Cambridge Lower Secondary Science From discovering how we breathe, to finding out how gravity works, Cambridge Lower Secondary Science gets you thinking like a scientist! Packed with opportunities to plan experiments, make predictions and gather results, the series helps you think and work scientifically. Each unit ends with a project, like using chromatographs to solve a mystery, to help you bring together what you have learnt and show how the topics relate to the real world. Cambridge Lower Secondary With vocabulary boxes, clear diagrams and supporting illustrations, the course makes science accessible for learners with English as a second language. ✓ Provides support as part of a set of resources for the Cambridge Lower Secondary Science curriculum framework (0893) from 2020 ✓ Has passed Cambridge International’s rigorous quality-assurance process ✓ Developed by subject experts ✓ For Cambridge schools worldwide Completely Cambridge Cambridge University Press works with Cambridge Assessment International Education and experienced authors to produce high-quality endorsed textbooks and digital resources that support Cambridge Teachers and encourage Cambridge Learners worldwide. To find out more visit cambridge.org/cambridge-international Registered Cambridge International Schools benefit from high-quality programmes, assessments and a wide range of support so that teachers can effectively deliver Cambridge Lower Secondary. PL E LEARNER’S BOOK 8 Mary Jones, Diane Fellowes-Freeman & Michael Smyth M This resource is endorsed by Cambridge Assessment International Education Science SA For more information on how to access and use your digital resource, please see inside front cover. LEARNER’S BOOK 8 • Talk and think about what you already know with ‘Getting Started’ boxes • Think and work scientifically with practical tasks in the ‘Think like a scientist’ feature • Topics throughout the series support the new earth and space strand of the curriculum framework • Reflect on what you have learnt with ‘Look what I can do’ sections at the end of each topic • Answers to all activities can be found in the accompanying teacher’s resource Cambridge Lower Secondary Science 9781108742825 Jones, Fellowes-Freeman & Smyth Lower Secondary Science Learner’s Book 8 CVR C M Y K We are working with Cambridge Assessment International Education towards endorsement of this title. Visit www.cambridgeinternational.org/lowersecondary to find out more. Second edition Digital access Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. PL E Cambridge Lower Secondary Science LEARNER’S BOOK 8 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. 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 PL E 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 M 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 SA 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. Cambridge International copyright material in this publication is reproduced under licence and remains the intellectual property of Cambridge Assessment International Education. 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. We are working with Cambridge Assessment International Education towards endorsement of this title. Introduction Introduction Welcome to Stage 8 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? PL E 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? M 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. SA We hope you enjoy thinking and working like a scientist. Mary Jones, Diane Fellowes-Freeman, Michael Smyth iii to publication. Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior We are working with Cambridge Assessment International Education towards endorsement of this title. Contents Contents Science strand Thinking and Working Scientifically strand Science in Context 1 Respiration 1.1 The human respiratory system 1.2 Gas exchange 1.3 Breathing 1.4 Respiration Biology: Structure and Function Biology: Life processes Models and representations Carrying out scientific enquiry Scientific enquiry: purpose and planning Scientific enquiry: analysis, evaluation and conclusions Discuss how scientific knowledge is developed through collective understanding and scrutiny over time Describe how science is applied across industries, and in research Evaluate issues which involve and / or require scientific understanding 2 Properties of materials 2.1 Dissolving 2.2 Solutions and solubility 2.3 Planning a solubility investigation 2.4 Paper chromatography Chemistry: Materials and their Structure Chemistry: Properties of materials Scientific enquiry: purpose and planning Carrying out scientific enquiry Scientific enquiry: analysis, evaluation and conclusions Describe how science is applied across industries, and in research 3 Forces and energy 3.1 Forces and motion 3.2 Speed 3.3 Describing movement 3.4 Turning forces 3.5 Pressure between solids 3.6 Pressure in liquids and gases 3.7 Particles on the move Physics: Forces and Energy Models and representations Carrying out scientific enquiry Scientific enquiry: analysis, evaluation and conclusions Scientific enquiry: purpose and planning Evaluate issues which involve and / or require scientific understanding 4 Ecosystems 4.1 The Sonoran desert 4.2 Different ecosystems 4.3 Intruders in an ecosystem 4.4 Bioaccumulation Biology: Ecosystems Carrying out scientific enquiry Discuss how scientific knowledge is developed through collective understanding and scrutiny over time Evaluate issues which involve and/or require scientific understanding Discuss how the uses of science can have a global environmental impact SA M PL E Page Unit iv Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. Contents Science strand Thinking and Working Scientifically strand Science in Context 5 Materials and their structure 5.1 The structure of the atom 5.2 Purity 5.3 Weather and Climate 5.4 Climate and Ice ages 5.5 Atmosphere and climate Chemistry: Materials and their structure Chemistry: Changes to materials Earth and Space: Planet Earth Earth and Space: Cycles on Earth Carrying out scientific enquiry Scientific enquiry: purpose and planning Models and representations Scientific enquiry: analysis, evaluation and conclusions Describe how people develop and use scientific understanding as individuals and through collaboration, e.g. through peer-review. Discuss how the uses of science can have a global environmental impact 6 Light 6.1 Reflection 6.2 Refraction 6.3 Making rainbows 6.4 Galaxies 6.5 Rocks in Space Physics: Light and Sound Earth and Space: Earth in Space Scientific enquiry: purpose and planning Carrying out scientific enquiry Scientific enquiry: analysis, evaluation and conclusions Models and representations Evaluate issues which involve and / or require scientific understanding 7 Diet and growth 7.1 Nutrients 7.2 A balanced diet 7.3 Growth, development and health 7.4 Moving the body Biology: Structure and Function Biology: Life processes Scientific enquiry: purpose and planning Carrying out scientific enquiry Evaluate issues which involve and/or require scientific understanding 8 Chemical reactions 8.1 Exothermic reactions 8.2 Endothermic reactions 8.3 Metals and their reactions with oxygen 8.4 Reactions of metals with water 8.5 Reactions of metals with dilute acids Chemistry: Changes to materials 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. 9 Magnetism 9.1 Magnetic fields 9.2 The Earth as giant magnet 9.3 Electromagnets 9.4 Investigating electromagnets Physics: Electricity and magnetism Earth and Space: Planet Earth Scientific enquiry: purpose and planning Scientific enquiry: analysis, evaluation and conclusions Models and representations Carrying out scientific enquiry Discuss how scientific knowledge is developed through collective understanding and scrutiny over time. Evaluate issues which involve and/or require scientific understanding. SA M PL E Page Unit v to publication. Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior We are working with Cambridge Assessment International Education towards endorsement of this title. How to use this book How to use this book 1 Cells This book contains lots of different features that will help your learning. These are explained below. 1.1 1.1 Characteristics Characteristics of of living living things things This list sets out what you will learn in each topic. You can use these points to identify the important topics for the lesson. PL E In this topic you will: In this topic you will: • think about what makes living things different from • think aboutobjects what makes living things different from non-living non-living objects • learn about the seven characteristics of living things • learn about the seven characteristics of living things Getting started Getting started In your classroom, find one living thing and one thing which has In yourbeen classroom, never alive. find one living thing and one thing which has never been alive. With your partner, make a list of things that the living thing can With your make a list of things do, but thepartner, non-living thing cannot do. 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. Be ready to share your ideas with the rest of the class. This contains questions or activities to help find out what you know already about this topic. 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 margin. You will also find definitions of all these words in the Glossary and Index at the back of this book. living organisms non-living nutrition living organisms non-living nutrition growth movement excretionrespiration living nutrition sensitivity sensitivity growth movement sensitivity excretion reproduction respiration organisms growth excretion reproduction respiration non-living movement reproduction Activity 1.1 Is a car alive? The picture shows a car. M Here are some facts about cars. SA 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. This provides an opportunity for you to practice and develop scientific enquiry skills with a partner or in groups. 2 2 • Cars use fuel and oxygen. • 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 light on automatically. Questions 1 In your group, make a list of similarities between a car and living things. 2 Make a list of differences between a car and living things. 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. 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 • some green grapes • purple 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? vi Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. How to use this book 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 ……………… . 1.2 Plant ce 7 ForMost things can change theyourself: shape and position of their eachliving of these statements, rate This is called ………………… . inside a plant cell. The liquid Sapbodies. vacuole: This is large, fluid-filled space After completing an activity, this provides you with the opportunity to either assess your own work or another student’s work. inside is a solution of sugars and other substances dissolved in water. Activity 1.1 is called cell sap. The solution PL E Chloroplast: are did in the sunlight often contain Is aif car youalive? thinkPlant you cells that if you it quite if you didn't do chloroplasts. This plants make their food.itChloroplasts look did it veryshows well,isawhere all, or needed The picture car. well, or needed green because they contain a green substance called chlorophyll. with no help some help a lot of help Here are some facts about cars. Mitochondrion: All plant cells have mitochondria (singluar: •mitochondrion). Cars fuelInside and I cut ause piece of theoxygen. inside layer ofenergy onionisthat was about mitochondria, released from food. 1 cm square. •Questions Inside the engine of the car, the fuel and to of make • I wasoxygen able toprovide spread energy the piece onion flat in the 1 the Look atmove. the photograph of the plant cells. What do you think the car drop of water. little green circles inside the cells are? Why are they green? What is • The produces waste gases, theirengine function? including carbon dioxide. These are 2 given Describe differences between a cell wall and a cell membrane. off four in the exhaust of the car. This contains questions that ask you to look back at what you have covered and encourages you to think about your learning. Some cars have sensors. For example, they can sense when • Howithave yourand tried to the remember difference between a cell wall is dark turn light onthe automatically. and a cell membrane? How successful do you think you have been? Questions 1 In your group, make a list of similarities between a car and living things. Think like a scientist 2 Making Make aa model list of differences between a car and living things. of a plant cell In this activity, you will make a model to represent a cell. You will then think about the strengthschecklist and limitations of your model. Summary Here is a list of materials and objects you could use to make your model. This list summarises the important topics that you have learned in the topic. I can list the seven characteristics of living things boxes boxes and large plastic bags filled with water • transparent • cardboard • small I can describe the meaning of each of these characteristics • 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 Project: Cells discovery timeline model of a plant cell. Then make your model. SA M 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. These questions look back at some of the content you learned in each session in this unit. If you can answer these, you are ready to move on to the next unit Be ready to explain gradually your model to others. This project is about how scientifi c knowledge develops over time. You are going to work in a group to do research, and then use your findings to help to make a Questions time line. 1 Compare your model cell with the models made by other groups. Science never stays still. When one scientist makes a new discovery, this suggests new Areinvestigate. there are any features of your model that are better than theirs? questions that other scientists can Are they any The features of other groups' models that are better than yours? You are going to help to produce a timeline. timeline will show how scientists gradually discovered that thingshow arewell made of cells. 4 all 2 living Discuss your model cell represents a real plant cell. 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. 1670 Anton van Leeuwenhoek improves the microscope and is able to see living cells in a drop of pond water. Check your Progress 1 Different cells have different functions. Choosing from this list, name the cell that each function describes. 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 vii to publication. Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior 7 We are working with Cambridge Assessment International Education towards endorsement of this title. Science Skills Science Skills Laboratory apparatus Laboratory apparatus 250 ml 200 PL E 150 100 50 graduated beaker beaker test tube boiling tube funnel spatula forceps M syringe glass rod dropper pipette thermometer pestle metre rule burette SA measuring cylinder conical flask timer lamp forcemeter boss clamp candle tripod and gauze mortar Petri dish mounted needle Bunsen burner cover slip top pan balance microscope slide microscope retort stand viii Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. Science Skills Science Skills Making better measurements In Science, we often take measurements. We do this to find out more about something that we are interested in. Measurements are taken using measuring instruments. These include rulers, Laboratory apparatus balances, timers and so on. PL E We want our measurements to be as accurate as possible. In other words, we want them to be as close as possible to the true answer. Then we can be more confident that our conclusions are correct. Measuring instruments How can we be sure that our measurements are as accurate as possible? We need to think about the instruments we use. Here are two examples: You want to measure a 50 cm3 volume of water. It is better to use a 100 cm3 measuring cylinder than a 50 cm3 beaker, even though the beaker may have a line indicating the level which corresponds to 50 cm3. A 100 cm3 measuring cylinder is better than one which measures 1000 cm3 because 50 cm3 is only a small fraction of 1000 cm3. • You want to time a toy car moving a distance of 1.0 m. You could use the clock on the wall, but this is not a good choice as it is not accurate. You could use a stopwatch, but it is tricky to start and stop the watch at the exact moments when the car crosses the starting and finishing lines. You would have to take account of your reaction time. It is best to use light gates since these automatically start and stop as the car passes through. The gates are connected to a timer which will show you the time taken to within a fraction of a second. SA M • light gate timer Choose an accurate method of measurement. ix to publication. Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior We are working with Cambridge Assessment International Education towards endorsement of this title. Science Skills Science Skills We also need to think about how we use measuring instruments. For example: When using a ruler to measure the length of an object, the ruler needs to be placed directly alongside the object. Make sure that one end of theapparatus object is exactly next to the zero of the ruler’s scale. Laboratory 0 1 cm 2 3 4 PL E • 5 6 7 8 9 10 11 12 13 14 15 Don’t do it like this. You might think the end of the leaf stalk is at 0 cm but it is actually at 0.2 cm. • When using a measuring cylinder, look horizontally at the surface of the liquid and read the scale level with the bottom of the meniscus. M meniscus SA Don’t do it like this. You might read this as 48, when it should be read as 45. • When using a balance to weigh an object, check that it reads zero when there is nothing on it. Similarly, a forcemeter should read zero when no force is pulling on it. It may be possible to reset these instruments if they are not correctly set to zero. Don’t use it like this. x Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. Science Skills Improving accuracy PL E You can see that to make your measurements as accurate as possible, you need to think carefully about the measuring instruments you use and how you use them. It can help to make repeat measurements; measure the same quantity several times and then to calculate the average. With practice, you will find that your measurements become more accurate and so you will be able to trust your findings more. Anomalous results Sofia did an experiment to find out how light intensity affects the rate of photosynthesis of a water plant. She placed a lamp at different distances from the plant, and counted the number of bubbles it gave off in one minute. Paula made three counts for each distance of the lamp from the plant. This table shows her results. Distance of lamp from plant / cm 20 40 1st try 2nd try 80 3rd try 28 29 27 19 33 18 12 14 13 8 10 10 M 60 Number of bubbles per minute SA Paula thought that one of her results didn’t look right. Can you spot which one it is? A result like this, that does not fit the pattern of all the other results, is called an anomalous result. If you get something that looks like an anomalous result, there are two things that you can do. 1 The best thing to do is to try to measure it again. 2 If you can’t do that, then you should ignore the result. So Paula should not use this result when she is calculating the mean. She should use only the other two results for that distance from the lamp, add them up and divide them by two. Spotting an anomalous result in a results table can be quite difficult. It is often much easier if you have drawn a graph. Arun did an experiment to investigate how adding ice to water changed its temperature. He added a cube of ice to 500 cm3 of water and stirred the water until the ice had completely melted. Then he measured the temperature of the water before adding another ice cube. The graph on the next page shows his results. xi to publication. Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior We are working with Cambridge Assessment International Education towards endorsement of this title. Science Skills 15 10 temperature in °C PL E 5 0 0 1 2 3 number of ice cubes 4 5 It’s easy to see that the point at (3, 3) doesn’t fit the pattern of all the other results. Something must have gone wrong when Arun was making that measurement. M When Arun draws the line on his graph, he should ignore this result. He should also think about why it might have gone wrong. Perhaps he misread the thermometer – was the correct reading 8 °C? Or perhaps he forgot to stir the water and measured the temperature where the cold ice had just melted. If you think about why an anomalous result has occurred, it can help you to improve your technique and avoid such problems in the future. SA 15 10 temperature in °C 5 0 0 1 2 3 4 5 Ignore the anomalous result when you draw the line. xii Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. Science Skills Understanding equations speed = _______ distance time distance = speed × time time = _______ distance time PL E In Topic 3.2 Speed, you studied three equations which relate speed, distance and time. Here are the three equations: How can you remember these three equations? It will help if you think about the meaning of each quantity involved. It can also help to think about the units of each quantity. Speed is the distance travelled per second or per hour. The word ‘per’ means ‘in each’, and this should remind you that the distance must be divided by the time. Another way to think of this is to start with the units. Speed is measured in metres per second, so you must take the number of metres (the distance) and divide by the number of seconds (the time). SA M Distance is how far you travel. The faster you go (the greater your speed), and the longer you go for (the greater the time), the greater the distance travelled. This tells us that the two quantities must be multiplied together. The train is travelling at 75 m/s. Time to pass observer = 3.6 s. length of train = speed × time = 75 × 3.6 = 270 m xiiito publication. Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior We are working with Cambridge Assessment International Education towards endorsement of this title. 1 Respiration In this topic you will: PL E 1.1 The human respiratory system • learn the names of the different parts of the human respiratory system • observe carefully, and record your observations, as the structure of lungs is demonstrated Getting started Key words Respiration is one of the characteristics of living things. With a partner, decide which statement in each pair is correct. M Be ready to share your ideas. Respiration happens inside all the cells in your body. or Respiration only happens in cells in your lungs. Second pair: Respiration releases energy from food. or Respiration uses up energy. Third pair: Respiration happens in all living things. or Respiration happens in animals but not plants. SA First pair: aerobic respiration air sac bronchiole bronchus cartilage larynx respiration respiratory system trachea vocal cords voicebox windpipe 2 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 1.1 The human respiratory system Why we need oxygen You may remember that one of the characteristics shared by all living things is respiration. Respiration is a series of chemical reactions that happens inside every living cell. The kind of respiration that usually happens inside our cells is called aerobic respiration. Aerobic respiration uses oxygen. The cells produce carbon dioxide as a waste product. PL E The air around you contains oxygen. When you breathe, you take air into your lungs. Some of the oxygen from the air goes into your blood. The blood delivers the oxygen to every cell in the body, so that the cells can use it for respiration. The blood collects the waste carbon dioxide from the cells, and takes it back to the lungs. The organs that help you to take oxygen out of the air, and get rid of carbon dioxide, make up the respiratory system. Can you name any of the other organs shown in the picture? In this model of the human body, the lungs are shown in pink The structure of the human respiratory system SA M This is a diagram of the human respiratory system. The white entrance to nose spaces in this diagram are the entrance to mouth ‘tubes’ that air moves through, as it goes into and out of voicebox (larynx) your lungs. windpipe (trachea) rings of cartilage lung bronchiole bronchus (plural: bronchi) air sacs rib bone muscles between ribs (intercostal muscles) diaphragm The human respiratory system. 3 to publication. Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior We are working with Cambridge Assessment International Education towards endorsement of this title. 1 Respiration Questions 1 Put your finger on the entrance to the nose or mouth in the diagram of the respiratory system. Move your finger along the white space and down into the lungs. Write down the structures that the air passes through, as it moves down into your lungs. Write them in the correct order. 