic Table

Questions 1 What are atoms? 2 If there are 94 different kinds of naturally occurring atom, how many different naturally occurring elements are there?

Atoms joining together

PL E

In six of the elements, such as neon (which is a gas), atoms move around freely, not attached to one another. But in most elements, such as gold and other metals, atoms are packed closely together.

SA M

In a small number of elements, such as oxygen and sulfur, atoms join together to form small particles. An oxygen particle is made from two oxygen atoms. A sulfur particle is made from eight sulfur atoms.

Atoms of neon

Atoms of gold

Particles of oxygen

Particle of sulfur

Arranging the elements

Scientists have developed a very useful way of arranging the elements. This is called the Periodic Table. The full Periodic Table containing all of the 118 known elements is very large and complex. (There may be one on the wall of your science laboratory.) You are just going to look at the first 20 elements.

SEE QUERY LOG 118 = 94 natural + 24 man-made. Consider adding a brief explanation that 118 = 94 natural + 24 man-made to the text. Tech-Set:- Query log confirmation column has no information in. And nothing is marked on the PDF as to what needs to be entered.

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2 Materials and their structure

metals non-metals

H

He

hydrogen

helium

Li

Be

B

C

N

O

F

Ne

lithium

beryllium

boron

carbon

nitrogen

oxygen

fluorine

neon

Mg

Al

Si

P

S

Cl

Ar

magnesium

aluminium

silicon

phosphorus

sulfur

chlorine

argon

K

Ca

potassium

calcium

PL E

Na sodium

Groups and periods

The Periodic Table is organised into rows and columns. The rows are called periods. The columns are called groups.

The atoms are organised so that, as you read across each row (period) from left to right, the atoms increase in mass. Hydrogen atoms have the smallest mass, then helium atoms, then lithium atoms, and so on.

Chemical symbols

SA M

Each of the elements has been given a symbol. This is a useful shorthand way of referring to them. Sometimes the symbol is the first letter of the English name of the element. For example, the symbol for oxygen is O.

Aluminium, Al

Sometimes the symbol is the first letter of the English name plus another letter from its name. For example, the symbol for helium is He.

Sometimes the symbol is taken from another language. For example, the symbol for sodium is Na, from the old Latin name ‘natrium’.

Zinc, Zn

Bromine, Br

Lead, Pb

Copper, Cu

The first letter of the symbol is always upper case and the second letter, if there is one, is always lower case.

Iron, Fe

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2.5 Atoms, elements and the Periodic Table

Questions 3 What are the names of the elements with the symbols Mg, Be, Li and N? 4 Find the symbols for the elements aluminium, boron, fluorine and potassium. 5 Which element has atoms with the smallest mass?

PL E

6 Which of the elements in the first 20 elements of the Periodic Table has atoms with the greatest mass? 7 Give the names (not symbols) of two elements in the same period as magnesium. 8 Give the symbols (not names) of two elements in the same group as helium.

Metals and non-metals

The Periodic Table is organised so that elements with similar properties are close together.

SA M

In the diagram of the Periodic Table, all the elements that are metals are in yellow boxes. All the elements that are non-metals are in blue boxes. Activity

Learning the symbols for the elements

Here is a list of twenty elements and their symbols. Your task is to make up a game to help you learn them. You could make one set of cards with the names on them and another set with the symbols on them. Think how you could use these to make a game. Your game could be for one or two people, you decide. Element

Symbol

Element

Symbol

Hydrogen

H

Sodium

Na

Helium

He

Magnesium

Mg

Lithium

Li

Aluminium

Al

Beryllium

Be

Silicon

Si

Boron

B

Carbon

C

Phosphorus Sulfur

P S

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2 Materials and their structure

Continued Symbol

Element

Symbol

Nitrogen

N

Chlorine

Cl

Oxygen

O

Argon

Ar

Fluorine

F

Potassium

K

Neon

Ne

Calcium

Ca

PL E

Element

How do you learn facts? Does a game help? Which is the most effective way of learning for you? Summary checklist

I can explain what an atom and an element are. I can identify twenty elements and their symbols. I can use symbols to represent elements. I can describe the Periodic Table.

SA M



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2.6 Compounds and formulae

2.6 Compounds and formulae In this topic you will: • learn about the differences between elements and compounds • learn how to name compounds

Getting started

PL E

• use symbols to represent compounds.

bonding compound formula sodium chloride

SA M

You have three minutes. Test your partner on the symbols for the elements.

Key words

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2 Materials and their structure

What is a compound? You have looked at elements in the Periodic Table. An element is made up of only one type of atom. Many substances are made up of more than one type of atom. If the different types of atom are joined tightly together, then the substance is a compound.

PL E

The chemical term for two atoms joining tightly together is bonding. In a compound, two or more different kinds of atom are bonded. For example, when sodium atoms bond with chlorine atoms, they form the compound sodium chloride.

Properties of elements and compounds

A compound is very different from the elements from which it is made. When two different elements are bonded, they completely lose the properties of the individual elements. The compound has totally new properties.

SA M

The first two photographs show the two elements sodium and chlorine. The third photograph shows the compound that is made when sodium and chlorine atoms bond together. This compound – sodium chloride – is not at all like either sodium or chlorine.

+

Sodium, an element

Chlorine, an element

Sodium chloride, a compound

You may have eaten some sodium chloride today. Sodium chloride is common salt. You would not want to eat any sodium or chlorine, though.

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2.6 Compounds and formulae

Questions 1 Describe two ways in which sodium chloride is different from sodium. 2 Describe two ways in which sodium chloride is different from chlorine.

Naming compounds

PL E

Each compound has a chemical name. The chemical name usually tells you the elements that the compound is made from. There are important rules to remember when naming compounds. •

If the compound contains a metal, then the name of the metal comes first in the name of the compound.

•

If the compound contains a non-metal, the name of the non-metal is usually changed. For example, the compound made from sodium (a metal) and chlorine (a non-metal) is not sodium chlorine, but sodium chloride.

•

When two elements form a compound the name often ends in ‘ide’.

Questions

SA M

3 Which two elements are combined in sodium chloride?

4 Which two elements are combined in hydrogen sulfide? 5 Which two elements are combined in magnesium oxide? 6 A student wrote this name for a compound made of calcium and sulfur:

sulfur calcium



What is wrong with this name? Write the correct name for the compound.

These are crystals of copper sulfate. Copper sulfate is a compound made up of copper, sulfur and oxygen.

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2 Materials and their structure

Questions Some compounds contain two different elements, plus a third element – oxygen. These compounds often have names ending with ‘ate’. For example, a compound of calcium, carbon and oxygen is called calcium carbonate. 7 Which three elements are combined in calcium nitrate? 8 Which three elements are combined in magnesium carbonate?

PL E

9 Which three elements are combined in lithium sulfate? Sometimes, the name of a compound tells you how many of each kind of atom are bonded together.

O

C

O

C

A particle of carbon dioxide

O

A particle of carbon monoxide

Carbon dioxide particles are made up of one carbon atom joined to two oxygen atoms. ‘Di’ means two.

SA M

Carbon monoxide particles are made up of one carbon atom joined to one oxygen atom. ‘Mon’ or ‘mono’ means one.

Particle diagrams

Particle diagrams, like those for carbon dioxide and carbon monoxide, show which atoms of which elements make up the particle. It is easy to decide if a substance is a compound by looking at the particle diagram. If there are different kinds of atom bonded together, then it is a compound.

O

C

O

A molecule of carbon dioxide, CO2

H

O

H

A molecule of water, H2O

H

H C

O

O

A molecule of oxygen, O2

H

H

A molecule of methane, CH4

Carbon dioxide, water and methane are all compounds because their particles are made up of different kinds of atom. Oxygen is an element because the atoms in the particle are both oxygen atoms.

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2.6 Compounds and formulae

Using formulae Every compound has a chemical name. For example, the compound of sodium and chlorine is sodium chloride. Some compounds also have an everyday name. For example, sodium chloride is also known as common salt. Every compound also has a formula. The formula contains the symbols of the elements that are bonded together in the compound.

Chemical name

PL E

The table shows the chemical names and formulae of six compounds. Formula

What the compound contains

calcium oxide

CaO

one calcium atom bonded with one oxygen atom

carbon dioxide

CO2

one carbon atom bonded with two oxygen atoms

carbon monoxide

CO

one carbon atom bonded with one oxygen atom

hydrogen sulfide

H2S

calcium carbonate

CaCO3

one calcium atom, one carbon atom and three oxygen atoms bonded together

sodium hydroxide

NaOH

one atom of sodium, one atom of oxygen and one atom of hydrogen bonded together

SA M

two hydrogen atoms bonded with one sulfur atom

Be very careful reading the symbols of the elements. You do not want to confuse the symbol for carbon, C, with the symbol for calcium, Ca. The little number written below and to the right of some symbols tells you how many atoms of each element are found in the particle of the compound. If there is no number, it means there is just one atom of that element.

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2 Materials and their structure

Questions 10 Which of these substances are elements, and which are compounds? Explain your answer. K

O2

NaCl

Al

Ca

CaCl2

H2

11 The formula for sulfur dioxide is SO2. How many different elements are combined in sulfur dioxide?

b

How many atoms of oxygen are combined with each atom of sulfur?

PL E

a

12 The formula for water is H2O. a

Which two elements are combined in water?

b

What does the formula tell you about the numbers of each kind of atom that are combined together?

13 The compound with the formula CO is called carbon monoxide. Suggest why it is not simply called ’carbon oxide’. 14 Suggest the names of the compounds with these formulae: MgO

b

NaCl

SA M

a c

CaCl2.

15 The formula for sodium hydroxide is NaOH; the formula for potassium hydroxide is KOH. Which two elements are do you think contained in all hydroxides?

16 What is the name of the compound with the formula LiOH? 17 How many different elements are combined together in LiOH? Activity 2.6.1

Making models of particles

You are going to make models of at least five of the compounds mentioned in this topic. You will need:

• coloured card or paper, scissors and glue

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2.6 Compounds and formulae

Continued 1 Cut out circles of different colours to represent the different atoms of the elements. 2 Write the symbol for that element on the atom. 3 Arrange them to form the formula of one of the compounds mentioned in this topic.

PL E

4 Stick them on to a poster and write the name of the compound and its formula underneath. 5 Display them in your classroom. Summary checklist

SA M

I can explain the difference between elements and compounds. I can name compounds. I can use symbols to represent elements and compounds.

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2 Materials and their structure

2.7 Compounds and mixtures In this topic you will: • make a compound and a mixture • learn about the difference between a compound and a mixture

Getting started

PL E

• give examples of mixtures.

Key words

• Which of these are elements and which are compounds? nitrogen O2

carbon dioxide calcium chloride CaO

CH4

H2O

sodium K

• What is the difference between an element and a compound?

SA M

• Discuss with a partner and be prepared to share with the class.

composition evaporating basin filings mineral mixture natural emissions pipe-clay triangle pure

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2.7 Compounds and mixtures

Compounds and mixtures When atoms of elements are bonded tightly to form a compound, the properties of the compound are completely different from the properties of the elements that it is made from.

PL E

For example, iron is a metal. It is hard, grey, strong, conducts heat and electricity and is magnetic. Sulfur is a non-metal. It is yellow, brittle, does not conduct heat or electricity and is not magnetic.

This miner is carrying baskets of sulfur from the crater of a volcano in Indonesia.

SA M

When these two elements are heated, they combine together to form the compound iron sulfide. Iron sulfide is not magnetic and does not conduct heat or electricity.

This blacksmith is using iron to make a bracelet.

sulfur atom

iron atom

When iron and sulfur are heated together, iron atoms and sulfur atoms bond together to form the compound iron sulfide.

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2 Materials and their structure

Think like a scientist Using iron and sulfur You are going to use iron and sulfur to make a mixture and a compound. This will help you understand the differences between a mixture and a compound. You will need:

Safety

PL E

safety glasses, beaker, stirrer, boiling tube, test tube holder, Bunsen burner, powdered sulfur, iron filings, mineral wool

Do not touch your face or eyes when handling the iron filings. The pieces have sharp edges and can damage your skin and eyes. Wear safety glasses. Carry this activity out in a well-ventilated room. Mixing iron and sulfur

1 Place some iron filings in a beaker. 2 Add some yellow powdered sulfur.

SA M

3 Stir the mixture so that the two elements are spread out evenly.

You now have a mixture of iron and sulfur. The iron and sulfur both still have their properties. They have not changed chemically in any way. The different properties of the two elements can be used to separate them from the mixture.

4 Use a magnet to remove the iron filings. Making a compound from iron and sulfur

1 Make a mixture of iron and sulfur, just as you did in steps 1–3. 2 Heat some of the iron and sulfur mixture in a boiling tube. 3  Stop heating as soon as the mixture starts to glow. The iron and sulfur will combine together and form iron sulfide. 4 Leave the tube to cool.

5 Use a magnet to try to separate the iron. You can try through the wall of the tube.

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2.7 Compounds and mixtures

Continued Questions 1 Describe the appearance of: a a mixture of iron and sulfur b the iron sulfide.

Air is a mixture

PL E

2 Can you remove the iron from the iron sulfide by using a magnet? Explain your answer.

When you mix iron and sulfur together, you make a mixture of two elements.

78% nitrogen

In science, the word pure is used to describe something that only contains a single substance. Pure water contains only water, with no other substances mixed with it. A mixture is not pure. It is made up of different kinds of particle that are mixed together. The mixture may be of elements, compounds or both. There are solids, liquids and gases that are mixtures.

SA M

For example, air is a mixture of several different elements and compounds. Air contains nitrogen, oxygen, carbon dioxide, water vapour and small quantities of some other gases.

The composition of air varies because the amount of water vapour changes all the time, depending on the weather.

1% carbon dioxide, argon, water vapour and other gases

21% oxygen

A pie chart showing the composition of air.

The amount of carbon dioxide and other gases also change. This can be a result of natural emissions, such as when animals and plants produce carbon dioxide when they respire. Plants also use carbon dioxide when they make food, so this removes carbon dioxide from the air. The changes in the composition of air can also be as a result of human activity increasing the amount of carbon dioxide that is given out as a result of burning fossil fuels. Other forms of pollution also change the composition of the air. The composition of air has changed over millions of years; at one time there was much less oxygen in the atmosphere.

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2 Materials and their structure

carbon dioxide

oxygen

water

PL E

nitrogen

Air is a mixture of several elements and compounds.

Questions

The diagram shows some particles in air. The red circles represent oxygen atoms. The black circles represent carbon atoms. The blue circles represent nitrogen atoms. The white circles represent hydrogen atoms.

SA M

1 Which is the most common element in air?

2 How many different kinds of substance are shown in the diagram?

3 Which is the least common compound in this sample of air?

Mineral water is a mixture

The label on a bottle of mineral water lists many minerals. There is more than just water in the bottle. The bottle contains a mixture of water and other substances. The minerals are dissolved in the water. The mineral water is a solution. A litre of water may have about of minerals dissolved in it.

Question

4 Look at the picture of a mineral water label.

List the three most abundant minerals in this bottle of mineral water.

TYPICAL ANALYSIS mg/l CALCIUM MAGNESIUM POTASSIUM SODIUM BICARBONATE CHLORIDE SULPHATE NITRATE IRON ALUMINIUM DRY RESIDUE AT 180°C pH AT SOURCE

55 19 1 24 248 37 13 < 0.1 0 0 280 7.4

The label shows the minerals found in mineral water.

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2.7 Compounds and mixtures

Think like a scientist Is water really a mixture? You are going to investigate if drinking water contains anything other than water.

safety spectacles

tongs

Tech-Set:- this is the only illustration we have recieved

evaporating basin

You will need:

pipe clay-triangle

The apparatus shown in the diagram.

tripod

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Safety

water

She should be wearing a lab coat. Updated artwork has been supplied.

Wear safety glasses. Take care during step 2 as the solution may start to spit. Do not touch the evaporating basin with your hands – use tongs.

bunsen burner

Read the health and safety notes before you start.

1 Put some water in the evaporating basin and heat it until it boils.

2 Once the water starts to boil, turn the heat down and continue to heat it gently.

SA M

3 When you have evaporated off some of the water (or the solution has started to spit) remove it from the heat. 4 Leave the evaporating basin to cool. The water may take a day or two to evaporate completely. It will depend on the temperature. Questions

1 Use ideas about particles to explain why the water evaporated. 2 What was left in the evaporating basin? 3 Where has this substance come from?

4 Was the water you used pure water, or was it a mixture of water and other substances? Explain your answer.

5 Why did you need to wear safety glasses?

Summary checklist

I can distinguish between a compound and a mixture. I can explain the difference between a compound and a mixture. I can give examples of mixtures.

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2 Materials and their structure

Project: What’s in the parcel? Imagine you are given a parcel. You’ve been told you cannot open it for a few days. But you’re desperate to know what’s inside! What would you do? • How could you get some information about what is inside?

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• What sort of things could you find out?

• What sort of things could not be found out without looking inside?

Each group will be given a parcel with a number on it. 1 Your group has a few minutes to find out as much as they can about what is in the parcel but you must not open the parcel. 2 Discuss ideas in your group and try to give reasons for your ideas.

3 Write down your ideas on a piece of paper or a sticky note.

SA M

4 Swap parcels with another group. Repeat steps 1 and 2. Write your ideas on a new piece of paper or sticky note.

5 Repeat until you have tried to discover what is inside all the parcels. When all the groups have examined all the parcels, work together as a class to create a poster about how you carried out the investigation. Each group will share their ideas, with reasons on each parcel, with the whole class. By discussing this with all the other groups the class can work together to reach some conclusions for each parcel. This is how scientists work. They cannot always see or touch what they are investigating. Scientists have to use the information that is available to come up with ideas.

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2 Materials and their structure

Check your Progress 2.1 Which state of matter has the strongest forces between its particles?

[1]

2.2 Name the state of matter that fits each description. Particles do not touch one another.

[1]

b

Particles are close together in a regular pattern.

[1]

c

Particles are closely packed but not in a regular pattern.

[1]

2.3 Water in a puddle on a pathway disappears on a warm day. Explain what happens to the water particles.

[2]

2.4 a

Which are the two correct statements about liquids? i

Liquids can flow and be poured into a container.

ii

The particles in liquids are far apart.

iii

The particles in liquids are arranged randomly.

iv

The particles in a liquid can only vibrate.

v

Liquids only form at temperatures above 100 °C.

[2]

A liquid changes to a solid when it freezes.

SA M

b

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a

Describe what happens to the particles during this process.

[2]

2.5 Which of these terms matches the two facts?

precipitation  evaporation  condensation  groundwater

a

This falls from clouds.

Rain, snow and hail are forms of this.

b

This is what happens when water vapour cools down.

This is a change from water vapour to a liquid.

c

[1] [1]

When this happens, liquid water changes to water vapour. Water from rivers and the ocean is taken up into the atmosphere.

[1]

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2 Materials and their structure

2.6 Zara heated a liquid and recorded its temperature every minute. Here are her results. Temperature in °C

0

20

1

25

2

19

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Time in minutes

3

39

4

47

5

56

6

58

7

59

8 a

58

Copy the axes and labels below, onto graph paper.

SA M

60

50

Temperature in °C 40

30

20



0

1

2

3 4 5 Time in minutes

Plot Zara’s results on the grid.

6

7

8

[4]

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2 Materials and their structure

b

Draw a line of best fit through the points you have plotted.

[1]

c

Which reading does not fit the pattern?

[1]

d

Suggest a reason for this.

[1]

e

What happens to the temperature between 5 and 8 minutes?

[1]

f

Explain why this happens.

[1]

A

B

D

SA M

C

PL E

2.7 The diagrams in the boxes show different arrangements of particles. C

D

SEE QUERY LOG Explain that each colour represents a different atom; otherwise A and B could be the same, and so could C and D. In 2.7, consider adding an explanation that each colour represents a different atom.

Tech-Set:- no comments in query log for additional text to be inserted. Marked PDF doesn't have this information either!

Give the letter of the diagram that represents: a

particles of a compound

[1]

b

particles of an element

[1]

c

atoms of a mixture

[1]

d

atoms of an element.

[1]

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2 Materials and their structure

b

Give the symbol for each element. i

magnesium

[1]

ii

oxygen

[1]

iii

hydrogen

[1]

iv

calcium

[1]

v

boron

[1]

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2.8 a

Name the element with the given symbol. i

C

ii

Na

iii

K

iv

Cl

v

Si

[1] [1] [1] [1] [1]

Explain why scientists use symbols for the elements.

[1]

d

Explain why some symbols, such as Cl and Si, have two letters.

[1]

SA M

c

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3

Forces and energy

In this topic you will:

PL E

3.1 Gravity, weight and mass • understand that the force of gravity acts between objects

• learn about what affects the strength of the force of gravity on an object • practise using the correct terms ‘weight’ and ‘mass’.

Key words

Getting started

Work individually to answer these questions.

1 Describe how gravity affects an object such as a textbook.

SA M

2 Copy and complete this sentence by choosing the correct word from the list. length

mass

volume

weight

The newton, N, is a unit of …………………

3 Copy and complete this sentence.

The kilogram, kg, is a unit of …………………

accurate acts towards the centre contact force Earth force of gravity formula triangle gravity kilograms mass newtons quantity weight

Will need a different background image as the KW box will need to move to where the surfer is.

Tech-Set: Please advise

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3 Forces and energy

Gravity When you drop an object, it falls to the ground. What pulls the object down? The Earth you live on is a large object with a mass of about . Objects with large mass, such as the Earth, cause strong forces of gravity.

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All objects, even pens and pencils, cause forces of gravity. Objects with small mass, such as pens and pencils, cause very weak forces of gravity. That means we do not notice other objects being attracted to them. The force of gravity caused by an object acts towards the centre of the object.

You can imagine the Earth as a giant ball in space. The force of gravity at positions around the Earth acts towards the centre. That means when you drop an object, the object falls in a line that points towards the centre of the Earth.

SA M

The strength of gravity decreases as you go further from a large object such as Earth. For example, if you travelled away from Earth in a spacecraft, the force of gravity from the Earth acting on you would get smaller.

The force of gravity caused by the Earth acts toward the centre of the Earth.

Questions

1 Draw a circle to make a diagram of the Earth.

A

Put arrows around your diagram to show the direction of the force of gravity.

2 Use your diagram from question 1 to explain why people who go to the South Pole do not fall off the Earth. Discuss your answer with a partner. D 3 The diagram shows the Earth. It is not to scale.

B

A ball is dropped from four different places, A, B, C and D.

Draw arrows to show the direction in which each ball will fall. The first one has been done for you.

C

Query log: For Q3, learners need to be told to make a new diagram to draw the arrows onto because the arrows will already be on their drawing for Q1. Tech-Set: NO replacement in query log or is not final and is subject to further changes prior to publication. Original material © Cambridge University Presstext 2021. This material 70 on marked PDF please advise ISBN_9781108742788.

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3.1 Gravity, weight and mass

4 The Moon has a mass of about . Some people think there is no gravity on the Moon. Are they correct? Use the information in this question to explain why.

Weight The force of gravity on an object is called its weight.

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It is difficult to lift a heavy object because gravity is pulling it towards the centre of the Earth. By lifting, you are pulling against gravity. Weight is a force and it is measured in newtons, N. The weight of an apple is about 1 N. That means gravity from the Earth is pulling on the apple with a force of 1 N. You need to apply a force of 1 N to hold the apple.

The force of gravity is making it difficult to hold these weights. You can see the effect of the force bending the bar.

SA M

The weightlifter in the picture is holding about !

The contact force

When a book with a weight of 5 N is resting on a desk, gravity is still pulling it down with a force of . So why is the book not moving down through the desk?

Updated version of this was supplied in July (muted character smiles) Tech-Set: This is the only version we have been supplied. Please advise

The answer is because the desk is pushing back up on the book with an equal force of .

This force from the desk is called the contact force. The contact force acts up from any surface to support an object. The contact force is always equal to the weight of the object when the surface is not moving. Sometimes the weight of the object is larger than the contact force. If this happens, the surface will break, or the object will sink into the surface.

Your weight pulls you down, but an equal contact force pushes you up.

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PL E

3 Forces and energy

The weight of this car is greater than the contact force from the sand.

SA M

Can you think of any other examples where the weight of an object is larger than the contact force? Discuss your answers in pairs.

Questions

5 The diagram shows a box on a desk. Copy this diagram. box

desk

On your diagram:

a

add an arrow to show the weight of the box. Label this arrow W.

b

add an arrow to show the contact force from the desk. Label this arrow C

6 A large rock rests on the ground. The weight of the rock is 8000 N. Write down the size of the contact force from the ground.

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3.1 Gravity, weight and mass

7 An elephant is standing on four feet. The weight of the elephant is 40 000 N Calculate the contact force from the ground on each of the elephant’s feet. 8 A car travels into soft mud. The contact force needed to support each wheel is 24 000 N At first, the contact force from the mud on each wheel is 2000 N. Explain why the wheels will start to sink.

b

The contact force from the mud increases with depth. Explain what will happen to stop the wheels sinking.

PL E

a

Weight and mass

Weight is the force of gravity on an object. It is measured in newtons, N.

Mass is the quantity of matter in an object. It is measured in kilograms, kg. People often confuse mass with weight. They often say things such as: ‘The weight of my bag is 10 kg.’ This sentence is not correct because it makes a statement about weight, but gives a mass. The correct sentence is: ‘The mass of my bag is 10 kg.’

SA M

On Earth, the force of gravity is 10 N on every 1 kg of mass.

Writing this as an equation:

W

weight (N) = mass (kg) × 10 (N/kg)

or, using letters:

W = m × 10

m × 10

You can use a formula triangle for this equation.

To use a formula triangle, cover the part of the equation that you want to find. Then, do the calculation that is shown in the uncovered part. For example, if you want to find the mass, you cover . The uncovered part is then

W 10

Divide the weight by 10 to get the mass. Remember that m must be in kg.

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3 Forces and energy

The force of gravity that pulls on 1 kg tells you the strength of gravity. On Earth, this is 10 N As 10 N acts on 1 kg, you say this as ‘10 newtons per kilogram’, or 10 N/kg. For example, if a person has a mass of 45 kg, their weight on Earth is 45 × 10 = 450 N.

PL E

You can use the equation to calculate mass if you know the weight. For example, a computer games console has a weight of 28 N. The mass of the console is 28 = 2.8 kg. 10 The strength of gravity is not 10 N/kg in all parts of the Solar System. The diagram shows the strength of gravity in some other parts of the Solar System.

Moon Jupiter 25 N/kg Earth 1.6 N/kg 10 N/kg Mercury 3.7 N/kg

Uranus 8.7 N/kg

Neptune 11 N/kg

Mars 3.7 N/kg

SA M

Venus 8.9 N/kg

Saturn 10 N/kg

The weight of an object changes when the strength of gravity changes. If you want to calculate your weight somewhere other than Earth, you can use the same equation but you must change the number 10 to the value of the strength of gravity wherever you are calculating it. The mass of an object does not change.

Questions

9 The strength of gravity is 10 N/kg on Earth. a

Calculate the weight of an adult who has a mass of 75 kg.

b

Calculate the mass of a car that has a weight of 8500 N.

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3.1 Gravity, weight and mass

10 Use the information in the diagram of the planets on the previous page to answer these questions. Give the location where your weight would be greatest.

b

Name the planet where you would have the same weight as on Earth.

c

Calculate the weight of a 25 kg mass on Mars.

d

Explain how your mass on Earth would compare with your mass on Mercury.

PL E

a

11 When you stand on scales you see your mass in kg. Explain whether it is your mass or your weight that makes the scales work. Discuss your answer with a partner.

12 In 1969, a spacecraft carrying people went from the Earth to the Moon. The people explored part of the Moon. The spacecraft then brought the people back to Earth.

SA M

Explain why a larger force is needed for a spacecraft to go from Earth to the Moon than to come back from the Moon to the Earth. Use the information in the diagram. Assume the mass of the spacecraft is the same on both journeys. Activity

Mass or weight?

On a large piece of paper, draw a table with two columns: one for mass and one for weight. Each of the statements below should start with either the word ‘mass’ or the word ‘weight’. Work in pairs to decide which column to put each of the statements in. When you have decided, write the statement in the appropriate column. The statements are:

… of an object is affected by the strength of gravity on a planet. … is measured in newtons, N.

… is measured in kilograms, kg. … is not affected by gravity.

… of an object decreases as the object moves further away from Earth. … is the quantity of matter in an object.

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3 Forces and energy

Continued … can be measured in grams, g. … is the force needed to lift an object. … is equal to the contact force on a level surface that is not moving.

PL E

… is the property of a planet that makes it have gravity.

• How did you decide which statements were about weight and which were about mass? • Did your strategy work?

• Could you use this strategy again, or would you change it? Think like a scientist

Linking weight and mass

clamp stand

In this investigation, you will find the weights of some masses and draw a graph of your results.

SA M

You will need:

force meter

• force meter  • clamp stand • mass hanger and masses

Set up the equipment as shown in the diagram.

1 Start by hanging the force meter from the clamp stand. Leave enough space to hang the masses, remembering that the spring will extend.

masses on hanger

Finding the weight of a mass.

2 Hook the mass hanger to the force meter. Record all your results using the kg unit for mass. Remember that is . 3 Using the force meter, carefully measure the weight. Remember that this result is in newtons, N. 4 Increase the mass by adding one mass at a time. (That is the same as adding each time.) Use the force meter to measure and record the weight after every increase.

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3.1 Gravity, weight and mass

Continued  5 Record the weights in a table. Remember to put the units in the column headings and not in the table itself. 6 Measure the weights as accurately as possible. Being accurate means being close to the true value. 7 Your results should go from up to .

Questions

PL E

8 Draw a line graph of your results. Put mass in kg on the horizontal axis and weight in N on the vertical axis. 1 When you have finished your graph, copy and complete these sentences. As the mass gets bigger, the weight gets … . When the mass doubles, the weight … .

2 Is the weight of 1.0 kg exactly 10 N as in the equation W = m × 10? If not, what is the weight of 1.0 kg?

3 The strength of gravity at the Earth’s surface varies slightly between 9.7639 and 9.8337 N/kg Explain why you can use the value of instead of these more accurate values.

SA M

Self-assessment

1 For each of these statements about your experiment, decide how well you think you did. • I worked safely, taking care not to drop any masses or knock the clamp stand over.

• I took the reading from the force meter as accurately as possible. • I continued to record actual results, even when I thought I could see a pattern developing. • I wrote down or drew my results clearly, so that someone else could understand them. • I made my graph accurate and clear.

2 Write down one thing that you did really well. 3 Write down:

• one thing that you could do better next time • how you will try to improve next time.

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3 Forces and energy

Summary checklist I can describe why objects such as planets have gravity. I can describe how the force of gravity acts around the Earth. I can describe weight as the force of gravity on an object. I can describe mass as the quantity of matter in an object. I can understand the difference between weight and mass. I can use the mass of an object and the strength of gravity to calculate weight.

SA M

PL E



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3.2 Formation of the Solar Systemaxis

3.2 Formation of the Solar System axis

In this topic you will: • learn about how scientists think the Solar System was formed

PL E

• think about objects in space growing larger and increasing in mass • understand that as these objects increase in mass, their gravity increases

• understand that as their gravity increases, they can attract even more mass.

Key words

Getting started

Choose one correct answer to each question.

SA M

1 An object causes a strong force of gravity. What must the object have? large size

large mass

small size

small mass

2 Which of these objects has the largest mass in the Solar System? Earth

Jupiter

Sun

Neptune

3 Which of these objects is at the centre of the Solar System? Earth

Moon

Mercury

Sun

axis contradict evidence formed model nebula observe orbit plane spin support

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3 Forces and energy

Where did the Solar System come from? When the Solar System formed, there were no people to observe how it was made. Observe means to watch something happening. So how do we know what happened? Scientists can try to solve a problem like this in two different ways. They can look for evidence, in the form of facts from observations or experiments to support their theory, and then try to explain what they have found.

•

They can think of a testable theory, called an hypothesis, and then look for evidence to support the hypothesis.

PL E

•

Facts about the Solar System Look at the diagram of the Solar System.

Neptune

SA M

Earth

Jupiter

Mercury

Venus

Mars Uranus

Saturn

The Solar System.

Here are some facts about the Solar System: •

All the planets in the Solar System follow a path or orbit around the Sun in the same direction.

•

The Sun and all the planets (except Venus and Uranus) spin on their axes (singular: axis) in the same direction.

•

Most of the moons of the planets orbit their planets in the same direction as the planets rotate around the Sun.

•

The direction of spin of the Sun and the planets (except Venus and Uranus) is the same as the direction in which the planets orbit the Sun.

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Where did the Solar System come from?

•

All the planets orbit the Sun in the same plane. Objects that are in the same plane could all be placed on the same flat surface, just like all the objects on a desk. That means the Solar System looks flat.

Scientists can use these facts as evidence.

Watching the birth of stars

PL E

Scientists can see distant stars forming in other parts of space. These stars are being formed from clouds of dust and gas.

A cloud of dust and gas in space is called a nebula. The picture shows one of these clouds of dust and gas. You can see the young stars in the cloud. Some young stars can also be seen with a flat disc of dust around them. Scientists think our Solar System was formed this way.

SA M

Using models

The Orion Nebula – stars are being born here.

Scientists cannot observe a star or Solar System forming in an experiment. Instead they use computers to create models. A model is a way of representing something that is difficult to observe directly. The scientists put many of the known laws of physics into a computer program. Then the computer uses this information to predict what will happen, starting with a cloud of dust and gas. The result is a prediction that a star will form, surrounded by planets.

How do stars and planets form out of dust and gas? The picture shows what scientists think our Solar System looked like as it was forming. You saw in Section 3.1 that any object can act as a source of gravity. All the particles of dust and gas in the pictures have their own weak gravity.

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3 Forces and energy

The particles of dust and gas pull on each other with very weak forces due to their own gravity. As they stick together, their total mass increases. As their mass increases, so does the strength of their gravity. That means they attract more dust and gas with a stronger force. This starts to form a small ball.

PL E

Gradually, this ball gets bigger.

If the ball gets beyond a certain size, it will get hot enough to become a star. Otherwise it will become a planet. Most of the facts about the Solar System support or agree with this hypothesis.

This is how our Solar System may have looked 4.6 billion years ago. The fact that Venus spins on its axis in the opposite way to all the other planets seems to contradict this hypothesis. Contradict is the opposite of support – it means to go against something.

Scientists think the planet Jupiter almost reached the size to be a star.

SA M

It takes millions of years to form a star or a planet.

Questions

1 Use words from the list to copy and complete this sentence. different directions the same direction opposite directions random directions All the planets in the Solar System orbit the Sun in ….

2 All the planets in the Solar System orbit the Sun in the same plane. Explain what ‘the same plane’ means.

3 Which of these is the name given to a cloud of dust and gas in space? planet

star

nebula

moon

4 Name the force that can pull particles of dust and gas together in space.

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Where did the Solar System come from?

Activity Solar System story board Work in groups. Use a large piece of paper to make a storyboard to tell people about how the Solar System formed. A storyboard is a series of drawings that tell a story. There can be writing with the drawings. In your storyboard you should show:

PL E

• a nebula and what it contains

• how a star such as the Sun forms

• how planets form around the Sun.

Include in your storyboard reasons why:

• all planets orbit the Sun in the same direction

• most of the planets spin on their axes in the same direction. Self-assessment

1 For each of these statements about your experiment, decide how well you think you did. • I contributed ideas to the group.

SA M

• I worked in a team, cooperating with others.

• I thought the storyboard communicated ideas clearly.

2 Write down the most interesting thing you learned about the formation of the Solar System.

3 Write down one thing that still puzzles you about the formation of the Solar System.

Think like a scientist Using models

In this task you will be thinking about how scientists use models and how they use an hypothesis. Scientists use computers to model how the Solar System was formed. One reason for using a model is that it takes millions of years to form a star and planets from a cloud of dust and gas. A model can speed this up.

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3 Forces and energy

Continued  Questions 1 Suggest one other reason for using a model in this way. 2 Models are not real, so may not be accurate. Which term describes this? an error

a mistake

a limitation

a strength

PL E

3 Look at the facts about the Solar System given earlier in this section.

Scientists use facts like these to support their hypothesis of how the Solar System formed. An hypothesis is a theory or idea that is testable.

a Give two facts about the Solar System that seem to contradict this hypothesis. b Explain why these facts seem to contradict the hypothesis.

4 Which two of these statements describe the hypothesis of how the Solar System formed? • It has been proven to be correct.

• Most, but not all, of the evidence supports it. • The model that is used has limitations.

SA M

• It can be fully tested by experiments. Summary checklist

I can recall that there are clouds of dust and gas in space. I can recall that stars and planets are formed from dust and gas. I can understand that gravity can pull particles of dust and gas together. I can describe how stars and planets are formed. I can understand how scientists use a model to test an hypothesis.

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3.3 Movement in space

3.3 Movement in space In this topic you will: • learn about what keeps the planets in orbit around the Sun • understand why planets move at different speeds

Getting started

PL E

• discover why objects moving in space do not slow down as they do on Earth.

1 Write the names of the planets in order, starting with the one that is closest to the Sun.

air resistance circlar speed vacuum

SA M

2 Name the object that orbits the Earth and not the Sun.

Key words

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3 Forces and energy

The Sun In Section 3.1 you saw that objects with more mass have more gravity. The Sun is the object with the largest mass in the Solar System.

PL E

The mass of the Sun is times greater than the mass of the Earth. In fact, the mass of the Sun is more than the mass of all the other planets added together! The strength of gravity on Earth is . On the Sun it is .

The Sun’s gravity

The Sun’s gravity is 27 times stronger than the Earth’s gravity.

It holds all the planets in their orbits. The Sun’s gravity gets weaker as the distance from the Sun increases.

This photograph of the Sun was taken from a spacecraft, using a special camera. You should never look directly at the Sun or try to photograph it yourself.

SA M

The planet Neptune is 30 times further from the Sun than Earth is. The mass of Neptune is about 17 times the mass of Earth. So although the Sun’s gravity gets weaker, it is strong enough to hold Neptune in orbit.

Orbits of planets

The orbits of the planets, including Earth, are almost circular. Circular means in the shape of a circle.

To keep any object moving in a circle, there needs to be a force causing it to turn.

direction of orbit planet direction of force from the Sun’s gravity

Sun

The diagram shows how the force of gravity acts on a planet to keep it in orbit. The force of gravity from the Sun that acts on a planet always acts towards the Sun. If this force did not act in this way, the planet would travel off in a straight line into space!

The force of gravity from the Sun keeps a planet in orbit. The diagram is not to scale.

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3.3 Movement in space

Mercury, which is the closest planet to the Sun, has the strongest pull from the Sun’s gravity. This causes Mercury to orbit with the highest speed of all the planets. The average speed of Mercury around the Sun is 170 000 km/h! The average speed of the Earth around the Sun is about 100 000 km/h.

Speed in space

PL E

On Earth, all objects that move have forces acting on them to slow them down.

Air resistance is one of those forces. It is caused by a moving object having to push against the particles in the air. Air resistance acts in the opposite direction to movement. The faster an object moves, the greater the air resistance on the object.

Look at the picture of the aeroplane wing.

This aeroplane has landed and is using extra air resistance to help it slow down.

SA M

The aeroplane can slow down faster with extra air resistance. The shape of the wing can be changed to produce extra air resistance. In space there is no air. There are very, very few particles in space. A space where there are no particles is a vacuum. Look at the spacecraft in the picture.

This spacecraft, called the Juno probe, would have a lot of air resistance if it were moving on Earth.

In space, where there is a vacuum and no air resistance, the Juno probe reached a speed of as it passed Jupiter. It became the fastest object that people had ever made. This speed would not be possible for the Juno probe on Earth because of air resistance.

Earth and the other planets are also moving in a vacuum. This means there is no air resistance to slow them down.

This spacecraft reached a speed of in July 2016.

The only force acting on the planets is from gravity.

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3 Forces and energy

Questions 1 State the direction in which the force of gravity from the Sun pulls on a planet. 2 Other objects, such as comets and asteroids, also orbit the Sun. Suggest what keeps these other objects in orbit around the Sun. 3 The Sun has the strongest gravity in the Solar System.

PL E

Suggest which object in the Solar System has the second strongest gravity. Discuss your answer in pairs.

4 State the word used to describe a space that has no particles in it.

5 Voyager 1 is a space probe launched in 1977. Voyager 1 is now outside the Solar System and is travelling at . Explain why Voyager 1 could not travel at this speed on Earth. 6 Which of these forces acts on the Earth as it orbits the Sun?

gravity only   air resistance only    gravity and air    gravity, air resistance    resistance      and friction

SA M

7 The orbits of the planets are not exact circles. The distance from the Sun of each planet varies slightly as it goes around in its orbit. This change in distance makes the speed of the planet change slightly. Suggest how the speed of a planet changes with distance from the Sun during its orbit.

Activity

Planet speeds

The table shows the average speed of each planet’s orbit around the Sun. The speeds are given in kilometres per second (km/s) as they are so fast. Name of planet

Speed of orbit in km/s

Mercury

48

Venus

35

Earth

30

Mars

24

Jupiter

13

Saturn

10

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3.3 Movement in space

Continued Name of planet

Speed of orbit in km/s

Uranus

7

Neptune

5

Questions

PL E

Use the information in the table to draw a bar graph. Put the names of the planets, in order from Mercury, across the horizontal axis. Space them evenly so your bars are not touching.

1 Copy and complete the sentence. As the distance from the Sun increases, the speed of orbit of the planets … . 2 Explain the advantages of presenting this information in a graph rather than in a table. 3 Explain the reason for the trend in your graph. 4 Explain why a bar graph is used for this information rather than a line graph. Self-assessment

1 For each of these statements about your activity, decide whether you did it very well, fairly well or not at all.

SA M

• I drew a bar graph with the correct information. • My bars were evenly spaced and not touching. • All my lines were drawn with a pencil and ruler. • All my bars were the correct height.

• I understood the advantages of drawing a graph to display information.

2 Write down one thing that you did really well. 3 Choose one thing that you think you could do better next time and explain how you will try to improve it.

Think like a scientist Discovering planets

In this task you will find out about how scientists discovered the planet Neptune. The planet Uranus was discovered in the year 1781. It was thought to be the most distant planet from the Sun. In 1821, a French scientist called Alexis Bouvard made calculations about the orbit of Uranus. He worked out where Uranus would be at different times.

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3 Forces and energy

Continued  1 Which one word best describes these calculations? The actual orbit of Uranus was different to the calculations. observations

predictions

conclusions

measurements

2 The planet was seen to move further away from the Sun at regular times. These results were recorded. observations

PL E

Which word best describes these results? predictions

conclusions

secondary information

3 Scientists thought that another source of gravity was pulling Uranus further from the Sun. Which word best describes this statement? observation

conclusion

measurement

secondary information

4 Scientists then made predictions about another planet further away than Uranus. They used the results from the orbit of Uranus to predict where this other planet would be. Then, in 1846, scientists found another planet, which they called Neptune.

SA M

Neptune was very close to where they predicted it would be.

5 Use words from the list to copy and complete these sentences. Uranus moving further away from the Sun about its orbit.

the original prediction

Scientists found Neptune using careful testable

a fair test

contradicted

results

conclusions

supported

observations

measurements

Summary checklist

I can name the force that keeps the planets in orbit around the Sun. I can describe the direction that this force acts on a planet. I can understand why planets closer to the Sun move faster.

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3.4 Tides

3.4 Tides In this topic you will: • find out what tides are • learn about tidal forces and where they come from

Getting started

PL E

• discover how tidal forces affect the oceans and the land.

Work in groups to answer these questions.

1 Which object has the strongest gravity in the Solar System? 2 What large object orbits the Earth?

SA M

3 What force keeps the object that orbits the earth in its orbit?

Key words

coastal depth earthquake earth tide force of attraction harbour tidal force tidal range tide

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3 Forces and energy

What are tides?

In some parts of the world, the depth of the ocean changes by several metres during the day. The depth is the distance from the surface of the water to the bottom of the ocean. The picture shows the same place at two different times. The pictures were taken six hours apart.

SA M

PL E

This change in depth of the water is called a tide.

Tides change the depth of the oceans. High tide (left) and low tide (right) are six hours apart.

The difference in depth of the water between high and low tides is the tidal range. The largest tidal range in the world is 16.3 m in the Bay of Fundy in Canada. Some of the smallest tidal ranges in the world are less than in the Caribbean and Mediterranean seas. Tides also cause the land to change in height through the day! This is called earth tide. The tidal range due to earth tide is about 30 cm

High tides are about 12 hours apart. Low tides are also about 12 hours apart. The time between high and low tide is six hours.

What causes tides? The Moon orbits the Earth.

The Moon stays in orbit because of the force of gravity from the Earth but the Moon also has gravity, and this gravity pulls on the Earth.

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What are tides?

As the oceans are made from water, the gravity from the Moon can pull the water more easily than the land. The pull from the Moon’s gravity is called a tidal force. The diagram shows how this happens.

low tide direction of Earth spinning on its axis

high tide Moon

high tide

Look at the drawing of the Earth and Moon. The Earth is viewed from above the North Pole.

PL E

pull of gravity from the Moon

The side of the Earth closer to the Moon will have high tide.

low tide

The Earth takes 24 hours to spin on its axis.

The blue line around the Earth represents the ocean depth. The difference in depth is caused by the pull of gravity from the Moon. The drawing is not to scale.

This means that 12 hours later, the side that was closest to the Moon is now furthest away.

You can see from the drawing that the side furthest away also has a high tide. This is why the time between high tides is 12 hours.

SA M

The Sun also produces a tidal force on Earth, but this is weaker as the Sun is further away than the Moon. When the Sun and the Moon are in line with Earth, this produces a larger tidal force. The next drawing shows how this happens. greater tidal range when Earth, Moon and Sun are in line

pull of gravity from the Sun and the Moon Moon

Sun

Larger tidal forces affect the Earth when the Earth, Sun and Moon are in line. The drawing is not to scale.

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3 Forces and energy

Effects of tides Some harbours can only be used at certain times of the day. If the water in the harbour is not deep enough, boats cannot move safely. Harbours are places where boats and ships can load and unload passengers and cargo. In weather with strong winds, coastal areas are more likely to have flooding at times of high tides. Coastal areas are parts of the land that are close to the oceans.

PL E

The flow of water in and out of some coastal areas can be dangerous for small boats.

In some places, tides affect food chains, including the human food chain. For example, at low tide birds can eat some types of shellfish when they are not covered with water. Some types of fish move to find food according to tides in coastal areas. Volcano eruptions have been linked with earth tides. By studying Earth tides, scientists may be able to predict when a volcano will become dangerous. Earthquakes may also be linked with earth tides.

Movement of water with tides can be used to generate electricity.

SA M

Questions

1 Which of these causes the force of gravity for tides on Earth? the Sun only   the Moon only   the Sun and Moon   the Sun, Moon and other stars 2 What is the name given to the pull of gravity that causes tides? high tide

low tide

tidal range

tidal force

3 State the time between: a

one high tide and the next high tide

b

one low tide and the next low tide

c

a high tide and the next low tide.

4 Explain why some harbours cannot be used at low tide. 5 Explain why the largest tidal ranges happen when there is either a full moon or a new moon. 6 The average depth of water in a place near the coast of the Pacific ocean is . The largest tidal range in that place is . Calculate the maximum depth of water at that place.

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What are tides?

Activity Investigating tides Work in groups. You will need:

PL E

card or paper, some circles to draw around, scissors Cut out a small, a medium and a large circle. Label these ‘Moon’, ‘Earth’ and ‘Sun’ in order of increasing size. Next, cut out two thin crescents that will fit around your Earth, as shown here.

Call these two crescents ‘set 1’.

SA M

Now, cut out two thicker crescents that will also fit around your Earth, as shown here.

Call these two crescents ‘set 2’.

The crescents represent the ocean depth around the Earth. Part 1: Why tides happen

For part 1, you do not need the shape that represents the Sun. Set it to one side for now. Put the Earth and Moon on a desk about away from each other. This is not to scale. Now put the crescents that represent the ocean depth, set 1, on either side of the Earth. The deepest parts should be in line with the Moon.

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3 Forces and energy

Continued Question 1 Why are the deepest parts of the oceans in line with the Moon? Part 2: Times of the tides Mark a point at the coast on your Earth. The activity will work best if you choose a point close to the edge of the circle, which is the equator.

PL E

Now, slowly turn your Earth. You should turn it in the opposite direction to the movement of the hands on a clock. You should only turn the Earth, not the ocean depth shapes as well. Questions

2 How many high tides does your chosen point get in one full rotation? 3 How many low tides does your chosen point get in one full rotation?

4 The Earth takes 24 hours to rotate once like this. Try to use the model to explain why: a high tides are 12 hours apart b low tides are 12 hours apart.

5 The Moon does not stay in one place like this. It orbits the Earth.

The Moon orbits the Earth in the same direction as the Earth rotates on its axis. The Moon takes 27 days to orbit Earth once.

SA M



a Explain whether high tides will happen at the exact same time each day.

b Try to work out how much earlier or later high tides will be each day.

Part 3: Why tidal range also depends on the Sun For part 3 you will need your shape that represents the Sun. You will need to change the ocean depth shapes to set 2. Put your Earth, Moon and Sun in a line like this (it is not to scale).

Earth

Moon

Sun

Questions

6 Can you explain why set 2 is now better than set 1 to show what happens with tides? 7 Name this phase of the Moon as it appears from Earth in this position.

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What are tides?

Continued 8 Now move the Moon to the other side of the Earth, but keep the Moon, Earth and Sun in line. Name this phase of the Moon. 9 a W  hat can you conclude about the times when the highest tides happen, in terms of how the Moon appears?

Self-assessment

PL E

b The length of time taken by the Moon to orbit Earth is called a lunar month. How many of these highest tides will occur each lunar month?

In your groups, discuss each of these questions. • What was my role in the group?

• How did my role help me understand the tides?

• How did other people in the group contribute to my understanding? Think like a scientist

Discovering the causes of tides

SA M

In this task, you will find out about how scientists used evidence to discover what causes tides.

In 330 BCE, a sailor from Greece noticed that the depth of water in some parts of the oceans changed regularly. He noticed that the depth increased to a maximum twice every day. He thought that this was because of the Moon.

People did not know about gravity until much later. 1 Use words from the list to copy and complete the sentences. a conclusion

an observation

a prediction

a measurement

an explanation

a model

The sailor noticed that the depth of water changed. This was

.

The sailor thought that the change was caused by the Moon. This was The sailor did not know about gravity, so could not give

. . for the tides.

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3 Forces and energy

Continued  Around the year 1600, a scientist from Germany suggested that there was a force of attraction between the Moon and water. He thought this force caused the tides. People in 1600 did not know about gravity. This German scientist said that the force of attraction was magnetic. We now know that the attractive force between the Moon and the water in the oceans is not magnetic.

PL E

2 Describe what could be done to show that there is no magnetic force between the Moon and water in oceans.

People did not believe that the Moon or the Sun could have an effect on the oceans because gravity had not been described. The problem of what causes tides was finally solved by Newton in the year 1687. Newton had already described the effects of gravity.

He then used his ideas about gravity to calculate the tidal forces, without the need for experiments.

These calculations were accurate enough to show people that gravity from the Moon and the Sun caused the tides.

SA M

People then accepted that tidal forces were caused by gravity from the Moon and the Sun.

3 Which two statements explain why people accepted Newton’s ideas about gravity? • Newton did experiments on the tides that were fair tests. • Newton provided evidence to support an hypothesis. • Newton made observations whereas previous scientists did not. • Newton made predictions that were shown to be accurate.

Summary checklist

I can understand what tides are. I can understand where tidal forces come from. I can explain the part played by the Moon in causing tides. I can explain the part played by the Sun in causing higher tides. I can understand why there are two high tides and two low tides every day.

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3.5 Energy

3.5 Energy In this topic you will: • find out what energy is • learn about different energy stores and transfers

Getting started

Tech-Set: there is no information for the 3rd bullet point in the query log!

PL E

• discover how some ways that energy can be stored more easily than others.

The sentence at the second bullet point makes no sense. Author to rewrite it.

With your partner, make a list of:

1 some things that you need energy to do

SA M

2 some of the types of fuel that you know.

Key words

chemical elastic potential electrical energy fuel gravitational potential joule kinetic light luminous sound stored thermal transferred

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3 Forces and energy

What is energy? Energy is something that must be changed or transferred in order to do something. There are many different ways that energy can be stored or transferred. For example, kinetic energy is the energy in movement. The unit for measuring the amount of energy is called the joule (J). You need about: to walk up the stairs between two floors in a building. for every metre you run to bring 1 litre of cold water to boiling point.

PL E

• • •

Energy stores and transfers

SA M

There are many different ways in which energy is being stored or transferred around you all the time.

These runners have kinetic energy as they are moving.

The table describes some of these stores and transfers. energy

description

energy store or energy transfer

kinetic

energy stored due to movement of an object

store

chemical

energy stored in food, batteries, chemical fuels such as wood, oil and coal

store

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3.5 Energy

description

energy store or energy transfer

thermal

heat energy stored in hot objects and transferred to colder objects

store or transfer

elastic potential

energy stored when things are stretched or squeezed to change their shape

store

gravitational potential

energy stored when an object is lifted away from a source of gravity

store

electrical

the flow of current in a circuit transfers electrical energy

transfer

sound

energy transferred from vibrating objects

transfer

light

visible energy from luminous objects (objects that give out their own light) that you can see

transfer

PL E

energy

Look at the descriptions of energy in the picture.

SA M

chemical – the bus carries fuel

kinetic – the bus is moving

electrical – for lights

thermal – the engine is hot sound – the engine makes noise

gravitational potential – the bus is going uphill

elastic – the tyres get squeezed

This bus has many types of energy.

• How will you learn the different stores and transfers of energy? • Can you think of a way to help you remember them?

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3 Forces and energy

Storing energy Energy can be stored more easily in some ways than in others. For example, you can keep uncooked rice for a long time. That is a store of chemical energy.

PL E

Coal and crude oil are stores of chemical energy that formed millions of years ago. This shows that some energy stores can last for a very long time. A battery is another example of how chemical energy can be stored. It is quite easy to store chemical energy. Gravitational potential energy is also easy to store. The picture shows a tank containing water. A pump has been used to lift up the water. The water stores gravitational potential energy.

The tennis ball has a store of kinetic energy while it is moving.

Some energy stores only last for a short time.

Thermal energy (heat) is one example. Hot objects will eventually cool down (they will lose their store of thermal energy).

SA M

Kinetic energy is another example. Kinetic energy is more difficult than chemical or gravitational potential energy to store.

The tennis ball in the picture has a store of kinetic energy while the ball is moving, but the ball will eventually stop moving.

Rice is a store of chemical energy.

The tank contains water that has been lifted up by a pump. The water in the tank stores gravitational potential energy.

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3.5 Energy

Questions 1 Look at the picture of the circuit. Copy and complete these sentences. Choose from the stores and transfers of energy you have learnt about. a

energy is stored in the battery.

b

energy is transferred in the wires.

a food b gasoline (petrol) c a falling rock

PL E

2 Name the energy store in each of these. There may be more than one for each.

d a book that has been lifted up onto a shelf

3 a Name two energy stores that will last for a long time.

b Name one energy store, apart from thermal energy, that will not last for a long time.

SA M

4 Describe an example that shows thermal energy cannot be stored for a long time. 5 The human population in the world is growing. Many countries are developing rapidly.

Explain how this is affecting the amount of energy being used in the world. Use some examples of different energy stores and transfers in your answer. Discuss your answer with a partner. Activity

Finding energy stores and transfers

You will need some magazines with pictures that can be cut out. Work in pairs or small groups.

Look for pictures that show different energy stores and transfers. Some pictures may show more than one. Cut out the pictures. Stick the pictures on a large sheet of paper to make a poster.

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3 Forces and energy

Continued Your poster should show as many energy stores and transfers as possible. Make sure the energy stores and transfers in each picture are clearly labelled. Peer assessment Swap posters with another group. 1 Does the poster show all the energy stores and transfers?

PL E

2 Are all the energy stores and transfers clearly labelled? 3 What did you like about the other group’s poster?

4 Suggest one way that the other group might be able to improve their poster. Summary checklist

I can recall the ways that energy is stored and transferred. I can describe each energy store and energy transfer. I can give examples of each energy store or transfer. I can understand that some energy stores last longer than others.

SA M



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3.6 Changes in energy

3.6 Changes in energy In this topic you will: • learn about energy changing • discover that energy changes when something happens

Getting started

PL E

• learn how to give examples of changes in energy.

1 Make a list of all the energy stores and transfers that you can remember.

change event process

SA M

2 Give an example of each store or transfer on your list.

Key words

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3 Forces and energy

How does energy change? In Section 3.5, you learned that energy is something that must be changed or transferred in order to do something. Before energy can be changed or transferred, it is stored. When energy is stored, the energy is not doing anything.

PL E

The picture shows a cooking pot being heated on a fire. The fuel for the fire is wood. Wood is a store of chemical energy.

Burning the wood changes the chemical energy to thermal energy (heat). The thermal energy is then transferred to the pot and the food inside.

The people in the picture are walking up stairs. They are changing chemical energy from their food into kinetic energy for movement.

Energy changes can be useful.

SA M

The movement is taking the people higher, so kinetic energy is being changed to gravitational potential energy. This picture shows a power station.

This power station is changing energy.

Walking up stairs needs energy to be changed.

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How does energy change?

This power station is using the chemical energy stored in natural gas. The gas is burned, which changes chemical energy to thermal energy. The thermal energy is then changed to kinetic energy in large generators that spin around. The kinetic energy is then changed to electrical energy.

PL E

The electrical energy is then transferred through wires into homes and buildings.

Energy changes are not always helpful. Typhoons, hurricanes, earthquakes and tsunamis are some examples of how energy changes can be very dangerous. In all these examples, there is a process or event that changes or transfers the energy. For example, burning is a process.

Strong wind can transfer energy in a damaging way.

Burning changes chemical energy stored in a fuel to thermal energy.

You can represent the processes as arrows and draw diagrams to show changes in energy. Here are some other examples.

SA M

A fire that burns wood changes chemical energy to thermal energy. chemical

thermal

A television converts electrical energy to sound and light. sound

electrical

light

When a book falls from a shelf, that is an event. When the book is on the shelf, the book has stored gravitational potential energy. This energy is changed to kinetic energy as the book falls. You can also represent events such as this in a diagram. gravitational potential

kinetic

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3 Forces and energy

The energy changes shown in these diagrams are useful energy changes. That means the energy is changed in a way that we want. Some energy changes are not useful. You will learn more about energy that is not useful in Section 3.7.

Questions 1 Copy and complete the sentence. or

.

PL E

When something happens, energy is

2 The useful energy change in a candle can be written as

chemical to light

Write down the useful energy change in each of these. a

an electric lamp

b

a bus

c

a radio.

3 Draw diagrams to show the energy changes in:

a motorcycle that uses gasoline (petrol) for movement

b

a wood-burning fire used for cooking

c

a bird using movement to fly higher

d

a ball rolling down a hill.

SA M

a

Activity

Freezing water

Work in groups.

When you put water in the freezer, it turns into ice. Discuss and then answer these questions about this process in your group. 1 What happens to the temperature of the water in the freezer? 2 How can you tell the temperature has changed in this way, without using a thermometer or touching the water?

3 How is energy being transferred when the water freezes? 4 Where does this energy come from? 5 Where does it go?

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How does energy change?

Continued Once you have agreed on your answers, ask your teacher to check them. Make a display to show the energy change when water freezes. Your display could be a leaflet, a poster or a presentation.

Think like a scientist Candle energy

PL E

Your display should give other people the correct information as clearly as possible.

You will now do an experiment to investigate a change in energy. Work in pairs or small groups. You will need:

candle, safety glasses, glass beaker or a metal can, tripod and gauze, thermometer, timer, heat-proof mat, stirring rod, cooking oil, matches Set up the equipment as shown in the diagram.

SA M

1 Measure the temperature of the cooking oil and write this down.

2 Light the candle and place it under the beaker. Start the stopwatch or record the time.

3 Stir the cooking oil at regular intervals. Use the stirring rod. Do not stir with the thermometer!

4 Measure the temperature of the cooking oil every minute. Record both the time and the temperature.

5 Stop heating when the temperature of the cooking oil has gone up by 10°C. 6 Carefully blow out the candle.

This has been amended to include a lab coat, supplied in July. Tech-Set: new illustration has not been supplied

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3 Forces and energy

Continued  7 Draw a table for your results. 8 Draw a line graph of your results. Put the temperature of the cooking oil on the vertical axis. Questions 1 Explain why you should not use a thermometer for stirring.

PL E

2 Explain where the energy came from to heat the cooking oil.

3 Describe what happened to the candle during the experiment.

4 In this experiment, not all of the thermal energy is transferred to the cooking oil. List two other things that get heated in this experiment.

5 Suggest changes to this experiment to transfer more of the thermal energy into the cooking oil.

6 Explain why a line graph is a better way to display the results from this experiment than a bar chart. Self-assessment

Discuss each of these statements with your partner or small group.

SA M

• We worked safely at all times.

• We recorded all the results at the right times.

• We took readings from the thermometer as accurately as possible. • We put the correct column headings with units in the table. • We drew the graph correctly and it shows the trend in the results.

Summary checklist

I can understand that energy can be changed. I can give examples of some changes in energy. I can draw diagrams to show energy changes.

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3.7 Where does energy go?

3.7 Where does energy go? In this topic you will: • discover that when energy is changed, some of it may be wasted

Getting started

PL E

• learn that some of this energy can never be recovered.

Work with a partner. Discuss the energy that is changed or transferred in each of these processes. • Burning wood for cooking. • Walking up stairs.

Key words

dissipated recovered useful wasted energy

• Cycling on a level road.

SA M

In each case, state where the energy comes from and the useful energy that is changed.

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3 Forces and energy

Useful and wasted energy Every time you use energy to make something happen, energy is transferred or changed. Some of the energy transferred or changed is useful, but some of it is wasted. Look at the picture of fuel being added to a motorcycle. The motorcycle engine uses the chemical energy stored in the fuel.

PL E

This chemical energy is changed to useful kinetic energy to move the motorcycle and rider. But chemical energy from the fuel is also changed into thermal energy and sound energy.

In fact, only about 14 or 25% of the chemical energy in the fuel is used for movement.

The other 34 or 75% of the energy is wasted energy. This wasted energy is dissipated and cannot be recovered. Dissipated energy is energy that spreads out where there is no use for it.

SA M

You cannot gather thermal energy or sound and bring them back into one place to be stored, changed or transferred. Look at the two types of lamp in the picture.

A

Petrol (gasoline) is a store of chemical energy. The motorcycle engine changes only some of this into kinetic energy. The rest of the energy is wasted.

B

These two lamps emit the same brightness of light but they waste very different quantities of energy.

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3.7 Where does energy go?

Both lamps A and B in the picture change electrical energy to light energy. Lamp A only changes about 15% of the electrical energy into light. 85% of the electrical energy is wasted as thermal energy from this lamp. This is dissipated as thermal energy. Lamp B changes about 50% of the electrical energy into light. 50% of the electrical energy is dissipated as thermal energy from this lamp.

PL E

Every time energy is changed or transferred, there is some thermal energy is wasted. This wasted thermal energy is dissipated.

Even when you want to produce thermal energy, some of it is wasted. Look at the water being heated in this picture.

In the picture, chemical energy from wood is being changed to thermal energy by the process of burning. Thermal energy is being used to heat the water.

Thermal energy is also being used to heat the rocks, the metal container and the air around it.

SA M

Some of the thermal energy is escaping in the steam.

The fire is also changing energy into light. All these represent wasted energy that is dissipated and cannot be recovered.

Thermal energy from the fire is being used to heat water. Not all of the thermal energy can be made to go into the water – some of it dissipates.

For everything that uses energy change or transfer, some of that energy will always be dissipated.

Questions

1 Which of these terms describes energy that is dissipated? energy that spreads out and becomes less useful

energy that becomes more useful

energy that can be used later

energy that is not useful but can be stored

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3 Forces and energy

2 Which of these can be dissipated? Choose all that are correct. chemical

thermal

light

sound

elastic

3 List all the energy changes in these processes.

PL E

List the energy as either useful or wasted. a

Using electricity in a lamp.

b

Using petrol (gasoline) in a car engine.

c

Using electricity in a motor.

4 As you move away from a hot object, you feel less heat from it. The temperature will go down as you move further away.

22

Temperature Temperature

Temperature Temperature

Distance Distance

Distance Distance

33

44

Temperature Temperature

Temperature Temperature

Distance Distance

Distance Distance

SA M

Which of these graphs shows how the temperature changes with increasing distance from a hot object?

11

• How do you work out what the shape of a graph will look like? • Can you explain why you chose the answer that you did? You can do this by describing what will happen to the temperature in each case. Activity

Ripple tanks

Work in groups. You will need:

waterproof rectangular tray (about 40 cm × 20 cm × 5 cm), water, a ruler

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3.7 Where does energy go?

Continued 1 Put water into the tray so the water is about 1 cm deep. 2 Lift the short edge of the tray a little above the desk. Then drop the tray. You should see a wave move across the water. The wave should start at the end that was dropped and move towards the opposite end.