2 Now write the same structures in the order in which air passes through them as it moves out of your lungs and back into your surroundings. PL E Air gets into your body through your mouth or nose. Your mouth and nose both connect to your trachea. The trachea is sometimes called the windpipe. It has strong rings of cartilage around it. These rings of cartilage keep the trachea open and prevent it collapsing so that air can be kept moving in and out of your body. If you put your fingers on the front of your neck and move them downwards, you can feel the rings of cartilage on your trachea. The trachea branches into two bronchi (singular: bronchus). The bronchi also have cartilage to support them. One bronchus goes to each lung. Each bronchus carries air deep into the lungs. Each bronchus divides into several smaller tubes called bronchioles. These structure of these branches allow the air to reach deeper into the lungs. M The bronchioles end by branching into many tiny structures called air sacs. This is where the oxygen goes into the blood, and the carbon dioxide comes out. You can find out more about this in the next topic. Think like a scientist Looking at lungs SA In this activity, you are going to look carefully at some real lungs. You will practise using your senses of touch and sight, to make observations, and recording your observations. Before you start this activity look carefully at the questions and make a risk assessment. Think about how you will reduce or overcome any risks. be prepared to share your ideas. You will need: • a set of lungs from an animal, such as a sheep or goat (from a butcher) • a big board to put the lungs onto • hot water, soap and towels to wash your hands after handling the lungs Questions 1 Describe what the lungs look like. If you prefer, you could make a labelled drawing instead of writing about them. 4 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 1.1 The human respiratory system Continued 2 Touch the lungs. What do they feel like when you push them? Can you suggest why they feel like this? (Look at the diagram of the human respiratory system to help you.) Look at the tube that carries air down into the lungs. a What is the name of this tube? b Feel the tube. What does it feel like? c Follow the tube towards the lungs. Can you find where it divides into two? PL E 3 What are the names of these two tubes? d Now look at the top of the big tube, where it is wider. What is the name of this wide part? What is its function? The diagram of the respiratory system includes a lot of new words. How are you going to learn this diagram and all of its labels? M Remember that, in a test, the diagram might not be exactly the same as this one. Activity 1.1.1 What does the larynx do? Hold the fingertips of one hand against your larynx (voicebox). Keep your lips together, and make a loud humming sound. SA Can you feel the larynx vibrating? Your larynx contains your vocal cords. These are bands of muscle that stretch across your larynx. You can think of them as being rather like guitar strings. When these cords vibrate, they make a sound. Now make a higher-pitched humming sound. Then try a really deep pitched one. Can you feel the larynx changing when you make the different sounds? Summary checklist I can name the parts of the respiratory system, and identify them on a diagram. I can list the organs that air passes through, as it moves into and out of the lungs. 5 to publication. Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior We are working with Cambridge Assessment International Education towards endorsement of this title. 1 Respiration 1.2 Gas exchange In this topic you will: find out how oxygen gets into your blood from the air, and how carbon dioxide goes in the other direction • do an experiment to help you to think about why the air sacs in the lungs need to be very small • do an experiment to compare how much carbon dioxide there is in the air you breathe in and the air you breathe out PL E • Key words Getting started This topic is about two gases – oxygen and carbon dioxide. Look at these diagrams. B C M A With your partner, answer these questions. Which diagram shows the particles in a gas? 2 Choose the correct phrases to complete these sentences: SA 1 alveoli analogy capillaries diffusion expired air gas exchange haemoglobin inspired air limewater In a gas, the particles are far apart / touching each other. In a gas, the particles move freely / vibrate on the spot. 6 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 1.2 Gas exchange Air sacs The photograph shows a tiny part of the lungs, seen through a powerful microscope. You can see the lungs are mostly holes. These holes are called air sacs. Another name for them is alveoli. PL E There are also lots of very tiny blood vessels in the lungs, wrapped around the air sacs. You cannot see them in the photograph, but they are shown in the diagram below. These blood vessels are capillaries. Part of the lungs, viewed through a powerful microscope The structure of an air sac M This diagram shows one of the air sacs in the lungs. The air sac has a wall made of one layer of cells. These cells are very thin. air moving in SA blood flowing from the heart air inside sac thin wall of air sac thin wall of blood capillary air moving out blood flowing towards the heart diffusion of oxygen diffusion of carbon dioxide red blood cell blood plasma An air sac in the lungs You can see that there is a blood capillary around the outside of the alveolus. The capillary is pressed tightly against the alveolus. The wall of the capillary is also made of a single layer of very thin cells. 7 to publication. Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior We are working with Cambridge Assessment International Education towards endorsement of this title. 1 Respiration Gas exchange in the air sacs Inside the air sacs, oxygen from the air goes into the blood. Carbon dioxide from the blood goes into the air. This is called gas exchange. PL E Think about the blood capillary on the left of the diagram. The blood inside this capillary comes from the heart. Before reaching the heart, it came from the organs in the body. These organs contain cells that respire, using up oxygen and making carbon dioxide. So, the blood in this capillary contains only a small amount of oxygen, and a lot of carbon dioxide. Now think about the air inside the air sac. It came from outside the body, where the air contains a lot of oxygen and only a small amount of carbon dioxide. Inside the alveolus, this air is very close to the blood. There are only two very thin cells between the air and the blood. The oxygen particles in the air are a gas, so they are moving freely. They can easily move from the air, through these thin walled cells and into the blood. This is called diffusion. You can find out more about diffusion in Topic 3.7. The oxygen molecules move from where there are a lot of them (in the air) to where there are fewer of them (in the blood). M When the oxygen gets into the blood, it dissolves. (You can find out about dissolving in Topic 2.1.) It goes into the red blood cells where it combines with haemoglobin. You will find out what happens to it after that in Topic 1.6. SA Now think about the carbon dioxide. There is a lot of it in the blood in the capillary, and only a small quantity in the air inside the air sac. So, the carbon dioxide diffuses into the air in the air sac. Activity 1.2.1 Gases in and out Copy this diagram. 1 On your diagram, draw a green arrow to show how oxygen diffuses from the air into the blood. 2 How many cells does the oxygen move through, as it leaves the blood and goes into the air? 3 On your diagram, draw a blue arrow to show how carbon dioxide diffuses from the blood into the air. 8 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 1.2 Gas exchange Think like a scientist Why are air sacs so small? In this activity, you will use some agar jelly to represent the lungs, and some coloured liquid to represent oxygen in the air. You will need: PL E • two Petri dishes filled with agar jelly • two cork-borers, one with a diameter of 10 mm and the other with a diameter of 5 mm • some coloured dye Method • a dropper pipette Use the larger cork-borer to make eight holes in the jelly in one of the dishes. Space the holes evenly in the dish. 2 Now use the smaller cork-borer to make 32 holes in the jelly in the other dish. Try to space the holes evenly in the dish. 3 Using the dropper pipette, carefully fill each hole in both dishes with the coloured dye. Try to put the same quantity of dye into each hole. It’s really important not to get any dye on the jelly! 4 Leave both dishes for at least 15 minutes. 5 Predict what you think will happen. 6 After 15 minutes (or a little bit longer if things are happening slowly) record your observations. M 1 SA Questions 1 The holes that you made in the jelly represent the air sacs in the lungs. The coloured dye represents oxygen in the air sacs. The holes in the jelly are an analogy for the air sacs, and the dye is an analogy for oxygen. Explain how your observations help to show what happens to oxygen in the lungs. 2 The total volume of the 32 small holes is the same as the total volume of the eight large holes. Use your observations to suggest why it is better to have a lot of very small air sacs in the lungs, rather than just a few large ones. 3 Do you think that the agar jelly with holes is a good model for what happens in the lungs? Explain your answer. 9 to publication. Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior We are working with Cambridge Assessment International Education towards endorsement of this title. 1 Respiration Think like a scientist Comparing the carbon dioxide content of inspired air and expired air In this activity, you will use limewater to compare how much carbon dioxide there is in the air that you breathe in and the air that you breathe out. Work with a partner to do this activity. You will need: • glass tubing as shown in the diagram PL E • rubber tubing • two rubber bungs to fit the test tubes Safety • 2 test tubes • limewater It is very important that the rubber tubing is perfectly clean before you use it. Do not share the mouthpiece with anyone else or put it on the work surface when you have finished. Method Read through the method and make an assessment of all the risks and decide how you will overcome or reduce these risks. 2 Look carefully at the apparatus. M 1 Starting with the rubber tubing, follow the glass tube as it branches into the two test tubes. rubber tubing glass tubing rubber bung test tube limewater A B What is different about the glass tubing that goes into test tube A and test tube B? Now think about what might happen if you gently blow down the rubber tube. SA 3 Predict the tube in which you think bubbles will appear. Why do you think that? 4 Gently blow into the rubber tubing, until bubbles appear in one of the tubes. Was your prediction correct? 5 Now think about what might happen if you gently suck the rubber tube. Try it. Was your prediction correct? 6 Put your mouth over the end of the rubber tubing, and gently breathe in and out. Bubbles will appear in one tube as you breathe out, and in the other tube as you breathe in. Your partner will check the bubbles and can tell you if you are doing it correctly. Be careful – don't suck too hard! Limewater is not poisonous, but it is not a good idea to get it into your mouth. 7 Continue until the limewater in one of the tubes has gone cloudy. Make a note of which tube it is. 10 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 1.2 Gas exchange Continued Questions 1 The air that you breathe out is called expired air. In which tube did your expired air bubble through the limewater? 2 The air that you breathe in is called inspired air. In which tube did your inspired air bubble through the limewater? In which tube did the limewater go cloudy first? 4 Name the gas that makes limewater go cloudy. 5 Copy and complete these sentences. Use some of these words: PL E 3 A B expired inspired less more The limewater went cloudy first in tube This is the limewater that . air bubbles through. Our results show that expired air contains inspired air. Self-assessment carbon dioxide than Think about how you did the experiment. M Copy each statement, and then draw a face next to each one according to how well you think you performed. I think I did this really well. I did OK, but I could probably do better. SA I didn't do this very well at all. • I worked out which tube the air would go into when I breathed in and when I breathed out. • I managed to breathe in and out with just the right force to make the air bubble through the limewater. • I stopped as soon as the limewater in one of the tubes went cloudy. • I understand what this experiment shows about how much carbon dioxide there is in inspired air and expired air. Is there anything that you would do differently if you did this experiment again? 11to publication. Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior We are working with Cambridge Assessment International Education towards endorsement of this title. 1 Respiration Summary checklist SA M PL E I can describe how oxygen gets into my blood from the air, and carbon dioxide goes the other way. I can explain why it is better to have lots of very small air sacs in the lungs, rather than a few big ones. I can describe how to do an experiment to compare how much carbon dioxide there is in inspired air and expired air. 12 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 1.3 Breathing 1.3 Breathing In this topic you will: measure how much air you can push out of your lungs in one breath • learn how the muscles between your ribs and your diaphragm move air into and out of the lungs Getting started PL E • On your own, answer each of these questions. What is gas exchange? • Where does gas exchange happen in your body? • Does the air you breathe in contain more or less oxygen than the air you breathe out? • Is there any carbon dioxide in the air you breathe in? • Do you think there is any oxygen in the air you breathe out? breathing contract relax SA M • Key words 13to publication. Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior We are working with Cambridge Assessment International Education towards endorsement of this title. 1 Respiration How much air do you use? Think like a scientist Measuring the volume of air you can push out of your lungs You will need: PL E How much air do you think you can push out of your lungs in one breath? In this experiment, you will use some very simple apparatus to find out. • a big plastic bottle with a lid • measuring cylinder • bendy tubing • marker pen Safety • water • big bowl The bottle and bendy tubing must be clean, and the water you use must be safe to drink. You may get water on the floor as you do your experiment. Take care not to slip in it. Method 1 You are going to use the plastic bottle to measure volumes. M In your group of three, discuss how you can use the measuring cylinder to mark a scale on the plastic bottle. Then mark the scale on the bottle. The scale should go all the way from the bottom to the top of the bottle. Fill the bottle right to the top with water. Put the lid on. 3 Pour water into the big bowl until it is about half full. Turn the bottle upside down, and hold it in the bowl. Very carefully take the lid off the bottle. You should find that all the water stays in the bottle. SA 2 4 Carefully slide the bendy tubing into the top of the bottle, under water. 5 Take a deep breath in, then put your mouth over the tubing and breathe out as much air as you can through the tubing. Your expired air will push out some water from the bottle. Use the scale that you drew on the bottle to record the volume of air you breathed out. 6 If you have time, repeat steps 2 to 5 two more times. Use your three results to calculate a mean value for the volume of air you can breathe out of your lungs. 14 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 1.3 Breathing Continued 7 Replace the tubing with another piece of clean tubing. Now another person in your group can try the experiment. 8 Record all of your results in a table. Questions 2 Share your results with the rest of the class. Can you see any patterns in the results? For example: PL E 1 • Do you think that the volume of air a person can breathe out is related to their size? • If there is anyone in your class who plays a wind instrument, does this seem to have an effect on how much air they can breathe out? Plan an experiment to investigate this hypothesis: SA M People who play the trombone can breathe out more air in one breath than people who play the violin. Activity 1.3.1 What happens when you breathe in? Sit quietly for a moment. Shut your eyes and think about your breathing. Put a hand just underneath your ribs. Take a deep breath in. You may be able to feel your ribs moving upwards. You might also be able to feel something moving inwards as you breathe. 15to publication. Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior We are working with Cambridge Assessment International Education towards endorsement of this title. 1 Respiration Breathing Look at the diagrams of the human respiratory system, in Topic 11.1. Find the ribs, and the intercostal muscles between them. Find the diaphragm. Remember that air is a gas. The pressure of a gas increases when the volume of its container is decreased. You can find more about pressure in Topic 3.6 Pressure in liquids and gases. The intercostal muscles between the ribs contract (get shorter). This pulls the ribs upwards and outwards. • The muscles in the diaphragm contract. This pulls the diaphragm downwards. • These two movements make more space inside the chest cavity. They increase the volume inside it. • When the volume increases, the pressure inside the chest cavity and lungs decreases. • Air moves down through the trachea into the lungs, to fill the extra space. M • When you breathe out, these things happen: air moves out of lungs The intercostal muscles between the ribs relax (return to normal size). This allow the ribs to drop down into their natural position. SA • air moves into lungs PL E When you breathe in, these things happen: • The muscles in the diaphragm relax. This allows the diaphragm to become its normal, domed shape. • These two movements make less space inside the chest cavity. They decrease the volume inside it. • When the volume decreases, the pressure increases. So air is squeezed out of the lungs. 16 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 1.3 Breathing Think like a scientist Using a model to represent breathing movements You will need: • rubber bung with a hole in it • syringe with end cut off Carefully and steadily, pull the plunger of the syringe out. Note what happens. 2 Now push the plunger back in again. Note what happens. the trachea • the diaphragm • the rib cage Explain why the balloon inflates when you pull the plunger out. 5 Explain how pulling the plunger out represents what happens in your body when you breathe in. 6 Describe one way in which this model does not completely represent what happens when you breathe in. SA 1 plunger M 4 Questions balloon 50 • 40 the lungs syringe with end cut off 30 • 20 Which parts of the model represent these structures in the body? rubber bung 10 3 small hole PL E 1 • balloon Copy and complete this table. Use these words: contract relax Action What do the diaphragm muscles do? What do the intercostal muscles do? Breathing in Breathing out 17to publication. Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior We are working with Cambridge Assessment International Education towards endorsement of this title. 1 Respiration 2 Copy and complete these sentences. Use these words: decrease increase into out of When we breathe in, the muscles in the diaphragm and between the the volume of the chest. This makes air move ribs the lungs. Summary checklist PL E When we breathe out, the muscles in the diaphragm and between the the volume of the chest. This makes air move ribs the lungs. SA M I can use a measuring cylinder to make a volume scale on a bottle. I can do an experiment to measure the volume of air I can breathe out in one breath. I can describe how the diaphragm and intercostal muscles cause breathing movements. I can explain how these breathing movements make air move into and out of the lungs. 18 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 1.4 Respiration 1.4 Respiration In this topic you will: find out how every living cell gets the energy it needs to stay alive • do an experiment to investigate how, in respiration, some energy is released as heat • think about the difference between breathing and respiration Getting started PL E • Think back to Stage 7, where you learned about energy. With a partner, think about this question: Key words glucose mitochondria What has to happen to energy, in order to make something happen? Can you give some examples? SA M Be ready to share your ideas. 19to publication. Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior We are working with Cambridge Assessment International Education towards endorsement of this title. 1 Respiration Using energy to stay alive We use energy when we move around. PL E Our bodies need energy for many different reasons. For example: We use energy to send electrical impulses along neurones. We use energy to keep our bodies warm when it is cold. All of our energy comes from the food that we eat. Carbohydrates are especially good for giving us energy. When we eat food containing carbohydrates, our digestive system breaks the carbohydrates down to a kind of sugar called glucose. The glucose goes into our blood. The blood delivers glucose to every cell in the body. The cells use the glucose to get the energy that they need. M Releasing energy from glucose Energy must be changed from one type to another, or be transferred, in order to do something. SA The energy in glucose is locked up inside it. Glucose is an energy store. Before your cells can use the energy, it has to be released from the glucose. This is done by tiny structures called mitochondria that are found inside cells. Most cells have many mitochondria inside them. Mitochondria release energy from glucose, so that the cells can use the energy. glucose The mitochondria carry out a chemical reaction called aerobic respiration. Aerobic means that is uses oxygen, from the air. Here is the word equation for aerobic respiration: oxygen energy released glucose + oxygen → carbon dioxide + water In this reaction, some of the energy inside the glucose is released. This is done in a very controlled way. Just a little bit of energy is released at a time – just enough for the cell’s needs. water carbon dioxide A cell with a mitochondrion inside 20 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 1.4 Respiration Questions 1 Neurones contain more mitochondria than cheek cells. Suggest why. 2 Look at the word equation for aerobic respiration. What are the reactants in this reaction? b What are the products of this reaction? Use the equation for aerobic respiration to explain why the air that you breathe out contains more carbon dioxide than the air that you breathe in. PL E 3 a Respiration and heat production In Stage 7, you learned that every time energy is transferred, or transformed, some of it is changed to heat energy. In respiration, chemical energy stored in glucose is transferred to other substances, so that cells can use it. In this process, some of the energy is changed to heat energy. So respiring cells get a little bit warmer than their surroundings. Think like a scientist M Investigating respiration in peas All living things need energy. So all living things respire. Even seeds respire. SA Seeds respire especially quickly when they are germinating, because they need a lot of energy to do this. You can make pea seeds start to germinate by soaking them in water for about an hour. You will need: • 2 thermometers • cotton wool • 2 flasks • insulating material to wrap round the outside of the flasks • some dead peas • the same number of live, germinating peas 21to publication. Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior We are working with Cambridge Assessment International Education towards endorsement of this title. 1 Respiration Continued Method Set up your apparatus as shown in the diagram. Take care to make everything exactly the same in each piece of apparatus. The only difference is that one flask contains dead peas, and the other flask contains live, germinating peas. 2 Measure the temperature inside each flask. Record it in a results chart. 3 Continue to measure and record the temperature at regular intervals. For example, you could do this every hour during the school day. cotton wool 100 100 90 90 80 80 70 70 60 60 50 50 40 40 30 30 20 20 10 ask 10 0 0 insulating material wrapped round the outside dead peas live, germinating peas M Display your results as a line graph. • Put time in hours on the horizontal axis. • Put temperature in °C on the vertical axis. • Plot the points for the live peas as neat crosses. • Plot the points for the dead peas as dots with a circle around them. • Join the points for each set of peas with ruled, straight lines between the points. SA 4 thermometer PL E 1 Questions 1 What was the variable that you changed in this experiment? 2 Which variables did you keep the same? 3 Which variable did you measure? 4 Suggest an explanation for your results. 5 If you did the experiment again, would you expect your results to be exactly the same? Explain your answer. 6 Suggest any improvements you would make to your experiment, if you were able to do it again. Explain why each of your suggestions would improve your experiment. 22 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 1.4 Respiration Activity 1.4.1 Thinking about a thermogram The photograph is a thermogram of a woman working at her computer. The colours on the photograph show the temperatures of the different objects. PL E In a group of three, think about the photograph, and discuss these questions. Be ready to share your ideas. 1 Which object in the photograph has the highest temperature? Can you suggest why? 2 What is the approximate temperature of most of the woman's body? 3 Explain why the woman's body has a higher temperature than the chair she is sitting on. Activity 1.4.2 Explaining the difference between breathing and respiration M Many people who have not studied science think that respiration and breathing mean the same thing. In your group of three, think about the meanings of these two words. (Look at Topic 1.3 to remind yourself about breathing.) Think of a good way of explaining the differences between respiration and breathing, to someone else. Choose one of these methods to give your explanation: making a poster • producing a slide presentation • giving an illustrated talk. SA • Decide how to share the tasks between you, and then work on your explanation. Self assessment How well did you do each of these things as you worked on this activity? • I made sure that I really understood the difference between breathing and respiration. • I helped to decide which method we would use to give our explanation. • I carried out my part of the task really well. • I helped others in my group to carry out their tasks. • I discussed what I was doing with the others in my group. • I think that our explanation helped other people to understand the difference between breathing and respiration. 