PL E

This has been amended to change character to Zara. Supplied in July. When located, please ensure that ‘box’ is changed to ‘tray’. Tech-Set: new illustration has not been supplied

SA M

drop this end of the tray

3 Count how many times the wave moves backwards and forwards across the tray until you can no longer see it.

4 Change the depth of the water. Can you make the wave travel across the tray any more times by changing the depth of water? 5 Now try making the wave go across the tray by lifting and then dropping the long edge. Does the wave travel across the tray any more times in this direction? Questions

1 State one variable that must remain the same when you change the direction of the wave. 2 Which way (along or across the tray) does the wave travel the longest total distance? 3 Name the energy that is stored by the wave as it moves. 4 Use words from the list to copy and complete the sentence. stays the same  dissipates  increases  goes slower As the wave travels, the energy in the wave ………………… .

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3 Forces and energy

Think like a scientist Energy dissipation In this task you will investigate the dissipation of energy. You will need: very hot tea in a cup, thermometer, plastic spoon,

Safety

PL E

timer or clock with a second hand

Take care not to scald yourself with the hot tea. Work as a whole class.

Taking turns, measure the temperature of the hot tea every minute. Stir the tea before measuring the temperature. Use the spoon, not the thermometer, to stir the tea.

Record the time and the temperature in a place where the whole class can see the results. Questions

Work on your own to answer the questions.

1 Plot a line graph with time on the horizontal axis and temperature on the vertical axis.

SA M

Make sure your line is as smooth as possible. It should go through all of the points if the temperatures have been measured correctly.

2 Describe the pattern shown in your graph. Use the words ‘temperature’ and ‘time’ in your description. 3 Explain why you should stir the tea before measuring the temperature.

4 The higher the temperature of the tea in the cup, the more thermal energy there is in the tea. What do the results show about what happens to the thermal energy with time?

5 List some places where the thermal energy could have gone. 6 Suggest how you could:

a make the tea cool more quickly, without adding anything into the tea.

b make the tea cool more slowly, without heating it again and without adding more hot tea.

7 Explain whether the tea in the cup will keep cooling, or whether it will stop cooling.

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3.7 Where does energy go?

Did you have any idea what shape the graph might be: • before you did the experiment? • when you looked at the temperatures that were recorded? Summary checklist

PL E

I can recall that when energy is changed or transferred, some of the energy is useful and some is wasted. I can understand the meaning of the word ‘dissipate’. I can understand that energy can be dissipated more easily in some ways than in others. I can understand that energy which has dissipated cannot be recovered.

Project: Discoveries about energy Background

string

James Prescott Joule was born in the year 1818.

pulley

SA M

Joule was interested in how things worked and where the energy came from to make things happen.

Joule made the machine shown in the picture.

He used the machine in the picture to show how energy could be changed.

thermometer

water

paddle

mass ruler

James Prescott Joule made this machine in the year 1845.

When the mass was allowed to fall, it pulled on the string.

The string passed over a pulley and was wrapped around a piece of wood. The piece of wood then rotated. This made a paddle rotate.

The paddle rotated in water.

Joule discovered that when he did this, the temperature of the water increased. Joule’s ideas and his results from experiments challenged the accepted ideas about energy. His ideas were not accepted at first.

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3 Forces and energy

Continued Your task Make a presentation to tell others about how Joule’s machine works. Your presentation should include this information: • The energy changes and transfers that happen in Joule’s machine. You should include the terms: • kinetic • thermal.

PL E

• gravitational potential

• What did Joule’s result show?

You should use all these words correctly: • mass • weight • gravity • height.

• You could finish your presentation by answering these questions.

SA M

Do you think all of the energy was changed in the way that Joule had wanted? If not, where did any wasted energy go?

Why were the old ideas about energy eventually rejected and Joule’s ideas accepted?

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3 Forces and energy

Check your Progress 3.1 Write the word used to describe each of these. a

The force of gravity on an object.

[1]

b

The quantity of matter in an object.

[1]

Explain why the Sun has more gravity than any of the planets.

[1]

b

The strength of gravity on Earth is .

PL E

3.2 a

Calculate the weight of each of these.

Show your working and give the unit in your answer.

c

i

a book of mass 

[2]

ii

a calculator of mass 

[3]

In the year 1959 a spacecraft called Luna 2 was launched from Earth. Luna 2 landed on the Moon. i

[1]

Describe how the mass of Luna 2 would compare between when it was on Earth and when it was on the Moon.

[1]

SA M

ii

Describe how the weight of Luna 2 would compare between when it was on Earth and when it was on the Moon.

3.3 a

b

Explain what keeps the Earth in its orbit.

[2]

Explain why the planet Mercury travels faster in its orbit than Earth does.

[1]

3.4 The diagram shows the Earth and Moon. The diagram is not to scale. a

b

c

Write the letter or letters where there will be high tide on Earth in this diagram.

There is also low tide at a place in the diagram.

[1]

A D

B C Earth

Moon

State the number of hours until the next low tide in the same place.

[1]

Draw a diagram to show the positions of the Earth, Moon and Sun that would produce the highest tides on Earth.

[1]

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3 Forces and energy

d

Use a word from the list to copy and complete the sentence.

[1]

gravity     force     mass     energy The Moon causes a tidal ……………….. on the Earth. 3.5 Which two measurements have the same units? Write the letter. weight and mass

B

mass and energy

C

energy and force

D

weight and force

PL E

A

[1]

3.6 a Which of these words means to spread out and become less useful?

[1]

thermal     decrease     dissipate     loss b

An electric motor works on electrical energy.

[2]

The motor changes electrical energy in three ways. Write the energy in the correct columns.

wasted

SA M

useful

3.7 Which row in the table shows the forces on a planet in orbit around the Sun? Put a tick (✓) in the box beside the correct row. air resistance

gravity

no

no

no

yes

yes

no

yes

yes

[1]

3.8 A container of water is placed over a fire that burns wood. a

Name the energy that is transferred from the fire to the water.

b

Not all of this energy is transferred to the water.



List two other places where this energy could go.accurate

[1] [2]

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4 Grouping and identifying organisms In this topic you will:

PL E

4.1 Characteristics of living organisms

• think about what makes living organisms different from non-living things

• learn about the seven characteristics of living organisms.

SA M

Getting started

In your classroom, find one living thing and one thing that has never been alive. With your partner, make a list of things that the living thing can do, but the non-living thing cannot do. Be ready to share your ideas with the rest of the class.

Key words

excretion growth movement nutrition organism reproduction respiration sensitivity

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4 Grouping and identifying organisms

Living and non-living How do you know when something is alive? If it is a person, you can check to see if they are breathing, or if they have a heartbeat. Plants don’t breathe or have hearts, yet they are alive. Living things are called organisms. Living organisms have a set of seven characteristics that make them different from non-living things. Movement: Living organisms can move.

PL E

Growth: All living organisms grow.

SA M

Nutrition: Plants feed by photosynthesis. Bears eat meat.

Sensitivity: Living organisms are sensitive to changes going on around them.

Excretion: Living organisms get rid of waste materials, such as carbon dioxide.

Reproduction: Living organisms can produce young.

Respiration: Food is broken down inside cells to provide energy.

Questions

These questions are about the picture of the polar bears. Copy and complete the sentences. Use these words. You can use each word once, more than once or not at all. carbon dioxide  chewing    feeding  growth  movement oxygen  sight  smell  reproduce  respiration

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4.1 Characteristics of living organisms

1 Another word for taking in nutrition is

.

2 Polar bears can sense things in their environment. For example, with of meat. their nose they can sense the 3 All living organisms excrete waste substances. Animals excrete when they breathe out. 4 Living organisms kind of organism.

to make more of the same

PL E

5 Young plants and animals get bigger. This is called …………………….. .

6 All living organisms break down some of the food they eat, to provide them with energy. This happens in a process called ……………………… . 7 Most living organisms can change the shape and position of their bodies. This is called ……………… . Activity 4.1.1 Is a car alive? The picture shows a car.

Here are some facts about cars. • Cars use fuel and oxygen.

SA M

• Inside the engine of the car, the fuel and oxygen provide energy to make the car move.

• The engine produces waste gases, including carbon dioxide. These are given off in the exhaust of the car.

• Some cars have sensors. For example, they can sense when it is dark and turn the lights on automatically. Questions

1 In your group, make a list of similarities between a car and living organisms. 2 Make a list of differences between a car and living organisms.

Summary checklist

I can list the seven characteristics of living organisms. I can describe the meaning of each of these characteristics.

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4 Grouping and identifying organisms

4.2 Viruses In this topic you will: • learn about the structure of a virus • discuss whether viruses are non-living or living. Key words

PL E

Getting started

Work with a partner to answer these questions.

Respiration is one of the characteristics of living things. List the other six characteristics.

SA M

Now explain the meaning of each of the words in your list.

electron microscope influenza protein replicate RNA virus

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4.2 Viruses

What is a virus? Viruses are very, very small. A virus is much smaller than one of your cells. You cannot see a virus with the kind of microscope that you use in school. To see a virus, you need to use a special kind of microscope called an electron microscope.

PL E

Viruses are not made of cells. They do not have a cell membrane or cytoplasm. The blue-green outer layer in the photograph is a coat made of protein. There are little pegs on the outside of this coat.

This scientist is working in Jakarta, Indonesia. She is using an electron microscope. The microscope is the grey object on the right-hand side of the photograph. It produces a picture on the screen in front of the scientist.

SA M

The orange part inside contains a substance called RNA. The RNA is made of little threads that contain a set of coded instructions for making more viruses.

This photograph of viruses was taken by using an electron microscope. The viruses in the photograph look 100 000 times bigger than they really are. It is almost impossible to imagine just how small a virus is.

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4 Grouping and identifying organisms

Think like a scientist Making a model of a virus You will need: modelling clay, paper that you can tear into little pieces, push pins

PL E

Use the materials to make: • an outer coat of protein

• some little threads of RNA, inside the protein coat • some pegs on the outer coat.

You could take a photograph of your model, then stick the photograph into your notebook.

How viruses replicate

SA M

Viruses cannot do anything at all on their own. They do not respire, feed, excrete or grow. They are not sensitive and cannot move. Viruses have to get inside a living cell before they can make copies of themselves. The brown viruses in the photograph are H3N2 influenza viruses. This kind of virus can invade (get inside) cells of birds, humans and other mammals. The viruses get into your body by going up your nose when you breathe in. The little pegs on the virus’s coat help it to stick onto one of your cells and then get inside the cell. When the viruses are inside the cell, each virus bursts open. The virus forces the cell to copy the instructions on its RNA, and make many new viruses. This is called replication. This kills the cell. Then the new viruses burst out of the dying cell, ready to infect more cells.

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4.2 Viruses

This makes the animal whose cells are infected feel ill. H3N2 viruses cause a very unpleasant and dangerous kind of influenza (flu). In 1968–1969, these viruses killed approximately one million people. These flu viruses are just one of thousands of different kinds of viruses we know about. Each kind of virus has a particular kind of cell that it infects. Some viruses infect plant cells.

PL E

In 2019, a new virus appeared. We do not know exactly where it came from, but scientists think it developed in a wild animal and then spread to humans. The new virus is similar to the viruses that cause flu and colds. Its official name is SARS-CoV-2. The illness it causes is called Covid-19. This stands for coronavirus disease 2019. The virus quickly spread all over the world.

This is a drawing of a SARS-CoV-2 virus. The red bits on the outside are called spike proteins. They help the virus attach to cells and get inside.

SA M

Many people get the virus without being ill at all, or just have mild symptoms. But in some people, it causes dangerous illness and even death. Scientists will work hard for many years to find the best ways of preventing this, including vaccination, and drugs to treat Covid-19. Activity 4.2.1

Are viruses alive?

Some scientists consider that viruses are living organisms. Others think that they are not. In a group of three, discuss the question: Are viruses living organisms? Make a list of reasons for your decision. Be ready to share your ideas with others.

Summary checklist

I can describe what a virus is and how it replicates. I can give reasons for classifying viruses as living or non-living.

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4 Grouping and identifying organisms

4.3 What is a species? In this topic you will: • look carefully for similarities and differences between organisms • compare two different species of organism

Getting started

PL E

• find out how scientists decide if two organisms belong to the same or different species.

All living things belong to groups called species.

Imagine you are looking at two birds in your garden. They look quite similar, but are not exactly the same.

Discuss this question with your partner: How would you decide if the two birds belong to the same species or two different species?

fertile identical infertile offspring species specimen variation

SA M

Be ready to share your ideas.

Key words

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4.3 What is a species?

Species Scientists group living organisms into different kinds. Each kind of organism is called a species. Activity 4.3.1 Comparing two species of elephant

PL E

With a partner, look at the two pictures of elephants. These elephants belong to two different species. Make a list of the similarities that you can see between the two species of elephant.

SA M

Then make a list of differences that you can see between them.

Indian elephant

African elephant

Species and reproduction

All the organisms in a species share the same characteristics but they are not all identical to each other. For example, some Indian elephants have straighter tusks than others. They have pink markings on their skin in different places. There is variation between the individual Indian elephants. Variation between individuals can sometimes make it difficult to decide whether two organisms belong to the same species. To be sure, scientists try to find out if they can reproduce with one another. Indian elephants reproduce only with other Indian elephants. They do not reproduce with African elephants. Each species reproduces only with

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4 Grouping and identifying organisms

other members of its own species. When they have offspring (children), the offspring belong to the same species as their parents. The offspring are fertile. This means they can also produce offspring. Organisms that belong to different species cannot usually reproduce with one another. Very rarely, two organisms from different species do reproduce together. This sometimes happens in a zoo. It can happen if two animals from different species are put into the same enclosure.

PL E

For example, a male lion and female tiger in a zoo sometimes reproduce together. They will only do this if they do not have a member of their own species to reproduce with.

The young animals that are produced are called ligers. Ligers are healthy animals. But ligers cannot reproduce. They cannot have offspring. They are infertile.

SA M

So, we can describe a species as a group of organisms that can reproduce together to produce fertile offspring.

A male lion (left) can breed with a female tiger (centre) to produce a liger (right).

Questions

1 Copy and complete these sentences. Choose from these words. bigger

different

identical

similar

Organisms that belong to the same species usually look to one another. They look

from organisms belonging to other species.

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4.3 What is a species?

2 Explain why biologists say that lions and tigers belong to different species, even though they can sometimes reproduce together. Think like a scientist Comparing organisms belonging to different species

You will need:

PL E

This task will give you practice in looking very carefully at specimens (samples) of organisms. You will also practise describing similarities and differences.

• specimens of two similar species of organism Safety

If you handle live organisms, wash your hands carefully afterwards.

Look carefully at the specimens. The organisms belong to two different species. Questions

1 Write down five similarities between the two species.

2 Now write down some differences between them. Try to find at least two differences.

SA M

3 Suggest what a scientist would do to be sure that these organisms really do belong to two different species.

Summary checklist

I can compare organisms belonging to different species. I can describe what is meant by the word ‘species’. I can explain how scientists decide whether organisms belong to the same species.

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4 Grouping and identifying organisms

4.4 Using keys In this topic you will: • learn how to use a key to identify an organism, or to classify it into a group

Getting started

PL E

• change a key from one style to a different style.

Discuss this question with a partner.

Imagine you have found an insect that you have never seen before. You want to know what its name is.

Key words

dichotomous key

SA M

How would you try to find out? Try to think of at least three ways in which you could do this. Which way do you think would be the best?

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4.4 Using keys

Identifying organisms Biologists often want to identify an organism that they have found. A good way to start is to look at pictures in a reference book, or on the internet. The biologist may be able to find a picture of the organism, with its name. But this does not always work.

PL E

Biologists also use keys to help them to identify organisms. A key is a set of questions about the organism you want to identify. The answer to each question takes you to another question. You work through all of the questions until you arrive at the name of the organism.

Here is a simple key to help someone to identify an organism. It is a dichotomous key. Dichotomous means ‘branching into two’.

SA M

You will have to imagine that you have the whole animal to look at, not just these pictures. To use the key: •

Choose one organism you want to identify.

•

Starting at the top of the key, answer the first question – yes or no?

•

Follow the line to the next question. Keep going until you arrive at the name of the organism.

Does it have legs?

Yes

No

Does it have more than six legs?

Is its body made up of rings?

Yes

No

Yes

No

crab

Does it have four wings?

earthworm

slug

Yes

No

dragonfly

housefly

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4 Grouping and identifying organisms

Keys are sometimes arranged differently. Here is the same key set out in a different way. Instead of a question, the key starts with a pair of statements to choose from. Instead of arrows pointing to where you go next, there is a number telling you which pair of statements to go to next. 1 a It has legs.

go to 2 go to 3

2 a It has exactly six legs.

go to 4

PL E

b It does not have legs.

b It has more than six legs.

3 a Its body is made up of rings.

b Its body is not made up of rings. 4 a It has four wings. b It has two wings.

crab

earthworm slug

dragonfly housefly

Try working through the key to identify the dragonfly. You will work through steps 1a, 2a, 4a.

SA M

Questions

1 Using the key above, which steps would you go through to identify the earthworm?

2 Explain why the key is called a dichotomous key.

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4.4 Using keys

Think like a scientist Using a key to identify species of fish The pictures show four species of fish.

D

SA M

C

B

PL E

A

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4 Grouping and identifying organisms

Continued Questions 1 Use this key to identify the four species of fish. Remember: • Take one fish at a time. Start with fish A.

PL E

• Start at the top of the key and work your way through the questions and answers until you arrive at the name of the fish. • Then do the same for fish B, and so on.

Does it have stripes?

Yes

Yes

No

Are the stripes vertical?

horn shark

No

Do the fins have spines?

Yes

No

clown fish

SA M

dragon fish

zebra fish

2 Here is the beginning of the same key, written out in the style that uses pairs of statements for you to choose between. 1 a The fish has stripes. …………………….. go to 2 b The fish does not have stripes. …….…… horn shark



Write out the whole of the key in this style.

Which style of key do you find easier to use? Why do you think it is easier? Summary checklist

I can use a dichotomous key to identify an organism. I can write a key in a different style.

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4.5 Constructing keys

4.5 Constructing keys In this topic you will: • learn how to create your own key

Getting started

PL E

• learn how to change your key following feedback.

Here are four questions that could be part of a dichotomous key to identify some different plants. • Is the plant tall?

• Do the flowers on the plant have five or more petals? • Does the plant have dark green leaves?

• Are the leaves darker on the upper surface than on the lower surface? With a partner, think about these four questions.

Which two questions would not be good to use in a key?

SA M

Explain your answer.

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4 Grouping and identifying organisms

Constructing a key Look at the photographs of four learners. Imagine you are going to construct a key to help someone to identify these learners.

Step 1

PL E

Think of a way you can split the learners into two groups. For example, you could split them into male and female learners. So, your first question could be: Is the learner female?

Step 2

Deidre

Now look at just one of these groups – the female learners, for example. Think of a way to split these into two. For example, you could use the colour of their hair.

Step 3

Repeat Step 2 until you have thought of ways to identify each learner in turn.

SA M

Now use your ideas to complete the ‘Think like a scientist’ activity.

Ari

Ben

Elsa

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4.5 Constructing keys

Think like a scientist Making keys to identify four learners 1 Copy this key and complete it, to help someone to identify each of the four learners in the photographs. Is the learner male?

Yes Ben

No

PL E

Yes

No

Yes

No

Ari

Deirdre

Elsa

2 Now try writing your key in the other style, using pairs of statements, 1a and b, 2a and b and so on. You could use the same pairs of features as for your first key, or you could challenge yourself to use different pairs. Peer assessment

SA M

Exchange your key with a partner.

For each of the four statements below, give your partner: 2 marks if they did it really well

1 mark if they have done it quite well

0 marks if they have done it very badly, or not at all

• They have written a key that is made up of pairs of statements to choose from.

• It is easy to choose between the statements each time. • There are no more than three pairs of statements to choose from. • The key works – someone can use it to identify the four learners.

With your partner, look at the marks you have given each other. What could each of you do better next time?

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4 Grouping and identifying organisms

Think like a scientist Writing a key to identify species of cat

Leopard

SA M

Pallas’s cat

PL E

The photos show four different species of cat.

Lynx

Tiger

1 Write a key that someone can use to identify these four cat species. You can use either style of key. 2 Exchange your key with a partner and ask them to try it out. Does it work? Ask them for suggestions for improving it. Use their ideas to make some changes to your key so that it works better.

What problems did you have writing your key? How did you solve them?

Summary checklist I can write my own key. I can use feedback from a user to improve my key.

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4.5 Constructing keys

Project: Consequences of classifying organisms In this project, you will work in a group to think about how different decisions about classifying organisms can affect their chances of survival. You will produce a short play to show some of the viewpoints of people who may be affected by these decisions. Biologists often disagree about whether two kinds of organism should be classified as the same species or as different species. This can cause arguments about whether to try to save a particular kind of organism, or to protect a habitat.

PL E

Imagine there is a small area of rainforest where farmers want to plant coffee trees. Coffee traders want to build a factory to process and pack coffee beans, to sell.

Some biologists say that there are 200 different species of birds that live in this forest. If the forest is cut down, some of these species may become extinct. But other biologists disagree. They say that 100 of these ‘species’ are not different species at all. In your group, plan and act a short scene involving these people: I am sure there are at least 200 different species of bird here.

It was noted at an earlier proof stage that these artworks are very Primary level. They need to be redrawn.

If we build a coffee packing factory here, we can employ a lot of people.

SA M

Tech-Set:

I think a lot of your species are not different species at all; but certainly there are at least 100 different species of bird in the forest.

If I can plant coffee trees here, I can make a lot of money.

If you wish, you could include other people, such as children who like to play in the forest, or someone from an international conservation organisation.

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4 Grouping and identifying organisms

Check your Progress 4.1 The list describes some of the features of a horse. It can move.

•

It has a heart.

•

It has hair.

•

It feeds.

•

It respires.

•

It can sense changes in its environment.

•

It has a brain.

a

Write down each feature in the list that is a characteristic of all living things.

[4]

b

Write down two more characteristics of living things that are not included in part a.

[2]

PL E

•

4.2 The pictures show some animals that belong to different groups. B

C

D

E

SA M

A

Use the key to classify each animal into the correct class.

1

[5]

a has three pairs of legs………………………………………   class insects

b has more than three pairs of legs………………………   go to 2

2

a b  ody has many segments (rings) with a pair of legs on each segment…………………………………   class myriapods

b does not have a pair of legs on each segment…………   go to 3

3

a has eight legs………………………………………………   class arachnids

b has more than eight legs…………………………………   class crustacea

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4 Grouping and identifying organisms

4.3 A scientist studies birds in New Zealand. The photographs show two kinds of parakeet that live there.

Yellow-crowned parakeet

PL E

The scientist wants to find out if these two kinds of parakeet belong to different species.

Red-crowned parakeet

She searches in suitable habitats for pairs of parakeets that are making nests.

She never finds a yellow-crowned parakeet that has paired up with a red-crowned parakeet. The scientist concludes that the yellow-crowned parakeet and red-crowned parakeet belong to two different species.

SA M

a

What evidence does she have for making this conclusion?

b

[2]

Suggest what the scientist should do to be even more certain that her conclusion is correct. Choose from:

• looking at stuffed specimens of parakeets in a museum • checking more pairs of parakeets in the wild

• looking at other species of parakeets.



Explain your answer.

[2]

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4 Grouping and identifying organisms

4.4 The photograph shows six flowers, A to F. A is Limnanthes

D is Lunaria

B is Viola

E is Erodium

C is Potentilla

F is Silene B

C

SA M

PL E

A

D

E

F

Here is part of a key that someone could use to identify each of the flowers. Copy and complete the key.

1

[4]

a The flower has exactly four petals. ……………………    Lunaria

b The flower has more than four petals. ………………..    go to 2

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5.1 Metals and non-metals

5 Properties of materials In this topic you will:

PL E

5.1 Metals and non-metals • list the properties of metals and non-metals

• learn about the uses of metals and non-metals. Getting started

Look around the room you are in. Can you identify at least five different metals?

SA M

How do you know that they are metals? Compare your ideas with a partner.

Key words brittle conduct ductile insulators magnetic malleable materials shatter shiny sonorous

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5 Properties of materials

Metals Metals are very useful materials. Materials are the substances from which objects are made. There are many different metals. Metals are used to do different jobs.

Iron is used for bridges because it is strong.

PL E

Metals are strong and tough. They do not shatter when dropped and they do not crack easily. They can hold large weights without breaking. Metals are shiny when they are freshly cut or polished.

Author needs to provide an additional reason why gold is used to make jewellery. 'Because it's shiny…' is a bit lame. Tech-Set: no comment within query log. Please advise

Gold is used for jewellery because it is shiny.

SA M

Metals can be bent to shape them. Metals are malleable, which means they can be hammered into shape.

Iron is malleable.

Metals are ductile, which means that they can be drawn out into wires.

Copper is ductile.

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5.1 Metals and non-metals

Metals make a ringing sound like a bell when they are hit; the word for this is sonorous.

PL E

Cymbals make a ringing sound when hit.

Most metals do not melt easily. They have high melting points and high boiling points. Mercury is the only metal that is liquid at room temperature.

A lot of heat is needed to melt metal.

SA M

Metals are good conductors of heat. When you touch them they conduct heat energy away from the hand so they feel cold.

Steel conducts heat well, which is useful for cooking pans.

Some metals are magnetic. Iron, steel, nickel and cobalt are magnetic.

Some metals are magnetic.

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5 Properties of materials

Metals are good conductors of electricity. This means that an electric current can flow through them. You need to remember that: the surface of most metals will become dull after a while

•

big lumps of metal are hard to test for flexibility

•

bottles and cups also make a ‘ringing’ sound when they are hit, but they are not made of metal.

Questions 1 List ten metals.

PL E

•

Copper is used for electrical wiring because it conducts electricity well and is flexible.

2 Why are gold and silver used for jewellery? 3 Why is copper so useful?

4 What do ‘malleable’ and ‘ductile’ mean? 5 What are Olympic medals made from?

SA M

6 Where are metals found in the Periodic Table? Think like a scientist

Properties of materials

In this task you will investigate metal items such as electrical wire, scissors and a hammer. 1 Describe each item.

2 If you know what it is made from, name the metal. If you don’t know, try to find out. 3 Suggest which property of the metal is important in the function of this item. 4 Make a table of your results like this: Item

Metal

Useful property

Electrical wire

Copper

It conducts electricity. It is ductile.

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5.1 Metals and non-metals

Non-metals Non-metals are often very useful because of the chemical reactions they have with other substances. There is a lot of variation between non-metals.

Sulfur is added to rubber to make it hard.

PL E

Properties shared by almost all non-metals Non-metals look dull. They do not reflect light very well and the surface is not as smooth as metals. Non-metals that are solids are brittle. If you drop them they may shatter.

Most non-metals do not conduct heat energy well. This is very useful because some of them can be used to make handles for cooking pans, for example.

Most non-metals do not conduct electricity. This is very useful because some can be used to make coverings for electric plugs and cables, for example. They are known as insulators; this means they do not conduct heat or electricity.

Pure oxygen is used in hospitals for people with breathing difficulties.

SA M

Properties shared by many non-metals Non-metals are not as hardwearing as metals. Many non-metals are gases.

The non-metals that are not gases have low melting points and low boiling points.

Chlorine is used to kill bacteria. For example, it can be dissolved in water and then added to swimming pools.

Carbon is used to purify water and to treat indigestion.

These balloons are filled with helium.

Silicon is used to make computer chips.

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5 Properties of materials

Questions 7 Name five non-metals, other than sulfur and helium. 8 What is sulfur used for? 9 What property of helium makes it useful in balloons? 10 Where would you find the non-metals in the Periodic Table? Summary checklist

SA M

PL E

I can recognise the properties of metals and non-metals. I can identify the useful properties of metals and non-metals for a particular function. I can name ten metals and five non-metals.

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5.2 Comparing metals and non-metals

5.2 Comparing metals and non-metals In this topic you will: • compare the properties of metals and non-metals

Getting started

PL E

• investigate materials and decide if they are metals or non-metals.

What do the terms ‘ductile’, ‘sonorous’, ‘malleable’ and ‘brittle’ mean?

contact distinguish examine

SA M

Draw cartoon diagrams to help you explain their meanings.

Key words

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5 Properties of materials

Comparing metals and non-metals Metals and non-metals have different properties. Non-metals

• Most are solid at room temperature.

• Many are gases at room temperature.

• They are shiny.

• They are dull.

• They do not shatter.

• They are brittle.

• They conduct heat energy well.

• They do not conduct heat energy well.

• They conduct electricity.

• Most do not conduct electricity.

• They are malleable. • They are ductile.

SA M

• They are sonorous.

PL E

Metals

Look carefully at this photograph of a market scene. What do you see?

Questions

1 List five objects in the photograph of a market that are made of metal and five that are made of non-metals. 2 A material is dull, brittle and does not conduct electricity. Is it a metal or non-metal?

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5.2 Comparing metals and non-metals

3 Mercury is a metal. What unusual property does it have? 4 Write down two things that a metal can do better than a non-metal. Think like a scientist Investigating materials

You will need:

PL E

In this task, you will be given a number of different materials to investigate. You will examine each material closely and test it so that you can distinguish (identify) which are metals and which are non-metals.

a selection of materials to test, electrical wires, a lamp, a cell (battery), crocodile clips

1 Ask a number of questions for each of the materials you investigate. • What does the material look like? Is it shiny or dull? • Does it make a ringing sound when you hit it? • Is it brittle? • Can you bend it?

SA M

• Does it feel hot or cold?

cell

• Does it conduct electricity?

2 To test if the material conducts electricity, you can set up a circuit as shown in the diagram. Before you start, check that the lamp is working by connecting the crocodile clips together with no test materials. When you carry out the test make sure you have good contact between the crocodile clips and your test material.

lamp

clips

Testing a material to see if it conducts electricity.

Question

1 Draw a table for your results. Decide if each material is a metal or and non-metal.

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5 Properties of materials

1 Were any of the materials difficult to place in the metals or non-metals group? Explain your answer. 2 Which do you think was the most useful test to distinguish between metals and non-metals? Activity 5.2.1

PL E

Researching metals and non-metals

Choose one metal and one non-metal. Use reference books and the internet to find out about each of them. Here are some useful questions you could research. • What is the metal or non-metal used for? • What are its properties?

• How are these properties useful? • Where is it found?

• Does the metal or non-metal need to be processed before it can be used? If so, how is this done? • Are there any other interesting facts about it?

SA M

Present your research as reports or posters.

Write a paragraph comparing your metal and non-metal. Useful words and phrases might include ‘whereas’, ‘lighter than’, ‘higher melting point than’, ‘compared with’. Make sure you actually compare the two and do not just list the two sets of properties. For example: Metals have shiny surfaces whereas non-metals have dull surfaces.

Summary checklist

I can distinguish between metals and non-metals. I can carry out investigations to distinguish between metals and non-metals.

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5.3 Metal mixtures

5.3 Metal mixtures In this topic you will: • learn about metal mixtures (alloys)

Getting started

PL E

• use particle theory to explain the differences in the properties of metals and their alloys. Key words

Look at the diagrams below. Are they elements, compounds or mixtures? Give reasons for your answers. A

B

C

D

alloy bronze disrupt steel

SA M

SEE QUERY LOG This is a repeat of question 2.7 in Check your progress on page 66.

One of them should be replaced. The item here is a repeat of 2.7 in Check your progress on page 66, one of which should be replaced. Tech-Set: no comment within query log. Please advise

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5 Properties of materials

Alloys Metal mixtures are called alloys. Alloys are made by mixing different metals together and melting them. The atoms of the different metals mix but do not bond together. The properties of the alloys are different from the metals they contain.

SA M

PL E

Bronze is an alloy made by mixing copper and tin. Bronze is harder than either copper or tin.

People learnt to melt copper and tin together to make bronze a very long time ago. This bronze head (left) was made in what is now Iraq, more than 4000 years ago. The statue on the right was made in Greece, about 2500 years ago

Steel is an alloy, but an unusual one because one of the elements in the mixture is not a metal. Steel is a mixture of iron and carbon. Pure iron is not hard enough to be very useful but when it is mixed with other elements to form steel it is much harder. Sometimes, chromium and nickel are also added to steel. This type of steel does not rust and is used for cutlery. The reasons why the alloys have different properties from the pure metal is to do with the arrangement of the particles of the elements. In a pure metal, the atoms are all the same size and arranged in regular rows. The layers can slide over one another easily. This is what happens when the metal is hit with a hammer. What do we call this property? This also happens when the metal is stretched out. What do we call this property?

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5.3 Metal mixtures

force

force

PL E

When a force is applied, layers slide over one another easily in a pure metal.

a different sized atom disrupts the regular pattern

the atoms cannot slip past one another easily now.

An alloy. The layers of atoms can’t slide over each other as easily now. They get stuck in place. This makes the alloy a lot harder and stronger than the original metal.

Think like a scientist

Modelling a metal and an alloy

SA M

You will need:

The apparatus as shown in diagram.

syringe diluted washing up liquid

1 Make rows of small bubbles in the dish, as shown in the diagram. Push the syringe plunger in slowly and steadily to make sure the bubbles are all the same size. The bubbles represent the atoms in a metal. 2 Fill the dish with bubbles to model the close packed arrangement of atoms. Questions

Petri dish

a bubble raft A Petri dish containing diluted washing up liquid.

1 Do the bubbles line up in rows?

2 What happens when a bubble bursts?

3 Can you see how easily the rows of bubbles slide past each other? Describe what you see.

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5 Properties of materials

Continued Inject a larger bubble into the middle of the dish. You do this by pushing harder and for longer. You may have to have several goes to achieve it – it takes a bit of practice. This is like adding an atom of a different metal. You now have a model of an alloy. 4 Can you see how this disrupts the regular pattern of bubbles? Describe what you see.

PL E

How good a model of the particle arrangement in an alloy was this? How well did it help you to understand the idea?

Alloys in everyday life Coins

SA M

The coins in your pockets are made from alloys. Pure metals are too soft to withstand all the wear they get. The coins that look silver are not made of silver – it is too soft and far too expensive. The silver coins are made of alloys containing copper and nickel. The copper coins contain copper, zinc and tin. Coins must be hardwearing but also malleable enough to be stamped with complex patterns.

Jewellery

Most gold jewellery is not pure gold; it is an alloy of gold and copper. Pure gold is soft. If you used pure gold for something like a wedding ring (that gets a lot of wear and tear) it would wear away. A wedding ring should be made from something stronger. Pure gold is 24 carat: that means that 24 parts out of 24 are gold. 18 carat gold has 18 parts out of 24 of pure gold, and six parts of other metals such as copper, silver or zinc.

Aeroplanes

The metal used to build planes needs to be light but very strong. Planes are mainly made of aluminium, but pure aluminium would not be strong enough and the plane’s wings would fall off because of the great stress put on them during flight. By adding magnesium and copper, an alloy called duralumin is formed. Duralumin is about five times stronger than pure aluminium.

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5.3 Metal mixtures

Artificial joints

PL E

The joints in our bodies take a lot of wear and tear. Sometimes, the joints are attacked by arthritis. This is a very painful and crippling disease. Now people can be fitted with replacement joints. These are made of plastic and alloys, often alloys of titanium.

SA M

X-ray of the pelvis showing a hip replacement.

Titanium hip joint

Modern alloys

Modern alloys have been developed that have some very useful properties. Some glasses f rames are made of shape memory alloy. This alloy is called Nitinol. Nitinol is made of nickel and titanium.

Questions

SEE QUERY LOG No information is given about properties (returning to its original shape when heated), but knowledge is needed to answer Q9 on page 159. No information is given about the properties of shape memory alloys in the LB text, but question 9 on p159 expects some knowledge of these. Tech-Set: no comment within query log. Please advise

1 What is an alloy?

2 Which properties of aluminium make it useful for building planes?

3 Why is an alloy of aluminium used for making planes instead of pure aluminium?

4 Pure gold is 24 carat gold. What does this mean? 5 Explain the difference between the purity of 18 carat gold and 24 carat gold.

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5 Properties of materials

6 Why do we not use pure silver for our coins? 7 Why do we use pure copper for our coins? 8 What properties must an alloy used inside the body have? 9 Why are some glasses frames made from shape memory alloy?

Brass and bronze

PL E

Brass is an alloy of copper and zinc. There are different types of brass, made by using different amounts of copper and zinc. Sometimes, other elements such as lead, aluminium, manganese or silicon are added. Look at the table of information about copper, zinc and brass. Copper

Element or mixture?

element

Zinc

Brass

element

mixture

SA M

Name

Appearance

reddish brown soft metal

silvery grey soft metal

golden yellow, reddish gold or silver soft alloy

Melting point

1085 °C

419.5 °C

900−1000 °C

Properties

very ductile and malleable

less ductile and malleable than copper

less ductile than copper; more malleable than zinc and copper

conducts heat and electricity well

conducts heat and electricity less well than copper

conducts heat and electricity less well than zinc

Example uses electrical wiring; central to cover iron in a thin heating pipes layer to prevent it from rusting

resistant to corrosion musical instruments, plumbing

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5.3 Metal mixtures

Look at the melting points: copper and zinc have just one temperature listed. However, brass has a range of temperatures. There are many different types of brass, which are made by using different amounts of copper and zinc. So, there is no specific melting point for brass; it depends on the proportions of copper and zinc that have been used.

Copper

Tin

Bronze

Element or mixture?

element

element

mixture

Appearance

reddish brown soft metal

white metal

reddish brown not as bright as brass

Melting point

1085 °C

232 °C

860 −1150 °C

Properties

very ductile and malleable

soft, ductile and malleable

less ductile than copper; hard; brittle

conducts heat and electricity well

conducts electricity less well than copper

good conductor of electricity

does not corrode readily

corrosion resistant

coating the inside of food cans and in many different alloys

bronze sculptures; bells and cymbals; ship fittings (especially parts which are submerged under water); electrical connectors

SA M

Name

PL E

Another alloy of copper is bronze. Bronze is an alloy that is made by mixing copper with tin. Sometimes, other elements such as manganese, phosphorous, aluminium or silicon are added. Mixing different amounts of copper and tin makes the different forms of bronze. Each different mixture has its own different melting point.

Example uses

electrical wiring; central heating pipes

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5 Properties of materials

Questions 10 Why is a range of temperatures given for the melting point of bronze? 11 Give one property that brass and bronze share. 12 Give one property that copper and zinc share.

Summary checklist

PL E

13 Give one difference in properties between copper and tin.

SA M

I can describe some alloys and their uses. I can explain that alloys have different properties from the metals they are made from. I can explain the differences in the hardness of metals and their alloys using particle theory.

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5.4 Using the properties of materials to separate mixtures

In this topic you will:

PL E

5.4 Using the properties of materials to separate mixtures • use what you know about mixtures to separate them • choose apparatus to carry out a practical task • carry out practical work in a safe way. Getting started

1 What is the difference between a mixture and a compound? Discuss it with a partner.

condenser conical flask filter funnel filter paper

SA M

2 How could you separate a mixture of dry rice and peas? Discuss your ideas with a partner and be prepared to share them with the class.

Key words

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5 Properties of materials

Making mixtures Mixtures contain different substances that are not combined together chemically. You made a mixture with iron filings and sulfur in topic 2.7. You separated the iron and sulfur in your mixture by using a magnet. You used the difference in the properties of iron and sulfur to separate them. Iron is magnetic; sulfur is not magnetic.

PL E

Separating mixtures

Copper sulfate and water

The evaporating dish contains a mixture of water and copper sulfate. If it is left in a warm room, the water evaporates and leaves the copper sulfate behind in the dish.

Food dye and water

A mixture of food dye and water can be separated by using a piece of apparatus called a condenser. It is used to separate mixtures of two liquids.

SA M

The water and food dye mixture is heated and boils. The liquid water reaches the temperature where it changes state and becomes a gas. Water that is in the gas state is called steam when it has been formed by boiling the water. The gas travels along the tube into the condenser. The cold water that is circulating around the outside of the condenser cools the gas down. This makes the gas condense back into liquid water. The liquid water collects in the beaker. The food dye remains in the heated container.

The water evaporates and leaves the copper sulfate in the evaporating dish.

The food dye and water have different properties that allow you to separate them – they have different boiling points. water out

100 °C

the steam cools and condenses as water

the water in the red solution evaporates as steam

condenser

mixture of water and red food dye

cold water in heat

pure water

Separating water from a mixture of food dye and water.

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5.4 Using the properties of materials to separate mixtures

Questions 1 Explain how the water in the flask changes to a gas. 2 Explain how the steam changes back into a liquid in the condenser. 3 Which different properties of the water and the food dye are used to separate them? Think like a scientist

PL E

Separating sandy, salty water

Your task is to separate a mixture of sandy and salty water. You will need:

The apparatus shown in the diagrams.

clear liquid

beaker

filter funnel filter paper

safety glasses

tongs

clay pipe triangle

conical flask

tripod

clear liquid

bunsen burner

SA M

sandy, salty water

evaporating dish

1 Prepare a filter paper and place it in a filter funnel. Place the funnel in the conical flask. 2 Pour the mixture into the funnel. Take care to add it slowly so that the mixture does not go down the outside of the filter paper. Do not disturb the wet filter paper because it tears easily. 3 When you have filtered all the mixture, leave the filter paper in a warm place to dry. 4 Place the clear liquid from the conical flask in an evaporating basin. Wear safety glasses. Heat this gently. When the liquid starts to spit, remove it from the heat. 5 Leave the liquid in a warm place to evaporate. Questions

1 Suggest why the sand remains in the filter paper. 2 One group of students thought their mixture was taking too long to filter so they used a pencil to stir it up while it was in the filter paper. Explain why this is not a good idea.

3 What safety precautions should you take when heating the salty water? 4 How could you obtain the water from your mixture? 5 The salt left in the evaporating basin is a little dirty. Suggest what you could do to get cleaner salt.

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5 Properties of materials

How carefully did you carry out this practical task? How well did you consider safety? How could you improve the way you carry out a practical next time you do one? Think like a scientist Separating two solids

PL E

If you mix powdered black carbon and table salt together you have a mixture of two solids.

How can you separate the carbon from the salt? What do you know about the properties of carbon powder and table salt that might be useful here? Make a plan of how you could do this. Remember to think about safety.

Make a list of the equipment you would need. Discuss it in your group.

black carbon

beaker

salt

Making a mixture of powdered carbon and table salt.

Share your ideas with the class.

SA M

Did you change any of your ideas when you discussed them with the class? Carry out your plan, once it has been checked for safety. Questions

1 Which properties of the two solids did you decide to use to help separate them? 2 Write down your final list of the equipment you will need. 3 Write an outline of your final plan. Explain how the steps will enable you to separate the two solids. Draw diagrams if that helps to make your plan more clear.

4 What safety precautions should you take? Self-assessment

How successful were you in separating the two solids? How could you improve your results?

Summary checklist

I can identify properties of different substances in a mixture and use those to separate them. I can choose appropriate equipment for a practical task. I can carry out a practical task safely.

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5.5 Acids and alkalis

5.5 Acids and alkalis In this topic you will: • learn about the properties of acids and alkalis • learn how to work safely with acids and alkalis

Getting started

PL E

• find out about hazard symbols.

acid alkalis corrosive flammable harmful irritate oxidising toxic

SA M

What do you think of when you hear the word ‘acid’? Write down five words that describe what you think an acid is. Share these with a partner. Did you both come up with same or similar words? Be prepared to share them with the class.

Key words

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5 Properties of materials

Acids are everywhere Many things contain acid. Some foods contain acid. These foods have a sour, sharp tangy taste. Lemons and limes taste sour. They contain citric acid. This is a weak acid.

PL E

Common acids in the laboratory are hydrochloric acid, sulfuric acid and nitric acid.

SA M

Foods containing fruits often contain acids.

Some acids are dangerous

Some acids are strong. They are corrosive. The bottles have a hazard warning label. If strong acid gets onto your skin, it will dissolve the skin. You will get a chemical burn. Always use eye protection when using acids. Acids can be diluted with water. This makes them less dangerous.

dilute Sulfuric Acid

hydrochloric Acid

dilute Nitric Acid

Dilute acids are still harmful, they can irritate your skin and eyes. The bottles have hazard warning labels. If you spill acid, wash the area with lots of water. The water dilutes the acid.

Questions

1 Name a food that contains acid.

2 Describe the taste of lemons and limes. 3 What does corrosive mean? 4 What should you do if you spill acid?

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5.5 Acids and alkalis

Alkalis are everywhere Many cleaning products contain alkalis such as sodium hydroxide, which is a compound of sodium, hydrogen and oxygen. Sodium hydroxide is a strong alkali. Strong alkalis are dangerous. They are corrosive. If strong alkali gets on your skin, it dissolves your skin. Your skin feels soapy. You get a chemical burn. Alkalis are harmful if you get them in your eyes. Always wear eye protection when using alkalis.

PL E

Alkalis can be diluted with water. This makes them less dangerous. Common alkalis found in the laboratory are sodium hydroxide, potassium hydroxide and calcium hydroxide.

Acids and alkalis are chemical opposites. They cancel each other out when they are mixed together. The acidity or alkalinity of a substance is a chemical property of that substance.

SA M

sodium hydroxide

All these products contain alkalis.

Strong sodium hydroxide is corrosive.

Working safely with acids and alkalis When you handle chemicals you should: •

stand up to work, so that if you spill something it does not spill on to you

•

wear safety glasses, so nothing gets into your eyes

•

take the top of the bottle and place it upside down on the work surface, so that it does not get acid onto the surface or dirt into the acid

•

replace the bottle top as soon as you have finished using the bottle. This prevents spills and reduces the risk of replacing the wrong top on the wrong bottle.

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5 Properties of materials

Hazard warning labels Many chemicals are hazardous. Their bottles are clearly labelled with hazard warning symbols so that you know you must handle them carefully. Here is a list of the most common hazard symbols and what they mean.

A substance that can catch fire easily.

SA M

Flammable

PL E

Explosive

A substance that can explode if it comes into contact with a flame or heat.

Oxidising

A substance that gives off a large amount of heat when in contact with other substances.

Corrosive

A substance that can destroy living tissue. It can cause burns.

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5.5 Acids and alkalis

Hazardous to the environment

A substance that can kill or damage living things in the environment.

A substance that can cause harm such as irritating your skin and eyes.

SA M

Health hazard

A substance that can poison you.

PL E

Toxic

Serious health hazard

A substance that can cause a serious problem to your health.

When you use chemicals in the laboratory, make sure you look at the hazard symbols and listen to advice on how to use them safely.

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5 Properties of materials

Activity 5.5.1 Learning the hazard warning symbols. You will need: scissors • card •

PL E

Make three sets of cards: • one set with the hazard warning symbols on them • one set with the names of the hazards on them • one set with the details on them.

You must make up a game with these cards to help you learn the symbols and their meanings.

Play your game with a partner, and then play their game. Peer-assessment

SA M

Was your partner’s game useful to help you learn the symbols? How could they improve their game? How did your game compare?

Which methods of learning information like this are the most helpful to you? Summary checklist

I can identify the properties of acids and alkalis. I can explain how to work safely with acids and alkalis. I can identify and understand the hazard warning symbols.

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5.6 Indicators and the pH scale

5.6 Indicators and the pH scale In this topic you will:

PL E

• learn how to tell an acid from an alkali • learn how to make and use indicators

• use the pH scale to find out more about acids and alkalis. Getting started

indicator litmus neutral pH scale universal indicator

SA M

Draw one of the hazard warning symbols. Show it to your partner. Can they identify it? Test each other on as many as you can remember. Check up and see how many you got correct and how many you forgot.

Key words

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5 Properties of materials

Which is which?

PL E

These three containers all look the same. One contains water, one contains acid and one contains alkali.

You can tell them apart when you add a few drops of an indicator. An indicator turns one colour in an acid and a different colour in an alkali. Red cabbage juice can be used as an indicator.

SA M

red cabbage juice

Red cabbage indicator turns acids red in acids, blue in water and yellow in alkalis.. So, you now know what was in each beaker.

hydrochloric acid

water

sodium hydroxide

Indicators can be made from the brightly coloured berries, flowers and other parts of plants. These include: •

red cabbage

•

blackcurrant

•

beetroot.

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5.6 Indicators and the pH scale

Questions 1 How does an indicator show whether a substance is an acid or an alkali? 2 What is the colour change when red cabbage juice is added to lemon juice?

Litmus

PL E

Litmus is a very common indicator. It is a dye. You usually use litmus paper, which is made by soaking absorbent paper in litmus solution.

Litmus turns red in acids. Litmus turns blue in alkalis. Litmus turns purple when it is in a neutral substance. A neutral substance is one that is neither acid nor alkali. Litmus turns purple in water. Water is neutral. This means water is neither an acid nor an alkali.

This table shows the colours litmus goes in some substances and what those colours mean. Litmus colour

Type of substance

hydrochloric acid

red

acid

sodium hydroxide

blue

alkali

water

purple

neutral

lemon juice

red

acid

calcium hydroxide

blue

alkali

SA M

Substance

Questions

3 What does litmus do when it is added to sodium hydroxide? 4 What colour does litmus change to in an acid?

5 Is water an acid, an alkali or neutral? Give the reason for your answer.

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5 Properties of materials

Think like a scientist Making and using your own indicator solution In this task you will make your own indicator solution and use it to test various chemicals in the laboratory. You will need:

Safety

PL E

some plant material, such as red cabbage or beetroot, a knife and cutting board, a pestle and mortar, two dropper pipettes, test tubes and a test-tube rack, safety glasses, a range of laboratory chemicals, ethanol

Make sure you are careful and read all the hazard warning labels. Ethanol is flammable.

plant pieces

pestle

1 Cut up the plant material.

ethanol

2 Place some of the material into a pestle and mortar and crush it. 3 Use a pipette to add a little ethanol.

motar

Crush the plant pieces.

SA M

4 Crush the plant material again.

pipette

Add a little ethanol.

5 Use a different pipette to transfer some of the liquid from the mortar to a test tube. 6 Use the liquid you collect to test some everyday liquids and laboratory chemicals. 7 Make a table to record the chemicals you test and the colours you see.

Keep crushing until the colour comes out.

pipette

Use a pipette to put the liquid into a test tube.

Self-assessment

Compare your indicator with litmus. Does your indicator turn the same colour as litmus? Does it clearly show which is an acid and which is an alkali?

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5.6 Indicators and the pH scale

Other indicators Litmus and other simple indicators just show if a substance is an acid or an alkali. Universal indicator shows how acidic or alkaline a substance is. The acidity or alkalinity of a substance is one of its chemical properties. Universal indicator can change to many different colours. Universal indicator is made up of a mixture of different indicators. Colour of universal indicator

strongly acid

red

weakly acid

yellow

neutral

green

weakly alkaline

blue

strongly alkaline

purple

PL E

Type of substance

SA M

These strips of paper were soaked in universal indicator solution and then dried. The papers were then dipped into different liquids.

The strength of acids and alkalis is measured on the pH scale. Universal indicator changes colour and shows the pH of a substance. The pH of a substance is one of the chemical properties of that substance.

strongly acidic pH = 1 0

1

weakly acidic pH = 4

2

3

4

more acidic

neutral pH = 7

5

6

7

neutral

weakly alkaline pH = 10

8

9

10

11

12

strongly alkaline pH = 13 13

14

more alkaline

A colour chart for universal indicator showing the pH scale.

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5 Properties of materials

Questions 6 What does the pH scale measure? 7 What is the pH of a neutral solution? 8 A liquid has a pH of 1. What type of liquid is it? 9 What range of pH do strong alkalis have? 10 What colour does universal indicator turn in a liquid with a pH of 9?

Think like a scientist

PL E

11 Which colours does universal indicator turn in acids?

Investigating the pH of different substances

In this task you will test various laboratory chemicals with universal indicator to measure the pH and what type of chemical it is. You will need:

universal indicator papers, a range of liquids, test tubes and a test tube rack, safety glasses Safety

SA M

Read any hazard warning labels and take care not to spill substances on your skin. Make sure you know what to do if you do spill anything. 1 Put on your safety glasses.

2 Pour a small amount of liquid from a bottle of liquid into a clean test tube. 3 Test with universal indicator.

4 Record the colour of the indicator and the pH. 5 Record the type of each liquid, such as strongly or weakly acidic, neutral, strongly or weakly alkaline. You could use a table like this one. Liquid

Colour of universal indicator

lemon juice salt water

Type of liquid

4

weakly acidic

8

weakly alkaline

green

soap solution cola drink

pH

yellow

4

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5.6 Indicators and the pH scale

Continued  Self-assessment How well were you able to decide on the pH? Were the colours easy to match to the numbers?

Activity 5.6.1 Make your own pH chart

PL E

What safety considerations did you follow?

Make your own colour chart to show the colours to which universal indicator changes in liquids of different pH. You can do this by arranging different coloured pieces of paper in the correct order, starting with the colour that universal indicator turns in a liquid of pH 1. You could also use plain paper and paint or colour it yourself. You could do it on a computer and print it off in colour.

Try to make it interesting. You can cut out different coloured shapes, such as T-shirts on a washing line or racing cars on a track. You can do this on a large sheet of paper so that it can be displayed in your classroom.

SA M

On each item, write the pH that the colour represents and state if that pH means strong acid, weak acid, neutral, weak alkali or strong alkali. Try to add the names and/or pictures of substances next to various pH values.

Summary checklist

I can identify acids and alkalis by use of indicators. I can make an indicator. I can use the pH scale.

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5 Properties of materials

Project: Different steel for different jobs All over the world people use iron to make many things, such as car bodies and bridges, and to form the structures of buildings. They don’t use pure iron because it is not strong enough. Instead, they use an alloy of iron, called steel.

SA M

PL E

Mixing other substances with iron – such as carbon, chromium and nickel – makes steel. The amount of carbon used, and the amounts and types of other metals used, make different types of steel. Some different types of steel are mild steel, medium steel, high carbon steel and stainless steel.

Find information about the different types of steel. These questions give you a starting point.

1 What substances and how much are added to iron to form the different types of steel? 2 What are the properties of these different types of steel? 3 What are these different types of steel are used for? You should try to link this with their properties. 4 Where are these different types of steel made?

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5.6 Indicators and the pH scale

Continued 5 Where do the iron, carbon and other metals needed to make them come from? Do they have to be extracted or treated in some way before they can be used? 6 What does this mean in terms of the cost of manufacture? 7 Where does the steel get used? 8 What does this mean in terms of transport costs?

PL E

9 Can you find out about any other specialist steels? Present the information to your class.

SA M

You could make a poster, a slide presentation, a television interview with a presenter and an ‘expert’, a newspaper article or you could use any other way to present your information.

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5 Properties of materials

Check your Progress 5.1 C  opy the paragraph and choose words from the list to complete it. Each word may be used once, more than once or not at all. conduct

cut

ductile

electricity

malleable

metal

ring

Metals are shiny when freshly or polished. They are strong and if you tap them they like a bell. Metals heat energy and . Metals are , which means they can be beaten into shape. They are , which means they can be drawn out into wires.

PL E



brittle

5.2 a Why aren’t ‘silver’ coins made of pure silver? b

Explain, using particle theory, why alloys are harder than the metals they are made from.

[6] [2] [4]

5.3 a Which property of metals is most useful when: copper is used for electrical wiring

[1]

ii

gold is used for jewellery

[1]

iii

iron is used to build bridges

[1]

iv

stainless steel is used for cooking pans?

[1]

SA M

i

b

State three differences between metals and non-metals.

5.4 Marcus has dropped a glass bottle of copper sulfate crystals on the floor and it has broken into small pieces. He has swept the broken glass and crystals into a container. Explain how he can separate the mixture of glass and copper sulfate crystals. Remember to include a list of equipment he needs and to explain how he will stay safe. You could draw diagrams to help explain.

[3]

[6]

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5 Properties of materials

5.5 Litmus is a dye made from a living organism. It is red in acid. It is blue in alkali. It is purple in a neutral solution. a

What is the correct scientific term for a substance that changes colour in this way?

[1]

b

What colour is litmus in a liquid of pH4?

[1]

c

What colour is litmus in water?

[1]

SA M

PL E

5.6 This truck is loading acid at a factory.

a

The driver has placed an orange warning notice nearby.

[1]

Explain why this is important.

b

Suggest what could be done if there is an accident and some acid is spilt on the ground. Explain your answer.

[2]

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5 Properties of materials

5.7 The table gives information about the melting points and boiling points of some metals and non-metals. Substance

Melting point in °C

Boiling point in °C

gold

1064

2850

lead

328

1750

1082

2580

helium oxygen mercury aluminium nickel sulfur sodium a

PL E

copper

−270

−269

−219

−183

−39

357

660

2400

1455

2150

119

445

98

900

[2]

Copy and complete these tally charts. Melting point in °C

Tally

Boiling point in °C up to 0

0 to 499

0 to 999

500 to 999

1000 to 1999

1000 to 1499

2000 to 2999

SA M

up to 0

Tally

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5 Properties of materials

b

[6]

Plot the tallied figures on two separate frequency diagrams. Use the grid below to help you plan your frequency diagrams. 4

PL E

3

Number of metals and non-metals

SEE QUERY LOG To help with BOTH diagrams, it would be more useful here to have 'Temperature in oC' with no numbers along the axis. Consider using squared paper rather than graph paper for bar charts.

1

0

SA M

Tech-Set: no comment within the query log. Please advise

2

up to 0

0–499 500–999 Melting point in °C

1000–1499



Use the tables and your diagrams to help answer the following questions.

c

Which metals and/or non-metals are gases at room temperature of 25 °C?

[1]

d

Which metals and/or non-metals are liquid at room temperature of 25 °C?

[1]

e

Which metals and/or non-metals are solid at room temperature of 25 °C?

[2]

f

Which metal and/or non-metal has the smallest difference between its melting point and its boiling point?

[1]

Which metal or non- metal has the largest difference between its melting point and its boiling point?

[1]

g

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6 Earth physics

6

Earth physics

In this topic you will:

PL E

6.1 Sound waves • learn how sound comes from vibrations

• discover how particles vibrate in a sound wave

• find out why sound does not travel in a vacuum. Getting started

Work in groups to discuss the answers to these questions.

1 Give two examples of things that make very loud sounds.

2 Give two examples of things that make very quiet sounds.

SA M

3 Give two examples of high-pitched sounds. 4 Give two examples of low-pitched sounds.

Key words

backwards and forwards loudness medium particles pitch sound wave speed of sound

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6.1 Sound waves

Where does sound come from? Things that vibrate make sounds. To vibrate means to move backwards and forwards very quickly.

PL E

The men in the picture are hitting drums to make them vibrate. When the drums vibrate, the drums make a sound.

If you hit a drum with more force, it vibrates more. This makes a louder sound.

If you touch the front of your neck while you are speaking, you can feel a vibration. The vibration comes from your vocal cords, which make the sound when you speak.

Hitting a drum causes the drum to vibrate, which makes the sound.

Loudspeakers produce sounds from television, radio and music players. If you put small objects into the paper cone of a loudspeaker, the objects will bounce around. This shows that the paper cone in the loudspeaker is vibrating.

SA M

Not all sounds are the same.

Sounds can vary in both loudness and pitch. Thunder makes a sound with a low pitch.

A baby crying makes a sound with a high pitch.

Questions

1 A guitar is a musical instrument with strings.

Which one of these is needed to make a sound from the guitar?

Small plastic balls show the vibration of the cone in a loudspeaker.

Write the letter.

A The guitar is made from wood.

B The guitar strings vibrate.

C There is air inside the guitar. D There are metal parts on the guitar.

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6 Earth physics

2 Zara is playing the guitar by plucking a string. Which statement describes a way that Zara can make the sound louder? Write the letter. A Pluck the string with more force. B Pluck the string with less force. C Make the string tighter.

PL E

D Make the string looser.

3 Some flying insects make a buzzing sound. Describe what causes this sound.

Sound waves

Sound travels from a vibrating object to our ears. This is called a sound wave.

What is a sound wave?

When an object vibrates, it moves backwards and forwards.

SA M

Every time the object vibrates forward, the air in front of the object gets pushed forward. The particles in the air are made to vibrate backwards and forwards in time with the vibrating object.

vibrating cone

direction of sound wave

When the particles in front of the object vibrate, those particles make other particles in front of them vibrate. This makes a sound wave. The speed of sound waves in air is about 343 metres per second. The picture shows how a vibrating cone in a loudspeaker makes a sound wave.

vibration of air particles in sound wave

A sound wave travels to your ear by the vibration of air particles.

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6.1 Sound waves

The vibrations of the air particles in very loud sounds can cause damage to the ears. Vibrations from very quiet sounds can be too small for the ears to detect. Sound at a certain pitch can cause damaging vibrations, even when the sound is not very loud.

PL E

You saw in Topic 3.5 that sound is a way of transferring energy. Sound waves transfer sound energy.

The vibration of particles in the air is transferred to other objects. When the vibration is transferred, the other objects will start to vibrate.

SA M

The glass in the bottom right picture has broken because of the vibrations of a high-pitch sound.

This boy has thrown some feathers in the air. When they hit the floor there will be a sound but the vibrations will be too small for his ears to detect.

These people are wearing ear protection while working near an aeroplane.

Vibrations from sound can break objects.

Questions

4 Copy the sentence and use the correct word from the list to complete it. current   wind   wave   stream Sound travels through air as a sound………………… .

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6 Earth physics

5 Sofia is watching television. The sound from the television is travelling across the room, as shown in the diagram.

direction of sound

Which of these arrows shows how the particles in air vibrate? Write the letter.

A

B

PL E

direction of sound

C

D

6 Thunder can make objects inside a room vibrate. Explain what causes the objects to vibrate.

7 A fly is walking up a glass window. The fly’s feet make vibrations. Explain why people cannot hear the sound of the fly walking.

SA M

Sound waves on the move Sound waves travel by making particles vibrate. Sound will travel though anything that has particles: gas, liquid or solid.

You can demonstrate this by tapping on a table. Ask another person to listen to the sound. Then ask them to put their ear on the table and listen again. The first part of this demonstration shows that sound travels through air, which is a gas.

The second part shows that sound travels though the table, which is a solid. Sound also travels through liquids.

Animals such as whales and dolphins communicate with sounds.

Sound vibrations travel easily through solids.

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6.1 Sound waves

Sound waves move the same way in gases, liquids and solids. The sound wave makes the particles vibrate backwards and forwards. The substance that the sound wave moves through is called the medium. Therefore, solids, liquids and gases can all be a medium for sound.

PL E

Vibrations in a vacuum To hear a sound, there must be: •

a vibration to make the sound

•

a medium containing particles through which the sound wave can travel.

You saw in Topic 3.3 that a vacuum is a space where there are no particles.

These dolphins can use sound to communicate under water.

As there are no particles in a vacuum, there is nothing to vibrate to make a sound wave. Therefore, sound will not travel in a vacuum.

SA M

Space is a vacuum. If sound waves could travel through space, we would be able to hear the Sun! Scientists think that the Sun would make a high-pitched humming sound, with louder, low-pitched sounds from time to time. bell jar You can demonstrate that sound does not travel in a vacuum. If you put an electric bell in a glass jar, you can see it vibrate as it makes the sound.

If the air is pumped out of the jar to make a vacuum, you can see the bell vibrating but you cannot hear the sound of the bell.

electric bell

vacuum

to vacuum pump

Sound waves cannot travel in a vacuum as there are no particles to vibrate.

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6 Earth physics

Questions 8 Which of these can sound travel through?

Tech-Set: in unit 5 page 178. DYoung commented the following " left align numbering". Should this not be a global?

Select all the correct answers. Write the letters. A solid B liquid D vacuum

PL E

C gas 9 The Moon has no atmosphere. People who went to the Moon wore suits that contained air. The people who went to the Moon worked close together. They did work such as hammering and digging.

Explain why the people doing this work could not hear it happening. 10 Science fiction films are made in studios on Earth. These films often show explosions in space.

There is usually a loud bang when the explosion happens.

SA M

Explain whether you would really hear an explosion in space.

Activity

Modelling sound waves

Work in groups or as a whole class. You will need:

• a slinky spring for each group (slinky springs made from metal work better than plastic ones) • chalk or small pieces of paper

1 Stretch the spring across a smooth, flat surface such as a long bench or the floor. 2 Use chalk or small pieces of paper to mark positions on the spring. These represent particles. 3 One person holds one end of the spring and keeps it still.

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6.1 Sound waves

Continued

direction of hand movement

PL E

4 Another person holds the opposite end and moves the end of the spring backwards and forwards, as shown in the diagram. This will make a wave in the spring.

Movement of a slinky spring to show movement in a sound wave. The black arrows show possible positions of the chalk marks on the spring.

Questions

In your groups, discuss the answers to these questions.

1 In which direction does the wave in the spring move? 2 Does the whole spring move in that direction?

3 In which direction do the marks that represent particles move?

SA M

4 What did the person holding the fixed end of the spring feel from the spring?

• Did you see the representation of movement of particles in the wave? • Did this help you understand how particles in air move in a sound wave? Think like a scientist

Sound and vibration

You are going to investigate whether sound requires vibrations to travel. Work in groups of three. You will need:

2 disposable cups, a sharp object to make a small hole in the bottom of each cup, a string long enough to go across the classroom, scissors to cut the string

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6 Earth physics

Continued  Safety Take care when using the sharp object to make a hole in the cups. 1 Pass the string through the holes in the cups so that the open ends of the cups face away from each other. Make the string as long as possible. 2 Secure the string inside each cup by tying a knot.

PL E

3 Set up the equipment as shown in the diagram. This is sometimes called a string telephone.

SA M

4 Pull the string tight between the cups.

5 The person speaking puts the cup over their mouth. 6 The person listening puts the cup over their ear. 7 Speak as quietly as possible, so that the person hears the sound of your voice through the string. 8 Let the string go slack. Say the same thing, with the same loudness, when the string is slack.