23to publication. Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior We are working with Cambridge Assessment International Education towards endorsement of this title. 1 Respiration In the activity, you had to work out for yourself how to explain the difference between breathing and respiration. Do you think this helped you to understand the difference yourself? Or would it have been better just to be told the difference by your teacher? Summary checklist PL E Why do you think that? SA M I can explain that respiration is a chemical reaction that releases useful energy from glucose, in a controlled way. I can write the word equation for respiration. I can state that respiration happens inside every living cell. I can state that aerobic respiration uses oxygen, and happens inside mitochondria. I can explain the difference between breathing and respiration. 24 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 1.5 Blood 1.5 Blood In this topic you will: learn about the structure of blood • find out about the functions of red blood cells, white blood cells and blood plasma. Getting started PL E • With a partner, think about these questions. • What do red blood cells look like? • What is the function of a red blood cell? • How do the features of red blood cells help them to perform this function? antibodies blood plasma oxyhaemoglobin pathogens red blood cells white blood cells SA M Be ready to share your ideas. Key words 25to publication. Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior We are working with Cambridge Assessment International Education towards endorsement of this title. 1 Respiration Delivering the requirements for respiration in cells You have seen that all of your cells need energy to stay alive. Each cell gets its energy through a chemical reaction called respiration. Aerobic respiration happens inside the mitochondria in the cells. The reactants are glucose and oxygen: PL E glucose + oxygen → carbon dioxide + water So, every cell in your body needs a good supply of glucose and oxygen, and the carbon dioxide and water that the cell makes must be taken away. The delivery and removal is done by the blood. The blood moves around the body inside blood vessels. The heart pumps constantly, to keep the blood moving. What is blood? SA M Everyone knows that blood is a red liquid. But if you are able to look at some blood through a microscope, you may get a surprise. The photograph shows what you might see. This is the liquid part of the blood. This liquid is called blood plasma. You can see that it is not red at all. It is a very, very pale yellow. Blood looks red because it contains a lot of red blood cells, which float in this liquid. Most of the cells in our blood are red blood cells. An adult person has at least 20 trillion red blood cells in their body. There are about five million of them in every 1 cm3 of your blood. These are called white blood cells. There are not many of them, but some of them may be quite a lot bigger than the red blood cells. They don'tlook white in the photograph because a stain has been added to the blood, to make the cells show up more clearly. The dark purple areas in these cells are their nuclei. (Red blood cells don't have nuclei!) Blood viewed through a microscope 26 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 1.5 Blood Questions 1 Look at the photograph on the previous page. Approximately how many times more red blood cells are there than white blood cells? 2 The photograph on the right was taken with a powerful electron microscope. Plasma PL E What differences can you see between the red blood cell and the white blood cell? A red blood cell and a white blood cell Plasma is the liquid part of blood. It is mostly water. The red and white blood cells are transported around the body in the blood plasma. Plasma also has many other different substances dissolved in it. For example, glucose, dissolved in blood plasma, is transported from the digestive system to every cell. You will remember that carbon dioxide is produced in every body cell, by respiration. The carbon dioxide dissolves in blood plasma and is carried away from the cells. The blood takes it to the lungs, where the carbon dioxide diffuses out and is breathed out in your expired air. M Red blood cells Stage 7, Topic 1.3 described how the structure of red blood cells is related to their function. Now you are going to think about this in a little bit more detail. SA Red blood cells are very unusual cells. They do not have nuclei and they do not have mitochondria. They are full of a red pigment called haemoglobin. It is haemoglobin that makes blood look red. The structure of a red blood cell is related to its function. cell membrane cytoplasm • There is no nucleus, to make more room for haemoglobin. • The cytoplasm contains a red pigment called haemoglobin, which carries oxygen. • There are no mitochondria in the cytoplasm. A red blood cell 27to publication. Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior We are working with Cambridge Assessment International Education towards endorsement of this title. 1 Respiration The haemoglobin helps the red blood cells to transport oxygen. As the blood flows through the tiny capillaries next to the alveoli in the lungs, oxygen from the air diffuses into the blood, and into the red blood cells. • Inside the red blood cell, the oxygen combines with haemoglobin. It forms a very bright red compound called oxyhaemoglobin. • As the blood continues on its journey around the body, it passes cells that are respiring. The oxyhaemoglobin lets go of its oxygen and gives it to the cells. • The blood, which has given away most of its oxygen, now travels back to the lungs to collect some more. PL E • This explains why red blood cells have haemoglobin – but why don’t they have nuclei or mitochondria? Scientists think that not having a nucleus makes more space for haemoglobin. They also think that not having mitochondria stops the red blood cells from using up all the oxygen for themselves, instead of delivering it elsewhere. alveolus in lungs blood containing a lot of oxygen flows away from lungs M oxygen diffuses from alveolus into blood SA haemoglobin in red blood cells picks up oxygen blood containing a small amount of oxygen flows away from body cells haemoglobin in red blood cells gives away oxygen body cells oxygen diffuses into body cells How oxygen is transported around the body Another way in which red blood cells are adapted for their function is that they are quite a lot smaller than most cells in the body. Being so 28 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 1.5 Blood small helps them to get through very tiny blood capillaries. This means they can get really close to the alveoli in the lungs, and to the respiring cells in other parts of the body. Question 3 Explain why red blood cells might use up oxygen, if they have mitochondria. White blood cells PL E White blood cells are easy to distinguish from red blood cells. They always have nuclei, which red blood cells do not have. Some kinds of white blood cell – but not all – are larger than red blood cells. Some bacteria and viruses can cause illness when they get into the body. These bacteria and viruses are called pathogens. White blood cells help to defend us against pathogens. Some kinds of white blood cell can change their shape, and push their cytoplasm out to make ‘fingers’ that can capture a bacterium. The white blood cell then produces chemicals that kill and digest the bacterium. This is called phagocytosis. bacterium white blood cell M Other types of white blood cell produce chemicals that kill pathogens. These chemicals are called antibodies. They are shown as little Y-shapes on the diagram below. Different kinds of antibodies are needed for each different kind of pathogen. SA The antibodies stick onto the pathogen. Sometimes, they kill the pathogen directly. Sometimes, they glue lots of the pathogens together so that they cannot move. This makes it easy for other white blood cells to capture and kill the pathogens. 1 Bacteria may get into the body. Some kinds of of bacteria are pathogens. They could make you ill. 3 2 Some kinds of white blood cell make chemicals called antibodies. The antibody molecules stick to the bacteria. Sometimes, the antibodies simply kill the bacteria. Sometimes, they stick them together so that other white blood cells can come and kill them. 29to publication. Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior We are working with Cambridge Assessment International Education towards endorsement of this title. 1 Respiration Activity 1.5.1 Making a picture of blood You are going to make a picture of some blood, as it might look if you saw it through a microscope. Work as a pair, or in a small group. You will need: Method • some white card • scissors • glue 1 Use the red card to make some red blood cells. Think about how many you need to make. 2 Use the white card to make some white blood cells. Use a pen or pencil to draw a nucleus in each one. Think about how many you need to make. 3 Stick the red blood cells and white blood cells onto the white paper. The white paper can represent the blood plasma. 4 Write labels to stick onto the paper. Remember to label the blood plasma. Question Copy and complete this table. M 4 • some red card PL E • a sheet of plain paper Component of blood Appearance Function red blood cell white blood cell SA plasma 5 Name three things that are transported in blood plasma. Summary checklist I can describe what blood plasma is, and its function. I can explain how red blood cells, containing haemoglobin, transport oxygen. I can explain how white blood cells help to protect us against pathogens. 30 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 1 Respiration Check your progress 1 The list includes some of the structures that air passes through, as it moves from outside the body to the place where gas exchange happens. Write the structures in the correct order. bronchiole trachea bronchus alveolus (air sac)[2] a b Copy the diagram. Label: • the blood capillary • the wall of the air sac. d e 3 [2] Draw two red blood cells in the correct place on your diagram. [1] Draw an arrow to show the direction in which oxygen diffuses. Label your arrow O. [1] Draw an arrow to show the direction in which carbon dioxide diffuses. Label your arrow C. [1] SA c PL E The diagram shows an air sac and a blood capillary. M 2 Describe how the red blood cells transport oxygen to all the cells in the body. [2] In each of these groups of statements, only one is correct. Choose the correct statement, and write down its letter. a A Every living cell respires. B Only animal cells respire. C Respiration uses up energy. [1] 31to publication. Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior We are working with Cambridge Assessment International Education towards endorsement of this title. 1 Respiration b A Expired (breathed out) air contains only carbon dioxide. B Expired air contains more carbon dioxide than inspired (breathed in) air. C Expired air contains more oxygen than inspired air. c [1] A Respiration means using your diaphragm to move air into the lungs. B Respiration is the diffusion of gases between the air sacs and the blood. d [1] PL E C Respiration is a series of chemical reactions that releases useful energy from glucose. A Muscles in the lungs contract to make air move into them. B The diaphragm muscles contract to move air into the lungs. C Muscles between the ribs pull them downwards when we breathe in. The diagrams show two blood cells. a b c [1] Name two structures that most cells have, but that red blood cells do not have. [2] The white blood cell kills pathogens by phagocytosis. Describe how it does this. [2] Other kinds of white blood cell have a different way of killing pathogens. Explain how they do this. [3] SA d Copy the drawing of the red blood cell. Label the cell membrane and cytoplasm. M 4 [1] 32 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. Project Project: Helping white blood cells to protect us from pathogens This project is about how scientific knowledge develops over time, and how scientific discoveries can help people all over the world. Background Our white blood cells are amazing at keeping us safe from pathogens. Most of the time, they manage to destroy the pathogens so that we recover quickly from an infection. Your task PL E But there are some pathogens that white blood cells cannot destroy in time. The virus that causes rabies is one of these. If the rabies virus gets into a person’s body, the body needs outside help in order to stop the virus spreading. Without treatment, most people die if they are infected with the rabies virus. You are going to work in a group to find out information about rabies, and how it can be successfully treated. Each group will work on a different topic. Choose one or two of these topics to research with your group. Also choose how you will present your findings to others. You could make a poster, or give an illustrated talk. Discovering what causes rabies Who first discovered the cause of rabies, and when did they do this? First vaccine for rabies M Who created the first vaccine for rabies, and how did they do this? How rabies is transmitted SA How can a person be infected with rabies? Preventing rabies In which countries is rabies most common? What can people in these countries do to reduce the risk of getting rabies? Treatment for rabies What should someone do if they have been bitten by an animal with rabies? How do rabies vaccines help our white blood cells to fight the virus? 33to publication. Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior We are working with Cambridge Assessment International Education towards endorsement of this title. PL E 2 Properties of materials 2.1 Dissolving In this topic you will: • use the scientific terms associated with dissolving, correctly • investigate the properties of solutions • practise measuring mass and volume Getting started M With a partner: explain the differences between an element, a compound and a mixture • draw a diagram of the way particles are arranged in a liquid • share your answers with the class. SA • Key words conserved dissolving opaque solute solution solvent transparent 34 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 2.1 Dissolving What is a solution? When you place a lump of sugar in water, the sugar seems gradually to disappear. The sugar is dissolving. You are left with a colourless solution. The substance that dissolves is called the solute. The substance that it dissolves into is called the solvent. Sugar is the solute. Water is the solvent. PL E A solution is a mixture. So, in our example, the colourless solution is a mixture of sugar and water. Although the sugar seems to disappear, it is still there. The sugar particles have simply spread out among the water particles. When the sugar cube is added to the water, the sugar starts to dissolve. When the sugar has dissolved, the sugar and water mixture is the colourless solution. SA M The diagrams below show what happens to the sugar particles when the cube dissolves. 1 The sugar crystal is visible because it is made of lots of groups of vibrating particles that are tightly packed together. 2 As the water particles vibrate and slide past one another they bump into the vibrating sugar particles. The movement helps to separate the sugar particles and they get mixed up with the water particles. 3 Eventually, the water particles separate all the sugar particles. The sugar particles are no longer in groups and are too small to be seen. 35to publication. Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior We are working with Cambridge Assessment International Education towards endorsement of this title. 2 Properties of materials All solutions are transparent. This means you can see through them. Transparent doesn’t mean colourless. For example, if you dissolve a coloured salt, such as copper sulfate, the solution formed is blue. But you can still see through it. It is still transparent. PL E A liquid such as milk is not transparent. You cannot see through it. It is opaque. Because of this, you can tell that milk is not a solution. Copper sulfate forms a solution. It is transparent. Milk is not a solution. You can tell this because it is opaque. M It is easy to confuse melting with dissolving. Remember: dissolving needs two substances, a solute and a solvent. Examples of melting Sugar (solute) in black tea (solvent) Butter in a frying pan Instant coffee (solute) in hot water (solvent) Ice cream on a warm day Nail polish (solute) in nail polish remover (solvent) Candle wax as the candle burns SA Examples of dissolving 36 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 2.1 Dissolving Think like a scientist Dissolving and mass top pan balance 00.00 g You will need: • top pan balance • stirring rod • beaker of water filter paper salt stirring rod Method PL E • salt • filter paper 1 Place the filter paper on the top pan balance. Measure and record its mass. 2 Add about 20–25 g of salt. This is the solute. Measure and record the mass of the salt. 3 Remove the paper and salt from the balance. 4 Place a beaker containing at least 100 cm3 of water on the top pan balance. Measure and record the mass of the water and the beaker together. The water is the solvent. 5 Add the salt to the water. Stir until all the salt has dissolved. Measure the mass of the beaker and salt solution. M Questions beaker of at least 100 cm3 water What was the mass of salt used? 2 What was the mass of the water and the beaker? 3 What was the mass of the solution and the beaker? 4 What does this tell you about the salt solution? SA 1 When salt is added to water and it dissolves, it has not disappeared. The salt particles are still in the water. The mass of the solution equals the total mass of the solute and solvent. This is true for any solution. mass of solute + mass of solvent = mass of solution No mass has been lost. The mass has been conserved. 37to publication. Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior We are working with Cambridge Assessment International Education towards endorsement of this title. 2 Properties of materials Questions In a solution of sugar and water, which is the solvent and which is the solute? 2 What is the difference between dissolving and melting? 3 What mass of salt solution is made when 9 g of salt is dissolved in 50 g of water? Explain how you worked out your answer. 4 A green powder was placed into a beaker of water. After it was stirred, the water looked cloudy and lumps of powder could still be seen. Has a solution been formed? Explain your answer. 5 When measuring the volume of a liquid, what should you do in order to make your measurement as accurate as possible? Summary checklist PL E 1 SA M I can use the terms ‘solvent’, ‘solute’ and ‘solution’ appropriately. I can use particle theory to explain some of the properties of solutions. I can measure mass and volume of liquids accurately. 38 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 2.2 Solutions and soulbility 2.2 Solutions and solubility In this topic you will: make solutions of different concentrations • compare the number of solute particles in solutions of different concentrations • investigate solubility • compare the solubility of various solutes Getting started PL E • concentrated dilute insoluble saturated solubility soluble solution SA M You have one minute to think about the meanings of the words solvent, solute and solution. You have one minute to discuss them with a partner. Now write your meanings on different pieces of paper. Share them with the class. Key words 39to publication. Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior We are working with Cambridge Assessment International Education towards endorsement of this title. 2 Properties of materials Solutions A solution is made when a solute is dissolved in a solvent. More particles of the solute are dissolved in a concentrated solution than in a dilute solution. PL E sugar particle water particle A dilute solution of sugar has fewer sugar particles. A concentrated solution of sugar has a lot of sugar particles. Think like a scientist M Making different concentrations of a solution You will need: • safety glasses • test tubes • test tube rack. • pipette • 2 × measuring cylinders, suitable for measuring 10 cm3 • beaker of water SA • strong solution of food dye Method 1 Carefully measure out 10 cm3 of the strong food dye solution. When you have added about the correct volume you can use the pipette to add or remove the final amount drop by drop, so that your measurement is as accurate as possible.Place it in a test tube and leave it in the test tube rack. This is solution A. 2 Carefully measure another 8 cm3 of the strong food dye solution. Pour it into a test tube. 3 Measure out 2 cm3 water and add it to the food dye. Leave it in the test tube rack. This is solution B. 40 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 2.2 Solutions and soulbility Continued Use the table below to make up food dye solutions C, D and E. Place the solutions in the test tube rack, in order, from A–E. Solution Volume of strong food dye solution/in cm Volume of water/ in cm Total volume/ in cm A 10 0 10 B 8 2 10 6 4 10 4 6 10 2 8 10 C D E 5 PL E 4 Look carefully at the solutions you have made. Questions What do you notice about the solutions? 2 How can you tell which is the least concentrated? 3 If you repeated this task using a salt or sugar solution, would you be able to identify the most and least concentrated solutions? Explain your answer. 4 Why is it important to measure the food dye solution and the water accurately? 5 If you only had a measuring cylinder that measured up to 100 cm3, would using these same volumes of copper sulfate and water be accurate? SA M 1 6 Compare the number of particles of food dye in the most concentrated solution of food dye and the most dilute solution. Solubility A solid that dissolves in a solvent such as water is said to be soluble. Sodium chloride (common salt) and sugar are soluble. A solid that will not dissolve in water is insoluble. Iron filings are insoluble in water. If you keep adding a soluble solid to a beaker of water, there comes a point where no more of the solid will dissolve. You have made a saturated solution. 41to publication. Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior We are working with Cambridge Assessment International Education towards endorsement of this title. 2 Properties of materials Some soluble substances are more soluble than others. If you have 100 cm3 of water, you would be able to dissolve a lot of sodium chloride in it, but only a tiny amount of lead chloride. Sodium chloride has greater solubility than lead chloride. Think like a scientist You will need: • test tubes PL E Solubility in water • test tube rack • measuring cylinder • spatula • a range of solutes such as sodium chloride, potassium sulfate and sugar In this task you will use various solutes and investigate their solubility in water. You will use water at room temperature. Method Place a measured volume of water in a number of test tubes. Use a different test tube for each of the solutes. 2 Add the first solute to the water. Count how many spatulas of the solute you can add until no more will dissolve. After you add each spatula of the solute shake or stir the contents of the test tube carefully. SA M 1 3 Repeat for the other solutes. 4 Record your results in a table. Questions 1 Which was the most soluble of the solutes you used? 2 Which was the least soluble of the solutes you used? 3 In this investigation you used the number of spatulas as a measure of the quantity of solute added. Suggest another way of measuring the amount of solute used, to improve the accuracy of the results. How can you ensure your results are as accurate as possible? 42 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 2.2 Solutions and soulbility Comparing solubility To compare the solubility of different solutes you must measure how much of each solute will dissolve in a known amount of the solvent. The table shows the solubility of different salts. It shows how much of each salt can be dissolved when it is added to 100 g of water at 20 °C. Solubility (measured in grams) of solute in 100 g of the solvent at 20 °C sodium chloride copper sulfate calcium chloride potassium chlorate lead chloride Questions PL E Solute 36 32 74 7 1 What is a saturated solution? 2 How much copper sulfate will dissolve in 100 g water at 20 °C? 3 How much potassium chlorate would dissolve in 200 g water at 20 °C? 4 How much sodium chloride would dissolve in 50 g water at 20 °C? 5 Use the data in the table to draw a bar chart to show the solubility of the various solutes in 100 g water at 20 °C M 1 SA Temperature and solubility Most solutes will dissolve more quickly and easily in hot water than in cold water. Think about what happens to the particles when they have more energy. The more energy the particles have, the more they vibrate and move. You can dissolve a greater mass of the solute in hot water than in the same volume of cold water. In other words, as the temperature increases, the solubility of most solutes also increases. For example, if you have 100 g of water at 20 °C you can dissolve 204 g of sugar in it. If you heat the water to 80 °C, you can dissolve 362 g of sugar in it. 43to publication. Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior We are working with Cambridge Assessment International Education towards endorsement of this title. 2 Properties of materials Worked example Question 204 g of sugar dissolves in 100 g of water at 20 °C a How much will dissolve in 200 g of water at 20 °C? b How much sugar will dissolve in 50 g of water at 20 °C? PL E Answer a 200 g of water is twice as much as 100 g, so twice as much sugar will dissolve 204 × 2 = 408 g b In 100 g water, 204 g sugar dissolves In 1 g water, 204  100 g sugar dissolves = 2.04 g In 50 g water, 2.04 × 50 g sugar dissolves = 102 g Questions 6 How much sugar can be dissolved in 250 g of water at 20 °C? 7 How much more sugar can be dissolved if the 250 g of water is at 80 °C? M Comparing the solubility of different salts This table and the graph below show the solubility of three salts at a range of temperatures. Look carefully at the graph and answer the questions. Potassium nitrate in grams per 100 g of water 0 14 73 13 10 21 81 15 20 32 88 17 30 45 96 20 40 63 105 30 50 84 114 35 60 108 124 40 70 136 134 47 80 168 148 56 SA Temperature in °C Sodium nitrate grams Copper sulfate in grams per 100 g of water per 100 g of water 44 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 2.2 Solutions and soulbility 170 160 150 140 120 sodium nitrate 110 potassium nitrate PL E Mass of salt dissolved in 100 g water in g 130 100 90 80 70 60 copper sulfate 50 40 30 M 20 10 0 0 10 20 30 40 Temperature in°C 50 60 70 80 SA Graph showing the solubility of three salts at a range of temperatures Questions 8 What is the general trend for the solubility of all three salts? 9 What is the solubility of potassium nitrate a 45 °C? 10 Which of these three salts is most soluble at 10 °C? 11 Which salt is the most soluble at 80 °C? 45to publication. Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior We are working with Cambridge Assessment International Education towards endorsement of this title. 2 Properties of materials Other solvents PL E Water is not the only solvent. Some substances that are insoluble in water will dissolve in other solvents. For example, some types of oil paint are not soluble in water. So if you need to clean your brushes after you’ve used oil paint, you will need to use a solvent that the paint will dissolve in, such as methanol ( methylated spirits). Nail polish does not dissolve in water but dissolves in nail polish remover, most nail polish remover contains the solvent propanone (acetone). M These paint brushes are being cleaned in jars of methylated spirit. Summary checklist SA I can describe how to make solutions of different concentrations. I can compare the number of solute particles in solutions of different concentrations. I can carry out an investigation safely. I can compare the solubility of various solutes. 46 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 2.3 Planning a solubility investigation 2.3 Planning a solubility investigation In this topic you will: plan an investigation, considering all the variables • carry out an investigation Getting started PL E • Discuss with a partner the difference between accurate results and reliable results. Share your ideas with the class. Key words control variables dependent variable interval range variables SA M independent variable 47to publication. Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior We are working with Cambridge Assessment International Education towards endorsement of this title. 2 Properties of materials Dissolving salt in water These students are discussing how they will investigate how temperature affects the amount of salt that will dissolve in water. They are trying to think of all the different things that could affect the results. These are the variables. Questions PL E FPO 1 Which variables have the students identified? 2 How do you think the volume of water will affect the results if it is not kept the same? Explain your answer. M The students carry out the experiment. They decide to count the number of spatulas of salt (sodium chloride) that will dissolve in 50 cm3 of water. They will repeat the experiment at different temperatures from 20 °C to 80 °C. SA The variable they change is the temperature of the water. They will count the number of spatulas of salt that will dissolve. This is the variable that depends on the temperature of the water. The volume of water is the variable that the students keep the same, to ensure that the test is fair. The variable you change is called the independent variable. The variable you measure is called the dependent variable. The variables you keep the same are the control variables. When you plot a graph of your results, the independent variable always goes along the horizontal axis. The dependent variable always goes up the vertical axis. 48 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 2.3 Planning a solubility investigation cm3 spatula °C °C salt °C 100 50 50 90 80 50 40 40 40 70 30 60 50 30 30 20 20 20 40 10 30 20 0 10 10 0 0 PL E 10 The volume of water is kept the same. Questions The temperature is changed. The number of spatulas used is measured. Which variable is the independent variable in the students’ investigation? 4 Which variable is a control variable in the students’ investigation? Is there any other variable that needs to be controlled? (Hint: think about the spatula.) 5 Which is the dependent variable in this investigation? 6 What would the label be on the vertical axis of a graph of the results of this investigation? M 3 Think like a scientist Plan and carry out an investigation into the effect of water temperature on the amount of sodium chloride (common salt) that will dissolve in it SA Part 1: Planning the investigation In a group of two or three, discuss the plan for your investigation. You need to consider the variables, risk assessments, equipment and method. Discuss these questions. • • • • • What volume of water you will use? How you will change the temperature of the water and how you will keep it at that temperature while you add the sodium chloride? What range of temperatures you will use? (The highest and lowest temperatures you will use.) Remember to be practical about this. What interval between temperatures will you use? (Will you use gaps of 10 degrees between temperatures, or 5 degrees?) What will you do to ensure you are safe while carrying out your investigation? 49to publication. Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior We are working with Cambridge Assessment International Education towards endorsement of this title. 2 Properties of materials Continued • What equipment will you need? • What method will you use? You need to prepare a table to use for your results. Think about how many columns you will need. What headings will you use? What units will you use? How many readings will you take? Will you repeat your tests? PL E Once you have discussed your plan with your teacher, you may need to change a few things. Make sure you have a full plan written, including a step-by-step method, before you carry out the investigation. Have you considered everything you need for your investigation? How can you improve your planning? Think like a scientist Plan and carry out an investigation into the effect of water temperature on the amount of sodium chloride (common salt) that will dissolve in it M Part 2: Carrying out the investigation Collect the equipment that you chose in your plan. Make sure you have your step-by-step method to follow. Questions Plot an appropriate graph. 2 Explain what you have found out. 3 Would you expect similar results if you used another salt, such as copper sulfate or lead chloride? SA 1 How accurate were your results? How could you improve the accuracy? Summary checklist I can identify different types of variables. I can plan an investigation. I can carry out an investigation safely. 50 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 2.4 Paper chromatography 2.4 Paper chromatography In this topic you will: use paper chromatography to separate dissolved substances • interpret chromatograms • use scientific language accurately Getting started PL E • Draw diagrams to show the ways you could separate mixtures that involve solutions. Check your ideas with a partner. Key words chromatogram paper chromatography SA M permanent solvent front 51to publication. Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior We are working with Cambridge Assessment International Education towards endorsement of this title. 2 Properties of materials Colours in ink Black coloured ink looks as if it is just one colour – black. In fact, it is a mixture of different coloured inks. You can separate out the coloured inks by using a technique called paper chromatography. Special paper, a bit like filter paper, is used. PL E Look at the photograph. A small drop of black ink has been placed on the paper. The water in the beaker has soaked up into the paper. As the water moves up the paper, the different coloured inks that make black ink separate out. The resulting image on the paper is called a chromatogram. The coloured inks separate because the water dissolves them. Water is the solvent. As the water moves up the paper, it carries the ink particles with it. The different kinds of ink particles are carried different distances before they are left behind on the paper. This is because not all the ink particles have the same solubility. The more soluble the ink, the further its particles are carried. SA M In the photo, you can see the different coloured inks that make up the ink in three different coloured pens – green, black, and red. Some ink is not soluble in water, such as the ink in permanent marker pens. To separate out the colours in these inks, you would need to use a different solvent, such as alcohol. 52 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 2.4 Paper chromatography Think like a scientist Separating the colours in ink You will need: • chromatography paper (or filter paper) • glass rod or wooden spill • beaker • water • pencil and ruler • ink (pipette needed if it is liquid ink)or a pen PL E • various other inks and/or food dyes Method Take a strip of chromatography paper. Draw a pencil line about 1 cm from the end. 2 Place a spot of ink on the pencil line. The spot should be as small as possible. 3 Dry the spot and then add a little more ink. 4 ace about 2 cm depth of water in a beaker. 5 Hang the paper over a glass rod, pencil or wooden spill so that the end with the ink spot is just in the water. Make sure the ink spot stays above the level of the water. 6 Watch what happens as the water moves up the strip of paper. 7 Remove the strip of paper before the water reaches the top. You need to be careful as the wet paper can tear easily. SA M 1 8 Allow the strip to dry and then stick it in your book. This is your chromatogram. You can try this with all sorts of coloured liquids. Different inks and food dyes, especially from sweets or fruit syrup, are very good. You could also try this with permanent marker pens that have ink that is not soluble in water. Questions 1 Why did you use a line drawn in pencil on the paper? 2 Why was it important not to let the ink spot go under the water? 3 Why was it important to remove the strip of paper before the water level reached the end of the strip? 4 Describe your results. 53to publication. Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior We are working with Cambridge Assessment International Education towards endorsement of this title. 2 Properties of materials Did you have any difficulties carrying out this practical work? How did you overcome them? How could you improve the way you carried out this practical task PL E When comparing different substances, a scientist may use a large piece of chromatography paper and place spots of different items alongside each other. The scientist will allow the solvent to move up through all the samples at the same time. To do this, the paper needs to be placed in a large chromatography tank. SA M The chromatogram shown here has been produced using this technique. It shows the colours in a number of different felt tip pens. Scientists use chromatography to study the dyes used in food. Some food dyes contain only one substance; they are a pure substance. Other dyes contain a mixture of substances. It is important to know exactly what is being used when our food is processed – we need to know if any substances could be a health risk; for example, they could be toxic or cause allergic reactions. Questions The drawing of a chromatograph shows the results for some food dyes. 1 Which food dyes are pure substances? 2 Which food dye is not a pure substance? 54 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 2.4 Paper chromatography Which coloured substance in the food dyes is the most soluble? 4 Which coloured substance in the food dyes is the least soluble? blue PL E 3 brown yellow 5 The chromatogram for Sunny Red shows four separate substances. Are any not permitted? If so, which? 6 The scientist decides to run the test again. Why does she do that? 7 Which of the substances in Sunny Red is the most soluble? Give a reason for your answer M Public health scientists may also use chromatography to check that the colourings being used in products such as hair dye or the ink in pens are not harmful. To do this they compare chromatograms taken from a solution of the food, hair dye or ink and those of the colourings that are permitted. SA The diagrams in below show a chromatogram from a hair dye called Sunny Red and a chromatogram showing all the permitted dyes. D C B A chromatogram from Sunny Red chromatogram of permitted dyes Activity 2.4.1 Using the correct words This unit uses a number of words that look and sound similar. For example: solute, solvent, solution; chromatography, chromatogram; dissolve, dilute. Your task is to make up a game to help you learn them. You could make a set of cards with the words written on them, and another set of cards with the meanings written on them. Think how you could use these to make a game. Your game can be for any number of players, you decide how many you want to play. 55to publication. Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior We are working with Cambridge Assessment International Education towards endorsement of this title. 2 Properties of materials How do you learn new words and terms? Does a game help? Which is the most effective way of learning for you? Think like a scientist You will need: PL E Is the green colour in plant leaves pure? • fresh plant material such as spinach • pestle and mortar • ethanol • pipette • chromatography paper • beaker • pencil • glass rod or spill Safety When using ethanol, make sure you are in a well-ventilated room and there are no heat sources close to you. Method 1 1 Add a handful of spinach and a few drops of ethanol into the mortar. Use the pestle to crush the spinach and ethanol together. Let it stand for about 10 minutes to leave time for the green pigment to dissolve in the ethanol. Prepare the chromatography paper with a pencil line and a cross, about 1 cm from the end. 3 Use a pipette to load some of the green liquid from the mortar onto the cross. Allow the spot to dry before adding more of the liquid. M 2 Place the chromatography paper over a glass rod or pencil. Hang it in a beaker containing some ethanol, so that the pencil line is just above the ethanol. 5 Watch carefully and remove the chromatography paper before the ethanol reaches the top of the paper. The point that the solvent reaches is called the solvent front. SA 4 pestle mortar 2 3 4 Allow the chromatogram to dry and then stick it in your book. Questions 1 Why was ethanol used in this investigation and not water? 2 Is the green pigment in plants pure? What is your evidence for this? 56 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 2.4 Paper chromatography Did you have any difficulties carrying out this practical work? How did you overcome them? How could you improve the way you carried out this practical task? Summary checklist SA M PL E I can describe how to use chromatography to carry out a practical task to separate dissolved substances. I can explain what the results of a chromatograph show. I can use scientific language accurately. 57to publication. Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior We are working with Cambridge Assessment International Education towards endorsement of this title. 2 Properties of materials Check your progress 2.1 Copy and complete these sentences. Use the words from the list. You may use each word once, more than once or not at all. solvent mixture solution mass temperature solid saturated dissolve volume insoluble PL E A solute is a solid that … in a liquid. The liquid it dissolves into is called a … . Together they make a … A solid that does not dissolve in a liquid is called … . The solubility of a solid measures how much of a solute will dissolve. When you measure the solubility of a solute you must use the same … and type of solvent at a given … . [6] 2.2 The table below gives the colours and solubility in water of four compounds. Name sodium chloride zinc carbonate iron sulfate Solubility white soluble white insoluble green soluble green insoluble M copper carbonate Colour The compounds were added to separate beakers of water. There was enough water to dissolve the soluble compounds completely. The contents of each beaker were filtered. a [1] b What is the colour of the filtrate from this beaker? [1] c Describe how you could obtain pure crystals of iron sulfate from a mixture of copper carbonate and iron sulfate. [3] SA One of the compounds left a white solid in the filter paper. What is the name of this compound? 58 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. Check your progress 2.3 Some students have been investigating the mass of copper sulfate that can be dissolved in water at different temperatures. They added copper sulfate until no more would dissolve and they carefully measured the mass of copper sulfate they added. Here are their results. Temperature of water in °C 20 30 40 50 60 70 80 Mass of copper sulfate dissolved in g 22 24 28 32 30 46 58 a [1] b What range of temperatures did the students use? [1] c What interval did they use for the temperatures? [1] d Name a variable the students should keep the same. [1] e Which is the independent variable? [1] PL E What name is given to a solution when no more of the solute can be dissolved in it? Here is a graph of the results. 50 M Mass of copper sulfate dissolved in g 60 40 SA 30 20 20 30 40 50 60 Temperature of water in °C 70 80 f Identify any results that do not fit the pattern. [1] g What conclusions can the students draw about their results? [1] 59to publication. Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior We are working with Cambridge Assessment International Education towards endorsement of this title. 2 Properties of materials Project: The secret formula This project is to show how scientists work together and share their ideas. In this task, just like research scientists, you can only use the information available and make deductions. As you share your ideas, you will think about the information in different ways and then develop a theory and suggest more investigations. • 4 × black pens PL E You will need: • a solution of the ink from the notes Professor Sneeze has been working on a new medicine that will protect people from coughs and colds. If this medicine works it will save a lot of people from feeling ill and taking time off work or school. It will also make him famous and make a lot of money for the university. Unfortunately, news that he has produced the medicine has reached some people who want to steal the formula, sell it to a company that will make the medicine and make themselves rich. M While he is working in his laboratory, a note is delivered to Professor Sneeze asking him to meet Professor Clean in her laboratory at as she has an interesting experiment that will finish at that time and may help him in his work. Just before he goes off to Professor Clean’s laboratory. When he arrives, Professor Clean is pleased to see him but has no idea why he has come. She did not send the note. SA Dear Professor Sneeze, I have an experiment due to finish today. I think you will be very interested to see the results as they may help you to improve the way your new medicine can be produced. Please come to my laboratory at 11.00 am when the experiment will have finished and we can discuss the results. Best wishes, Professor Clean By the time Professor Sneeze gets back to his laboratory, the equipment has been damaged and the formula has been stolen. 60 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. Project Continued Your task Your group are going to help the professor try to find out who wrote the note. Ink from the note has been dissolved in water and given to you as a solution. Choose the equipment you will need and produce a chromatogram to show the different components in the ink. PL E The professor has borrowed pens from the four most likely suspects. Doctor Price: pen A; Doctor May: pen B; Doctor Burns: pen C and Professor Green: pen D. Your job is to test the ink from all four pens to identify which pen was used to write the note. In your group, discuss the these questions. • Who do you think wrote the note? Explain why you think that. • Explain how you produce a chromatogram. • What precautions must you take? • Is this enough evidence to be sure you have the person who has the formula? • What other evidence would you look for? SA M Present your evidence to the class. 61to publication. Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior We are working with Cambridge Assessment International Education towards endorsement of this title. 3 Forces and energy In this topic you will: PL E 3.1 Forces and motion • understand what is meant by balanced and unbalanced forces • describe the effects of balanced forces on motion • describe the effects of unbalanced forces on motion Getting started Work in groups to discuss answers to these questions. What is the unit of force? 2 How are forces shown on diagrams? 3 One or more forces always act on any object on Earth. Is this true? analogy balanced change direction direction force opposite slow down speed up unbalanced SA M 1 Key words 62 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 3.1 Forces and motion Balanced or unbalanced? Look at any object that is not moving. You may think that if an object is not moving, no forces are acting to push, pull or twist it. This is not true. Look at the rock in the picture. The force of gravity is pulling it toward the centre of the Earth. This force is called its weight. The rock does not move toward the centre of the Earth because the ground is pushing up on the rock. This force is the contact force. PL E contact force These two forces are balanced. This means the forces are equal in size and opposite in direction. rock There could be more than two forces acting on the rock. ground Imagine the wind is blowing. The wind will push the rock from one side. Why does the rock not move sideways? The pushing force from the wind is balanced by friction between the rock and the ground. SA M These forces can be shown in a force diagrams. In a force diagram, the arrows show the size and direction of each force. The longer the arrow, the bigger the force. So, when you draw a force diagram with balanced forces, make sure the arrows are the same length and point in opposite directions. Starting to move weight The force diagram shows the balanced forces acting on the rock. rock wind ground The forces acting on the rock when the wind is blowing. Imagine the rock is now pushed with a much larger force than the wind, such as a large vehicle. When the vehicle pushes on the rock, the pushing force will be larger than friction. friction contact force push from large vehicle friction weight The forces are no longer balanced and the rock will start to move. 63to publication. Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior We are working with Cambridge Assessment International Education towards endorsement of this title. 3 Forces and energy The rock will now move because the sideways forces are not balanced. This can be shown on the force diagram. The rock will now start to move in the direction of the larger sideways force. Slowing down PL E The rock will not move up or down because the forces acting up and down are still balanced. Unbalanced or unequal forces can also make moving objects slow down. A parachute makes a falling object slow down. When an object is falling quickly, the parachute causes a force of air resistance that is larger than the weight of the object. These forces can be shown in a force diagram. air resistance SA M air resistance weight weight When the parachute first opens, the forces are unbalanced. This unbalanced force makes the object slow down. When the object slows, the air resistance decreases, so the forces become balanced again. Then the object falls at a constant speed. This force diagram shows the object falling at a constant speed. 64 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 3.1 Forces and motion Changing direction Unbalanced forces can also make objects change direction. This tennis ball will change direction because of an unbalanced force. When the ball contacts the tennis racket, the ball pushes on the tennis racket. To make the ball go back in the opposite direction, the hitting force must be larger than the force from the ball. tennis racket hitting force on the ball PL E This can be shown in a force diagram. force from the ball on the tennis racket M The tennis ball will change direction because of an unbalanced force. Stage 7, Topic 3.3 described planets orbiting the Sun due to the force of gravity. The force of gravity on a planet is a constant, unbalanced force. SA When an object moves in a circle, its direction is always changing. A constant unbalanced force is needed to keep an object moving in a circle. direction of force from the Sun’s gravity direction of orbit planet Sun 65to publication. Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior We are working with Cambridge Assessment International Education towards endorsement of this title. 3 Forces and energy Summary When forces are equal in size and opposite in direction, the forces are balanced. • Balanced forces cause no change in movement. • When forces are not equal in size and/or act in directions that are not opposite, the forces are unbalanced. • Unbalanced forces cause change in movement: speeding up, slowing down or changing direction. Direction of forces Balanced or unbalanced Change in movement Equal Opposite Balanced None Equal Not opposite Unbalanced Change of direction Not equal Opposite Unbalanced Increase or speed Not equal Not opposite Unbalanced Increase or decrease speed and change of direction M Size of forces Questions 1 PL E • a Describe what is meant by ‘balanced forces’. b A box is on the floor. The box is not moving. Draw a labelled force diagram to show all the forces acting on the box. SA i ii 2 Amal pushes the box sideways. The box does not move. Draw another labelled force diagram to show all the forces acting on the box when Amal is pushing. A tug of war is a game played by two teams of people, each pulling on the same rope. The team that pulls the rope to their side wins. The picture shows a tug of war. The teams in this game are called Team A and Team B. 66 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 3.1 Forces and motion The rope is not moving. PL E Both Team A and Team B are pulling on the rope. Use ideas about forces to answer these questions. Explain why the rope is not moving. b The rope starts to move towards Team B. Give two changes that could make the rope move towards team B. The diagram shows the forces on an aeroplane in the air. a b Explain why this aeroplane is: i flying at a constant speed ii not getting higher or lower. drag weight go faster ii go higher or ‘lift’. SA Name the force that should decrease to make the aeroplane: i 4 thrust Name the force that should increase to make the aeroplane: i c lift M 3 a go lower ii go faster. A The picture shows a toy train moving around a circular track. The locomotive contains an electric motor that drives the train. The train moves in a circle at a constant speed. D Give the letter of the arrow that shows the direction of: a the driving force of the train b the force of friction on the locomotive c the force that keeps the train moving in a circle. direction of movement of toy train B toy train C track 67to publication. Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior We are working with Cambridge Assessment International Education towards endorsement of this title. 3 Forces and energy Activity 3.1.1 Balanced or unbalanced forces? On a large piece of paper, draw a table with two columns: one for balanced forces and one for unbalanced forces. Put each of these situations into the correct column, according to the forces that are acting. The situations are: a motorcycle going around a corner • a boy on a skateboard slowing down • a bowling ball rolling at constant speed in a straight line • a girl on a swing getting faster • a computer sitting on a desk • a helicopter going straight upwards at a constant speed • a coconut falling from a tree and getting faster. PL E • How did you decide which situations had balanced forces and which had unbalanced forces? Did your strategy work? M Could you use this strategy again, or would you change it? Think like a scientist Measuring balanced and unbalanced forces SA In this investigation, you will investigate the effects of balanced and unbalanced forces. Work in pairs. You will need: • two force meters • piece of string • coloured tape • scissors Set up the equipment as shown in the diagram. string coloured tape newton meter 100 90 80 70 60 50 40 30 20 10 0 newton meter 0 10 20 30 40 50 60 70 80 90 100 coloured tape fixed to desk 68 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 3.1 Forces and motion Continued Method 1 Each person in the pair holds one newton meter. The string should be tight. The coloured tape on the string should be lined up with the coloured tape on the desk. 2 Each person pulls with an equal force, for example,  PL E Questions 1 What directions must you both pull to keep the pieces of coloured tape lined up? 2 Both people increase the pulling force to, for example,  . Explain why the string does not move, even when the force is increased.Continued 3 One person decreases their force by . If the force was then decrease the force to . a Describe what happens to the string. b Use a force diagram to explain what happens to the string. 4 Now make the difference between the forces larger, for example the difference is now or . M How does the difference between the sizes of the forces affect the movement of the string? 5 Explain why the two newton meters do not have to be the same. 6 This investigation is an analogy of a tug of war. That means the investigation can be compared with a tug of war. State what is represented by the newton meters in this analogy. SA Self-assessment Decide how confident you are about each of these statements. Give yourself 5 if you are very confident and 1 if you are not confident at all. • I understand what balanced forces are. • I can draw force diagrams to show balanced forces. • I can draw force diagrams to show unbalanced forces. • I can predict some things that can happen when forces are unbalanced. • I understand that there can be forces acting on an object even when it is not moving. 69to publication. Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior We are working with Cambridge Assessment International Education towards endorsement of this title. 3 Forces and energy Summary checklist SA M PL E I can describe what is meant by balanced forces in terms of size and direction. I can understand that forces can be acting on an object that is not moving. I can recognise when forces are unbalanced. I can list some of the effects of unbalanced forces. 70 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 3.2 Speed 3.2 Speed In this topic you will: understand what is meant by speed • learn about the unit of speed • be able to calculate speed Getting started PL E • Work in groups to discuss answers to these questions. 1 What are the speed limits for cars where you live? 2 Signs showing speed limits usually do not have units. What are the units used for speeds of cars? Units of speed average speed calculate constant m/s metres per second speed SA M There are many different units of speed. Different units are sometimes used in different countries and for different things. For example, the speed of ships is often measured in knots, whereas aeroplanes often use Mach. Some countries have road speed limits in kilometres per hour, whereas some countries use miles per hour. Key words 71to publication. Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior We are working with Cambridge Assessment International Education towards endorsement of this title. 3 Forces and energy So, to avoid confusion, scientists use standard units for measurement in all countries. The standard unit for speed is metres per second. The word per means ‘in each’. Therefore, metres per second means the number of metres travelled in each second. For example, a horse running with a speed of 15 metres per second means the horse travels a distance of 15 metres in each second. PL E Metres per second is written as m/s. Calculating speed The way you calculate speed is linked to the unit metres per second, m/s. For example, think of a bus that travels a distance of 100 m in a time of 20 s. The bus has travelled 100 m in 20 s, so how many metres does it travel in each 1 s? travelled number of metres travelled in each second = _________________ total distance total time number of metres travelled in each second = speed, so M total distance travelled speed = _________________ total time 100 m = _____ 20 s SA = 5 m/s You can summarise this equation for speed as: speed = _______ distance time Note: the term average speed is sometimes used because the speed of an object during a journey is not always constant. Constant means not changing. Average speed is calculated in exactly the same way as speed. The equation for speed can be used in a formula triangle. This means you can also use the equation to calculate: • the distance travelled, if you know the speed and the time taken • the time taken, if you know the speed and the distance travelled. 72 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 3.2 Speed distance speed distance time Worked example Question speed distance time time = time distance speed distance speed time distance = speed × time PL E A formula triangle time speed speed = distance Question Marcus rides his bicycle at a speed of 4 m/s for 60 s. How far does he go in this time? Sofia is in a car travelling at a speed of 35 m/s. How long will the car take to travel 2100 m? Answer Answer time = _______ distance speed distance = speed × time = 4 × 60 M = 240 m = ____ 2100 35 = 60 s SA The worked examples above both use metres, seconds and metres per second. Sometimes, the values are given in different units. So, for example, if you have a distance in km and a time in hours, the equation will give you a speed in km/h as you are dividing a distance in km by a time in hours. Worked example Question An aeroplane travels  in a time of 5 hours. What is the speed of the aeroplane in km/h? Answer distance time = _______ speed = ________ 2500 km 5 hours = 500 km/h 73to publication. Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior We are working with Cambridge Assessment International Education towards endorsement of this title. 3 Forces and energy However, unless you are told otherwise, always work in metres, seconds and metres per second. Remember, in calculations, always: • show the steps you used in working out the answer • include the correct units with the answer. Questions a Write an equation for speed, when you know the distance travelled and the time taken. PL E 1 b Write down the standard scientific unit of speed. c Write an equation for distance travelled, when you know the speed and the time taken. d Write an equation for time taken, when you know the speed and the distance. In each calculation question that follows, show your working and give the unit with your answer. a An Olympic sprinter completes the 100 m race in a time of 10 s. Calculate the average speed of the sprinter. b A car travels a distance of 210 m in a time of 6 s. a Calculate the speed of the car in m/s. b Calculate the distance, in m, travelled by the car in 14 s. c Calculate the time taken, in s, for the car to travel a distance of 1925 m SA 3 Explain why this value is an average speed. M 2 4 5 a An aeroplane flies between two cities that are 8100 km apart. The aeroplane takes 9 hours to complete the journey. Calculate the average speed of the aeroplane, in km/h. b A different aeroplane can fly at 800 km/h. Calculate the distance, in km, that this aeroplane could fly in 6 hours. c Another aeroplane can fly at 950 km/h. Calculate the time taken, in hours, for this aeroplane to travel a distance of 7125 km. Anna sees a worm on the grass. Anna sees the same worm 2 hours later. The worm has moved a distance of 3 m in that time. Calculate the average speed of the worm, in metres per hour. 74 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 3.2 Speed Activity 3.2.1 Speed, distance and time Use a map or internet search engine to find the distances between some places near to where you live. You should include: some shorter distances, such as from home to school • some longer distances, such as between cities. PL E • The table gives some typical speeds for different methods of travel. Method of travel walking cycling horse riding bus small motorcycle car train aeroplane Typical speed in m/s 2 7 10 12 20 30 35 200 M Use the information in the table to calculate the times taken for your different distances. For each distance, choose some of the most appropriate methods of travel. Think like a scientist SA Calculating speed In this investigation, you will make measurements to calculate the speed of an object. Work in groups of three or four. You will need: • ramp • tennis ball • smooth level surface • 2 metre rules • coloured tape • books • stopwatch 75to publication. Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior We are working with Cambridge Assessment International Education towards endorsement of this title. 3 Forces and energy Continued Method Set up the equipment as shown in the diagram. ball ramp coloured tape colou height 2 3 4 5 6 7 8 coloured tape 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 27 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 77 79 70 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 PL E 0 1 cm metre rule 1 Use coloured tape to fix the bottom of the ramp to the desk or floor. 2 Fix some coloured tape 3 Fix some coloured tape near the top of the ramp to mark where you will release the object. 4 Measure the height from the desk or floor up to the position where you will release the object. 5 Release the object and measure the time the object takes to move between the two pieces of coloured tape on the desk or floor. 6 Repeat this two more times and calculate the average time to travel between the two pieces of tape. 7 Do this for a range of different heights. M from the end of the ramp. Results and questions Record your results in a table. 2 Use your results to calculate the speed of the object between the two pieces of tape. Add another column to your table, or draw a new table, to include the speed. Remember to put the unit of speed in the column header. SA 1 3 Plot a line graph of the results. Put height on the hoizontal axis and speed on the vertical axis. Include the units on each axis. 4 What is: a the independent variable in this investigation b the dependent variable in this investigation? 5 State two variables that were controlled in this investigation. 6 Explain why each measurement is repeated. Give two reasons. 7 Describe the trend in your results. 76 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 3.2 Speed Continued Self-assessment Decide how well you: • made measurements • recorded results in a table • drew the graph of the results. PL E Choose one thing that you could do better next time. How will you do this better next time? What will you change? Summary checklist SA M I know and can use the equation that links speed, distance and time. I can use the equation to calculate speed, given distance and time. I can use the equation to calculate distance, given speed and time. I can use the equation to calculate time, given distance and speed. I know that standard units are metres, seconds and metres per second. I can calculate speeds using different units. 77to publication. Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior We are working with Cambridge Assessment International Education towards endorsement of this title. 3 Forces and energy 3.3 Describing movement In this topic you will: learn how to use graphs to describe movement • understand what a distance–time graph shows • learn to draw a distance–time graph Getting started PL E • Work in groups to discuss the answer to this question. Imagine you are standing on a path. You start walking at a constant speed. at rest distance–time graphs safety precautions sketch stationary SA M What would a line graph look like if you plotted the distance you had walked on the vertical axis and time on the horizontal axis? Key words 78 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 3.3 Describing movement Distance–time graphs Scientists use graphs to describe how two variables are related. We can use graphs to describe the movement of an object. One way to do this is to plot distance travelled on the vertical axis and time on the horizontal axis. A graph like this is called a distance–time graph. Graphs are more useful than words for describing movement because: it is easier to see trends and patterns • you can read any value of distance or time during the journey, from the graph • other values, such as speed, can be calculated from a graph • information about the whole journey can be seen easily. PL E • This is a distance–time graph. It shows the journey of a car from a starting position A to a destination, C. The car then returns to its starting position. 1 2 3 4 M C Distance B A A SA Time Now take a closer look at what the graph shows in each of the four sections. These sections are in different colours so you can see them clearly. 1 At the starting position, A, the object has travelled zero distance. The car travels at a constant speed away from the starting position to point B. When moving at constant speed, the car travels the same distance in each second. The distance from the start increases with time. The distance–time graph show this as a straight, upward sloping line. 2 The car stops at B. It is stationary. Stationary means not moving, with a speed of zero. You can also use the term at rest to mean stationary. The distance of the car from the start position does not change when the object is stationary, but time still passes. The distance–time graph shows a straight line that is horizontal. 79to publication. Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior We are working with Cambridge Assessment International Education towards endorsement of this title. 3 Forces and energy 3 The car starts again and moves at a constant speed to its destination, point C. It moves faster than when it travelled between A and B, meaning it travels a greater distance each second. So, the distance–time graph show this as a steeper straight, upward sloping line. 4 From point C, the car travels at a constant speed back to the starting position, A. The distance of the object from the start will decrease with time. The distance–time graph shows this as a straight, downward sloping line. PL E The distance–time graph for the car journey was a sketch. If you draw a sketch graph you do not have to put numbers on your graph axes. Sometimes, distance–time graphs have values on the axes. This means you can use the graph to make calculations. Read the distance from the vertical axis, and the time from the horizontal axis. Then use the equation: distance speed = _______ time Worked example Question This distance–time graph shows a short train journey between two stations, P and R, that are 2000 m apart. M • The train leaves station P at time 0. • The train takes 200 s to travel from P to R. • The train stops at station R for 140 s. • The train then travels back to station P in a time of 100 s. SA 2500 arriving at R leaving R Distance in m 2000 1500 1000 500 arriving at P leaving P 0 0 100 200 300 400 500 Time in s e At what speed does the train travel from station P to station R? f What is the speed of the train on the way back from station R to station P? 80 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 3.3 Describing movement Continued Answer a The distance is 2000 m and the time taken is 200 s. distance speed = _______ time = 10 m/s PL E = ____ 2000 200 b The distance is 2000 m and the time taken is 100 s. distance speed = _______ time = _____ 2000 100 = 20 m/s Questions M a Sketch a distance–time graph for an object moving at a constant speed away from a starting position. b On the same graph, sketch another line to show another object moving faster, away from the same starting position. Label this line ‘faster’. c On the same graph, sketch another line to show another object moving more slowly away from the same starting position. Label this line ‘slower’. SA 1 2 Marcus is making a journey from home to a shop. For the first part of the journey, he rides his bicycle at a constant speed. Marcus then stops to talk to a friend. For the last part of the journey, he rides his bicycle at a lower constant speed than before. a Sketch a distance–time graph for Sam’s journey. b Label each part of Sam’s journey on your graph. 81to publication. Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior We are working with Cambridge Assessment International Education towards endorsement of this title. 3 Forces and energy 3 A boat goes straight across a lake. After some time, the boat crosses the lake again to return to the original position. The graph shows the journey made by the boat. Use information in the graph to answer these questions. How far did the boat travel when crossing the lake once? b Calculate the speed of the boat crossing the lake the first time. c How much time did the boat spend stopped before crossing the lake again? d Calculate the speed of the boat crossing the lake the second time. e How much time did the boat take for the complete journey? PL E a 100 90 80 60 M Distance in m 70 50 40 SA 30 20 10 0 0 10 20 30 40 50 60 70 80 Time in s 90 100 110 120 130 140 150 82 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 3.3 Describing movement Activity 3.3.1 My journey Think about a journey you made recently. The journey could be walking or any other method of travel. The journey could be coming to school or a longer journey. PL E Sketch a distance–time graph for that journey. Label your graph with what each part represents. Swap your graph with someone else. Can they understand your journey by looking at the graph? Can you understand someone else’s journey by looking at their graph? Think like a scientist M Walking and running In this activity, you will plan an investigation, make measurements, do calculations and draw a distance–time graph. Work in groups of three or four. You will need: SA • space where you can run safely • tape measure • stopwatch • one sheet of graph paper per person Method You need to calculate the average speed of walking for one person in the group, in m/s. You then need to calculate the average speed of running for one person in the group, in m/s. It does not have to be the same person. 1 Plan what measurements you will need to make and how you will make these measurements. 2 Make a list of the safety precautions that the person who is running should take. 3 Make your measurements safely and record them in a suitable way. 83to publication. Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior We are working with Cambridge Assessment International Education towards endorsement of this title. 3 Forces and energy Continued Questions and results 1 a Calculate the average walking speed for the person, in m/s. b Calculate the average running speed for the person, in m/s. Draw a distance–time graph. Put walking and running on the same graph and label the lines clearly. 3 Explain the difference between the two lines. Refer to distance and time in your explanation. Self-assessment 1 Decide how confident you are about each of these statements. Give yourself 5 if you are very confident and 1 if you are not confident at all. • I made useful contributions to planning. • I made useful contributions to making the measurements. • I drew my graph carefully, neatly and accurately. Which do you think is better: • drawing a distance–time graph for a journey, or • describing a journey in words? M 2 PL E 2 Explain your answer. Summary checklist SA I can sketch a distance–time graph for an object moving at a constant speed away from a starting position. I can sketch a distance–time graph for a stationary object. I can sketch a distance–time graph for an object moving at a constant speed back towards a starting position. I can tell whether objects are moving quickly or slowly, or are stationary, from a distance–time graph. I can tell what direction an object is moving from a distance–time graph. I can sketch a distance–time graph from a description of a journey. I can draw a distance–time graph accurately. I can read values from a distance–time graph. 84 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 3.4 Turning forces 3.4 Turning forces In this topic you will: recognise when a force causes something to turn • know how to use the term moment • be able to calculate the moment caused by a force Getting started Work in groups. PL E • lever moment newton metres pivot turn SA M Make a list of things, such as a door handle, that are turned by forces. Key Words 85to publication. Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior We are working with Cambridge Assessment International Education towards endorsement of this title. 3 Forces and energy Turning effects of forces When you push down on a door handle, the handle turns. When you push down on the pedal of a bicycle, the pedal turns. When you pull on a door, the door turns toward you. These are all examples of forces that cause an object to turn. The object that turns is called a lever. PL E The point around which the lever turns is called the pivot. The lever and pivot are shown in the picture of the bicycle pedals in Figure 3.4.1. When you bend your arm, the arm acts as a lever. Your elbow is the pivot. lever lever pivot pivot pivot M lever The human body has many levers and pivots. Can you see more levers and pivots in this picture? SA A bicycle pedal is an example of a lever that turns around a pivot when a force is applied. Calculating moments The moment of a force describes its the turning effect of a force. The moment of a force depends on: • the size of the force (the bigger the force, the bigger the moment) • the distance between the position where the force acts and the pivot (the greater the distance, the greater the moment). You can calculate a moment from this equation: moment = force × distance n 86 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 3.4 Turning forces Distance in the equation is the distance from the pivot to the position where the force acts. The unit of force is the newton and the unit of distance is the metre. Therefore, the unit of moment is newton × metre, which is written as newton metre or N m. Remember to use an upper case N and a lower case m when writing N m. Question PL E Worked example A pulling force of 35 N is needed to open a door. The distance from the door handle to the door hinges (the pivot) is 0.8 m What is the moment caused by the pull on the door? Answer moment = force × distance = 35 × 0.8 = 28 N m Question M Worked example SA Look at this diagram. What is the moment caused by the weight on the arm? 0.25 m pivot 20 N Answer moment = force × distance = 20 × 0.25 = 5Nm 87to publication. Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior We are working with Cambridge Assessment International Education towards endorsement of this title. 3 Forces and energy Balancing A seesaw is a type of lever. People sit on either side of the pivot of a seesaw and make the lever turn one way and then the other. Worked example Question PL E The result is that each person moves up and down. A seesaw will be balanced when the moments on both sides of the pivot are equal and opposite. Marcus, with a weight of  sits at a distance of  from the pivot of a seesaw. Arun, has a weight of 800 N. Where should Arun sit to make sure the seesaw is balanced? Answer Marcus will exert a moment of 600 × 2 = 1200 Nm For the seesaw to be balanced, the moment on the other side must also be 1200 Nm. M moment = force × distance So, distance = _______ moment force distance = 1200 Nm/800 N SA = 1.5 m 88 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 3.4 Turning forces Questions 2 a Describe what is meant by the word ‘moment’ in physics. b Write the equation that links moment, force and distance. c Write the unit of moment. Jon has a spanner for turning a nut. The direction that the nut must turn is shown by the arrow. The pivot is in the centre of the nut. a Which arrow shows the direction that Jon should push on the spanner to produce the largest moment in the direction needed to turn the nut? Write the letter. b 3 B A wrench nut PL E 1 nut will turn this way D C Explain your answer to a. The drawing shows a door handle. 4N Sofia pushes on the door handle with a force of 4 N at the position shown in the drawing. Calculate the moment caused by this force. The drawing shows a bicycle brake lever. M 4 0.12 m A moment of 1.8 N is needed to turn this brake lever. Calculate the force needed at position F to produce a moment of 1.8 N m. Zara weighs 450 N. Zara sits on a seesaw at a distance of 1.5 m from the pivot. SA 5 0.09 m F Sofia weighs 500 N. Sofia sits on the seesaw on other side of the pivot from Zara. Calculate the distance from the pivot that Sofia must sit to balance the seesaw. pivot 89to publication. Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior We are working with Cambridge Assessment International Education towards endorsement of this title. 3 Forces and energy Activity 3.4.1 Identifying moments Use old magazines to find pictures. Cut out pictures showing things that use moments to work. Remember: anything that turns when pushed or pulled uses moments. Stick the pictures to a large piece of paper to make a display. PL E Write the name of the object beside it. Think of a title for your display. Think like a scientist Calculating moments In this investigation, you will investigate how the force needed to turn an object varies with distance from the pivot. Work in groups of two or three. You will need: • ruler • newton meter • 2 clamp stands • elastic (rubber) band M • metre rule • string • sticky tape • G-clamp Set up the apparatus as shown in the diagram. loop of string stuck to meter rule with tape SA clamp stand pivot elastic band metre rule loop of string stuck to meter rule with tape newton meter clamp stand ruler G-clamp to secure clamp stand to table top 90 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 3.4 Turning forces Continued Make a prediction about what will happen to the force needed to pull the metre rule down as the distance between the force and the pivot decreases. Method Move the loop of string with the newton meter as far from the pivot as you can. 2 Record the distance between the pivot and the string. 3 Raise the newton meter so it is not pulling down on the metre rule. 4 Use the newton meter to pull down on the metre rule. The distance that you pull depends on the strength of the elastic band. The metre rule needs to be pulled down far enough to get a reading of about 1 N at the furthest point from the pivot. 5 Record this distance. This will be the distance you pull down on the metre rule each time. 6 Record the force. 7 Repeat this, pulling the metre rule down the same distance each time. Each time, use the loop of string to move the newton metre closer to the pivot. 8 Your results should be a set of distances and forces. 9 Decide whether you need to repeat any of your measurements. M Results and questions PL E 1 Describe how you made the experiment safe. 2 Record your results in a table. Make sure that you record distances in metres, so you may need to convert from cm or mm. Remember to reverse the order of your results, so in the table the distances are increasing. 3 Draw a line graph of your results. Put distance on the horizontal axis and force on the vertical axis. 4 Explain the pattern in your results. 5 Was your prediction correct? 6 Explain any improvements you could make to the method that would help get more accurate results. SA 1 Self-assessment 1 Describe anything you did during the investigation to help get more accurate results. 2 a Did you repeat any of your measurements? b Explain your answer to part a. 91to publication. Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior We are working with Cambridge Assessment International Education towards endorsement of this title. 3 Forces and energy Summary checklist SA M PL E I can understand that forces can cause turning effects. I can understand what is meant by the term moment. I know and can use the equation that links moment, force and distance. I know the unit of moment. 92 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 3.5 Pressure between solids 3.5 Pressure between solids In this topic you will: recognise that forces can cause pressure on an area • understand what affects pressure • be able to calculate the pressure caused by a force on an area Getting started Work in groups. PL E • The nail in the picture has a sharp point at one end. Make a list of some other objects that have sharp points or sharp edges. newtons per square metre point pressure sharp surface area SA M What are these things used for? Key word 93to publication. Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior We are working with Cambridge Assessment International Education towards endorsement of this title. 3 Forces and energy The pushing effect of a force PL E The picture shows a knife being used to cut modelling clay. What could you do if the clay was difficult to cut? The knife works because the force used to push down on the clay causes pressure on the clay. You can think of pressure as the pushing effect of a force. You could: M Suppose the clay is difficult to cut. How could you increase the pushing effect of the force? increase the force on the knife; as the force increases, the pressure increases • use a sharper knife (a sharp knife has less surface area in contact with the clay); as the area decreases, the pressure increases. SA • The equation linking pressure, force and area is pressure = ____ force area Pressure is force divided by area. The unit of force is the newton and the unit of area is the metre squared. That means the unit of pressure is newtons per metre squared, or N/m2. Sometimes you can use smaller areas, measured in cm2. If the area is in cm2 then the unit of pressure will be N/cm2. If the area was in mm2, what would the unit of pressure be? Some things have large areas to decrease pressure; others have small areas to increase pressure. 94 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 3.5 Pressure between solids PL E The camel has large feet. This means the force from the weight of the camel is applied over a large area. The pressure on the sand is decreased, so the camel will not sink in the sand. The woman in the picture is lying on a bed of nails. Each nail has a sharp point on the end. The weight of the woman acts on many hundreds of nails, so the pressure from each nail is very small. SA M The end of this pin has a sharp point. The sharp point has a small area to increase pressure. The increased pressure means the pin will easily go into wood or card. Scissors have sharp blades. The area along the cutting edge of each blade is small. This increases the pressure, making things easier to cut. 95to publication. Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior We are working with Cambridge Assessment International Education towards endorsement of this title. 3 Forces and energy Calculating pressure Worked example Question Question Imagine an elephant standing on four feet, as shown in the picture. The total weight of a bicycle and rider is 1000 N. PL E The bicycle has two tyres in contact with the ground and the weight is supported equally on both tyres. The area of each tyre in contact with the ground is 5 cm2 What is the pressure that each tyre exerts on the ground? The weight of the elephant is 50 000 N. The total area of all four feet is 0.4 m2. Answer M What is the total pressure that the elephant exerts on the ground? Answer force pressure = ____ area SA 50 000 = _____ 0.4 = 1 25 000 N/m2 The unit of pressure here is N/m2 because the area is given in m2. weight on each tyre = ____ 1000 2 = 500 N force pressure = ____ area 500 = ___ 5 = 100 N/cm2 Notice how the unit of pressure here is N/cm2 because the area of the tyres is given in cm2. 96 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 3.5 Pressure between solids Continued Question A hammer is used to push a nail into wood. The area of the point at the end of the nail is 1.5 mm2. The pressure needed for the nail to go into the wood is 50 N/mm2 Answer pressure = ____ force area so, force = pressure × area = 50 × 1.5 = 75 N Questions 2 a Write down the equation that links pressure, force and area. b Use the equation to explain why a nail that goes into wood has a sharp point ii shoes for walking on snow are wide and flat. Write down the unit of pressure when force is in newtons and area is in: a m2 b cm2 c mm2 A box has a weight of 60 N. The area of the box in contact with the ground is 0.5 m2. SA 3 i M 1 PL E Calculate the force needed from the hammer. Calculate the pressure that the box exerts on the ground. Show your working and give your answer in N/m2. 4 A car has a weight of 8000 N. The car is supported by 4 tyres. The weight on each tyre is equal. The area of one tyre in contact with the ground is 150 cm2. Calculate the pressure that one tyre exerts on the ground. Show your working and give your answer in N/cm2. 5 A thumb tack has an area of 0.5 mm2 in contact with a wall. A pressure of 40 N/mm2 is needed for the drawing pin to go into the wall. Calculate the force needed to push the drawing pin into the wall. Show your working and give the unit with your answer. 97to publication. Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior We are working with Cambridge Assessment International Education towards endorsement of this title. 3 Forces and energy Think like a scientist Calculating pressure In this investigation, you will investigate how the pressure that a person exerts on the floor varies. Work in groups of two or three. You will need: PL E • a person who is willing to be weighed, or who knows their body mass • a bathroom scale, if body mass is not known • sheets of squared paper • pencil Method 1 Measure or record the body mass of the person. 2 Convert the mass to weight using: weight in N = mass in kg × strength of gravity in N/kg Take the strength of gravity as  . Ask the person to place one foot on a piece of squared paper. They can do this while wearing shoes. 4 Use the pencil to draw around the foot of the person. M 3 Questions Use the shape of the outline on the squared paper to work out the area of the foot in cm2. 2 Calculate the area of both feet. SA 1 3 Calculate the pressure that the person exerts on the ground when they are: a standing equally on both feet b standing on one foot. 4 Explain the difference in your answers to 3a and 3b. 5 Now ask the same person to put the front of one foot on squared paper as if they were standing on their toes. 6 Use the same method as above to work out the area of the front of the foot in cm2. 7 Calculate the pressure exerted by the person on the ground when standing on the front of one foot. 8 A person can be supported by the front of one foot during some everyday activities. Give an example of such an activity. 98 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 3.5 Pressure between solids Continued 9 a Describe how you could work out the area in contact with the ground when the person is lying down. b i Predict how the pressure would change when the person was lying down compared to standing. ii Explain your answer. Self-assessment 2 Decide how confident you are about each: PL E 1 a how force affects pressure b how area affects pressure. Decide how confident you are about: a calculating pressure when you know the force and the area b working out the unit of pressure using the units of force and area. Summary checklist SA M I can understand that pressure is the pushing effect of a force. I know and can use the equation that links pressure, force and area. I can understand how the unit of pressure can be worked out from the units of force and area. 99to publication. Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior We are working with Cambridge Assessment International Education towards endorsement of this title. 3 Forces and energy 3.6 Pressure in liquids and gases In this topic you will: recall how particles move in liquids and gases • understand how particle movement causes pressure in liquids and gases • predict how changes in liquids and gases affects the pressure PL E • Key words Getting started altitude Work individually. Draw a diagram to show how particles are arranged in: a liquid b a gas. collide container depth sea level SA M a atmospheric pressure 100 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 3.6 Pressure in liquids and gases Pressure in liquids PL E Look at the picture of a dam. The wall of this dam is wider at the bottom than it is at the top. M The water comes out with more force than from the upper gaps Behind the wall of the dam, the water is almost to the top of the wall. You can see water coming out from two levels. The water coming out close to the top is coming out with less force. SA The water coming out from further down is coming out with more force. This is because pressure in the water increases with depth. The wall is wider at the bottom to make the wall stronger where the pressure from the water is greatest. Pressure and depth in liquids The pressure in a liquid increases with depth, but why? As you go deeper in a liquid, there is more liquid above your position. The weight of this liquid, caused by gravity, pushes on the particles of the liquid. When the particles of the liquid are pushed, they move with more force. As the particles in a liquid are moving randomly in all directions, then the pressure in the liquid is equal in all directions. 101 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 3 Forces and energy Pressure in gases Before you blow up a balloon, there is a small volume of air inside the balloon. The balloon is open at one end, so the pressure of the air inside is the same as the pressure of the air outside. As you blow air into the balloon, you are adding more gas particles. PL E Particles in a gas move randomly and collide with the walls of the container. The container is the balloon. Every time a gas particle collides with the wall of the container, the particle exerts a small force on the wall. The more particles there are in the gas, the more collisions happen with the walls, and so the force on the walls increases. As this force is exerted on an area, the force causes pressure. The pressure inside the balloon gets bigger as you blow in more air, pushing the walls of the balloon outwards. SA M Look at the tyre in this picture. The pressure of the air in this tyre is too low. Particles in a gas move randomly and collide with the walls of the container causing pressure. 102 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 3.6 Pressure in liquids and gases The air inside the tyre is at low pressure. The pressure is not enough to support the weight of the vehicle. If more air is put inside the tyre, the pressure will increase. More collisions will happen with the inside walls of the tyre, pushing the tyre outward and supporting the vehicle. Pressure and depth in gases As with liquids, the pressure in a gas increases with depth. PL E Most people on Earth live at low altitude. Altitude is height above sea level. The Earth’s atmosphere, which we call air, is made from gases. The atmosphere extends to a height of about above sea level. Sea level is, therefore, where the atmosphere is at its deepest. So, at sea level, atmospheric pressure is highest. As you go higher in the atmosphere, two variables that affect atmospheric pressure change: • the number of particles in of air decreases, so the concentration of gas particles decreases • the weight of air above your current position decreases. M Atmospheric pressure at sea level is about . This pressure is the equivalent of the weight of two large elephants pushing on every of surface! We are not aware of the pressure from the atmosphere because we live in the atmosphere all the time. Effects of atmospheric pressure SA The effect of atmospheric pressure can be shown by pumping the air out of a metal container. Before the air is pumped out, the pressure on the inside of the container is equal to the pressure on the outside. When the air is pumped out, the pressure inside the container becomes close to zero. The pressure on the outside does not change. The container is crushed by the pressure of the air outside the container. The picture shows a containercrushed by atmospheric pressure. 103 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 3 Forces and energy Pressure and temperature in gases Questions a Explain why submarines that go to the deepest parts of the oceans must be very strong. b The sketch graph shows how the pressure in a liquid changes with depth in the liquid. a Explain the pattern shown in the graph. b Copy and complete the sentence using the best word. Use information in the graph. SA 2 Explain why the wall of a dam is thicker at the bottom than at the top. M 1 PL E As the temperature of a gas increases, the speed of the particles in the gas increases. When particles are travelling faster, their collisions exert more force. This means that increasing the temperature of a gas will increase the pressure of the gas. High pressure can be used to cook food. The picture shows a type of cooking pot called a pressure cooker. Water and food are placed inside the pressure cooker. The pressure cooker has a sealed lid. When the water boils, the steam cannot escape so the pressure of the gas inside increases. On top of the pressure cooker, there is a weight to control the pressure and valves that allow steam to Steam inside a pressure cooker is at higher pressure because of the high temperature. escape, once the equired pressure has been reached. When the depth in the liquid doubles, the pressure in the liquid ……………….. 3 A fish is in water. The water exerts pressure on the fish. Pressure Depth in liquid Which of these causes pressure on the fish? Write one letter. A the weight of water beside the fish B the weight of water all around the fish C the weight of water above the fish D the weight of water below the fish 4 Marcus plays basketball. The ball is filled with air. a Explain what causes the pressure inside the ball. 104 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 3.6 Pressure in liquids and gases b The ball is too soft and does not bounce properly. Marcus uses a pump to put more air in the ball. Explain how putting more air in the ball will change the pressure inside the ball. c Marcus notices that the pressure inside the ball is lower on a cold day and higher on a hot day. Explain why the pressure inside the ball is higher on a hot day. 5 PL E A metal container is connected to a vacuum pump. A vacuum pump removes all the air from inside the container. There is now a vacuum inside the container. a Explain why the pressure in a vacuum is zero. b The container collapses when there is a vacuum inside. Explain why. Think like a scientist Observing the effects of pressure Part 1: Pressure and depth in liquids In this investigation, you will observe the effect of pressure increasing with depth, in water. Work in groups of two or three. M You will need: • a 1 or 2 litre empty plastic bottle • adhesive tape • something to make small holes in the side of the bottle SA • large tray or sink to collect water Method 1 Make three small holes in the side of the bottle at different heights. Try to make the holes the same size. 2 Predict what will happen when the bottle is filled with water. 3 Now use one piece of adhesive tape to cover all the holes. 4 Place the bottle in the tray or the sink. 5 Fill the bottle with water, but do not put the lid on the bottle. 6 Pull off the adhesive tape to open the holes. 7 Watch what happens. holes continued 105 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 3 Forces and energy Continued Questions 1 Did your observation fit with your prediction? 2 Draw a labelled diagram to show what you observe. 3 Explain what you observed, using ideas about pressure. Part 2: Pressure and temperature in gases PL E In this activity, you will observe the effect of changing temperature on the pressure in a gas. Work in groups of two or three. You will need: • an empty plastic bottle (0.5–2 litre) with lid • access to a warm place • access to a cold place, such as a refrigerator Method Take the lid off the bottle. 2 Leave the bottle and the lid in a warm place for 5–10 minutes. 3 Put the lid tightly on the bottle without squeezing the bottle. Do this while the bottle is still in the warm place. 4 Put the bottle into a cold place for 15–20 minutes. 5 Observe what has happened to the bottle. M 1 SA Questions 4 Draw a diagram of the bottle before and after the activity. 5 What happened to the pressure of the air inside the bottle when it was moved to the cold place? 6 Explain your answer to 5. 7 Predict what would happen if you did this activity the other way around. The open bottle starts in the cold place, then the closed bottle is taken to a warm place. Include ideas about particles and pressure and include the observation that you would make. 106 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 3.6 Pressure in liquids and gases Continued Peer-assessment Swap your answers for these activities with another group. Rate their score for each answer on a scale of 0–3. 3 means very good and well explained. 2 means good with some explaining. PL E 1 means difficult to understand, but some explaining is given. 0 means you cannot understand the answers or they are incorrect. Summary checklist SA M I can understand what causes pressure in a liquid. I can understand how pressure changes with depth in a liquid. I can understand what causes pressure in a gas. I can understand how altitude affects atmospheric pressure. I can understand how the quantity of gas in a container affects the pressure. I can understand how the temperature of a gas in a closed container affects the pressure. 107 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 3 Forces and energy 3.7 Particles on the move In this topic you will: describe how random movement of particles causes diffusion • understand how diffusion happens in liquids and gases Getting started Key words PL E • Work in groups to discuss the answers to these questions. How can you smell food cooking when you are some distance away from the food? 2 When you pour orange juice into water, why does all the water eventually turn orange? SA M 1 concentration diffusion 108 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 3.7 Particles on the move Mixing gases The particles in a gas move randomly. Both the speed of the particles and the direction of the particles are random. If we mix two gases in one container, each one will have particles that move randomly. That means each gas will spread to fill the container. The movement of the particles of each gas is called diffusion. PL E Diffusion means the overall random movement of particles from an area where they are in higher concentration to an area where they are in lower concentration. Concentration is the number of particles in a particular volume. Look at the diagrams. They show how two gases diffuse. 1 At the start, the tap is closed. The white gas particles are at high concentration on the left, and zero concentration on the right. The red gas particles are at high concentration on the right, and zero concentration on the left. The tap is opened and the gases start to spread out (diffuse). At random, some particles of each gas will pass through the space where the tap opens. M 2 SA The white gas particles are now at quite high concentration on the left, and low concentration on the right. The red gas particles are at quite high concentration on the right, and low concentration on the left. 3 After some time, the gases have completely diffused. There is equal concentration of both gases on both sides. Diffusion stops when the concentrations are equal. However, the movement of individual particles does not stop when diffusion stops. Diffusion explains how you can smell food cooking. When food is heated, some particles in the food change state and become gas. 109 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 3 Forces and energy The gas particles from the food move randomly and so spread out through the air by diffusion. The strength of the smell will get stronger as you move closer to the food. This is because the concentration of the particles is higher, the closer you get to the source of the particles. Mixing liquids PL E Many animals use this change in strength of smell to find food. Diffusion also happens in liquids. Particles in a liquid also move at random. SA M The picture shows what happens when blue ink is added to water. The blue ink moves from the area of high concentration to the areas of low concentration, until it is completely diffused throughout the water. Speed of diffusion The speed of diffusion depends on: • the difference in concentration of the particles • temperature. The bigger the difference in the concentrations of the particles, the faster the diffusion. The higher the temperature, the faster the diffusion. Higher temperature makes particles move faster, so the particles can spread out faster. For example, when you make a cup of tea, the tea diffuses through the water. It diffuses faster in hot water than it does in cold water. 