9 Pull the string tight again. The third member of the group should grip the string in their hand. Do this around the middle of the string and then in different places. 10 Say the same thing, with the same loudness, when the string is being gripped. Questions

1 State what the sound wave passes through to travel between the cups. 2 Describe the difference in what you heard when the string was tight and when the string was slack. 3 Describe what happened when the string was gripped in the middle. 4 State whether the position that the string was gripped made any difference to the sound that you heard.

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6.1 Sound waves

Continued  5 Explain what you can conclude from these observations. 6 It is very difficult to speak with the same loudness each time. Suggest an improvement for this so that the investigation is a fair test. Peer-assessment Swap your answers with a partner.

PL E

• Do your partner’s answers agree with your observations in the investigation? • Do you agree with your partner’s conclusion?

• Do you agree with your partner’s suggestion for making this a fair test? Summary checklist

I can understand that vibration makes sound. I can understand that sound travels as a wave. I can recall how the particles move in a sound wave. I can recall that sound can travel in solids, liquids and gases. I can understand why sound does not travel in a vacuum.

SA M



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6 Earth physics

6.2 Reflections of sound In this topic you will: • learn that sound waves can be reflected • discover what can happen when sound is reflected.

Work in groups.

Key words

PL E

Getting started

Discuss how you would describe the movement of particles in a sound wave.

SA M

For a challenge, try to do this without a diagram and without moving your hands.

echo effect on the sound property reflected unwanted

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6.2 Reflections of sound

Reflections One property of all waves is that they can be reflected from surfaces. Therefore, sound waves can be reflected. Reflection is like bouncing a ball off a wall. When a wave is reflected, the wave behaves like the ball. The only difference is that a wave is not affected by gravity.

PL E

A sound wave travelling towards a wall will hit the wall and come back.

Sound waves reflect best from large, smooth, flat surfaces. Surfaces such as glass, tiles, flat metal and smooth concrete give good reflections of sound.

If you stand between two flat walls you can hear the reflection from sound. You can do this in an empty room.

When you clap your hands, you hear a strange effect on the sound. An effect on a sound means the sound is changed. The sound of the clap seems to last longer than usual, then fade away.

SA M

Clapping your hands makes a sound wave. The sound wave will travel away from your hands in all directions.

When the sound wave hits a wall, it is reflected back. The reflection of a sound wave is called an echo.

Stand between two flat walls and clap your hands once. What do you hear?

Reflection of a sound wave is like bouncing a ball – the wave comes back off the wall.

This room would give good reflections of sound.

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6 Earth physics sound waves from bat

Useful echoes

reflected sound waves

Echoes can be useful.

PL E

Bats use echoes to find insects for food. The bat makes a sound. The sound wave reflects off the insect – there is an echo. The bat can work out where the insect is from the time taken for the echo to reach the bat, and the direction the echo comes from. Boats can use echoes to find the depth of water under the boat.

A sound is sent from the bottom of the boat. The sound travels through the water and reflects off the solid ground. The echo comes back to the boat. The time taken for the echo to come back can be used to work out the depth.

The sound wave from the bat (thin lines) echoes off the insect (wider lines).

SA M

Notice that the distance travelled by the sound is double the distance from the object making the sound to the reflecting surface. The sound has to travel from the object to the reflecting surface and back again. You can see this in the picture of the bat and insect, and in the picture of the boat. Echoes can also be used to make images from inside the body. Sounds sent into the mother’s body echo back out of her body. This method is used to make the image of the unborn baby.

This image of an unborn baby was made by using echoes.

Key sound waves w from shi ship reflected sound waves

This boat is using an echo to check the depth of the water.

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6.2 Reflections of sound

Unwanted echoes Sometimes echoes are unwanted. For example, when recording music, echoes change the sound. A musical note that is played once will repeat with an echo. This effect will spoil the recording. A room with large flat walls would give many echoes.

PL E

The picture on the left shows how the walls of a room are changed to stop echoes. This room can now be used to record music without the effect of echoes.

SA M

In a theatre, the audience needs to hear the voices of people on the stage. If there were echoes in a theatre, the voices would not be clear. Theatres are designed to stop echoes. Theatres usually have no large flat surfaces that could cause echoes.

The shapes on the walls of this room are made to stop echoes.

The design of this theatre will stop echoes.

Questions

1 Which statement describes what happens to a sound to make an echo? Write the letter.

A The pitch of the sound increases.

B The pitch of the sound decreases. C The sound gets reflected.

D The sound gets louder.

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6 Earth physics

2 Which one of these will give the best echo in a room? All of the materials have the same area. Write the letter. A soft curtains B glass window D wool blanket

PL E

C thick carpet 3 Arun goes to the same music concert in two different theatres, A and B.

SA M

The theatres are shown in the pictures.

A

B

Arun says the music sounded better in theatre B.

Use information in the pictures to explain why the music sounded better in theatre B.

4 Zara has an empty room where she can practise playing her drums. Which one of these materials could she put on the walls to stop echoes when she plays? Write the letter.

A flat wood sheets

B shiny metal sheets

C soft thick curtains D large flat mirrors

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Tech-Set: Please advise as there has been no instances of "Extension question" being used in any of the previous books.

5

6.2 Reflections of sound

Extension question. You can calculate the distance that a sound wave has travelled using a formula in this question. You do not need to learn this until you study Cambridge Lower Secondary Science Stage 8. A fishing boat uses an echo to find the distance from the boat to some fish.

reflected sound waves sound waves from ship

PL E

A sound is sent from the ship to the fish. The sound reflects back to the ship.

The speed of sound in water is 1500 metres per second.

The time taken for the sound to go from the ship and back to the ship is 0.2 seconds.

Use this equation to calculate the distance from the boat to the fish: distance = speed × time Remember that the distance travelled by the sound wave in 0.2 seconds is from the ship to the fish and back again.

SA M

Activity

Modelling echo location

Some animals, such as bats and dolphins, use echo location to find food. In this activity, you will use light and a mirror to model echo location. You will need:

a small plane mirror that can be propped up vertically, a flashlight or ray box, a piece of card or wood that will cover the mirror when placed horizontally, four items to support the piece of card over the mirror

You need to work in pairs, as learner A and learner B. Then swap roles. Learner A

1 Place the mirror vertically on a desk without letting your partner see.

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6 Earth physics

Continued 2 Place the card over the mirror. Support it so that the mirror cannot be seen, as shown in the diagram. light from flashlight or ray box

Learner B

sheet of card position of mirror under card

PL E

light source moved to locate mirror

1 Look at the apparatus from above, so that you cannot see where the mirror is. 2 Use the flashlight or ray box to locate the mirror. 3 Attempt to find:

• where the mirror is, as accurately as possible • what direction the mirror is facing. Questions

SA M

1 In this model, the light represents the sound made by the dolphin or bat. State what the mirror represents. 2 Make a list of:

a strengths of this model in representing echo location b limitations of this model in representing echo location.

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6.2 Reflections of sound

Think like a scientist How is sound reflected? You are going to investigate how sound is reflected. Work in groups of two or three. You will need:

PL E

2 plastic or cardboard tubes and a mobile phone, a large sheet of paper, or 2 A4 sheets taped together, a block or piece of hard plastic, metal or a tile for a reflecting surface, piece of wood for a barrier, a piece of soft material, such as foam or polystyrene as another reflecting surface 1 Set up the apparatus as shown in the diagram. reflecting surface

barrier

SA M

paper

mobile phone

cardboard tubes

2 Set the mobile phone to make a quiet sound that you can hear. Place the mobile phone as close as possible to, or inside, one of the tubes. Put the other end of this tube close to the reflecting surface. 3 Mark the position of this tube on the paper.

4 Set the other tube so one open end is close to the reflecting surface and also close to the other tube.

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6 Earth physics

Continued 5 Put your ear to the end of this tube. Turn this tube until the sound from the mobile phone sounds loudest. 6 Mark the position of this tube on the paper. 7 Repeat the investigation with the first tube (containing the mobile phone) in a different position. Questions

PL E

8 If you have time, change the reflecting surface.  1 Describe any trend or pattern you noticed in the positions of the tubes.

2 Describe the observations you made if you changed the reflecting surface. 3 If you did not have time to change the reflecting surface, suggest: • one surface that would be good for reflecting sound • one surface that would be bad for reflecting sound.

This investigation can be difficult to do.

Make a list of things you found difficult in this investigation.

SA M

Try to suggest improvements that could: • make the investigation easier

• give better results. Summary checklist

I can understand that sound can be reflected. I can recall what happens when sound is reflected.

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6.3 Structure of the Earth

6.3 Structure of the Earth In this topic you will: • describe a model of the structure of the Earth

Getting started

PL E

• understand how the continents on Earth have changed.

continental core crust drift magma mantle molten tectonic plates

SA M

Draw and label a diagram to show what the Earth would look like if it were cut through.

Key words

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6 Earth physics

What do we know about the Earth? Scientists have worked out that the Earth is about 4500 million years old. They have also worked out what is inside the Earth. The Earth has a crust of solid rock. Under the crust is the mantle, which is molten (hot liquid) rock that can flow.

PL E

In the centre of the Earth is the core. It is made of the metals nickel and iron. The outer part of the core is molten. The inner part of the core is solid.

The rocks found in the crust contain metals and non-metals. The pie chart below on the right shows the approximate proportions of the most common elements in the Earth’s crust.

aluminium, Al

crust (solid rock)

mantle (molten rock)

iron, Fe

silicon, Si

calcium, Ca

outer core (molten metals, mostly iron and nickel)

others

SA M

inner core (solid metals, mostly iron and nickel)

oxygen, O

Questions

1 State the name of the part of the Earth that forms the centre. 2 Name the metals found in this part.

3 Name the most common non-metal in the Earth’s crust. 4 Name the most common metal in the Earth’s crust. People used to think that the Earth was only a few thousand years old. They thought the Earth had never changed. In 1912, a German scientist called Alfred Wegener suggested that, millions of years ago, all the land was one large continent. Over millions of years the land broke up and drifted apart. This idea is called continental drift.

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6.3 Structure of the Earth

His evidence for this idea was that: •

the shapes of the continents fit together

•

the types of rock on the different continents match up where they fit together

•

the fossils on the different continents match up where they fit together.

PL E

Wegener could not explain how continental drift happened, so not everyone believed his ideas.

Laurasia

Pangea

Gondwana

150 million years ago

225 million years ago

Europe

Asia

SA M

North America

South America

North America

Africa

India Australia Antarctica

Europe

Asia

Africa

India

South America

100 million years ago

Australia

Antarctica Earth today

These drawings show how the continents have drifted apart over a very long time.

We now know that the Earth’s crust is made up of large tectonic plates. Some of the plates are under the oceans: they are called oceanic plates. Some of the plates form the continents: they are called continental plates. These tectonic plates move slowly on the liquid rock called magma beneath them. This is how continental drift occurs. The plates only move about 4 cm each year, which is about same speed as your fingernails grow.

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6 Earth physics Key plate boundary Juan de Fuca plate

Eurasian plate

North American plate

Arabian plate

Caribbean plate Cocos plate

Philippine Sea plate

Indian plate

African plate Nazca plate

South American plate

Indo-Australian plate

PL E

Pacific plate

Pacific plate

Scotia plate

Antarctic plate

The red lines show the edges of the tectonic plates.

Questions

5 What evidence did Wegener have for his idea of continental drift? 6 Why did some people reject his idea? 7 Which tectonic plate do you live on?

SA M

8 What causes the tectonic plates to move? Activity 6.3.1

Drifting plates

You are going to model continental drift. You will need:

some pieces of polystyrene, water, a large heat-proof dish, something to heat the water, such as a Bunsen burner

Safety

Take care when heating the water, as the dish may get very hot. 1 Pour some water into the heat-proof dish.

2 Place the pieces of polystyrene on the water. Wait for them to stop moving.

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6.3 Structure of the Earth

Continued 3 Heat the water gently. 4 Observe what happens. polystyrene pieces heat-proof dish

PL E

water

electric hot plate

Questions

1 In your model for continental drift, state what is represented by: a the polystyrene b the heat source c the water.

SA M

2 Explain the strengths and weaknesses of this model of continental drift. Summary checklist

I can describe the structure of the Earth. I can state the evidence for continental drift.

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6 Earth physics

6.4 Changes in the Earth In this topic you will: • explain how fold mountains and volcanoes are formed

Getting started Work with a partner.

PL E

• explain how earthquakes happen.

Make a list of ways that mountains and volcanoes are: 1 the same

SA M

2 different.

Key words

active dormant earthquake extinct fold mountains geological change inactive lava magnitude plat boundary subduction volcano

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6.4 Changes in the Earth

Geological change The places where tectonic plates meet are called plate boundaries. Geological change happens at plate boundaries. This is because the tectonic plates are always moving. Some of the geological change is very slow – it happens over millions of years. But some of the geological change is very sudden and violent.

PL E

This illustration shows the plate boundaries around the edge of the Pacific Ocean. There are many geological changes and events, such as volcanic eruptions and earthquakes, here. This area is often called the Pacific Ring of Fire.

Key

plate boundary ring of fire

Eurasian plate

North American plate

Philippine Sea plate

volcano

Caribbean plate

Cocos plate

Pacific plate

SA M

Nazca plate

Indo-Australian plate

South American plate

Pacific Ring of Fire

Movement of plates

The movement of tectonic plates creates three types of plate boundaries. Plates moving together One plate may slide underneath the other one. This is called subduction. The rocks in the Earth’s crust melt as they move into the mantle. They become part of the mantle.

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6 Earth physics

Plates moving apart As tectonic plates drift away from each other, they break and crack when they become too thin. Lava (liquid rock) erupts from the mantle and hardens to form new crust with new rocks. This causes a volcano.

PL E

Plates sliding past

SA M

Because the plates are very large and heavy, there is a lot of friction between the plates. Over the years, this makes the plates stick together. There is always force on the tectonic plates, so the pressure builds up and eventually the pressure causes violent movement. This is an earthquake.

Fold mountains

Sometimes, when tectonic plates move together, the rocks crumple and fold upwards. The mountains that this produces are called fold mountains.

rock layers pushed into folds

This can happen under the ocean or on land.

The newest fold mountains are between 10 and 25 million years old. These include the Himalayas in Asia and the Rocky Mountains in North America. The oldest fold mountains are more than 200 million years old. These include the Ural Mountains in Russia.

compression from tectonic plate movement

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6.4 Changes in the Earth

Volcanoes

PL E

The Himalayas, Rocky Mountains and Ural Mountains were all formed when tectonic plates pushed against each other.

ash cloud

Volcanoes are usually formed at the plate boundaries when magma from the mantle rises up through cracks in the Earth’s crust.

secondary vent

lava flow

layers of ash and lava

main vent

magma

SA M

At the Earth’s surface, magma erupts to form lava flows and ash deposits. Magma is the name for liquid rock when it is underground. Lava is the name for liquid rock when it is on the surface. The lava and ash harden as they cool to form new rocks. So each time the volcano erupts, it gets bigger.

crater

Sometimes, if the magma is really thick, and contains dissolved gas, pressure builds up and the eruption is violent. Gases and rock shoot up through the opening. Violent eruptions can even cause avalanches and earthquakes – and tsunamis if the volcano is close to the sea.

The parts of a volcano.

Some volcanoes are active and may erupt at any time. Some volcanoes are inactive or dormant, which means they have not erupted for a very long time. Other volcanoes are extinct, which means they will not erupt again.

A powerful eruption at Anak Krakatau volcano, Indonesia. Part of the volcano was blown off into the sea, causing a tsunami.

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6 Earth physics

Earthquakes Some earthquakes are extremely violent and cause a lot of damage. Some are so slight that they only register on scientific instruments.

Questions

PL E

The size or magnitude of the earthquake depends on the size of the faults at the plate boundaries, and how far the rocks move when the earthquake happens. In the largest earthquakes, the rocks can move tens of metres in seconds.

Earthquakes can cause damage to roads and buildings.

1 Which statement is true about tectonic plates? Write the letter. A They never move.

B They move in different ways.

C They always move towards each other.

D They always move away from each other.

2 Explain how tectonic plates can cause fold mountains to form.

SA M

3 Which word is used to describe the strength of an earthquake? Write the letter. A force

B energy

C magnitude

D destruction

4 Explain what causes an earthquake. Activity

Model for moving tectonic plates

Try out these models to show what happens where tectonic plates meet. You will need:

a large piece of cloth, 2 pieces of paper, modelling clay ,2 chocolate bars with soft centres (not solid chocolate)

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6.4 Changes in the Earth

Continued Model A Place a large piece of cloth on the table. Place your hands flat on the cloth, about 30 cm apart. Push your hands together. Model B

Model C

PL E

Place two pieces of paper flat on the table so that they are touching. Push them together. Can you make them slide so that one piece goes over the other one? This is similar to what happens when one tectonic plate slides over another. Can you make the pieces of paper form mountains? Use modelling clay and make two flat pieces. Place them on the table and then push them together. What happens? Model D

Push the two chocolate-covered bars together. What happens? Questions

For each of the models you used: 1 Describe what happened.

SA M

2 Explain what it was modelling.

3 Discuss the strengths and limitations of the model. 4 Could you improve that particular model in any way? 5 Which do you think was the best model? Why?

Summary checklist

I can describe how fold mountains are formed. I can explain how earthquakes occur. I can describe how volcanoes are formed.

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6 Earth physics

6.5 Solar and lunar eclipses In this topic you will: • find out how solar eclipses happen

Getting started

PL E

• find out how lunar eclipses happen.

Discuss the answers to these questions. Work in groups of three or four. 1 Which of these describes how light travels?

in curved paths  in straight lines  in circles   randomly in straight and curved paths 2 Explain how a shadow is formed.

3 Decide whether each of these statements is true or false.

Key words

lunar eclipse opaque partial ray shadow solar eclipse total

The Moon gives out its own light.

SA M

The Sun gives out its own light.

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6.5 Solar and lunar eclipses

Shadows An opaque object is an object that will not allow light to pass through. When an opaque object passes in front of a source of light, a shadow will form.

PL E

Look at the shadow of the aeroplane in the picture. The shadow looks dark because the light from the Sun has been blocked from reaching the ground. The aeroplane is made from metal which is opaque.

The grass around the shadow looks brighter because light from the Sun is reaching those areas.

The aeroplane is opaque so it makes a shadow on the ground.

The next picture shows how the shadow is formed.

SA M

aeroplane in the air

rays of light from the Sun

shadow on the ground

Light travels in straight lines called rays. Light rays from the Sun cannot pass through the aeroplane, so light rays that reach the aeroplane cannot reach the ground. Imagine you were standing on the grass. When the shadow of the aeroplane passes you, it will seem to go dark. When the shadow has gone, it will get brighter again.

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6 Earth physics

Solar eclipse A solar eclipse happens when the Moon comes between the Sun and the Earth. The Moon is made from rock, so is an opaque object. The Moon blocks the rays of light coming from the Sun.

Sun

rays of light from the Sun

partial solar eclipse is seen here

Moon Earth

A solar eclipse happens when the Moon comes between the Sun and the Earth.

PL E

The shadow of the Moon forms on the Earth.

total solar eclipse is seen here

The diagram shows how the shadow of the Moon is formed on the Earth. In the middle of the shadow, all the light rays from the Sun are blocked. People in the middle of the shadow observe a total solar eclipse. The left picture shows what a total solar eclipse looks like.

A total solar eclipse is seen from the middle of the Moon’s shadow.

SA M

Away from the middle of the shadow of the Moon, some of the light rays from the Sun can reach the Earth. Away from the middle of the shadow there is a partial solar eclipse.

A partial solar eclipse is seen away from the middle of the shadow of the Moon.

The right picture shows what a partial solar eclipse looks like.

The picture below shows a series of photographs taken as the Moon passes between the Earth and the Sun. The picture on the next page shows what a solar eclipse looks like from space. The dark part of the Earth is in the shadow of the Moon. At the centre of the shadow, there is a total solar eclipse. Away from the centre, there is a partial solar eclipse.

The Moon is passing between the Sun and the Earth in these photographs.

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6.5 Solar and lunar eclipses

You must never look directly at the Sun, even when there is an eclipse. The light from the Sun is very bright and can cause permanent damage to your eyes.

Lunar eclipse A lunar eclipse happens when the Earth comes between the Sun and the Moon.

PL E

The Earth is also an opaque object, so the Earth blocks the light from the Sun. The shadow of the Earth is formed on the Moon. The diagram shows how the shadow of the Earth forms on the Moon.

The dark part of the Earth is in the shadow of the Moon. People here see a solar eclipse.

The picture shows a series of three photographs of the shadow of the Earth passing across the Moon.

You might think that solar and lunar eclipses should happen every month. The Moon takes 28 days to orbit the Earth, but the orbit of the Moon is tilted slightly. The orbit of the Moon is not exactly in the same plane as the orbit of the Earth around the Sun.

SA M

It is only when the Sun, Earth and Moon are in the same straight line that eclipses can happen.

Sun

partial lunar eclipse when Moon is here

rays of light from the Sun

Moon Earth orbit of Moon

total lunar eclipse when Moon is here partial lunar eclipse when Moon is here

A lunar eclipse happens when the Earth comes between the Sun and the Moon.

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PL E

6 Earth physics

The Earth is passing between the Sun and the Moon in these photographs.

Questions

1 Which of these describes how a solar eclipse happens? Write the letter.

A The Sun comes between the Moon and the Earth.

B The Earth comes between the Moon and the Sun.

SA M

C The Moon comes between the Earth and the Sun.

2 Which of these describes how a lunar eclipse happens? Write the letter.

A The Sun comes between the Moon and the Earth. B The Earth comes between the Moon and the Sun. C The Moon comes between the Earth and the Sun.

3 Explain why a solar eclipse can only ever be seen in the daytime.

4 Write true or false for this statement.

A total lunar eclipse can only ever be seen in the daytime.

Explain your answer.

Activity 6.5.1

Classroom eclipses

In this activity, you will make models to show how eclipses happen. Work in groups of four or five.

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6.5 Solar and lunar eclipses

Continued You will need (per group): an electric lamp and power supply – 12 V lamps work well, a white soccer ball, a tennis ball, a paper cup, a light string or thread, adhesive tape Safety Take care not to touch the lamp because it will be hot.

In your model:

PL E

You need to work in a shaded position in the room. You should turn the classroom lights off. If your classroom has blinds or curtains, these should be closed. • the electric lamp will be the Sun

• the white soccer ball will be the Earth • the tennis ball will be the Moon.

1 Attach the string to the tennis ball with the adhesive tape.

2 Place the soccer ball on the plastic cup. This will lift the ball off the desk and also stop the ball from rolling. 3 Place the lamp about 50 cm from the soccer ball. Switch on the lamp.

SA M

4 One side of the soccer ball should be lit from the lamp. The other side of the soccer ball should be in the shade. Questions

1 In your model, which side of the Earth is in the day and which side is in the night? Hold the string so the tennis ball hangs down. Move the tennis ball between the lamp and the soccer ball. The shadow of the tennis ball should be seen on the soccer ball.

2 What type of eclipse is the model showing?

3 Point out where there is a total eclipse and where there is a partial eclipse. Now move the tennis ball to the other side of the soccer ball. Make sure the tennis ball is in the shade of the soccer ball.

4 What type of eclipse is the model showing now?

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6 Earth physics

Continued Self-assessment Give each of these statements a number from 1 to 5. 1 means ‘strongly disagree’ and 5 means ‘strongly agree’. • I understood why a lamp was used to model the Sun. • I understood why the model of the Earth was bigger than the model for the Moon.

PL E

• I understood how the model showed a solar eclipse.

• I understood how the model showed a lunar eclipse.

• How did you decide which type of eclipse happened in your model? • How well do you think the model showed eclipses? Think like a scientist

Making predictions about eclipses

In this task, you will think about making observations and using them to make predictions.

SA M

Astronomers in the Middle East made the earliest known predictions of when eclipses would happen. The astronomers were working about 3000 years ago. 1 List the facts that need to be given when making a prediction about an eclipse. 2 These astronomers 3000 years ago knew that the pattern of solar eclipses repeats after every 223 lunar months. One lunar month is 29.5 days.

Calculate the number of days in 223 lunar months.

3 Suggest what must happen to the Sun, the Moon and the Earth every 223 lunar months. 4 Explain how a pattern of observations can be used to make future predictions.

5 Scientists working in the present day have predicted eclipses into the future. Scientists think these predictions are accurate until 17 April 3009. Describe how the accuracy of an eclipse prediction can be tested.

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6.5 Solar and lunar eclipses

Continued  6 Suggest why the accuracy of eclipse predictions decreases as the time into the future of the prediction increases.

PL E

7 Scientists working in the present day have also calculated when eclipses happened in the past. There was a battle in Greece in the year 585 BCE. People at that time recorded that there was an eclipse during the battle. Scientists in modern times have worked out that the battle happened on 28 May 585 BCE. Explain how scientists can use information about the eclipse to work out the exact date of the battle.

A solar eclipse occurred during a battle in Greece in 585 BCE.

SA M

8 What type of eclipse is shown in the photograph? Explain your answer.

Summary checklist

I can understand how a solar eclipse happens. I can understand how a lunar eclipse happens.

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6 Earth physics

Project Volcanoes and earthquakes The actions of volcanoes and earthquakes change the rocks and the shape of the land on Earth. You have four tasks to complete in your group. 1 Make a model to show how a volcano erupts or an earthquake takes place.

PL E

You may use any materials you choose but you need to label the parts.

2 Explain how the volcano erupts or an earthquake takes place. You can do this by making a poster or writing a statement as if you are an expert who needs to explain, to a journalist, why a recent volcanic eruption or earthquake has happened. 3 Research a recent volcanic eruption or earthquake. Write a report about: • the immediate damage it has caused, and how this affects people

• the long-term effects to the lives of people, plants and wildlife in the area. You will present your model and explanations to the whole class.

4 Research how scientists detect movements in the Earth’s crust. Include how this technology: • has developed over the last 2000 years

SA M

• can be used to make predictions about earthquakes and volcanic eruptions.

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6 Earth physics

Check your Progress 6.1 Which of these is needed for a sound to be made?

[1]

heat  light  liquid  vibration 6.2 Arun drops his pen on the floor. Sofia hears the pen hit the floor. [2]

PL E

Copy the sentences and use words from the list to complete them. You can use the words once, more than once or not at all.

the pen  sound wave  Sofia’s ears  air  particles A ………………… travels from ………………… to ………………… . The ………………… travels through the ………………… .

6.3 Draw an arrow to show the direction of a sound wave. Your arrow can be in any direction. Now show the direction of movement of the particles in your sound wave.

[3]

6.4 A slinky spring can be used to show how particles move in a sound wave. Which of these describes this use of a slinky spring?

[1]

SA M

modelling  predicting  concluding  observing 6.5 a 

Match the parts of the of the Earth’s structure, A–D, with the descriptions, W–Z. [2] Parts of the Earth’s structure

A Inner core

B Outer core C Mantle D Crust

Descriptions

W molten iron and nickel at the centre X solid outer layer of the Earth Y molten rock below the crust Z solid iron and nickel at the centre of the Earth

b

What are tectonic plates?

[2]

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6 Earth physics

6.6 State what can happen when tectonic plates rub against each other in opposite directions.

[1]

6.7 Describe how new fold mountains form.

[2]

6.8 Copy the sentence and use words from the list to complete it. Each word can be used once, more than once or not at all.

[2]

PL E

light  the Sun  the Moon  shadow A solar eclipse happens when the ………………… of ………………… forms on the Earth. 6.9 Make two copies of this diagram. Your copies do not have to be accurate.

Sun

Earth

Add the Moon to your first diagram to show how a lunar eclipse happens.

[1]

b

Add the Moon to your second diagram to show how a solar eclipse happens.

[1]

SA M

a

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7 Microorganisms in the environment In this topic you will:

PL E

7.1 Microorganisms

• learn about the different kinds of microorganism • grow some microorganisms on agar jelly. Getting started

Work individually to answer these questions.

SA M

1 Some bacteria can cause diseases in humans.

Can you name two diseases caused by bacteria?

2 What other kinds of organisms can cause disease?

Key words

agar jelly algae bacteria colony fungi microorganism mushroom Petri dish protozoa single-celled sterile toadstool yeast

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7 Microorganisms in the environment

What is a microorganism? A microorganism is a living organism that is so small that you can only see it clearly by using a microscope. Like all living organisms, microorganisms are made of cells. Many microorganisms are made of only one cell: they are single-celled.

Bacteria

PL E

There are several different kinds of microorganism. They include bacteria, microscopic fungi, protozoa and algae. Each of these microorganisms is described later in this topic.

Bacteria are everywhere. (Bacteria is a plural word. The singular word, for just one of them, is bacterium.)

Each bacterium is made of a single cell. Cells of bacteria are much smaller than animal cells or plant cells. You could fit 1000 of the bacteria in the photograph, lined up end to end, between two of the millimetre marks on your ruler.

SA M

Most bacteria are harmless but there are a few kinds that can make you ill.

Fungi

These bacteria live in our digestive systems. They are completely harmless.

Fungi (singular: fungus) are not always microorganisms. Many fungi, including mushrooms and toadstools, are large and easy to see.

Mushrooms and toadstools are only part of the fungus’s body, though, and they only grow at certain times of year. Most of the time, the fungus is just a tangle of very thin threads. The threads often grow under the ground, or inside a dead log. The threads are so thin that they are difficult to see without a microscope.

There are also some kinds of fungi that do not produce mushrooms or toadstools. They are made of single cells, not threads, so they are

The white ‘powder’ on these grapes is yeast. The yeast cells feed on sugar in the grapes.

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7.1 Microorganisms

definitely microorganisms. The powdery substance that you sometimes see on the surface of grapes is made up of millions of cells of yeast, which is a microscopic fungus.

Questions

PL E

1 Viruses are even smaller than bacteria. Suggest why they are not usually said to be microorganisms. 2 We can see yeast on the surface of fruit. Why is yeast classed as a microorganism?

Growing microorganisms

A single microorganism is too small to see without a microscope, but when left to grow, a single cell of a bacterium or fungus divides repeatedly to make a collection of many cells. This collection of cells is called a colony. The colonies are big enough for you to see without a microscope.

This is a group of yeast cells seen through a microscope. If you look closely, you can see little buds growing out of some of the cells. This is how yeast reproduces. Yeast is a microscopic fungus.

SA M

This can be done safely in the laboratory. Scientists let microorganisms grow in a Petri dish containing a special kind of jelly, called agar jelly. The dish and the jelly have to be sterile. This means that any living organisms on them have been killed.

Petri dish

agar jelly

Think like a scientist

Growing microorganisms from the air

Microorganisms are so small that they can float around in the air. You cannot see them, but they are there. In this experiment, you will use agar jelly to grow some bacteria and fungi from the air. You will need:

a sterile Petri dish containing sterile agar jelly, some sticky tape, a pen that can write on plastic

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7 Microorganisms in the environment SEE QUERY LOG Sorry, but I have no idea what this sentence means. Please rewrite to make some sense.

Continued 

Tech-Set: Please advise as no comments in the query log!

Safety

Do not breathe or talk over the top of the jelly. You do not want to grow bacteria from your breath. It is very unlikely that any of the bacteria or fungi that you grow are harmful. But – just in case – keep the lid on the Petri dish after step 2. That way, you cannot accidentally touch them or breathe them in.

PL E

Read the safety notes before you start.

1 Take the lid off the dish. Leave the dish open for about 5–10 minutes. This allows microorganisms in the air to get onto the jelly.

2 Put the lid back on the dish. Use sticky tape to fasten the lid onto the dish.

taping the lid onto the dish

3 Turn the dish upside down. This is so that any droplets of water that form inside the dish do not make puddles on the jelly. The puddles might drown the microorganisms. 4 Label the bottom of the dish with your name and the date.

5 Leave the dish in a safe place for a few days. Do not take the lid off the dish.

SA M

6 After a few days, look at the surface of the jelly in the dish. You will see colonies of bacteria and fungi growing on the jelly. Each colony began as a single microorganism. Questions

1 The jelly contains nutrients for the microorganisms. Can you suggest what the word ‘nutrients’ means? (You will find out more about nutrients in Topic 7.4.)

2 Suggest why the Petri dish and agar jelly must be sterile. 3 Make a drawing of the colonies of microorganisms on the surface of the jelly. You may have some colonies of bacteria, and some colonies of fungi. Label them.

Colonies of bacteria usually have smooth edges. Colonies of fungi are usually furry, or have rough edges.

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7.1 Microorganisms

Microscopic algae and protozoa

PL E

If you look at some pond water through a microscope, you will see many tiny living organisms in the water. Some of them are tiny plant-like organisms, called algae. Some of them are animal-like organisms, called protozoa. (The singular forms of these two words are alga and protozoan.)