110 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 3.7 Particles on the move Questions 1 Zara’s mother opens a bottle of perfume. Zara is at the other side of the room. After a few minutes, Zara can smell the perfume. a Which of these explains why Zara smells the perfume? Write one letter. A All the gas particles of the perfume move in one direction. All the gas particles of the perfume move randomly. PL E B C All the particles in the air move in one direction. D All the particles in the air are stationary (not moving). b Which of these changes would result in Zara smelling the perfume in a shorter time? In each case, no other variable changes. There is more than one correct answer. A The air in the room is at a higher temperature. B Zara moves further away from the bottle of perfume. C Zara’s mother puts the lid on the perfume bottle. D The perfume in the bottle is at a lower temperature. Describe what is meant by the term ‘diffusion’. 3 The diagram shows two types of particle in containers, A and B. The containers have the same volume. M 2 Explain whether the particles in the containers are in solid, liquid or gas state. b Explain how the concentrations of the blue particles compare in containers A and B. c Explain how the concentrations of the red particles compare in containers A and B. container container B B SA a container container A A 4 Sofia is making an orange flavour drink. She pours a small volume of concentrated orange juice into a glass. She then adds water to the glass until the glass is full. a Explain how the orange colour from the juice spreads into the water. b Arun says: ‘When the orange colour has stopped spreading, the particles in the liquid have stopped moving.’ Explain whether Arun is correct. 111 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 3 Forces and energy 5 Which of these will result in diffusion? Write the letters for all the correct statements. A adding milk to coffee B adding sand to water C adding salty water to pure water D allowing gas from a cylinder to escape into the air throwing small pieces of rock into the air Activity 3.7.1 Watching diffusion PL E E In this activity, you will observe the diffusion of a coloured solution in water. You will need: • a transparent container, such as a 200 cm3 (or larger) glass beaker • water • ink, such as food dye Method • dropper pipette • a glass tube or drinking straw Fill the container with warm water. 2 Leave the container to stand for a few minutes so the water stops moving. 3 Use the dropper pipette to add one or two drops of dye to the bottom of the water in the beaker. 4 Observe what happens. M 1 SA Questions 1 Write about what you did in this activity. Write this in your own words and do not copy the method shown here. 2 Make a series of labelled drawings to show your observations in this activity. 3 Predict what would happen if the activity was repeated with water at higher temperature. 112 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 3.7 Particles on the move Think like a scientist The effect of temperature on the speed of diffusion In this investigation, you will investigate how temperature affects the rate of diffusion in liquids. Work in groups of two or three. You will need: • water • a way to heat the water PL E • three or more identical beakers • a way to cool the water (optional) • water-soluble ink • measuring cylinder • thermometer • dropper pipette Method • stopwatch 1 Add equal volumes of water at different temperatures to each of your beakers. 2 Measure and record the temperature of the water in each beaker. 3 Use the dropper pipette to carefully add a small volume of the ink to the bottom of each beaker. Squeeze the top of the pipette gently so the ink does not squirt out into the water and start mixing. Add the ink to the water in order from the lowest to the highest temperature. Use a stopwatch to time diffusion process in each beaker. 5 Stop the stopwatch when the ink has fully spread out through the water of the beaker being tested. M 4 Questions Describe the trend in your results. 2 Explain this trend. 3 Explain why you used equal volumes of water in all the beakers. 4 Suggest at least two improvements to the method that would give better results. SA 1 Peer-assessment Swap your answers with another group. You will assess their answers to 2 and 4. Instead of marking their answers, write some feedback to the group. Include: • what they have done well in their answers • how they could improve their answers. 113 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 3 Forces and energy Summary checklist SA M PL E I know how to describe diffusion. I can understand how diffusion happens in gases. I can understand how diffusion happens in liquids. I can understand that the speed of diffusion is affected by the difference in concentration and by the temperature. 114 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 3 Forces and energy Check your progress 3.1 An object has balanced forces acting. Which of these describes the movement of the object? [1] Give two letters. The object could be moving at a constant speed in a straight line. B The object could be moving at a constant speed in a circle. C The object could be stationary. D The object could be getting faster in a straight line. PL E A 3.2 Describe the effects of the unbalanced forces on each of these objects. b c A bicycle is moving in a straight line. There is an unbalanced force opposite to the direction the bicycle is moving. [1] A car is moving in a straight line. There is an unbalanced force in the same direction as the car is moving. [1] A ball is moving in a straight line. There is an unbalanced force sideways to the direction the ball is moving. [1] M a 3.3 Which of these is the standard unit of speed used by scientists? [1] Write one letter. A m/s SA B km/h C N/cm2 D Nm 3.4 Marcus goes running. After some time, Marcus gets tired and starts walking. Marcus does not stop. Sketch a distance–time graph for Marcus. [3] 3.5 A train travels a distance of in at a constant speed. a Draw a distance–time graph for the train. [4] b Calculate the speed of the train. Show your working and give the unit with your answer. [3] 115 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 3 Forces and energy 3.6 There have been different units of measurement through history. This picture shows the unit of length called the rod. One rod is the total length of the left feet of 16 people. PL E In the picture, the 16 people have been chosen at random. a Explain one disadvantage with the rod as a unit of length. [1] b Explain one advantage of the rod as a unit of length. [1] M 3.7 Zara has a metre rule, a stopwatch and a newton meter. Zara can directly measure some quantities with this equipment. Zara must calculate some quantities that cannot be directly measured using this equipment. SA Copy this table. Can be measured Must be calculated Write each of these quantities into the correct column in the table. [2] force moment length area pressure time speed 116 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 3 Forces and energy 3.8 a b [1] Write the equation that links moment, force and distance. Arun is trying to turn a nut with a spanner. Arun exerts his maximum force on the spanner, but the nut will not turn. b [2] Write the equation that links pressure, force and area. [1] The picture shows four different types of shoes. A PL E 3.9 a Explain why Arun can make the nut turn if he uses a longer spanner. B C D Give the letter of: i the shoes that will be best for not sinking in snow [1] ii the shoes that could make holes in a soft wood floor. [1] M 3.10 Which statement is true about a liquid? [1] Write one letter. A B Pressure decreases with depth. Pressure does not depend on depth. SA C Pressure increases with depth. D There is no pressure in a liquid. 3.11 Write down two variables that will increase the speed of diffusion in a gas. [2] 117 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 3 Forces and energy Project: Making a balance for weighing This project is about using moments to find the weights of objects. You will make a balance and then use it to find some unknown weights. Background The earliest balances for weighing needed equal weights on both sides of the balance. PL E The unknown weight was placed on one side, and known weights were added on the other side until the system balanced. A system such as this is balanced because there are two moments acting. One moment tries to pull one side down. The other moment tries to pull the other side down. M When the moments are equal and opposite, the system is balanced. This happens when the weights are equal because the distances from the pivot are also equal. Your task SA Make a balance that can be used to weigh a range of different weights without changing the known weight. Your balance will work in a different way to the one in the picture, so yours will not look like this. Work in groups. You can use equipment such as: • a metre rule • a triangular prism • a known weight • any other equipment that your teacher makes available. 118 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. Project Continued Remember: • do not confuse weight with mass • weight is a force • the moment caused by a force depends on the distance from the pivot. SA M PL E When your balance is made and working, you can demonstrate to the class how it works. 119 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 4 Ecosystems In this topic you will: PL E 4.1 The Sonoran Desert • find out about some of the animals and plants that live in a desert • think about how these animals and plants interact with each other • learn what an ecosystem is • think about some of the different habitats in a desert ecosystem Getting started M Cacti (the plural of cactus) are plants that are adapted to live in deserts. Look at a cactus, or a picture of one. With a partner, discuss these questions. Why is a desert a difficult place to live? • How are cacti adapted to live in a desert? SA • Key words adaptations ecology ecosystem environment food web habitat interact nectar nocturnal pollen pollinating 120 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 4.1 The Sonoran Desert A desert in Arizona The photograph shows the Sonoran Desert in Arizona, in the USA. Deserts are not easy places for animals and plants to live. Deserts do not get much rainfall, so the organisms that live there must have adaptations that help them to survive with little water. PL E The tall plants in the photograph are saguaro cacti. They grow very slowly, and those in the photograph may be more than 100 years old. Their roots spread out widely just underneath the soil, ready to absorb any rain that falls. Many animals live among the cacti and other desert plants. Gila woodpeckers make holes in the cacti, to make their nests. Other birds also visit these holes. SA M Cactus wrens often use a different kind of cactus, called a teddy bear cholla, to make their nests. Teddy bear chollas are so spiky that very few other animals will get close to them. So the cactus wren’s eggs and young ones are protected from predators. 121 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 4 Ecosystems During the hot days, lizards, tortoises and other animals rest in the shade of the plants, or burrow into the soil where it is cooler. At night, when the temperature falls, kangaroo rats come out to feed, wary of their predators such as rattlesnakes and coyotes. PL E In the Sonoran Desert, it usually rains heavily at least once a year. When the rains come, the desert is transformed. Many plants quickly produce flowers. Insects feed on the nectar and pollen in the flowers, helping the plants to reproduce by pollinating them. At night, bats feed on nectar from the flowers of agave plants. A kangaroo rat Seeds fall to the ground and are collected by ants, to take into their nests to provide a food store. Many months or years later, some of the uneaten seeds may germinate to produce new plants. Interactions in the Sonoran Desert A bat feeding on agave nectar SA M As you read the information above, and looked at the photographs, you may have realised that all the different animals and plants depend on each other. They interact with each other. The actions of one organism affect another. Ants collecting seeds 122 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 4.1 The Sonoran Desert Activity 4.1.1 Interactions between organisms in the desert Work with a partner. You will need: • a large sheet of paper • coloured pens PL E • (optional) pictures of the animals and plants in the desert, that you can cut out • (optional) scissors and glue Read the information about life in the Arizonan Sonora Desert, and look at the photographs. Make a list of different ways that the animals and plants interact with one another. Now think about how you could show these interactions in a picture. On a piece of rough paper, make a rough sketch of the design for your picture. Build up your picture on a large sheet of paper. You could draw pictures of the organisms, or stick cut-out pictures of them onto the paper. Write descriptions about how they interact with each other. M Non-living things in the desert It is not only other organisms that affect the plants and animals in the Arizona desert. There are also interactions between the organisms and the non-living parts of their environment. SA • Light: The bright sunlight helps the plants to photosynthesise, producing food that other organisms can eat. • Temperature: The temperature is often very high during the day, but much lower at night. Some animals are nocturnal, which helps them to avoid overheating or drying out. It is cooler underneath the soil, so some animals – such as the tarantula in the picture – dig burrows for shelter during the day. • Soil: Rocks and soil provide minerals for the plants to grow, as well as building material for ground-nesting birds. 123 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 4 Ecosystems • Water: All organisms need water to keep their cells alive. Rain, when it comes, allows them to become more active and to reproduce. • Air: The desert air provides carbon dioxide for the plants to use in photosynthesis, and oxygen for all the organisms to use in respiration. PL E The organisms also affect their environment. For example, droppings from the kangaroo rats become part of the soil. The gases that they take in and give out affect the composition of the air. The desert ecosystem Everything in the desert interacts with everything else. All of these interactions make up the desert ecosystem. An ecosystem is a network of interactions between all the living organisms and the non-living things around them. rattlesnake M Some of the interactions in an ecosystem involve food webs. Remember that plants are the producers in a food web. They use energy in sunlight to make food. As animals eat the desert plants and each other, the energy is passed through the desert food web. red-tailed hawk h SA Food webs are a very important part of the interactions in an ecosystem, but they are not the only interactions. For example, plants may provide places for some of the animals to make nests. Plant roots help to hold the soil together, so that it does not wash away when it rains. Animals help plants to reproduce by pollinating their flowers or spreading their seeds. kangaroo rat prickly pear cactus collared lizard grasshopper brittlebrush A food web in the Sonoran Desert. The interactions in an ecosystem are usually very complicated. The study of ecosystems is called ecology. No ecologist would ever claim to have discovered all of the different interactions in an ecosystem. There is always something new to find out, even in an ecosystem that scientists have been studying for a long time. 124 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 4.1 The Sonoran Desert Questions Name two producers in the diagram of a food web in the Sonoran Desert. 2 Explain why the food web could not exist without the producers. 3 What do the arrows in the food web represent? 4 Give two examples of interactions between organisms in the desert that are not to do with feeding. PL E 1 Habitats in a desert ecosystem The place where an organism naturally lives is called its habitat. There are many different places to live in a desert. The habitat of a saguaro cactus is the open desert. • The habitat of a Gila woodpecker is a saguaro cactus (where it makes its nest) and the air and ground in the open desert (where it collects food). • The habitat of a desert ant is underneath the rocks and soil and on the soil surface. • Termites live at the base of the saguaro stems. • Sap beetles live inside the saguaro flowers. • Kangaroo rats live in burrows and come out to look for food at night. Question Explain the difference between an ecosystem and habitat. SA 5 M • Activity 4.1.2 How a species fits into the desert ecosystem Work in a group of three or four for this activity. You are going to choose one species that lives in the desert. You could continue to think about the Sonoran Desert in Arizona, or you could choose a different desert. Investigate how your species interacts with other organisms, and with the non-living things around it. You could choose one of the species mentioned in this topic, or a completely different species. 125 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 4 Ecosystems Continued Use the internet and the library to find out as much as you can about your species. Concentrate especially on how your species interacts with other organisms, and with its environment. For example, you could try to find out: what it eats, and what eats it • the habitat it lives in within the desert ecosystem • how the species is adapted to survive in its habitat • how its actions (other than feeding) affect other organisms, or non-living parts of the ecosystem • how other organisms and non-living things affect it (other than feeding). PL E • Use your information to make an illustrated poster or presentation that you can share with the rest of your class. Questions 6 Where did you find the best and most interesting information? 7 When you used the internet to find information about your species: which web sites were most relevant for your research? b how did you choose web sites that were most likely to provide correct information? M a Summary checklist SA I can describe some of the interactions between the organisms in a desert ecosystem. I can describe some of the interactions between the organisms and the non-living parts of the environment in a desert ecosystem. I can name some of the different habitats in a desert ecosystem. I can explain the difference between a habitat and an ecosystem. 126 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 4.2 Different ecosystems 4.2 Different ecosystems In this topic you will: learn about some of the many different kinds of ecosystem on Earth • describe some of the different habitats in an ecosystem Getting started Work with a partner. PL E • Marcus says that an ecosystem is a place. Sofia says that an ecosystem is not just a place – it is more than that. SA M Who is correct? Think about this on your own, then share your ideas with your partner. 127 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 4 Ecosystems More about ecosystems The ecosystem in the Arizona Desert is just one of many different ecosystems on Earth. Here are three more examples of ecosystems: mangrove forests, sea ice in the Arctic Ocean, and a rice paddy. Mangrove forest Mangroves are trees that can grow with their roots in sea water. They form forests along the coasts of many tropical countries • Young fish live among the mangrove roots, safe from larger fish that might eat them. Mud skippers climb out onto the mud when the tide is out, feeding on whatever they can find. • As the mangrove leaves fall onto the mud, they are decomposed by bacteria. Prawns and crabs eat the partly decomposed leaves. • Crab-eating macaques, a type of monkey, climb through the trees and catch crabs on the tree roots and mud. M PL E • Sea ice in the Arctic Ocean During the winter in the Arctic Ocean, it is so cold that some of the sea water freezes. • Seals hunt for fish in the water, but have to come to the surface to breathe air. • Polar bears patrol the ice, looking for seals to kill and eat. Polar bears are good swimmers, and can move from one ice floe to another. • Arctic foxes also look for food on the ice. • Enough light passes through the ice to allow tiny algae (single-celled plants) to grow on the underside of the ice floes. • Tiny shrimp-like organisms eat the algae. Fish eat the shrimps. SA • 128 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 4.2 Different ecosystems Rice paddy Not all ecosystems are natural. This area of rice paddies in Malaysia is farmed by people. • At some times of year, the paddy fields are flooded with water. Algae grow in this shallow water, and on the mud at the sides of the flooded areas. • Fish swim into the flooded paddies from the irrigation canals. Frogs and dragonflies breed in the water. • Because the water is shallow, it heats up quickly during the day, and cools down quickly at night. • Farmers often add fertiliser to the paddy fields, making not only the rice but also the algae grow faster, providing more food for the animals. • Many birds feed in and around the paddy fields. Activity 4.2.1 Habitats in an ecosystem PL E • M Choose one of the ecosystems shown in the photographs. Use the internet to find out more about your chosen ecosystem. SA Make a list of the different habitats in this ecosystem, and some of the organisms that live in each of the habitats in your list. Think like a scientist Investigating a local ecosystem You are going to investigate an ecosystem near your school. For example, you could investigate: • a garden area • a group of trees • part of the playing field • a pond. Safety You will be working outside. It is important to stay in the same area as the rest of your class. Always stay with a partner. 129 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 4 Ecosystems Continued You will need: PL E a selection of the apparatus and materials shown; choose what is suitable for the ecosystem you are studying. These items are not drawn to scale. This is a pitfall trap. This one is made from a plastic cup which has been set into the ground as shown. Small animals that crawl or run over the surface of the ground – such as beetles – fall in and cannot get out. This is a sweep net. It has a large net on the end of a long pole. It is useful for catching insects. You can sweep it through long grass. You can also use it to catch organisms in a pond or small stream. SA M It is important to check your pitfall trap regularly. If not, you may find just one extremely fat carnivorous beetle in it, and nothing else. A hand lens is useful for looking at very small organisms. A camera is useful for taking photographs of organisms, especially if you do not know their names. You can use your photos to try to identify the organisms later. You can use this apparatus to find insects living in the lower branches of trees. Gently hit a branch with the stick, as your friends hold the large piece of material or a sheet underneath. If you haven’t got any material, you can use an upsidedown umbrella. You can use books to try to identify the animals and plants that you find. Quick identification keys are also very useful. 130 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 4.2 Different ecosystems Continued It is important to remember that if you catch any animals, you must take great care of them. Do not take them away from their habitat. Release them exactly where you found them. Method Look all around the area you are studying. What kind of ecosystem is it? Write a short description of it or draw a picture. For example: How big is it? What kind of plants grow there? Is there a lot of light, or is it shady? Is it damp or dry? 2 Find different habitats in the ecosystem. For example, if you are studying a garden, habitats could include underneath stones, in the soil, on the soil surface, on leaves, in flowers, on tree trunks and in the air. 3 Look for organisms living in each habitat. Make a list of them. If you don’t know their names, take a picture or make a drawing. You might find some fungi, as well as plants and animals. If there are animals, what are they doing? 4 If possible, visit the ecosystem at different times of day – or even at night. How does it change? 