SA M

These microorganisms are in a drop of pond water.

Questions

3 Some of the microorganisms in the photograph are not single-celled. How are their cells arranged? 4 Some of these microorganisms have cells like animal cells, and some have cells like plant cells. a

Make a simple drawing of one of the microorganisms that has cells like animal cells.

b

Make another simple drawing of one of the microorganisms that has cells like plant cells.

c

Label your drawings to explain the differences between them.

Summary checklist

I can explain what a microorganism is. I can name some different kinds of microorganism. I can describe how to grow microorganisms on agar jelly.

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7 Microorganisms in the environment

7.2 Food chains and webs In this topic you will: • practise constructing food chains and food webs, using arrows to indicate energy transfer

PL E

• practise using the correct terms to describe the organisms in a food chain or food web • think about how well food chains and food webs describe feeding relationships. Getting started

Try to answer these questions on your own.

1 Tigers eat deer. Deer eat grass. Write this as a food chain.

SA M

2 Tigers also eat langur monkeys. Deer are also eaten by leopards. Add those animals to your food chain to make a food web.

Key words carnivore consumer ecology food chain food web herbivore predator prey producer

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7.2 Food chains and webs

Microorganisms in the environment The study of organisms in their environment is called ecology. All the different organisms that live together affect one another in some way. For example, one species of animal may eat another animal. A plant may provide shelter for an animal.

PL E

Microorganisms have important roles to play in the environment. In the rest of this Unit, we will look at how microorganisms affect other organisms in their environment, including their importance in food chains and food webs.

In this topic, you will look at how food chains and food webs describe how energy, in the form of food, is transferred between animals and plants. In the next topic, you will look at how microorganisms fit into food chains and food webs.

Food chains

Arun has chicken and rice for lunch. It gives him a lot of energy. The food you eat gives you energy. How did the energy get into the food?

The energy in food begins in the Sun. Energy from the Sun reaches the Earth in sunlight.

SA M

Plants use energy from sunlight to make their own food. Some of the energy from the sunlight goes into the food that the plant stores in its roots, stems, fruits and leaves.

When an animal – such as Arun – eats part of the plant, it eats the food the plant made. This is how the animal gets energy. This is called energy transfer. You can show how the energy passes from the Sun into the rice, and then into Arun’s body, by drawing a food chain. The arrows in the food chain show how energy is passed from the Sun to the plant, and then is transferred to the rice, and then to Arun.

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7 Microorganisms in the environment

The first organism in a food chain is a producer. Plants use energy from the Sun to produce food. All the other organisms in a food chain are consumers. Animals are always consumers. They have to eat ready-made food to get their energy. They consume (eat) plants or other animals. Consumers that consume only plants are herbivores. Consumers that consume other animals are carnivores.

Questions

PL E

Animals that catch, kill and eat other animals are predators. The animals they eat are their prey.

1 The chicken that Arun ate for lunch ate wheat. Wheat is a plant. Draw a food chain showing how the energy passed from the Sun to Arun when he ate the chicken.

2 Draw a food chain showing how energy from the Sun passed into you when you ate one of the things that you had for breakfast or lunch.

Food webs

Here are two more food chains. These food chains describe part of the feeding network of plants and animals on the African plains. springbok

cheetah

SA M

acacia tree grass

termite

aardvark

leopard

The diagram on the next page shows how the organisms in these two food chains, and some other organisms, are connected by their feeding habits. This diagram is a food web. Put your finger on the acacia tree in the food web. Then move it to the springbok, then to the cheetah. You are tracing the path of the energy as it transfers along a food chain. Now do the same for another food chain – the one that begins with grass and ends with a leopard.

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7.2 Food chains and webs

leopard

aardvark

PL E

hyena

cheetah

zebra

SA M

springbok

acacia

termite

grass

A food web on the African plains.

Questions

3 Write down two more food chains that you can find in the food web diagram. 4 Write the names of the two producers in the food web. 5 How many consumers are there in the food web? 6 How many herbivores are there in the food web?

7 Write the names of two carnivores from the food web. 8 Write the names of two predators and their prey, from the food web.

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7 Microorganisms in the environment

Activity Describing a food web Work in a group of four or five. Your task is to write a series of descriptions that someone else can use to build a food web using the cards and arrows. You will need:

PL E

• a diagram of a food web (each group needs a different food web to work with) • some cards that you can write on • some lined paper

• some arrows cut out of card or paper

1 Write the names of the organisms in the food web on the cards, one name on each card.

2 Write the descriptions on lined paper. For example, for the African food web, some of your descriptions could be:

SA M

Springbok eat acacia trees. Termites are eaten by aardvarks. Cheetahs and leopards eat zebras.

3 When your group has finished writing the descriptions, take your cards and arrows to another group. Ask this group to use your descriptions to build the food web.

Self-assessment

Could the other group use your descriptions to build the food web? Did they make the arrows point the correct way? How do you think you could make your descriptions easier to follow?

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7.2 Food chains and webs

Think like a scientist Using a food web as a model A food chain or a food web is a model. It tries to show how plants and animals that live in the same place depend on each other for food. In your group of two or three, discuss how well you think the African food web shows what really happens on the African plains. Here are some ideas you could discuss. • How complete do you think the food web is? Question

PL E

• Is it possible to draw a totally complete food web?

1 When you have finished your discussion, copy and complete these sentences. I think the food web is a useful model because ……………… .

I think the food web is not a perfect model because ……………… . Summary checklist

SA M

I can use descriptions to construct a food chain or a food web. I can use arrows to show how energy transfers from one organism to another. I can classify the organisms in a food web as producers, consumers, herbivores, carnivores, predators or prey. I can describe some strengths and limitations of food chains and food webs as models.

Tech-Set: Please note that 200134392-001 is the above image AND it has been used as section 7.2 opener image. Please advise.

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7 Microorganisms in the environment

7.3 Microorganisms and decay In this topic you will: • learn about microorganisms and decay • investigate how temperature affects the rate of decay

Getting started

PL E

• plan an experiment to test an hypothesis about decay.

In a group of three, think of three different ways to complete this sentence: A microorganism is ………………… .

decay decomposer mould organic matter rot

SA M

Be ready to share your ideas with the rest of the class.

Key words

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7.3 Microorganisms and decay

Decomposers and decay The food chains and food webs that you looked at in the previous topic did not include microorganisms. But microorganisms are everywhere. They live in the air, in the soil, in water, on our skin and inside our bodies.

PL E

The apple in the picture has microorganisms growing on its surface. Each spot on the apple is made up of millions of cells of microscopic fungi. This kind of fungus is sometimes called mould. The apple is mouldy. The microorganisms have changed the apple. They have made it decay. Organisms that make things decay are called decomposers. Many different kinds of microorganisms – including some kinds of bacteria and microscopic fungi – are decomposers.

The spots on the apple are colonies of fungi.

Apples come from plants, which are living organisms. Any substance that has been made by a living organism (by a plant or animal) is called organic matter. So, apples are organic matter.

SA M

Some microorganisms can break down organic matter when they feed on it. This is what has caused the apple to decay. The microscopic fungi have broken down the crisp, fresh apple and made it become brown and soft. They have made the apple rot. Activity 7.3.1

What can microorganisms decay? Here are three questions.

First, think quietly about the answers to the questions on your own. When your teacher tells you to, turn to your partner and discuss your ideas. Be ready to share your answers with the rest of the class. Questions

1 Which of these things are made of organic matter? bread  water  leather  rock  wood  fruit

2 Think of two more things that are made of organic matter, and two more things that are not made of organic matter. 3 Which of the things in your answers to Questions 1 and 2 can be broken down by microorganisms?

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7 Microorganisms in the environment

Questions 1 Some microorganisms are decomposers. Explain what this means. 2 Describe one way in which decay by microorganisms is not useful. 3 Suggest one way in which decay by microorganisms is useful. Think like a scientist Investigating how temperature affects decay by microorganisms

You will need:

PL E

Doing this investigation will give you practice in carefully collecting results and using them to make a conclusion.

• 2 similar pieces of bread  • 2 paper plates

• 2 plastic bags or some transparent food wrap • a dropper pipette

1 Put two similar pieces of bread onto two paper plates.

2 Add a little water to both pieces of bread. Take care not to get them too wet.

SA M

3 Leave the bread open to the air for about 30 minutes. Then cover each plate with a plastic bag or food wrap. 4 Put one plate in a warm place. Put the other plate in a refrigerator.

5 Record the appearance of each piece of bread each day, for several days.

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7.3 Microorganisms and decay

PL E

Continued  6

This bread has several patches of blue mould growing on it.

Questions

This is what bread mould looks like through a microscope. You can see the tiny threads that it is made of.

1 Compare the results for the bread in the warm place and the bread in the cold place. 2 Did other people in your class get similar results? If they were not the same, suggest possible reasons for the differences.

SA M

3 Make a conclusion from the results of your investigation. Self-assessment

1 For each of these statements about your experiment, decide whether you did it very well, fairly well or not at all: • I was careful to add the same amount of water to each piece of bread.

• I made a careful record of the appearance of each piece of bread each day. • I wrote down or drew my results clearly, so that someone else could understand them. • I made my conclusion from my actual results, not from what I thought should happen.

2 Write down one thing that you did really well. 3 Choose one thing that you think you could do better next time, and explain how you will try to improve it.

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7 Microorganisms in the environment

Think like a scientist Investigating how moisture (water) affects decay You are going to plan your own experiment. You can use ideas from the investigation about how temperature affects decay by microorganisms. Plan an experiment that you could do to test this hypothesis:

Think about:

PL E

Moist bread decays more quickly than dry bread • the variable you will change, and how you will do this

• the variable you will observe or measure, and how you will do this • the variables you will keep the same

• the results you predict you will obtain if the hypothesis is correct.

You may be able to do your experiment. If you can, collect results and use them to make a conclusion. Summary checklist

I can explain how microorganisms make things decay. I can explain what a decomposer is. I can use the results of my experiment to make a conclusion. I can decide which variables to change, measure and keep the same in an experiment.

SA M



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7.4 Microorganisms in food webs

7.4 Microorganisms in food webs In this topic you will:

PL E

• draw and interpret food webs that include microorganisms as decomposers • think about how microorganisms contribute to food webs. Getting started

With a partner, discuss whether each of these statements is correct.

Key words dung nutrients

1 The arrows in a food chain show the direction in which energy flows from one organism to another.

2 All animals are consumers, and all plants are producers.

SA M

3 Some consumers are herbivores and some are carnivores.

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7 Microorganisms in the environment

Roles of decomposers No-one would want to eat a rotten apple. The microorganisms that make an apple decay have spoiled the food. But most of the time, decay by microorganisms is useful. Microorganisms break down dead bodies and animal waste. They decompose this material. Almost all decomposers are microorganisms. Fungi and bacteria are the most important decomposers.

PL E

If the dead bodies and waste are not broken down by decomposers, they would just build up. There would be heaps of dead plants, dead animals and animal dung everywhere.

But there is an even more important reason why decomposers are useful. The dead bodies and waste contain substances that living organisms can use to supply them with energy, or to help them to grow. These substances are called nutrients. When microorganisms decay organic matter, they return the nutrients to the soil. Plants can then use the nutrients to help them to grow. This is really helpful for the plants.

SA M

This also helps animals, because there are more plants to eat.

This fungus is a decomposer. It is breaking down the elephant dung.

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7.4 Microorganisms in food webs

Activity 7.4.1 Decomposing fruit You will need: • a piece of fruit, such as a lemon or strawberry • a plate or dish to put the fruit onto

Tech-Set: Please advise as query log has no comments in

PL E

• a pen to write on the plate or dish

Query log: Can we write on a plate with a pen? Suggest they use pen, paper and sellotape, or a pen and sticky note.

1 Write your name on a dish. Put the fruit onto the dish. Do not cover the fruit. 2 Leave the fruit in the laboratory, or another warm place.

3 Look at the fruit every two or three days. Take digital photographs of the fruit, or make drawings of it. Questions

1 What changes can you see in the fruit?

SA M

2 Explain what happens to the fruit.

What sort of decomposers are growing on these oranges?

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7 Microorganisms in the environment

Decomposers in food webs Decomposers feed on almost every organism after it dies. They also feed on waste from animals. This is how decay microorganisms get their energy. Energy from the dead organisms and their waste is transferred to the decomposers.

python

fruit bat

PL E

You can show this by adding decomposers to food chains or food webs. You do not usually do this because you have to draw an arrow from every organism in the food chain or food web to the decomposers. This makes it look very complicated. The diagram shows a simple food web with decomposers added to it.

parrot

banana

SA M

Questions

microorganisms

1 Write a food chain of your own. Add decomposers to your food chain. 2 Look at the food web above. Are decomposers producers or consumers? Explain your answer. Activity 7.4.2

Are all decomposers microorganisms?

In this activity, you will think about how fungi fit into food chains. Look at the photograph.

The toadstools in the photograph are not microorganisms. You can see them easily, without a microscope. In the photograph, the part of the fungus that you cannot see is inside the log, breaking it down.

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7.4 Microorganisms in food webs

Activity 7.4.3 Questions In a group of three, discuss these questions about the photograph. Be ready to share your ideas with the rest of the class. 1 Is this fungus a decomposer? Explain your answer. 2 Is this fungus a microorganism? Explain your answer.

PL E

3 A slug eats the fungus. Explain where the energy obtained by the slug originally came from. 4 Draw a food chain that describes your answer to question 3.

5 Apart from fungi, what other kinds of microorganisms act as decomposers? Activity 7.4.4 Making a mind map

On a large sheet of paper, construct a mind map to link ideas about food webs, microorganisms and decay.

Compare your mind map with a partner’s mind map. Ask your partner to explain their mind map to you. Then explain your mind map to them.

SA M

Are there any similarities between the mind maps? What are the differences? Do you think one is better than the other? If so, why do you think that?

Which is better for helping you to understand what you have learned in this unit – making your own mind map, or looking at someone else’s? Why do you think that? Summary checklist

I can draw a food chain or food web including decomposers. I can explain why microorganisms are important in food chains and food webs.

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7 Microorganisms in the environment

Project: DDT and malaria Most microorganisms are not harmful. But some microorganisms cause disease. Malaria is a serious disease that is caused by a microscopic protozoan. The microorganism that causes malaria is spread by mosquitoes. In some countries, a chemical called DDT is used to kill mosquitoes. This reduces the number of cases of malaria. Unfortunately, DDT harms other animals as well as mosquitoes.

PL E

• The World Health Organization, WHO, thinks we need to carry on using DDT until better alternatives are found, to save thousands of human lives. • The Worldwide Fund for Nature, WWF, thinks we need to stop using DDT as soon as possible, to protect the environment.

Work in a group of three or four. You are going to pretend that you represent the WHO or the WWF. Your task is to put together a case to support your point of view. You will then use your ideas in a debate about the different points of view. You can use the information on these pages. You may also want to look for other information on the internet. When you do this:

• think carefully about who has produced the web pages you are looking at, and decide whether you can trust the information to be unbiased

SA M

• decide how relevant the information is to this task and use only the most relevant information.

DDT and food chains

DDT does not break down completely in an animal’s body. When an animal eats another animal that has DDT in its body, it also eats the DDT. If an animal moves from one place to another, it takes the DDT with it. DDT effects on animals

DDT is very poisonous to fish, and quite poisonous for frogs and other amphibians. We are not sure yet how poisonous DDT is to humans.

Midway Atoll, where this black-footed albatross lives, is thousands of miles from any land where DDT is used. But DDT has been found in the albatrosses there.

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7.4 Microorganisms in food webs

DDT and birds of prey

1.4 1.2 1.0 0.8

PL E

DDT in birds of prey makes the shells of their eggs very thin. The eggs break before the young birds hatch. In the USA, numbers of bald eagles fell when DDT was used. DDT was banned in 1972.

Average number of young per breeding area

Continued

0.6 0.4 0.2

0.0 1966 1968 1970 1972 1974 1976 1978 1980 1982 Year DDT ban

Indoor residual spraying

SA M

In many countries where malaria is present, DDT is sprayed inside houses. The DDT sticks to the walls and kills mosquitoes. The DDT continues to work for up to 6 months. This method needs much less DDT to control mosquitoes than spraying it outside.

Deaths from malaria

In 2015, 212 million people had malaria. 429 000 people died from it. In 2016, there were 216 million cases and 445 000 deaths.

More than two-thirds of people dying from malaria are children under the age of 5.

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7 Microorganisms in the environment

Continued Where is malaria present? Malaria occurs where the mosquitoes that transmit it live. These mosquitoes only live in tropical or subtropical countries. Key Area with no malaria

PL E

Area with malaria

Malaria and global warming

SA M

The Earth's mean temperature is increasing. This may mean that the mosquitoes that transmit malaria may be able to move into new areas. Other methods of controlling malaria

Other chemicals can be used to kill mosquitoes. However, most of these are much more expensive than DDT. Sleeping under a bed net can help to reduce the risk of being bitten by a mosquito. A malaria vaccine?

Scientists are trying to make a vaccine for malaria. The best one they have found so far needs four injections. It only halves the risk of getting malaria. DDT persistence

DDT is a persistent chemical. This means that it lasts for a long time. If DDT gets into a lake or river, over half of the DDT will still be there 150 years later. Where is DDT used?

DDT has been completely banned in 34 countries. Many countries, including India and many African countries, still use DDT.

Woukd be good if we can use this image across both pages in the spread.

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7 Microorganisms in the environment

Check your Progress 7.1 Yeast is a single-celled organism that grows on fruit, such as grapes. Yeast feeds on sugar in the grapes. It breaks down the grapes and makes them rot. [2]

Which sentences about yeast are correct? Yeast is a producer.

B

Yeast is a decomposer.

C

Yeast is a microorganism.

D

Yeast is a virus.

PL E

A

7.2 Draw a food chain that includes microorganisms as decomposers.

You do not need to draw pictures – just write the names.

[2]

7.3 A farmer keeps cattle in a field of grass.

SA M

The cattle leave dung in the field. Fungi grow on the dung. The farmer notices that the grass looks greener, and grows taller, when it grows next to cow dung. The farmer measures the length of five grass leaves close to some cow dung, and another five grass leaves where there is no cow dung. Here are her results.

Next to cow dung: 11 cm, 13 cm, 9 cm, 12 cm, 8 cm No cow dung: 9 cm, 10 cm, 6 cm, 7 cm, 9 cm

a

Record the farmer's results in a suitable results table.

[4]

b

Calculate the mean length of the grass leaves next to cow dung. Then calculate the mean length where there is no cow dung. Write the mean lengths in your results table.

[2]

The farmer concludes that grass grows longer next to cow dung. Do you think she has enough evidence to make this conclusion? Explain your answer.

[3]

Explain how the fungi and cow dung might help the grass to grow better.

[2]

c

d

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7 Microorganisms in the environment

7.4 Some bacteria are decomposers. They break down food and change it. Usually this makes the food unpleasant, but sometimes it changes it to something that is good to eat. One kind of bacterium changes milk to yoghurt. When the bacteria do this, they change sugar in the milk to acid. Many people like the sharp taste that the acid provides. Sofia makes some yoghurt. She washes out a plastic container with boiling water.

•

She lets the pot cool down, then puts some fresh milk into the container.

•

She adds a small spoonful of yoghurt she bought.

•

She covers the container with cling film.

•

She puts the container in the refrigerator.

PL E

•

S of ia’s ’ Yoghur t

S of ia’s Yoghur t

SA M

live YOGHURT

a

Explain why it is a good idea to wash the container with boiling water.

[1]

b

Suggest what is in the yoghurt that Sofia bought, that helps to turn her fresh milk into yoghurt.

[1]

c

It takes a long time for Sofia’s milk to turn into yoghurt. Suggest what she can do to make it happen faster. Explain your answer.

d

[2]

Sofia measures the pH of the milk before she puts it into the pot. She measures it again after it had been in the pot for four days. Suggest how the pH changes. Choose from: becomes higher   becomes lower   stays the same

Explain your answer.

[2]

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8 Changes to materials In this topic you will:

PL E

8.1 Simple chemical reactions • learn about the chemical properties of some metals

• learn to recognise that a chemical reaction has taken place. Getting started

Draw each of these hazard symbols and write down the scientific word for:

SA M

• a substance that can poison you

• a substance that catches fire easily

Key words

chemical reaction combine productreact reactant

• a substance that can dissolve your skin.

Check your answers with a partner. Be prepared to share them with the class.

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8 Changes to materials

Chemical and physical properties The physical properties of a substance are features such as: •

what colour it is

•

if it is a solid, liquid or a gas

•

what its boiling or melting temperature is

•

if it is heavy or light.

PL E

For example, some of the physical properties of iron are that it is a grey, heavy solid with a melting point of 1538 °C. One of the physical properties of hydrochloric acid is that it is a colourless liquid. The chemical properties of a substance are features such as: •

how acidic or alkaline it is

•

how it reacts with water, acids or metals

•

how readily it reacts.

Some of the chemical properties of iron are that it combines with sulfur when heated to form iron sulfide, and it combines with oxygen to form iron oxide or rust. One of the chemical properties of hydrochloric acid is that it is has a pH of 2.

SA M

Chemical changes

Chemical changes are different from physical changes. In a physical change, no new substances are formed. For example, when liquid water freezes, the water has changed state but it is still the same substance after the change. In a chemical change, new substances are formed. For example, when iron and sulfur are heated together, they form a new substance (a compound called iron sulfide).

iron

+

sulfur

iron sulfide

The iron and the sulfur have reacted together to form a new substance. A chemical reaction has taken place. The iron atoms have combined and bonded with the sulfur atoms. The reactants (the substances that react together) are the iron and the sulfur. The products are the new substances made in the reaction. In this reaction, there is only one product – iron sulfide.

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8.1 Simple chemical reactions

In some chemical reactions, a substance breaks apart to make new substances. For example, water can be split apart to form oxygen and hydrogen.

oxygen

+

hydrogen

PL E

water

Chemical reactions happen everywhere. They happen inside plants when they grow and when they decay. Chemical reactions happen inside your body to keep you alive, for example, when you digest food.

Burning

Burning is a chemical reaction. When a substance burns, the substance reacts with the oxygen in the air. Sometimes ashes are formed. The ashes contain new substances. The new substances in the ashes are oxides.

SA M

Charcoal is made up of the element carbon. When carbon burns it combines with oxygen in the air to make the gas carbon dioxide.

carbon

oxygen

+

carbon dioxide

When charcoal burns, ash is left behind.

When magnesium metal is burnt, a white powder is formed. This powder is magnesium oxide. A new substance has been formed from magnesium and oxygen. Magnesium and oxygen are the reactants. Magnesium oxide is the product. A chemical property of magnesium is that it burns in air to form magnesium oxide by combining with oxygen.

magnesium

oxygen

+

magnesium oxide

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8 Changes to materials

Think like a scientist Burning magnesium In this task you will burn some magnesium and produce a new product. You will need: • safety glasses  • a Bunsen burner  • a heat-proof mat  • tongs

Safety

PL E

• a piece of magnesium ribbon

Wear safety glasses. While the magnesium ribbon is burning, do not look directly at the flame. Magnesium burns very brightly and the bright light could harm your eyes. 1 Set up the Bunsen burner on the heat-proof mat.

2 Take a small piece of magnesium ribbon and place it in the tongs.

3 Hold the tongs at arm‘s length and place the magnesium ribbon in the Bunsen flame.

SA M

4 Once the magnesium ribbon has caught fire, remove it from the flame.

Magnesium ribbon

Burning magnesium ribbon

Magnesium oxide

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8.1 Simple chemical reactions

Continued  Questions 1 Describe what happens to the magnesium ribbon. 2 Describe what has been formed. 3 Name the reactants in this chemical reaction. 4 List all the safety precautions you need to take while carrying out this experiment.

PL E

Not all metals have the same chemical properties as magnesium. They may not burn in the same way. You could try holding pieces of other metals, such as copper, zinc or iron, in the Bunsen flame and record what happens.

Properties of reactants and products

This table compares the properties of the reactants and products when you burn magnesium. You can see that the properties of the product are different from those of the reactants. Reactants

oxygen

SA M

magnesium

Product

magnesium oxide

Element or compound?

element

element

compound

State at room temperature

solid

gas

solid

Appearance

soft, shiny, malleable

colourless, has no smell

white, powdery

Conducts electricity?

yes

no

no

Melting point in °C

651

– 214

2800

Questions

1 Compare the melting points of magnesium, oxygen and magnesium oxide. 2 Find one similarity between magnesium oxide and one of the reactants.

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8 Changes to materials

PL E

3 For each of these photographs, say if it is a physical change or a chemical reaction, and explain why you think so.

a  Making toast

b Melting chocolate c  Fireworks going off

d  Ice melting

e Coal burning

SA M

f Copper roof turning green

Reactions with water

Some substances react very violently with water. Some substances do not react with water at all. Potassium (a metal) is very soft and can be cut with a knife. This is a physical property. Potassium is so reactive that it has to be stored under oil to prevent it reacting with the water vapour in the air. This is a chemical property. When a very small piece of potassium is placed in a large trough of water, hydrogen gas is given off. The reaction produces so much heat that the gas burns.

Potassium reacting with water in a large glass trough

Safety

You cannot carry out the potassium and water reaction yourself. If your teacher shows it to you as a demonstration, you must wear safety glasses and there must be a safety screen in front of the beaker to protect you.

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8.1 Simple chemical reactions

Reactions with acid

magnesium + hydrochloric acid

PL E

When magnesium is placed in hydrochloric acid, bubbles of gas are given off. The magnesium has reacted with the hydrochloric acid and formed new substances. The gas is hydrogen, and magnesium chloride has been formed. This is a chemical property of magnesium.

magnesium chloride + hydrogen

When you see bubbles forming in a reaction, you know that a gas is being produced. But you cannot tell what type of gas it is.

The diagrams show you how to test a gas to find out if it is hydrogen. Hydrogen gas burns with a squeaky pop. To carry out the test you light a splint and place it in the mouth of the test tube. You need to keep your finger over the end of the test tube until the last moment or you will have no hydrogen left to test. This is because hydrogen gas is lighter than air.

Magnesium in acid

SA M

When the hydrogen pops, it is reacting with oxygen, in the air, to form water.

hydrochloric acid

magnesium pop

splint

Hydrogen can be produced on a larger scale by collecting the gas produced in the reaction over water, as shown in this diagram. You could try this for yourself.

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8 Changes to materials acid

delivery tube

thistle funnel

measuring cylinder

glass lid

hydrogen gas bee-hive shelf water

acid

Think like a scientist

PL E

conical flask metal

Reactions with water and acid You will need:

• safety glasses  • test tubes  • a test tube rack  • water  • hydrochloric acid • small pieces of a selection of metals such as magnesium, iron, copper, zinc

SA M

Safety

Wear safety glasses. Remember to pay attention to hazard warning labels when you use chemicals. Part 1: Reactions with water

1 Place a small piece of each of the metals into a different test tube. 2 Take one tube at a time and add water, so that the test tube is half full. 3 Record your observations and findings in a table. Part 2: Reactions with acid

1 Place a small piece of each of the metals into a different test tube. 2 Take one tube at a time and add hydrochloric acid, so that the test tube is half full. 3 If you see bubbles given off, test for hydrogen gas. 4 Record your observations and findings in a table. 5 For each reaction with acid, write down the reactants and the products.

6 What safety precautions did you take? 7 Explain how you tested for hydrogen.

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8.1 Simple chemical reactions

Comment on any difficulties you had testing for hydrogen and how you tried to overcome them. What have you found out about the chemical properties of the metals you tested?

Questions 4 Give two of the chemical properties of magnesium. 5 Give two of the physical properties of magnesium.

Summary checklist

PL E

6 What are the products when zinc reacts with hydrochloric acid?

SA M

I can describe some of the chemical properties of some metals. I can recognise that a chemical reaction has taken place. I can test a gas to see if it is hydrogen.

Tech-Set: Maybe an incidental image could be used here

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8 Changes to materials

8.2 Neutralisation In this topic you will: • learn how to make a neutral solution • learn why neutralisation is important. Key words

PL E

Getting started

What does the word ‘neutral’ mean? Discuss with a partner all you know about the properties of a neutral liquid. How can you tell if the liquid you have is neutral?

SA M

Be prepared to share your ideas with the class.

burette decay digest filtrate indigestion neutralisation neutralised

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8.2 Neutralisation

Mixing acids and alkalis Acids and alkalis can cancel each other out. When you mix them together they react and make a neutral solution. This is called neutralisation. This is another chemical change. Neutrality is also a chemical property of a substance. If you add too much acid to an alkali, it makes an acidic liquid. If you add too little acid to an alkali, it stays as an alkaline liquid.

alkali

SA M

acid

PL E

You can add the acid very slowly, adding a few drops at a time. This makes it easier to judge exactly when it becomes neutral.

neutral

Mixing acid and alkali to make a neutral solution.

Questions

1 What colour is universal indicator when the solution is neutral? 2 What sort of reaction happens when an acid and an alkali are mixed?

Making a neutral solution

You can use a special piece of equipment called a burette to neutralise an alkali very accurately. You add universal indicator to the alkali in the flask.

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8 Changes to materials

0 cm3

burette 25 cm3

28 cm3

PL E

acid

50 cm3

conical flask

alkali and universal indicator

50 cm3

50 cm3

SA M

Using a burette to add acid to a flask of alkali.

Look at the three diagrams of a burette.

In the first diagram, the pH in the flask is about 13. As the acid is added, the pH becomes lower. The acid is added slowly. The flask is shaken each time some acid is added. In the second diagram, 25 cm3 of acid has been added to the flask. The pH in the flask is now 7. The liquid is now neutral. The acid has reacted with the alkali and neutralised it. In the third diagram, a little more acid has been added to the flask. The pH in the flask is now about 6. The liquid is weakly acidic. When this happens there is a chemical reaction and new substances are formed. If you use hydrochloric acid and sodium hydroxide (an alkali), these are the reactants. When they react together, the products that form are sodium chloride and water.

hydrochloric acid

+

sodium hydroxide

sodium chloride

+

water

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8.2 Neutralisation

Activity 8.2.1 Rainbow neutralisation In this activity you will demonstrate the different colours shown by universal indicator solution. You will need

Safety Wear safety glasses.

PL E

The apparatus shown in the diagram.

1 Fix a test tube into a clamp stand and place it somewhere it will not get moved. 2 Place a crystal of washing soda in the bottom of a test tube.

3 Carefully add some water until the tube is about two-thirds full. 4 Add a few drops of universal indicator.

5 Carefully pour some acid on the top. Do not shake the tube.

SA M

6 Leave the tube to stand for a few days.

SEE QUERY LOG Zara should be wearing a lab coat. CUP to supply updated image, please do not deliver revised proofs until you've received it

universal indicator solution

Tech-Set: Please advise

hydrochloric acid

clamp stand

water

crystal of washing soda

Questions 1 What is the pH at the top part of the test tube? 2 What is the pH at the bottom of the test tube?

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8 Changes to materials

Continued 3 Which is the most alkaline part of the tube? 4 Why did you have to keep the tube still when you left it for a few days? 5 Which hazard symbols are displayed on the equipment you used? What do these mean? How does the rainbow appear?

PL E

At the top of the test tube

The acid has turned the universal indicator red at the top of the tube. This shows it is strongly acidic. The acid particles gradually move down the tube. They mix with more water and the universal indicator turns yellow. This is more weakly acidic. In the middle of the test tube

The acid and the washing soda solution mix. They react together. The universal indicator is yellow. The washing soda solution and acid have neutralised each other. At the bottom of the test tube

SA M

The washing soda has dissolved in the water around it. The universal indicator is purple or dark blue around the washing soda. The washing soda is a strong alkali. The particles of the washing soda gradually move up the test tube. They mix with more water and the universal indicator turns a lighter blue. This shows it is more weakly alkaline.

The rainbow neutralisation experiment after a few days.

Self-assessment

How successful was your rainbow? Was there anything you could have done to improve the outcome?

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8.2 Neutralisation

Neutralisation in everyday life Indigestion

SA M

PL E

Your stomach produces hydrochloric acid. This acid gives the stomach the right conditions to digest your food. When your stomach produces too much acid, you have indigestion. It can be very uncomfortable. There are many medicines that can help. They are all alkalis and they neutralise the acid. Sometimes these medicines are called antacids.

Antacid medicines for indigestion

Toothpaste

There are millions of bacteria in your mouth. These bacteria feed on the pieces of food left on your teeth. The bacteria produce acid when they feed. This acid damages your teeth and makes them decay. Toothpaste contains alkali and this helps to neutralise the acid.

Neutralising lakes

Toothpaste helps to neutralise the acid in your mouth.

In some parts of the world there are harmful chemicals in the air that make the rain acidic. This acid rain damages trees and changes the pH of the lakes, rivers and ponds. The plants and animals that live in the lakes cannot live in acid conditions. Some countries drop alkalis into the lakes to neutralise the acid.

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8 Changes to materials

Growing crops In some areas, the soil is very acidic and plants do not grow well. Farmers spread lime on the soil to neutralise the acid so that the plants can grow better.

Questions 3 Why is toothpaste alkaline?

PL E

4 Where does the acid in your mouth come from?

5 Why is an alkaline substance dropped into lakes in some countries? 6 What do farmers spread onto acidic soil? Explain why they do this.

Lime is added to acidic soils, to neutralise the acid.

SA M

Think like a scientist

Testing the pH of the soil

In this task you will test a soil sample to find the pH. You will need:

• 2 test tubes  • a beaker of water  • a filter funnel

• filter paper  • universal indicator  • a sample of soil

1 Take a sample of soil in a test tube and add some water. 2 Shake the tube.

3 Filter the mixture in the tube.

4 Add a few drops of universal indicator to the filtrate. (The filtrate is the liquid that comes through the filter paper.)

5 Record your results.

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8.2 Neutralisation

Continued 

filter funnel filter paper

water

PL E

universal indicator

filtrate

1 Add water.

2 Shake.

Question

3 Filter.

4 Test.

SA M

Use books or the internet to find out what sort of plants will grow well in this type of soil. Summary checklist

I can describe neutralisation as a change to a pH of 7. I can explain how to make a neutral solution. I can explain why neutralisation is important.

filler image needed Getty 129374971

Tech-Set: Please advise is this is the correct image

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8 Changes to materials

8.3 Investigating acids and alkalis In this topic you will: • discuss questions that you can test • plan an investigation

Getting started

Tech-Set: Please advise as no comments in the query log

PL E

• think about what the results of an investigation tell you.

SEE QUERY LOG Author to rewrite this. We do not test questions. We devise and carry out tests to look for answers to questions.

remedy variable

SA M

With a partner, write down the different colours of universal indicator when it is added to solutions with different pH. How good were you at remembering the colours and what they mean?

Key words

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8.3 Investigating acids and alkalis

Asking questions Scientists ask questions. These are some questions about neutralisation that scientists might try to answer. •

How much lime should be added to an acid lake to neutralise it?

•

Which is the best indigestion remedy (treatment for an illness or injury)?

•

How much toothpaste is needed to neutralise the acid in your mouth?

PL E

Let’s look at the second question: ‘Which is the best indigestion remedy?’ It is not a very precise question. What does ‘best’ mean? Does ‘best’ mean the most pleasant tasting, the cheapest, the most effective or the most cost-effective? Scientists need to write their question in a way that they can test. So, instead of asking: ‘Which is the best indigestion remedy?’, a scientist might ask: •

‘Which indigestion powder neutralises the acid, using the least amount of powder?’ Think like a scientist

SA M

Asking questions

In a group of three or four, discuss and write down four questions about acids and alkalis that you could investigate. Share your ideas with the rest of the class.

Could each of your questions be investigated?

Planning an investigation

When you plan to do an investigation, you have to design an experiment. If you are investigating the effect of indigestion powders on stomach acid, you cannot use your own stomach acid. You have to use a model instead, such as a beaker of acid. There is a lot to think about.

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8 Changes to materials

What will I do to stay safe?

What will I measure?

What equipment do I need?

What will I change in the investigation and what will I keep the same?

PL E

How will I make my test fair?

The things that change are called variables.

How will you know when the powder has neutralised the acid?

•

What will you see happen?

•

How will you carry out the investigation?

•

How will you record the results?

SA M

•

Think like a scientist

Planning an investigation

Working in the same group as before, choose one of the questions from Think like a scientist: Asking questions. In your group, plan how you could carry out the investigation. When you have discussed it in your group, divide up the tasks. These might include ‘equipment list’, ‘method’, ‘safety’, ‘results table’ and so on. Each group member should produce something to put onto a large piece of paper and share with the class. You may be able to carry out your investigation, once it has been checked for safety. Self-assessment

How well did your group do? Was your plan safe? Would your plan work? Was the test fair?

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8.3 Investigating acids and alkalis

Which powder is best at neutralising acid? Marcus and Arun put 20 cm3 of hydrochloric acid into each of three beakers. The acid has a pH of 1. This is like the strong acid in your stomach. They also put a few drops of universal indicator in each beaker.

spatula

indigestion powder

SA M

hydrochloric acid and universal indicator

PL E

They add the indigestion powder, spatula by spatula, until the acid is neutralised and the universal indicator is green. They do this with each of the three powders A, B and C. They record the number of spatulas they used.

Here are Marcus and Arun’s results. Powder

Number of spatulas used to neutralise the acid

A

10

B

6

C

24

Questions

1 Marcus and Arun are using acid that is pH 1. What should they do to stay safe? 2 Which variables are they keeping the same in this investigation? 3 Which variable is being changed? 4 What is being measured? 5 Which is the most effective powder?

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8 Changes to materials

6 Which is the least effective powder? 7 Do you think there is enough evidence to be certain of your answers to questions 5 and 6? Marcus and Arun repeat their investigation twice more. The table shows all their results. Powder

Number of spatulas used to neutralise the acid Second try

Third try

Mean

A

10

9

11

10

B

6

17

16

13

C

24

23

25

24

PL E

First try

8 Now which powder do you think is the most effective? 9 Which result looks ‘wrong’?

10 Suggest why Marcus and Arun might have got this ‘wrong’ result. 11 What should they have done about it?

SA M

12 Should they have included the ‘wrong’ result when working out the mean? What do the three sets of results tell you about carrying out an investigation? When you see evidence from someone else’s investigation, what do you need to ask? Summary checklist

I can word a question so that it can be tested. I can plan an investigation. I can look critically at what the results of an investigation tell me.

SEE QUERY LOG Again, we do not test questions. We devise and carry out tests to look for answers to questions. Author to rephrase this. Tech-Set: Please advise as no comments in the query log

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8.4 Detecting chemical reactions

8.4 Detecting chemical reactions In this topic you will: • learn about different ways of telling if a chemical reaction has happened • test gases given off in reactions so that you can identify them

Getting started

PL E

• carry out practical tasks safely.

What is the difference between: • reactants and products

• chemical and physical changes • acids and alkalis?

Key words

cloudy glowing precipitate

SA M

Think about these three questions for a minute, then spend one minute writing your answers. Compare your answers with a partner. Take two minutes to improve your answers. Be prepared to share your answers with the class.

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8 Changes to materials

What happens in a chemical reaction In a chemical reaction, new products are formed from the reactants. How can you tell this has happened? There are some clues you can look out for that might mean a reaction has taken place.

A gas is given off Reaction 1

PL E

One of the most useful clues to help decide if a chemical reaction has taken place is whether a gas is given off. Consider these three reactions.

SA M

You have seen the reaction of magnesium with acid and seen bubbles of the gas hydrogen given off in Topic 8.1. You learnt how to test for hydrogen.

Magnesium reacting with hydrochloric acid

magnesium + hydrochloric acid

magnesium chloride + hydrogen

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8.4 Detecting chemical reactions

Reaction 2 When baking powder and vinegar react, a gas is also given off. This gas is carbon dioxide. You can test for carbon dioxide by using limewater.

PL E

When limewater mixes with the carbon dioxide, the limewater turns cloudy.

Limewater turns cloudy when carbon dioxide is bubbled through it.

SA M

Reaction 3

When a piece of apple is placed in hydrogen peroxide it bubbles. A gas is given off. This gas is oxygen. To test for oxygen you use a glowing splint. When the glowing splint is placed in the mouth of the test tube, it will relight if the gas is oxygen.

hydrogen peroxide piece of apple

When hydrogen peroxide and the chemicals in the apple react, oxygen is given off. Oxygen will relight a glowing splint.

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8 Changes to materials

Activity 8.4.1 Testing gases Try these reactions and test the gas that is given off. You will need:

Safety Wear safety glasses.

PL E

The apparatus shown in the diagrams

Testing for carbon dioxide

1 Pour limewater into a test tube until it is about half full.

2 Place a small amount of calcium carbonate into another test tube.

3 Add some hydrochloric acid to the calcium carbonate in the test tube. 4 Quickly fit the rubber bung and delivery tube.

5 Ensure the delivery tube reaches into the limewater.

SA M

delivery tube

SEE QUERY LOG He should he be wearing a lab coat. CUP to supply updated image, please do not deliver revised proofs until you've received it

rubber bung

calcium carbonate and hydrochloric acid

Tech-Set: Awaiting new artwork

limewater

test tube

Testing for oxygen

1 Pour hydrogen peroxide into a test tube until it is about half full. 2 Add a spatula of manganese dioxide. 3 Place a glowing splint into the neck of the test tube.

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8.4 Detecting chemical reactions

Continued

hydrogen peroxide

Questions

PL E

manganese dioxide xid de

1 Describe the changes to the limewater when you tested for carbon dioxide.

2 Describe what happened to the glowing splint when you tested for oxygen.

SA M

How easy was it to carry out the tests for gases? What difficulties did you have? How did you attempt to overcome them?

Other chemical reaction clues Reactant ‘disappears’

When magnesium ribbon reacts with acid, hydrogen is produced and the magnesium ribbon ‘disappears’. The magnesium is used up in the reaction; it combines with the chlorine from the hydrochloric acid to form magnesium chloride.

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8 Changes to materials

Colour change Gently heating black copper oxide with sulfuric acid produces a blue solution of copper sulfate. copper oxide (black) + sulfuric acid → copper sulfare + water

Safety

Heat is produced

PL E

If you try this in the laboratory, make sure you do not boil the blue liquid, as harmful fumes will be given off.

copper oxide + sulfuric acid (black)

copper sulfate + water (blue)

When potassium is placed in water, hydrogen gas is given off. The reaction produces so much heat the hydrogen burns. Safety

This reaction should only be done by a teacher.

SA M

When you added zinc to hydrochloric acid, hydrogen gas was given off and the test tube felt hot.

hydrochloric acid

Change in pH

When you neutralise an alkali, there is a change in pH. It is called a neutralisation reaction.

sodium hydroxide + hydrochloric acid → sodium chloride + water

sodium hydroxide

In this reaction, sodium chloride and water are produced.

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8.4 Detecting chemical reactions

A precipitate is formed If you mix solutions of silver nitrate and calcium chloride, a chemical reaction takes place. When the two solutions (liquids) are mixed, a solid is formed. This solid is called a precipitate. In this example, the solid is silver chloride.

SA M

PL E

silver nitrate + calcium chloride → silver chloride + calcium nitrate

When silver nitrate and calcium chloride react, a precipitate is formed.

As carbon dioxide is bubbled into limewater, a precipitate is formed.

When you tested for carbon dioxide gas, you used limewater. Limewater is a solution of calcium hydroxide. You saw that the limewater turned cloudy when carbon dioxide was bubbled into it. This is because a precipitate of calcium carbonate formed. You added a gas to a liquid, and a solid was formed. calcium hydroxide + carbon dioxide → calcium carbonate + water

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8 Changes to materials

Think like a scientist Chemical reactions or not? A series of experiments will be set up in the laboratory. You will be told which ones to carry out. Safety Before trying any of these reactions, you must carry out a risk assessment. Think about how you will stay safe.

Experiment A You will need:

PL E

Try some or all of these activities and decide if a chemical reaction has taken place. Share them with the class. You do not need to carry out these investigations in any particular order. For each investigation, state what you did and mention any safety considerations. What clues help you to decide?

• safety glasses  • black copper oxide powder  • dilute sulfuric acid • a beaker and a stirring rod

You will need:

• safety glasses  • a test tube  • a test tube rack  • a small piece of zinc  • dilute hydrochloric acid  • a beaker and a stirring rod

Half-fill a test tube with dilute hydrochloric acid. Add a small piece of zinc.

SA M

Add some black copper oxide powder to about 150 cm3 dilute sulfuric acid in a beaker. Stir gently.

Experiment B

What do you observe? Has a chemical reaction taken place? What evidence do you have?

What do you observe? Has a chemical reaction taken place? What evidence do you have?

Experiment C

Experiment D

When you hold the test tube in your hands, do you notice anything?

You will need:

You will need:

• safety glasses  • limewater  • a test tube  • test tube rack  • a straw

• safety glasses  • a piece of chocolate • test tube  • test tube rack • a beaker  • access to hot water

Half-fill a test tube with limewater. Use the straw and blow gently into it. Fill a beaker with hot water. Place a small piece of chocolate in a test tube. Stand the What do you observe? Has a chemical test tube in the beaker of hot water. reaction taken place? What evidence do you have?

What do you observe? Has a chemical reaction taken place? What evidence do you have?

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8.4 Detecting chemical reactions

Continued Experiment E

Experiment F You will need:

• safety glasses  • copper sulfate solution  • evaporating dish  • pipe-clay triangle  • tripod  • Bunsen burner  • tongs

• safety glasses  • sodium hydroxide • conical flask  • measuring cylinder • universal indicator  • hydrochloric acid  • burette

PL E

You will need:

Place a solution of copper sulfate in an evaporating dish. Heat gently until the solution starts to spit. Turn off the heat and leave the evaporating basin to cool. What do you observe? Has a chemical reaction taken place? What evidence do you have? Experiment G You will need:

What do you observe? Has a chemical reaction taken place? What evidence do you have? Experiment H

You will need:

• safety glasses  • test tube  • test tube rack  • solution of silver nitrate • solution of calcium chloride

SA M

• safety glasses  • baking powder • spatula  • vinegar  • test tube  • test tube rack

Place of sodium hydroxide in a conical flask and add a few drops of universal indicator solution. Add acid slowly from a burette until the universal indicator changes to green.

Put a few spatulas of baking powder in a test tube. Add vinegar. What do you observe? Has a chemical reaction taken place? What evidence do you have?

Place silver nitrate in the test tube, about half full. Add calcium chloride solution slowly. What do you observe? Has a chemical reaction taken place? What evidence do you have?

What clues helped you to decide if a chemical reaction had taken place? Summary checklist

I can list different ways of identifying that a chemical reaction has taken place. I can test gases for hydrogen, oxygen and carbon dioxide. I can carry out practical work safely.

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8 Changes to materials

Project: Moving dangerous chemicals Acids and alkalis need to be moved from where they are produced to where they are used. This can be very dangerous if there are spills and accidents.

PL E

Work in a group of three. You are a team of reporters who are going to write a report about a serious accident that has happened on a major road. The accident involved a truck carrying concentrated acid. The emergency services attended the accident and dealt with the spill of acid.

Here is a list of some things you could consider.

SA M

• Why is an acid spill so dangerous?

• What would happen if people drove their cars through the acid spill? • How do the emergency services know which chemical they are dealing with? • What must the emergency services do to the spilt acid? • How will they know when the task is complete? • What safety measures must be taken by the emergency services to deal with the spill? • What would be the effect of the acid reaching the soil alongside the road?

• What regulations are in place in your area about the transport of dangerous materials? • What considerations are there for moving dangerous chemicals by sea or air? Decide which of you will research each of the suggestions above. Set a time limit and then meet to share your findings. You may need to do further research or discover other areas you want to find out about. Your report could be written as if it is for a newspaper or magazine. It could be in the form of a radio or television interview or a presentation to the class. Choose a form that you have not used in another science project.

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8 Changes to materials

Check your Progress 8.1 Draw a table to sort the following list into either physical change or chemical reaction. [5] burning a piece of wood

•

melting chocolate

•

cooking an egg

•

heating glass and bending it

•

baking a cake

PL E

•

8.2 The diagram shows an experiment where zinc metal is added to sulfuric acid. a

What is the name of the gas given off in this reaction? [1]

b

How do you test for this gas?

[2]

c

What products are formed in this reaction?

[2]

d

How do you know when all the acid has reacted?

[1]

SA M

8.3 Magnesium ribbon burns in air.

sulfuric acid

zinc

a

Write the chemical symbol for magnesium.

[1]

b

Name the element in the air that reacts with magnesium when it burns.

[1]

c

Name the compound formed when this element reacts with magnesium.

[1]

d

Magnesium also reacts with chlorine. Suggest the name of the product of this reaction.

[1]

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8 Changes to materials

8.4 Look at these reactions. Carbon combines with oxygen to form carbon dioxide.

B

Sodium hydroxide reacts with hydrochloric acid to produce sodium chloride and water.

C

Potassium and water react to form potassium hydroxide and hydrogen.

D

Copper carbonate reacts to produce copper oxide and carbon dioxide.

PL E

A

Write the letter of the reaction that: a

produces a metal oxide

[1]

b

is a neutralisation reaction

[1]

c

is a burning reaction.

[1]

8.5 Zara and Sofia put 50 cm3 of alkali into a conical flask. They added a few drops of universal indicator to the alkali. They used a burette to add acid to the alkali. Zara added the acid 10 cm3 at a time. Sofia stirred the contents of the conical flask each time acid was added. They recorded the pH after each addition of acid. The table shows their results.

Volume of acid added in cm3

0

10

20

30

40

50

pH of solution

12

11

10

9

8

7

SA M



burette acid

alkali and universal indicator

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8 Changes to materials

a

What colour was the alkali and universal indicator solution at the start?

[1]

b

What colour was the solution in the flask at the end?

[1]

c

Which one of the statements is correct?

[1]

• The acid was stronger than the alkali. • The alkali was stronger then the acid.

PL E

• The acid and the alkali were equal in strength. Explain your answer.

Draw a line graph of Zara and Sofia’s results on graph paper. Place the pH on the vertical axis.

[4]

SA M

d

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9 Electricity In this topic you will:

PL E

9.1 Flow of electricity • understand how electricity flows around a circuit

• learn about the electrons that flow to make electric current. Getting started

Key words

Work in groups to discuss answers to these questions.

1 Which of these must be present in a complete circuit for current to flow? lamp

cell

switch

wire

SA M

2 Which of these flows around a complete circuit? voltage

wires

current

heat

attract battery cell components current electrons free to move negative charge repel terminals

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9.1 Flow of electricity

Current Look at the circuit in the picture. When you close the switch, the lamp lights. A cell stores chemical energy that can be changed to electrical energy in a circuit. A battery contains two or more cells joined together.

PL E

The cell in the circuit has two connections, called terminals.

cell

All cells, batteries, power supplies and many other components have two terminals.

The terminals are labelled with + and − symbols, meaning positive (+) and negative (−).

switch

lamp

What happens to make the lamp light?

You can see these symbols in the photograph of these three cells.

The photograph below shows one of the batteries from an electric car. You can see that the battery is made from many cells.

SA M

When connected into a circuit, the negative terminal of a cell, battery or power supply pushes electrons around in the wires. All materials contain atoms. Atoms contain smaller particles. An electron is one type of smaller particle in an atom. The flow of electrons in the circuit is called current.

This battery pack from an electric car is made from hundreds of separate cells connected together.

The + and – symbols on these cells show the positive and negative terminals.

flow of electrons

The flow of current in a circuit is the movement of electrons around the circuit.

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9 Electricity

More about electrons Some of the electrons in a metal are free to move. That means they can move through the metal. In a metal, these electrons move randomly, as shown in the diagram. Electrons are very small and this diagram is not to scale.

metal −

−

− −

− −

−

−

− −

−

−

Electrons in a metal move randomly.

−

−

−

−

−

−

−

− −

−

−

−

−

−

− −

− −

−

−

electrons

−

−

PL E

When the metal is placed into a circuit, the electrons move in the same direction.

−

−

−

+

−

−

−

−

−

−

−

−

−

−

−

−

−

−

−

−

−

−

−

−

−

−

−

−

−

−

−

−

−

−

−

−

−

−

−

−

−

+

−

−

Electrons are negatively charged so they move toward the positive terminal in a circuit.

Electrons have a negative charge.

Opposite charges attract, and like charges repel. To attract means to pull together and repel means to push apart. That means: positive and negative attract

SA M

• •

positive and positive repel

•

negative and negative repel.

Therefore, electrons will be attracted towards the positive terminal of the power supply and be repelled from the negative terminal. If there is a break in the circuit, all the electrons stop flowing. Electrons can only flow in a complete circuit.

Questions

1 Name the particles that move around a circuit when current flows. 2 Copy the sentences and use words from the list to complete them. Each word may be used once, more than once or not at all.

attracted  repelled  positive  negative  electrons  atoms



Current in a circuit is the movement of ………………… .



These particles have a ………………… charge.



These particles are ………………… by the positive terminal of a battery and ………………… by the negative terminal of a battery.

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9.1 Flow of electricity

Activity 9.1.1 Modelling electron flow In this activity, you will use a model to show how current flows in a circuit. Work in groups of four to six. You will need:

PL E

• a ball of string, scissors, coloured tape or coloured marker pen 1 Tie the ends of the string together to form a large loop. The loop must be long enough to be held by all the people in the group. Attach coloured tape or make coloured marks on the string at equally spaced intervals. The intervals should be about 10 cm long. 2 In your group, stand in a circle facing toward the centre of the circle.

3 Each person should hold the loop of string in front of them in both hands, so the string forms a circle. Hold the string so that it is quite tight but can move.

SA M

4 The people in the group are the components in the circuit. One person is the cell. The person who is the cell must pull the string around through the hands of the other group members. The other group members can be components such as lamps or buzzers. 5 Watch how the string moves. Use the coloured marks to see the movement of the string. Questions

Discuss these questions in your group.

1 What part of the circuit made the string move? 2 When the string started to move, was the speed the same all the way around the circuit or different?

3 Was it possible for the string to be moving in one part of the circuit and not moving in another part? 4 Name the particles represented by the coloured marks.

5 In what ways does this model:

a correctly represent what happens in a circuit

b not correctly represent what happens in a circuit?

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9 Electricity

Think like a scientist Making predictions about current In this task, you will make and test predictions about the flow of current in a circuit. Work as a whole class. You will need:

PL E

• a power supply or battery • wires longer than 2 metres, or many short wires that can be connected end to end • 4 identical lamps that can operate in series from the power supply

1 Make a circuit with one lamp close to the negative terminal of the power supply.

2 Place the next lamp several metres away from the first lamp, and another lamp a similar distance from this lamp. 3 Place the fourth lamp close to the positive terminal of the power supply. Do not switch on the lamps yet. Questions

Discuss these questions as a whole class.

SA M

1 What will happen when the power supply is switched on? Will all the lamps come on at the same time? If not, in what order will they light?

2 a Is this prediction testable?

b What name is given to a testable prediction?

Now switch on and see what happens. 3 Describe what you observed.

4 Try to explain what happened in terms of the flow of electrons.

Self-assessment

What did you learn about current in a circuit? List as many things as possible. Is there anything you’re still unsure about current in a circuit?

Summary checklist I can describe how electrons move in circuits. I can understand how to work out the direction that electrons move.

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9.2 Electrical circuits

9.2 Electrical circuits In this topic you will: • learn how to draw and compare circuit diagrams

Getting started Work in pairs.

PL E

• learn the circuit symbols for cells, switches, lamps, buzzers and ammeters.

Discuss with your partner the role of each of these components in a circuit: a cell b switch c lamp d buzzer

ammeter circuit diagram circuit symbols

SA M

e ammeter.

Key words

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9 Electricity

Circuit diagrams Circuits can be shown in a drawing or a circuit diagram.

Advantages of circuit diagrams compared with pictures • •

Circuit diagrams are easier to draw. The components have standard symbols.

PL E

•

cell

switch

lamp

This is a drawing of a simple circuit.

Wires are drawn with straight lines, which is easy to interpret.

Circuit symbols

Components in circuits can look very different.

The picture shows how different some lamps can look.

Standard circuit symbols are used in circuit diagrams so there is no confusion. The same symbols are used in all countries.

SA M

The table shows the names, symbols and functions of some components. Name

Ammeter

Symbol

A

These are all different types of lamp but they all have the same circuit symbol.

Function

measures current in the circuit

Cell

provides energy to make current flow

Lamp

gives out light

Switch (open)

stops the flow of current when opened

Switch (closed)

starts the flow of current when closed

Buzzer

makes a buzzing sound

Common circuit symbols

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9.2 Electrical circuits

In the circuit symbol for a cell, the positive is the longer of the two lines. The negative is the shorter line. −

+

Take care when drawing circuit diagrams. Make sure: there are no gaps in the lines, especially at the corners and where wires meet components

•

wires are not drawn through components.

PL E

•

Comparing circuit diagrams Different circuits are used to do different jobs.

SA M

This circuit contains a cell, a switch and a buzzer. The circuit could be used in a doorbell. If the switch is pushed outside a door, it makes the buzzer sound and attracts attention inside.

This circuit contains a cell, a switch, a lamp and an ammeter. The ammeter measures the electric current. This circuit could be used to light a room and measure the current flowing though the circuit. By measuring the current, you could tell if the cell needs to be replaced – a smaller current means the cell is low on stored energy. The lamp would also become less bright, but you might not notice until too late and you find yourself sitting in the dark!

A

Questions

1 Draw the circuit symbol for: a

a lamp

b

a cell

c

a buzzer

d

a closed switch.

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9 Electricity

PL E

2 Arun draws a circuit diagram with a cell, a switch and a lamp. He makes three mistakes.

Describe the three mistakes in the diagram.

3 Which of these circuits could be used to measure the current in a buzzer? A

B

–

–

+

+

D

SA M

C –

–

+

+

A

A

Think like a scientist

Drawing circuit diagrams Work individually.

Draw circuit diagrams for each of these jobs.

A Two lamps that can be switched on and off together in a car. B A buzzer on a front door with a lamp that comes on at the same time as the buzzer. C Three lamps that operate all the time, with a way to measure current in the lamps.

Questions

1 Now swap your circuit diagrams with someone else. Are they the same? 2 Can two circuit diagrams be different and both correct? Explain your answer.

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9.2 Electrical circuits

Continued Self-assessment Write a number from 1 to 5 for each of these statements. The number represents how confident you are. Use 1 for ‘not confident’. Use 5 for ‘very confident’.

PL E

• I can remember all the circuit symbols in the table.

• I can draw circuit diagrams correctly and accurately.

• I can tell what the circuits in different circuit diagrams could be used for. Activity 9.2.1 Circuit uses

Work in groups of three or four. Look at this circuit diagram.

–

Make a list of all the possible uses.

+

SA M

Discuss what this circuit could be used for.

Summary checklist

I can recognise the circuit symbols for a cell, a switch, a lamp, a buzzer and an ammeter. I can draw the circuit symbols for a cell, a switch, a lamp, a buzzer and an ammeter. I can draw a circuit diagram containing any of these components. I can recognise and compare the jobs of different circuits from their circuit diagrams.

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9 Electricity

9.3 Measuring the flow of current In this topic you will:

PL E

• learn the unit for measuring current • learn how to measure current

• learn a rule about current in series circuits. Getting started

1 Name the particles that move in wires when current flows.

2 a  Name the component that is used in a circuit to measure current.

Key words amps in series

SA M

b Draw the circuit symbol for this component.

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9.3 Measuring the flow of current

Measuring current In Topic 9.1 you saw that electrons move when current flows. When electrons move more quickly, the current increases.

0

5

10 15

A

20

When electrons move more slowly, the current decreases.

PL E

In Topic 9.2 you saw that you can use an ammeter to measure current.

Current is measured in units called amps. Amps have the symbol A.

There are different types of ammeter but they all do the same job.

The picture shows two different ammeters.

Look carefully at the ammeters in the picture. They both have two terminals, for wires to be attached. One terminal is red and the other terminal is black. In a circuit, the red terminal of the ammeter must be connected to the positive terminal of the power supply. The red terminal may be connected directly, or through other components, to the positive terminal of the power supply.

SA M

Both ends of the ammeter are the same in a circuit diagram. You do not need to show the red and black terminals on the circuit symbol for an ammeter. Ammeters are always connected in series with other components in a circuit. If the components are connected in series they are all connected end-toend, one after another, and there are no branches in the circuit.

The drawing shows an ammeter connected in series with a battery, a switch and a lamp. The circuit diagram shows the same circuit.

switch

lamp

this will be changed back to version showing Marcus in full, please don't supply next proofs until you have it. CUP to supply.

cell

+

Tech-Set: Awaiting new artwork

– 1 : 27

ammeter

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9 Electricity

Questions 1 Name the unit used to measure current. 2 The diagram shows four different ammeters in four different circuits. Write down the current shown on each ammeter. Include the unit in your answer. 5 0

10

15

6 8

2 4

A

1500 1000

10

500

PL E

A

0

0

A

B

C

D

3 Copy the sentence and use words from the list to complete it. Each word may be used once, more than once or not at all. slower  faster  electrons  atoms

The greater the current in a circuit, the ………………… the flow of ………………… . 4 Marcus has a circuit with a cell, a lamp and a buzzer. He wants to measure the current in the circuit.

SA M

Which is the correct way to connect the ammeter in this circuit?

A

B

A

–

–

+

+

C

+

–

D

+

–

A

A

Activity 9.3.1

Drawing ammeter scales

In this activity, you will draw the scale for ammeters. Work in pairs.

Draw an ammeter scale and mark the scale with numbers and divisions. The scale should look like one of those in question 2. Do not add the pointer to the scale.

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9.3 Measuring the flow of current

Continued Write a current beside your ammeter scale. Make sure the current you write is within the scale you have drawn. Start with a whole number of amps, such as 4 A or 2.0 A. Swap your drawing with your partner. Your partner will add the pointer to the drawing. The pointer should be in the correct place to match your current. Swap your drawings back again. Is the pointer in the correct place?

PL E

You can progress to decimal numbers, such as 1.7 A. Make sure your drawing has the correct number of divisions between whole numbers. Swap drawings again and check them as before. Self-assessment Which was more difficult:

• drawing the scale correctly

• putting the pointer in the correct place? Think like a scientist

SA M

Making predictions about current

In this task, you will make and test predictions about current in a circuit. Work in groups.

You will need (for each group):

a cell (or cells) that can operate two lamps in series, a switch, lamps, an ammeter, wires and connectors

Part 1

1 Connect the circuit so that the lamps and the switch are in series with the cell (or cells), as shown. Do not include the ammeter yet.

+

–

2 Copy the circuit diagram.

3 Add arrows to your circuit diagram to show the direction that electrons flow through the circuit.

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9 Electricity

Continued  Question

A

X

PL E

1 You are going to measure the current at different positions in the circuit. You will do this by placing the ammeter in the positions X, Y and Z, as shown.

A

A

Y

Z

a Predict what will happen to current going around the circuit. Choose one statement.

A Current will stay the same all the way around the circuit. B Current will decrease as it goes around the circuit. C Current will increase as it goes around the circuit.

SA M

b Explain your prediction. Part 2

4 Connect the ammeter into your circuit. Connect it at position X. 5 Close the switch and record the ammeter reading.

6 Do this two more times, once with the ammeter in position Y, and once with the ammeter in position Z. Remember to open the switch before you make changes. 7 Copy the three circuit diagrams.

8 Write your ammeter readings next to each circuit diagram. Questions

2 Describe the trend in your results.

3 Was your prediction from question 1 correct? 4 Explain your results. Use ideas about how electrons move in wires.

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9.3 Measuring the flow of current

Answer the questions that apply to you. If your prediction was not correct: • Did the result surprise you? • How will you remember this result? If your prediction was correct: • How did you work out what would happen?

Summary checklist

I can recall the unit of current and its symbol. I can take accurate readings from an ammeter. I can draw a circuit diagram with an ammeter connected correctly. I can explain how to connect an ammeter in a circuit.

SA M



PL E

• How will you remember this result when you use other series circuits?

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9 Electricity

9.4 Conductors and insulators In this topic you will: • discover the difference between electrical conductors and insulators • learn about uses for conductors and insulators

Getting started Work in pairs.

PL E

• test some materials for electrical conduction or insulation.

Complete the sentences. Use words from the list.

The words may be used once, more than once or not at all.

are free to move  cannot move electrons atoms  wires When current flows, particles called ………………… move.

allow current to flow conduct electricity conductor inhibit insulator

SA M

In metals, these particles ………………… .

Key words

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9.4 Conductors and insulators

Conductors Conductors are materials that conduct electricity. That means conductors allow current to flow. Electric current can flow through a conductor.

PL E

You saw in Topic 9.1 that electrons move when current flows.

Therefore, a conductor is a material in which electrons are free to move. Conductors allow electrons to flow. All metals are conductors.

Wires that carry electric current are made from metal.

Metals conduct electricity because electrons in metals are free to move.

Most wires in houses and schools are made from copper, with a plastic coating.

Copper wire

SA M

Wires that cover long distances are usually made from aluminium or steel. These metals are cheaper than copper. Some circuits, such as those in phones and laptops, do not use wires. The printed circuit board in the bottom right picture has copper tracks instead of wires. The tracks are green because the copper is coated with another material.

Some wires are hundreds of km long.

Plastic coating

This printed circuit uses copper tracks instead of wires.

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9 Electricity

Insulators Electrical insulators are materials that do not allow current to flow through. Most non-metals, such as plastic, wood, air and cotton, are insulators. In an insulator, the electrons are not free to move.

PL E

Because the electrons are not free to move, current cannot flow. Insulators inhibit electron flow. Insulators are used to keep people safe from electricity.

The plug in the picture below is made from plastic so people can touch the plug. The wire coming from the plug is also coated in plastic to protect people from electric shocks.

Plastic insulation on wires is also useful because the plastic can be coloured differently to identify each wire.

metal pylon insulators

conductors

SA M

The insulators on these power lines stop the current from flowing from the wires into the metal pylon. If the current flowed to the pylon, electrical energy would be dissipated into the ground. Also, people and animals touching the pylon would get electric shocks.

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9.4 Conductors and insulators

Questions 1 Copy the sentences and use words from the list to complete them. plastic  steel  aluminium  wood Examples of electrical conductors include ………………… and ………………… Examples of electrical insulators include ………………… and …………………

PL E

2 Copper is used to make wires for home use. Copper is a good conductor of electricity. Silver is a better conductor of electricity than copper.

Suggest why wires for home use are not made from silver. 3 The drawing shows some types of plugs that are used in different countries.

SA M

body

pins

Explain why:

a

the bodies of the plugs are made from plastic

b

the pins on the plugs are made from metal.

4 Explain, in terms of particles, the difference between conductors and insulators.

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9 Electricity

Activity 9.4.1 Conduct or insulate? Work in groups. You will need: • a piece of paper  • a pen  • a pencil  • a ruler

Object

PL E

Use the ruler to make a large table on a sheet of paper, with these headings.

Conductor or insulator

Reason

SA M

Put the names of each of these objects into the table and complete the other columns.

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

Self-assessment How many of the objects did you classify correctly as conductors or insulators? Did you get the reasons correct?

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9.4 Conductors and insulators

Think like a scientist Conductor or insulator? In this task, you will test some materials to find out whether they are conductors or insulators. Work in pairs or groups of three. You will need (for each group):

PL E

• a battery or cell  • a lamp  • crocodile clips  • wires

• a selection of materials to test, such as items found in the classroom 1 Set up a circuit as shown in the drawing.

Updated artwork now showing Sofia supplied in July.

SA M

Tech-Set: new artwork has not been supplied

cell

lamp

clips

2 Touch the crocodile clips together and watch what happens to the lamp. 3 Test some materials by connecting the materials between the crocodile clips. Questions

1 Explain why you touched the crocodile clips together before you started. 2 Explain how the test works.

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9 Electricity

Continued 3 Present your results in a suitable way. 4 Describe any trends or patterns in your results. 5 Some objects that are made from metal may appear to be insulators in this test. a Explain why.

Summary checklist

PL E

b Describe how you could show that these metals are actually conductors.

SA M

I can describe what is meant by ‘electrical conductor’ and ‘insulator’. I can understand how conduction and insulation work, in terms of electrons. I can recall some examples of conductors and insulators. I can describe some uses of conductors and insulators.

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9.5 Adding or removing components

9.5 Adding or removing components In this topic you will:

PL E

• find out what happens to current when you add more cells in a circuit • find out what happens to current when you add more lamps in a circuit. Getting started

Work in pairs to answer these questions.

1 a Name the unit for measuring current. a Give the symbol for this unit. 2 Complete the sentences.

adding components dimmer position removing components

SA M

a Current in a circuit is the flow of particles called ………………… .

Key words

b As current increases, the flow of these particles gets ………………… .

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9 Electricity

Current in a series circuit If you did Think like a scientist: Making predictions about current in Topic 9.3, you may remember that current is the same all the way around a series circuit.

A

+

–

A

+

The ammeter will give the same reading in both these circuits if the components are identical.

PL E

You can think of the electrons in a series circuit like a train. All parts of the train move at the same speed on the track. The back of the train cannot go faster than the front of the train. As soon as one part of the train moves, all of the train will move.

–

Electrons flow at the same speed in the wires of a series circuit. When electrons start to flow in one part of the circuit, they all start to flow. That means you can put an ammeter at any position in a series circuit and it will give the same result.

It also means that you can put the same components of a series circuit in a different order and the current will be the same.

SA M

Adding components or removing components will affect the current. The effect depends on what components are changed.

Adding or removing cells

You saw in Topic 3.5 that cells and batteries are stores of chemical energy. In a complete circuit, the chemical energy gets changed to electrical energy. That means if you add more cells to a circuit, you have more chemical energy to change into electrical energy in the circuit.

A

A

1.4 A

2.8 A

Look at the two circuits. Each component is identical in both circuits. The circuit with two cells has double the electrical energy of the circuit with one cell. The lamp will be brighter.

The ammeter in the circuit with two cells shows that the current is doubled.

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9.5 Adding or removing components

You need to be careful adding more cells to a circuit. The lamps can be damaged and the wires can get hot. Adding more cells increases the current when the other components are kept the same. Removing cells decreases the current when the other components are kept the same.

PL E

Adding or removing lamps

You saw in Topic 3.5 that lamps change electrical energy to light energy and thermal energy. Electrons carry electrical energy around a circuit. When the electrons pass through a lamp, the electrons transfer some of their electrical energy to the lamp. The lamp changes the electrical energy into light energy and thermal energy.

Remember that the current is the same at all positions in a series circuit. Putting a lamp in a circuit will make the electrons move more slowly, but they move more slowly the whole way around the circuit.

SA M

The circuit with two lamps transfers twice as much energy as the circuit with one lamp. The lamps will be dimmer. That means they do not shine as brightly.

This makes the electrons move at half the speed, so the reading on the ammeter is halved.

A

A

1.4 A

0.7 A

Adding more lamps decreases the current when the other components are kept the same.

Removing lamps increases the current when the other components are kept the same.

Questions

1 Which statement is true about current in any series circuit?

Write the letter.

A Current decreases around the circuit. B Current increases around the circuit.

C Current stays the same around the circuit. D Current increases and decreases around the circuit.

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9 Electricity

2 Look at these two circuit diagrams. Each component is identical in both circuits. A

B

A

PL E

A

a

Which of these circuits has a larger current? Write the letter.

b

Explain your answer.

3 Look at these two circuit diagrams. Each component is identical in both circuits. C

D

A

SA M

A

a

Which of these circuits has a larger current? Write the letter.

b

Explain your answer.

4 Look at the circuit diagram.

A

a

Describe two ways to increase the current in this circuit.

b

Describe two ways to decrease the current in this circuit.

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9.5 Adding or removing components

Activity 9.5.1 Model circuits In this activity, you will make models of circuits from cards. Work in groups. You will need:

PL E

• paper or card   • scissors  • a pen or pencil Start by cutting out 10 equal-sized squares of paper or card. The squares should be about 4–5 cm wide. Draw circuit symbols on each card with wires that go to the end of the card. The cards will need to fit together to make circuits. You should have: • three cards with a cell

• three cards with a lamp

• four cards with circuit corners.

SA M

The cards should look something like this.

Work on a large sheet of paper, where you can draw extra lengths of wire if needed. Questions

1 Build a series circuit with three cells and three lamps. 2 a Make one change that would increase the current in your circuit. b Discuss in your group why this change would increase the current.

Put the circuit back together with three cells and three lamps.

3 a  Make one change that would decrease the current in your circuit. b Discuss in your group why this change would decrease the current.

4 Make another, different series circuit. Discuss whether the current will be different from the first circuit and why.

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9 Electricity

Continued Peer assessment • Did everyone in the group agree with the changes? • Did everyone in the group agree with the explanations?

Measuring current

PL E

Think like a scientist In this task, you will measure current in circuits when components are added and removed. Work in groups.

You will need (for each group):

• 3 cells   • 3 lamps   • an ammeter   • wires  • a switch Safety

You must avoid damage to components where possible. Follow these rules.

SA M

• Do not remove all the lamps from a circuit, leaving only the cells. • Do not connect an ammeter directly to cells without lamps. • If a lamp appears too bright, switch off immediately. Part 1

1 Build this circuit.

2 Close the switch and record the current.

3 Add another lamp.

4 Record the current with two lamps.

A

5 Repeat with three lamps. Questions

1 Discuss in your group the best way to display these results. 2 Display the results in the way your group decided.

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9.5 Adding or removing components

Continued Part 2 6 Build this circuit. 7 Close the switch and record the current. 8 Repeat with two and then three cells.

A

Questions

PL E

9 Display your results in an appropriate way. 3 a Make conclusions about your results.

b Suggest any limitations of the conclusions.

• How do you build a circuit from a circuit diagram?

• Is it easy or difficult to build circuits from circuit diagrams? Rate your answer from 1 (very easy) to 5 (very difficult).

• If you find building a circuit from a circuit diagram difficult, what could make it easier?

SA M

Summary checklist

I can understand that the current is the same all around a series circuit. I can predict what will happen to current in the same series circuit when more cells are added. I can predict what will happen to current in the same series circuit when more lamps are added.

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9 Electricity

Project: Paying for electricity Many homes and schools are connected to electricity supplies. People who use the electricity pay for how much they use. Task 1 Work individually for this task.

PL E

Find out how much current some electrical items use. Do not include items that work only on batteries. For example, most phone chargers use about 1.5 A.

SA M

When searching for this information, you may find a number with the unit W. This is not the current. You can find the current by dividing this number by the voltage. In most countries, the voltage is about 230 V. In some countries, the voltage is 110 V or 120 V. For example, if you find something with 500 W, and your 500 voltage is 230 V, the current used is = 2.2 A. 230 Display your results in a bar chart. Questions

1 Which electrical item in your list uses the most current? 2 Which electrical item in your list uses the least current? 3 Explain why a bar chart is better than a line graph for showing these results. Task 2

Work in groups for this task.

Around the year 1870, some cities had the first electricity supplies. People in 1870 also had to pay for electricity. The amount they had to pay depended on the number of electric lamps they had. Someone who had four lamps would pay double what someone who had two lamps paid. This method of payment was called the pay-per-lamp method. In 1870, there was no technology to measure the quantity of electricity that was actually used. Today, the amount people pay depends on the current they use and the time the current is flowing.

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9.5 Adding or removing components

Continued Questions In your groups, discuss answers to these questions. 1 Suggest reasons why the pay-per-lamp method was fair for 1870. 2 Suggest reasons why the pay-per-lamp method was not fair for 1870.

PL E

3 Would a pay-per-lamp method be fair today? Explain your answer.

SA M

An electric lamp from 1870

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9 Electricity

Check your Progress Name the particles that flow inside a wire when current flows.

[1]

b

State the charge on these particles.

[1]

c

Explain, with reference to the cell, what direction these particles flow in a circuit. [2]

9.2 a

b

Draw the circuit symbols for: i

a cell

ii

an open switch

[1]

iii

a lamp

[1]

iv

an ammeter

[1]

v

a buzzer.

[1]

[1]

PL E

9.1 a

[3]

Draw a series circuit with a cell, a lamp and a switch.

9.3 Which of these ammeters will give a correct result for the current in the lamp?

Write the letter.

[1]

A

10 15

5

0

A

B

20

C

20

+

−

D

+

0

5

10 15

A

−

20

9.4 Which of these can be measured in amps?

A

+

SA M

−

10 15

5

0

−

0

5

+

10 15

A

20

[1]

Write all the correct letters.

A brightness of a lamp

B loudness of a buzzer C current in a circuit

D speed of electron flow

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9 Electricity

9.5 Arun has a circuit for testing whether an object is a conductor or an insulator. cell

crocodile clips

PL E

lamp

a

Explain why the lamp will light if Arun connects a conductor into the circuit. [2]

b

Arun puts a different object into the circuit.

[2]

The lamp does not light.

Suggest two possible reasons for this result. c

Copy the sentences and use the words from the list to complete them.

[1]

inhibits  free to move  allows  not free to move A conductor … electron flow.



In a conductor, electrons are … .



An insulator … electron flow.



In an insulator, electrons are … .

SA M



9.6 Look at the circuit diagram.

Draw another circuit that would have: a

a larger current flowing than the one in this diagram

[2]

b

a smaller current flowing than the one in this diagram.

[2]

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Glossary and Index cell membrane

cellulose cell wall

chlorophyll chloroplast

SA M

cytoplasm

the smallest unit from which all living things are made; cells always have a cell membrane and cytoplasm, and usually a nucleus 2 a very thin layer surrounding every cell, which controls what enters and leaves the cell; in a plant cell, the cell membrane is pressed tightly against the cell wall and so cannot be seen as a separate structure 2 the material that the cell wall is made from 2 the outer layer of a plant cell, made from cellulose; it gives support to the cell, but does not control what enters or leaves it (note that fungi and bacteria also have cell walls, but these are not made of cellulose) 2 a green pigment that absorbs energy from light; this energy drives the reactions of photosynthesis 2 a structure found in some plant cells which looks green because it contains chlorophyll; chloroplasts are the site of photosynthesis 2 the material that fills a cell; it is a gel made of many substances, including proteins, dissolved in water 2 to make something look bigger 2 a structure inside the cell where energy is released from food 2 a structure found in most cells, surrounded by a membrane, in which chromosomes are found; information held on the chromosomes controls the activities of the cell 2 a structure that is often, but not always, present in plant cells; it contains a liquid called cell sap 2

PL E

1.1 cell

magnify mitochondrion nucleus

SEE QUERY LOG In the text, this word is used as a verb, but here it is defined as a noun. Tech-Set: For stain, no comment in the query log

sap vacuole 1.2 stain

1.3 axon capillary

a coloured substance or dye that is used to colour cells; often, the stain will colour different parts of the cell different colours, making it easier to pick out these parts when viewing the cells through a microscope

a long extension in a neurone the smallest type of blood vessel; capillaries supply blood to all tissues in the body

7

11 11

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cilia dendrite function haemoglobin

mucus

neurone

palisade cell

SA M

pigment red blood cell

a cell found in the lining of the trachea and oviduct; the cilia move in unison, like oars, which causes fluid to move along the tube tiny, hair-like structures that extend from the surface of some cells a short extension in a neurone the job that something does or the role that it has a protein that combines reversibly with oxygen; it takes up oxygen when this is in a high concentration, e.g. at the lungs, and releases oxygen when this is in a low concentration, e.g. in a respiring tissue a sticky substance that helps to trap dust particles and bacteria in the respiratory passages or to lubricate surfaces, e.g. in the lining of the digestive system sometimes known as a nerve cell; a cell that is specialised to transmit electrical impulses (action potentials) from one part of the body to another a cell found just beneath the upper surface of a leaf, specialised to carry out photosynthesis a coloured substance, such as haemoglobin the most common type of cell in blood; human red blood cells are circular with a depression in each side (biconcave); they contain no nucleus to make more space for haemoglobin one of hundreds of cells found on the outer surface of roots, close to the tip, which increase the surface area of the root and, therefore, speed up the absorption of water and mineral ions (of a cell) with a structure that increases its ability to carry out its function

root hair cell

specialised

1.4 ciliated epithelium lower epidermis onion epidermis organism organ

organ system

11 11 11 11

PL E

ciliated cell

a tissue made of animal cells with cilia that wave in unison the layer of cells on the lower surface of a leaf the thin sheet of cells that covers the inner surfaces of the layers in an onion a complete living thing several different tissues working together to perform a function, e.g. the stomach several different organs working together to perform a function, e.g. the digestive system

11

11

11 12 11

11

12 11

16 17 16 16 17 17

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spongy layer tissue upper epidermis 2.1 compressed decision flow hypothesis matter

2.2 boil boiling point changes of state condensation evaporation

freezes measuring cylinder melting point melts meniscus

17 17 16 17

squeezed into a smaller space conclusion (of a liquid or gas) to move it smoothly, to pour a suggestion for an explanation the term for any type of material; everything that has mass and takes up space is matter a very small piece of matter that everything is made up of (of a liquid or gas) to move it smoothly, to flow the features of a material and how it behaves all matter is either solid, liquid or gas an idea to explain evidence an area where there is nothing, that is, no particles at all to move backwards and forwards repeatedly the amount of space taken up by a solid, liquid or gas

22

heating strongly and changing a liquid to a gas the temperature at which a liquid changes to a gas when matter changes from one state to another changing from a gas to a liquid, for example water vapour changing to liquid water changing from a liquid to a gas, at a temperature below boiling point changing from a liquid to a solid a piece of glassware designed for measuring the volume of liquids the temperature at which a solid changes to a liquid changing from a solid to a liquid the slight curve at the surface of a liquid, more clearly seen when the liquid is in a narrow container

29 29 29

SA M

particle pour properties states of matter theory vacuum vibrate volume

the layer of tall photosynthetic cells just below the upper epidermis of a leaf the layer of photosynthetic cells just below the palisade layer; there are large air spaces between the cells a group of similar cells working together to perform a function, e.g. ciliated epithelium the layer of cells on the top surface of a leaf

PL E

palisade layer

22 79 22 23 22 22 22 23 26 24 22

29 29 29 30 29 29 30

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thermometer water vapour 2.3 attractive forces expand heat energy transferred 2.4 groundwater open water

these hold the particles together in solids and liquids to get larger heat, a form of energy, can move between the particles and the environment moved to or from one item to another

2.5 atoms element groups metals

nanotubes non-metals

Periodic Table periods symbol 2.6 bonding compound

29 30 29

35 35 35 35

rain water that has soaked into the soil 42 an expanse of an ocean, sea or large lake which is distant from land and has no nearby islands or other obstructions 42 a fall of rain, snow or hail 41 rain water that runs off the surface to rivers and streams 42 the process by which plants lose water to the atmosphere 41 the processes by which water is moved around the environment from rivers to clouds and back again 40

SA M

precipitation surface run-off transpiration water cycle

water vapour produced when water boils and changes from a liquid to a gas equipment to measure temperature water in the form of a gas

PL E

steam

tiny particles of matter a substance that is made of only one type of atom vertical columns in the Periodic Table types of element found on the left side of the Periodic Table nano means very small; so, a nanotube is a very small tube types of element found on the right side of the Periodic Table arrangement of elements in order of the mass of their atoms horizontal rows in the Periodic Table used as a shorthand way of referring to an element

45 45 47 48 45 48 46 47 47

the way in which atoms join together 51 a substance in which atoms of two or more elements are bonded together 51

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sodium chloride 2.7 composition evaporating basin filings mixture natural emissions

pipe-clay triangle pure

uses chemical symbols to show how many atoms of different elements are present in particle of an element or compound a compound of sodium and chlorine

what something is made up of a piece of laboratory apparatus used to heat and evaporate off water small pieces of pure iron substances that are mixed together but not chemically bonded gases given off during natural processes, such as respiration or photosynthesis (the process by which green plants make food) a piece of laboratory apparatus used to balance an evaporating basin on a tripod made of only one thing

SA M

3.1 accurate being close to a true value acts towards the centre gravity causes a force which pulls objects towards the centre of a planet or star contact force the force from a surface on an object that is equal and opposite to the weight of the object Earth the planet we live on a force of attraction which is an example of a non-contact force force of gravity a method of using an equation formula triangle gravity found around any object with mass; causes weight and a force of attraction on other masses kilograms the unit of measure for mass mass the quantity of matter in an object, measured in kg the unit of measure for force and weight newtons quantity the amount of something; quantity is preferred in science to ‘amount’ weight the force of gravity on an object, measured in newtons (N) 3.2 axis

contradict evidence

54 51

60 62 59 59

PL E

formula

an imaginary line through the middle of a planet, about which the planet spins to go against or disagree with something facts that support or contradict an hypothesis

60

62 60

76 69 70 69 69 72 69 72 69 70 72 70

79 81 79

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plane spin support 3.3 air resistance circular

speed

a force that acts against motion caused by objects having to displace the air in front of them in order to move the same shape as the circumference of a circle (orbits of planets are actually elliptical, but are assumed to be circular in this context) distance moved per unit time (the word velocity should not be used interchangeably with speed) a region with no particles such as the space between planets in the Solar System

SA M

vacuum

created 79 a testable prediction 79 a way to represent something that cannot be seen directly 80 a cloud of dust and gas in space 80 to watch something happening 79 the path of a planet around the Sun or a satellite (natural or artificial) around a planet 79 points are on the same plane if they could be placed on the same flat surface 80 the circular movement of a planet around its own axis, such as causes day and night on Earth 79 to agree with something 81

PL E

formed hypothesis model nebula observe orbit

3.4 coastal depth

earthquake Earth tide force of attraction harbour tidal force

tidal range tide volcano

describes places on land that are beside the sea or the ocean the distance from the bottom of the ocean to the surface of the ocean; how deep the ocean is sudden movement in the Earth’s crust the rise and fall of the land surface as a result of tidal forces any type of force that causes objects to come together a place (natural or artificial) where boats can load or unload with protection from large waves the force from the gravitational pull of the Moon and the Sun that causes tides on Earth difference in depth of water between high and low tides twice daily rise and fall in ocean depth caused by gravity from the Moon and the Sun mountain where lava and gas can escape from beneath the Earth’s crust

86

85 86 86

93 91 93 91 97 93 92 91 91 93

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99 100 100 99 99 100 99 99 100 100 100 99 99 99

3.6 changes in energy change event process

104 105 106 106

PL E

3.5 chemical form of energy stored in food a fuels elastic form of energy stored when objects change shape electrical energy carried in a circuit or stored in charged objects energy quantity that must be changed in order to do something fuel a store of chemical energy gravitational potential form of energy stored when objects move higher joule the unit of energy kinetic energy associated with movement energy that we can see light an object that gives out light luminous sound energy transferred through vibrations energy contained in one place stored thermal the scientific term for heat energy energy is transferred when it moves from one place to another transferred

SA M

when energy changes from one state to another when energy is converted from one store to another something which happens that involves a change in energy one or more events that result in energy changes

3.7 dissipated recovered useful

wasted energy 4.1 excretion

growth movement nutrition

reproduction

spread out into the surroundings in a way that cannot be recovered collected and used again energy is described as useful when it is changed in the way that we want this is energy that is changed in a way that we do not want; usually cannot be recovered

removing toxins or materials excess to requirements from the body a permanent increase in size changing the position of all, or part, of the body feeding: taking in nutrients to provide energy and materials for growth making more organisms of the same species

111 111 111 111

121 121 121 121 121

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respiration sensitivity

breaking down food to release energy that the organism can use 121 detecting changes in the environment 121

125 124 124

124

able to have offspring 129 exactly the same 128 unable to reproduce, usually because gametes cannot be formed 129 children 129 defined here as a group of organisms that can reproduce together to produce fertile offspring 125 a sample, for example a piece of rock, or a single organism of a species 130 differences between members of the same species 128

SA M

4.3 fertile identical infertile offspring species

124

PL E

4.2 electron microscope a microscope that uses electron beams instead of light beams; it is able to achieve much higher resolution than a light microscope influenza an illness caused by a virus, often known as flu; it affects the respiratory system and usually results in a high temperature polymers of amino acids; they are important nutrients protein for living organisms, as they are used in growth and repair RNA a nucleic acid found in all living cells; most cells contain both RNA and DNA, but some viruses contain only RNA a particle made of either RNA or DNA, surrounded virus by a protein coat; viruses hijack the machinery of a host cell to replicate

specimen variation

4.4 dichotomous

key

5.1 brittle conduct ductile

branching into two; most keys involve a statement to which the user answers yes or no, or pairs of contrasting statements to choose between 132 an identification tool for objects or organisms; most keys provide sets of statements for you to choose between, where the answer leads to you another set of statements and finally an identification 132

breaks with a snap can transfer heat or electrical energy can be drawn out into strands or wires

148 146 145

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5.2 contact crocodile clips

cannot transfer heat or electrical energy is attracted to a magnet can easily be hammered into shape the substances from which objects are made breaks into many pieces something that reflects light rings like a bell

148 146 145 145 148 145 146

PL E

insulators magnetic malleable materials shatter shiny sonorous

distinguish examine

touch 152 apparatus used in electrical circuits to join a wire to a material 152 tell the difference between 152 to investigate or look at in detail 152

5.3 alloys bronze disrupts steel

mixtures of metals an alloy of copper and tin upsets the pattern an alloy of iron

SA M

5.4 condenser conical flask filter paper filter tunnel 5.5 acid

alkali

corrosive

flammable harmful irritate

apparatus used to separate mixtures of liquids glass container shaped like a cone a paper placed in a filter funnel and used to separate a solid from a liquid apparatus used for separating a solid from a liquid

a substance which contains hydrogen particles and has a pH lower than 7; the chemical opposite of an alkali a substance that contains hydroxide particles; the chemical opposite of an acid able to dissolve or eat away other materials such as your skin a substance that catches fire easily causes damage to cause itching or sores to your body

155 155 156 155

163 164 164 164

167 168 167 169 167 167

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toxic 5.6 indicator litmus neutral pH scale universal indicator

a substance that gives off a large amount of heat energy when in contact with other substances able to poison you

a substance that changes to a different colour in acid and alkali a type of indicator a substance that is neither acid nor alkali, is at pH7 measures how acidic or alkaline a substance is a mixture of indicators that gives a range of colours in solutions of different pH

169 170

173 174 174 176

PL E

oxidising

176

SA M

6.1 backwards and forwards repeated movement in straight lines and in opposite directions 186 loudness a measure of how easy a sound of a certain pitch is to hear; loud sounds are easier to hear than quieter sounds 186 medium the substance that a wave passes through 190 smallest parts of a substance 187 particles pitch the highness or lowness of the tone of a sound, for example musical notes of high pitch are higher in the musical scale than those of low pitch 186 sound wave vibrations of particles parallel to the direction of transfer of sound energy 187 a measure of how fast a sound wave travels, which depends speed of sound on the medium 187 6.2 echo effect on the sound property reflected unwanted

6.3 continental drift core

a reflected sound wave how the features of a sound are changed a characteristic feature of something a wave is reflected when the wave meets a surface then comes back from that surface something which is undesirable or a nuisance

the theory that the Earth’s continents have slowly changed position the innermost part of the Earth, divided into a liquid outer core and a solid inner core

196 196 196 196 198

205 205

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mantle molten tectonic plates 6.4 active earthquake

extinct

fold mountains inactive

a volcano is active if it has erupted in the last few thousand years and is likely to erupt again sudden movement in the Earth’s crust and upper mantle caused by the build-up of pressure between two tectonic plates a volcano becomes extinct when it is very unlikely to erupt again because the volcano has no more supply of magma where the Earth’s crust is pushed upward because of two tectonic plates pushing against each other a volcano is inactive if it could possibly erupt in the future but has not erupted for thousands of years molten rock coming out onto the Earth’s surface the size of something; for earthquakes this is a number which allows comparisons to be made between the strength of  earthquakes the place where two or more tectonic plates are side by side one tectonic plate moving under another tectonic plate at a plate boundary openings in the Earth’s crust where lava, ash and gas can come out onto the Earth’s surface

SA M

lava magnitude

the outer layer of the Earth that is made from solid rock hot molten or semi-solid material in and below the Earth’s crust the layer within the Earth between the core and the crust that is mostly solid the word used to describe something which has melted pieces of the Earth’s crust and upper mantle that are about 100 km thick

plate boundaries subduction volcanoes 6.5 eclipse lunar opaque partial rays

205 206 205 205 206

PL E

crust magma

shadow caused by the Moon or caused by the Earth description of something to do with the Moon description of an object that does not allow light to pass through; the opposite of transparent description of a solar eclipse where the Moon only partly blocks the light from the Sun the straight lines that show the direction of light

212

211

212 211 212 211

213 210 210 211

217 217 216 217 216

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shadow solar total 7.1 agar jelly

area where light has been blocked by an opaque object description of something to do with the Sun description of a solar eclipse where the Moon completely blocks the light from the Sun

7.2 carnivore

an animal that eats only other animals

algae bacteria

colony

fungi

SA M

microorgansism mushroom

Petri dish protozoa

single-celled sterile

toadstool

217

228

PL E

yeast

a gel made by mixing agar powder with water and heating to dissolve; the liquid mixture can be poured into a Petri dish and allowed to set; nutrients can be added to encourage growth of microorganisms organisms made of a single cell, or several similar cells, that have a structure similar to plant cells single-celled microorganisms whose cells are smaller than those of plants and animals; they have cell walls but no nucleus in this context, a group of cells that have been produced by the repeated division of a single cell of a bacterium or fungus organisms with cells that have cell walls and a nucleus, but differ from plants in that the cell walls are not made of cellulose, and they never contain chlorophyll and do not photosynthesise; some fungi are microorganisms any organism that is too small to be seen without a microscope; many microorganisms are made of a single cell a reproductive body produced by a fungus at certain times of its life cycle; the word ‘mushroom’ tends to be used when the structure is edible a shallow, circular dish with a lid, made of clear plastic or glass organisms made of a single cell that has a structure similar to animal cells made of only one cell complete absence of living organisms; equipment for growing microorganisms must be sterilised before and after use a term that generally means the same as mushroom, but that tends to be used when the structure is not edible a single-celled fungus

216 6

227

227

228

227 227

227 228 227 227

228 227 228

233

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ecology energy transfer

food chain food web herbivore predator prey producer

7.3 decay

to cause something to break down and lose its form; decay of plant and animal remains releases nutrients from them into the environment an organism that causes decay; the term is generally used to refer to organisms that feed by releasing enzymes outside their bodies and then absorbing the soluble nutrients that are produced by the breakdown of substances in the medium in which they are growing any type of visible fungus, generally used to refer to a covering of fungus on food or other organic material such as leather or paper substances derived from living organisms another word for decay

SA M

decomposer

an organism that obtains its energy by feeding on other organisms the study of organisms in their environment the process in which energy is moved from one place to another; in a food chain, arrows show how energy is transferred from one organism to the next a flow diagram showing how energy moves from one organism to another through feeding a flow diagram showing how different food chains interact an organism that eats only plants an animal that kills and eats other animals an animal that is killed and eaten by other animals an organism that uses inorganic substances to make organic ones; the organic substances contain energy that can be passed on to other organisms; in most food webs, producers do this through photosynthesis, in which the source of energy is sunlight

mould

organic matter rot 7.4 dung

nutrients

233 232

232 232 232 233 233 233

PL E

consumer

animal faeces; generally used for the faeces of larger animals substances that are used by organisms to provide useable energy, or materials for building new cells

233

238

238

238 238 238

243 243

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combine reactant product react 8.2 burette

a process in which one or more substances are changed to one or more different substances. In the reaction, the atoms of the starting substances are rearranged, forming new substances that have different properties join together substance that you start with in a chemical reaction new substance made in a chemical reaction interact and change

253 253 253 253 253

PL E

8.1 chemical reaction

262 266 266 267 266 262 263

8.3 remedy variable

a treatment or medicine that relieves a disease or condition something that can change in an investigation

270 271

SA M

decay digest filtrate indigestion neutralisation neutralised

piece of laboratory glassware used for adding measured volumes of liquid to rot; e.g. acid in the mouth can cause the teeth to decay to break down food into small pieces that can be absorbed the liquid that comes through a filter paper pain or discomfort in the digestive system changing an acid or an alkali into a solution at pH 7 an acid or alkali that has been changed into a solution at pH 7

8.4 cloudy

glowing

precipitate 9.1 attract

battery cell

components current

as in a solution becoming cloudy; it starts to form a white deposit not fully alight, as when a lighted splint is shaken so that the flame goes out an insoluble substance that forms from a reaction in a solution

cause things to move closer together by a force; opposite of repel two or more cells connected together in series the component drives the flow of current by changing chemical energy to electrical energy; most cells are 1.5 V parts of a circuit such as cells, lamps and switches; wires are not considered to be components the flow of electrons in a circuit

276 276 280

289 288 288 288 288

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negative charge repel terminals

9.2 ammeter

circuit diagram circuit symbols

a device for measuring current; ammeters can be digital or analogue and their output shows the current in amps (A) or milliamps (mA) a way to represent a circuit using straight lines for wires and international standard symbol for components a set of international standard diagrams to represent electrical components

the unit of current; amps is a shortened and more commonly used form of the word amperes components are in series with each other when connected end-to-end so that the current has a single path to follow through the components

SA M

9.3 amps

negatively charged particles which flow in wires to create current electrons in conductors such as wires, are not fixed or attached in one position, so can move when a cell is connected into a complete circuit the property of electrons which makes them attracted to positive charges and repelled by other negative charges cause things to move apart by a force; opposite of attract the connectors on a component; some of these are labelled + and –, such as on a cell, a battery or an ammeter; others, such as on a switch or a lamp, are not labelled

in series

9.4 allow current to flow conduct electricity conductor inhibit insulator

9.5 adding components dimmer position removing components

288

289 289 289

288

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electrons free to move

294 293 293

298

298

having electrons that are free to move to allow current to flow a material where electrons are free to move so that current can flow to stop something from happening a material where the electrons are not free to move, so that current cannot flow

304 304

putting more cells or more lamps, and so on, into a circuit less bright (of a lamp) a specific point in a circuit taking cells or lamps out of a circuit

311 312 311 311

304 306 305

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SA M

PL E

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