5 Draw a diagram to show some of the interactions you have seen between the organisms, and between organisms and the non-living parts of the environment. For example, if you were looking at a garden: M PL E 1 Did you see any insects visiting flowers? • Did you see any animals eating anything? • Did you find anything hiding from predators or the hot sun underneath part of a plant? • Had anything made a burrow in the soil? • Did you see any decomposers? SA • It is important to remember that if you catch any animals, you must take great care of them. Do not take them away from their habitat. Release them exactly where you found them. Method 1 Look all around the area you are studying. What kind of ecosystem is it? Write a short description of it or draw a picture. For example: How big is it? What kind of plants grow there? Is there a lot of light, or is it shady? Is it damp or dry? 131 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 4 Ecosystems Continued Method Find different habitats in the ecosystem. For example, if you are studying a garden, habitats could include underneath stones, in the soil, on the soil surface, on leaves, in flowers, on tree trunks and in the air. 3 Look for organisms living in each habitat. Make a list of them. If you don’t know their names, take a picture or make a drawing. You might find some fungi, as well as plants and animals. If there are animals, what are they doing? 4 If possible, visit the ecosystem at different times of day – or even at night. How does it change? 5 Draw a diagram to show some of the interactions you have seen between the organisms, and between organisms and the non-living parts of the environment. For example, if you were looking at a garden: PL E 2 Did you see any insects visiting flowers? • Did you see any animals eating anything? • Did you find anything hiding from predators or the hot sun underneath part of a plant? • Had anything made a burrow in the soil? • Did you see any decomposers? M • Self-assessment Read these statements, then assess yourself on how well you did the activity. Give yourself: 0 if you did not try SA 1 if you think you did quite well 2 if you are quite pleased with how well you did. • I was careful to stay with the group and stay safe. • I made a good description or picture of the study area. • I found at least five different habitats in the ecosystem. • I used at least two different methods to find organisms. • I found at least ten different kinds of organism. • I made a good diagram, showing interactions in the ecosystem. If you gave yourself two marks for everything, the best possible score would be 12. How many marks have you given yourself out of 12? If you did a similar investigation in future, how could you do it better? 132 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 4.2 Different ecosystems Summary checklist SA M PL E I can describe some of the habitats and interactions in an ecosystem. I can use different methods to find out about habitats and interactions in an ecosystem near my school. 133 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 4 Ecosystems 4.3 Intruders in an ecosystem In this topic you will: learn about how new or invasive species can affect an ecosystem Getting started Work in a group of three. PL E • Think about the saguaro cacti in the Sonoran Desert. Now imagine that someone brings a new species of cactus that can grow and reproduce faster than the saguaro cactus. Key Words eradicate extinct native species What might happen to the saguaro cacti? What might happen to some of the other species in the Sonoran Desert? SA M Make a list of your ideas, ready to share. 134 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 4.3 Intruders in an ecosystem New species in an ecosystem In your studies of ecosystems, you have seen how all the different organisms interact with each other and their environment. In this topic, you will find out what happens if a new species suddenly arrives. How does the new species fit into the network of interactions? How does this affect the species already there? Introduced species in New Zealand PL E New Zealand is a country in the Pacific Ocean. New Zealand became separated from all the other areas of land in the world about 66 million years ago. Because of this separation, the species that developed in New Zealand were different from those elsewhere on Earth. Before humans arrived in New Zealand, there were no predatory mammals there. Many of the native species of birds nest on the ground. There were no predators to eat their eggs, so the eggs and young birds were safe. Even the adults of several species of native bird – such as the kiwi – cannot fly. M Nobody knows exactly when humans first arrived in New Zealand, but it was probably about 700 years ago. Humans brought species of animals with them that did not belong in New Zealand. For example, rats stowed away on their boats. Rats now live in most of the country. The rats eat birds’ eggs and defenceless young birds. SA Since then, other species have been introduced to New Zealand. Farmers brought sheep, to farm for their wool and meat. Rabbits were brought on sailing ships, to use as food. But the rabbits escaped and began to eat grass in the sheep pastures. So people brought stoats from Europe to control the rabbits. Now stoats have spread all over New Zealand. They are fierce hunters and breed rapidly. They can kill and eat birds much larger than themselves. Stoats have made several species of native bird extinct, including the laughing owl and the New Zealand thrush. Stoats eat almost 60% of kiwi chicks. People in New Zealand are now trying to eradicate (completely get rid of) stoats, but this is very difficult to do. The best that can be done is to control their numbers. Scientists think that 53 species of native bird in New Zealand have become extinct since humans arrived. The extinctions have been partly caused by people hunting and killing the birds, but mostly because of introduced invasive species. 135 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 4 Ecosystems Questions 1 In your own words, explain what a ‘native species’ is. 2 Name some native species in your own country. 3 Suggest why it is very difficult to eradicate an introduced species, once it has settled into a new place. Activity 4.3.1 PL E Why do some introduced species cause problems? Stoats normally live in Europe. Stoats are not a ‘problem animal’ in the ecosystems where they normally live. With your partner, think of ideas to explain why stoats are such a problem in New Zealand, but not a problem in their native countries. 2 When everyone is ready, share your ideas with the rest of the class. Make a list of the ideas on the board. 3 Once all your ideas have been listed, work together with the rest of the class to make a shorter list. For example, perhaps you can explain some of the ideas more clearly if you use fewer words. Or perhaps two of the ideas are really the same idea, and can be combined. Questions 1 M 1 Buffelgrass is native to Africa, Asia and the Middle East. It was planted in Arizona in the 1930s, as food for cattle. Now, it is spreading rapidly through the Sonoran Desert. SA What is the name for a plant, such as buffelgrass, that is growing in an ecosystem where it does not belong? 2 Buffelgrass grows in dense patches. It takes water and nutrients from the soil. Look at the picture that you made in Topic 4.1, showing interactions in the Sonoran Desert. Suggest how buffelgrass could affect some of the native species in the desert. Summary checklist I can explain how new or invasive species can affect an ecosystem. I can describe examples of invasive species and their effects. 136 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 4.4 Bioaccumulation 4.4 Bioaccumulation In this topic you will: find out about DDT • use a model to explain what happens to DDT in a food chain • learn what bioaccumulation is, and why it happens Getting started PL E • Think about what you learned about decomposers in Stage 7. With a partner, answer these questions. What is a decomposer? 2 What kinds of substance can decomposers break down? 3 What kinds of substance are decomposers unable to break down? accumulate bioaccumulation biomagnification insecticide persistent toxic SA M 1 Key words 137 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 4 Ecosystems DDT DDT is an insecticide. This means that it kills insects. PL E DDT was first produced in the 1940s. It was used to kill insects that transmit diseases. It was especially useful for killing mosquitoes that transmit malaria, and fleas that transmit a disease called typhus. DDT was also used to kill insects that eat crops. No one thought that DDT could harm organisms other than insects. This old picture was taken in the 1940s. It shows a beach being sprayed with DDT to kill mosquitoes. The people on the beach are being sprayed, too. DDT is very good at killing insects. But gradually, people began to realise that it was also harming animals that no one wanted to kill. In 1962, an American author called Rachel Carson wrote a book called Silent Spring. She described how DDT was killing not only mosquitoes, but also birds. M Her book made many people realise that some insecticides, including DDT, are very harmful to the environment. Scientists now understand how it causes harm to ecosystems. DDT in food chains SA We now know that DDT does not break down. It is a persistent chemical. It stays in the environment for many years. It is not broken down by decomposers. When DDT is sprayed, some of it is carried up high into the air. It can be blown for very long distances, far away from where it was used. When DDT gets into an animal’s body, it stays there for the whole life of the organism – it never breaks down. DDT is very harmful to many kinds of animal. It is toxic (poisonous). For example, it makes the shells of birds’ eggs very thin and easy to break. The old photograph in Figure 4.4.2 shows some eggs of a bird called an ibis. The eggs did not hatch, because the female ibis that laid them had DDT in her body. 138 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 4.4 Bioaccumulation Think like a scientist Modelling DDT in a food chain You will need: at least 25 people to do this activity – it’s even better with 30 • at least 200 tokens, some blue, some yellow and some red • a stopwatch • a cup or small bag for each person, to put tokens in • 1 card with ’eagle’ written on it • several cards (about 8 in a class of 30) with ’small bird’ written on them • more cards (about 21 in a class of 30) with ’insect’ written on them. • one larger bag, big enough to hold all the cards • a method of marking out an area of ground outside, for example, traffic cones (you could borrow something from the sports department, or you might be able to use a marked-out part of a pitch used for sports) • a clipboard and paper so that someone (the teacher, or the eagle) can record results M Method PL E • Mark out an area big enough for people to run around. It could perhaps be 25 m by 25 m, but the exact size does not matter. 2 Spread all of the coloured tokens randomly in the marked-off area. 3 Put all of the cards into the large bag. Each person puts a hand into the bag and takes one card. SA 1 4 Everyone takes a small bag, and then stands on the edge of the marked-off area. 5 One person (it could be your teacher) starts a stopwatch and says: ‘Go!’ Each ‘insect’ goes and ‘feeds’ in the area. They do this by picking up tokens and putting them into their bags. Only one token can be picked up at once! 6 After 15 or 20 seconds, the timer shouts: ‘Stop!’ The insects stop feeding. Each ‘insect’ counts the tokens in their bag. They count how many tokens of each colour they have. The recorder writes down the results for each ‘insect’. 7 The timer starts the stopwatch again, and the ‘small birds’ go and feed on the ‘insects’. They do this by tapping an ‘insect’ on the shoulder. The captured insect transfers their tokens into the small bird’s bag. A ‘small bird’ can only eat one ‘insect’ at a time. 139 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 4 Ecosystems Continued 8 After 15 or 20 seconds, the timer shouts: ‘Stop!’ The ‘small birds’ stop feeding. The ‘insects’ (whether or not they have been eaten) move outside the marked area. Each small bird counts the tokens in their bag. The recorder writes down how many tokens of each colour each small bird has. 9 Now repeat steps 6 and 7, but this time the ‘eagle’ feeds on the ‘small birds’. Questions 1 2 PL E 10 Go back into your classroom. The recorder can now write all of the results onto the board. a Calculate the mean number of red tokens that an ‘insect’ collected. b Calculate the mean number of red tokens that a ‘small bird’ collected. c How many red tokens did the ‘eagle’ collect? Copy and complete this 'food chain', using your results. insects … red tokens each small birds à … red tokens each eagle à … red tokens each Explain why the mean number of red tokens that each animal has, increases as you go along the food chain. 4 Now imagine that the red tokens represent DDT. What happens to the amount of DDT in an animal’s body, as you go up the food chain? Why does this happen? 5 In this activity, you modelled what happens to DDT in a food chain. Do you think this is a good model of what happens in a real ecosystem? Explain your answer. SA M 3 Bioaccumulation and biomagnification Imagine that DDT has been sprayed onto some water. Tiny algae take up some of the DDT. Shrimps eat the algae, and fish eat the shrimps. Cormorants (fish-eating birds) eat the fish. All the DDT in all of algae that a shrimp eats over its lifetime accumulates, or builds up, in its body. The longer the organism lives, and the more DDT it takes in, the more DDT it gets in its body. This process is called bioaccumulation. All of the DDT in all of the shrimps that a fish eats accumulates in the fish’s body. Eventually, all the DDT in all of the fish that a cormorant eats in its lifetime accumulates in the cormorant’s body. 140 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 4.4 Bioaccumulation This means that the concentration of DDT in an animal’s body increases as you go up the food chain. This is called biomagnification. DDT is sprayed onto water, to kill mosquito larvae. water 0.000 05 ppm minnows 0.50 ppm Shrimps eat a large quantity of protoctists. protoctists 0.04 ppm Minnows eat shrimps. shrimps 0.16 ppm SA Questions Cormorants eat minnows. cormorants 26.40 ppm M Tiny single-celled protoctists absorb DDT. PL E The next diagram shows how the concentration of DDT in the bodies of species in a food chain increases along the chain. The concentration is measured in parts per million (ppm). This is the number of grams of DDT in one million grams of the organisms. 1 How many times greater is the concentration of DDT in a cormorant’s body than in a minnow’s body? 2 Explain, in your own words, why the concentration in the cormorant is greater than in a minnow. People often get confused between bioaccumulation and biomagnification. How will you try to remember the difference between them? 141 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 4 Ecosystems Activity 4.4.1 Biodegradable insecticides Work in a group of three for this activity. Some insecticides are biodegradable. This means that they can be broken down by microorganisms in the environment, or inside an animal’s body. Questions PL E In your group, discuss these two questions. 1 Do you think biodegradable insecticides show biomagnification? Explain why. 2 Why doesn’t everyone stop using DDT, and change over to using biodegradable insecticides? Be ready to share your ideas with the other groups in your class. Summary checklist SA M I can explain what is meant by bioaccumulation. I can explain why DDT shows bioaccumulation. I can explain why organisms at the top of a food chain have higher concentrations of DDT in their bodies than organisms at the base of the food chain’ 142 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 4 Ecosystems Check your progress PL E 4.1 Tropical rainforests are very complex ecosystems. Many different species live in a tropical rainforest. Bromeliads are plants that grow in a tropical rainforest. They often grow on tall forest trees. b c [2] Suggest the advantages to bromeliads of growing in their particular habitat. [2] Suggest the advantages to the frog of living in their particular habitat. [2] Explain the difference between an ecosystem and a habitat. [2] SA d Use the photographs to describe two habitats in the tropical rainforestecosystem. M a Bromeliads have spiky leaves arranged in circles. They trap rainwater in their centres. Small animals often live in the little ponds in a bromeliad plant. 4.2 Coral reefs are formed by tiny animals called coral polyps. Their hard skeletons provide many different habitats where other species can live. One of these species is a single-celled alga that makes a toxic substance called ciguatoxin. Herbivorous fish eat the alga. Carnivorous fish eat the herbivorous fish. Humans often eat the carnivorous fish. a Thousands of different species live on coral reefs. Use the information to suggest why so many species can live there. [2] b What is meant by a toxic substance? [1] c Use the information to construct a food chain. [3] 143 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 4 Ecosystems d Ciguatoxin does not break down inside a fish that has eaten it. Instead, it builds up in the head, liver and skin of the fish. What is the name for this process? Choose one of these words. [1] People who have eaten fish containing ciguatoxin can become very ill. Suggest why eating a carnivorous fish is more likely to make you ill than eating a herbivorous fish. [2] PL E e bioaccumulation ecosystem poisoning 4.3 Winged loosestrife is a plant with purple flowers. It grows in North America. Purple loosestrife also has purple flowers. It normally lives in Europe and Asia. It is an introduced species in North America. Both species of loosestrife are pollinated by insects. After pollination, the flowers produce seeds. M Scientists noticed that numbers of winged loosestrife plants were decreasing in places where purple loosestrife had been introduced. They did an experiment to test this hypothesis: SA When purple loosestrife is present, fewer winged loosestrife flowers are successfully pollinated. • They grew plants of winged loosestrife in pots. They also grew plants of purple loosestrife in pots. • When all the plants had flowers, the scientists arranged the pots in a field. They used two different patterns. Key winged loosestrife plant purple loosestrife plant 144 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 4 Ecosystems • The scientists counted how many insects visited the flowers on each plant, over a 15 minute period. • They left the plants in their pots until they produced seeds. Then they counted how many seeds each plant produced. Their results are shown in the table. Mean number of insect visits per plant in 15 minutes Mean number of seeds per plant winged loosestrife alone 35 80 winged loosestrife and purple loosestrife 26 58 PL E Arrangement of plants Explain what is meant by an introduced species. [2] b Explain why the scientists used two different patterns, when they put the plants in the field. [3] Describe how the presence of purple loosestrife affected the number of insect visits to winged loosestrife. [2] d Do the results support the scientists’ hypothesis? Explain your answer. [2] e Suggest two ways the scientists could improve their experiment. Explain each of your suggestions. [4] SA c M a 145 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. Project Project: Impact of an introduced species This project is about how people develop and use scientific understanding, and how the uses of science can have a global environmental impact. Your task Work in a group of three or four. You are going to investigate how a new or invasive species has affected an ecosystem. PL E Use the internet to find an example of a species that has been introduced into an ecosystem in your country. Try to answer some of these questions. Where does the species normally live? • Why and when was the new species introduced to your country? • How has it affected the ecosystems it has been introduced to? • Is it an invasive species? If so, why is it invasive in your country, but not its native country? • Why did people not realise that the species might be a problem, when it was first introduced? How has understanding improved over time? • Are people trying to eradicate or control the species? If so, how are they doing this, and how successful are they? Is everyone happy about this, or do some people want to protect the species? M • SA Make a presentation about your findings, ready to share with others. 146 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 5 Materials and their structure In this topic you will: PL E 5.1 The structure of the atom • describe the structure of the atom • list the particles found in an atom • describe some of the properties of the particles found in an atom SA M Getting started These three cups have been filled with water. Would you expect these three cups to have: a exactly the same mass b masses that were nearly the same c masses that were very different? Key words atoms deflected electrical charge electrons electrostatic attraction neutrons nucleus protons sub-atomic particles Discuss this with a partner. Give reasons for your choice. 147 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 5 Materials and their structure Atoms In stage 7 you learnt that atoms are so small that you cannot see them without using the most powerful microscopes yet invented. The word ‘atom’ comes from a Greek word that means ‘cannot be split’. All the atoms of a particular element are the same. Different elements have different atoms. PL E What is an atom like? Scientists have discovered that atoms are made up of even smaller particles, called sub-atomic particles. Atoms are made up of three kinds of particles protons, neutrons and electrons. The particles are arranged in a similar way in all atoms. The protons and neutrons are grouped closely together in the centre of the atom. They form the nucleus of the atom. (Be careful not to confuse the nucleus of a cell with the nucleus of an atom.) − proton + neutron electron + nucleus − A helium atom The electrons move around the nucleus. M The three different particles in an atom have different properties. Protons and neutrons have much more mass than the electrons. In fact, electrons have almost no mass. • Protons and neutrons have the same mass. • Protons have a positive electrical charge. • Neutrons have no electrical charge. • Electrons have a negative electrical charge. SA • There is a lot of empty space between parts of the atom. This space really is completely empty – there is nothing in it at all. There is an attraction between the positive and negative charges. This electrostatic attraction between the positive charge on the protons and the negative charge on the electrons is what holds individual atoms together. 148 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 5.1 The structure of the atom Questions Which particle has a positive electrical charge? 2 Which of the three particles has the smallest mass? 3 Which particles make up the nucleus of an atom? 4 The size of the negative charge of an electron is exactly the same as the size of the positive charge on a proton. What is the overall charge of the helium atom shown in the diagram? 5 How are the individual atoms held together? PL E 1 How did scientists come up with this model of the structure of the atom? Scientists from many different parts of the world have worked on a number of different ideas that have led to the model of the atom, that they use today. M In the late 1890s a British scientist called J.J.Thompson discovered the electron. His model for the atom was that the electrons were scattered throughout the structure of the atom. It is sometimes called the ‘plum pudding model’ because the particles are arranged randomly throughout the model, like fruit in a cake or pudding. positively charged matter − − − − − − SA − − electrons − − Thompson’s model of the atom 149 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 5 Materials and their structure One of Thompson’s students was originally from New Zealand. His name was Ernest Rutherford. Rutherford discovered the proton in 1909 and the nucleus in 1911. Rutherford’s most famous experiment was the gold foil experiment. particle source PL E In this experiment Rutherford fired fast moving particles, smaller than an atom, at very thin gold foil. Most of the particles passed straight through the foil. Only a few of the particles (about 1 in 8000) were deflected in various directions. (Deflected means that the direction of the particle was changed.) gold foil particle detector Ernest Rutherford rare particle bounces back Rutherford’s gold foil experiment particles that have passed through the foil M The results of this experiment led Rutherford to have the idea that the gold atoms must be mostly empty space, with their particles packed into a dense nucleus at the centre. This helped to move towards the model of the atom that scientists use today. Rutherford’s model of the atom looked like this. SA James Chadwick also worked with Rutherford and Thompson. In 1932, he proved that neutrons exist. This discovery moved the model of the atom closer to the one scientists use today. When scientists make a discovery, they write about what they have done and what they think it means. Sometimes, if the work is very complicated, many different scientists may be involved. These different scientists can even be in different countries, still working together. This is called collaboration. Other scientists then look closely at the findings to see if they can repeat the experiments and that if the discovery is true. Some scientists actively look for mistakes in the work, or whether the conclusions about the results are wrong. This is called peer review. − − ++ + +++ − − − − Rutherford’s model of the atom Tunnel in the Large Hadron Collider 150 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 5.1 The structure of the atom Questions 6 7 8 9 PL E The stories of these scientists show how people from all over the world work together to develop their ideas. Each scientist builds on the ideas and the discoveries of others. Chadwick, Rutherford and Thompson won Nobel prizes for their work. Their experiments and ideas have helped us to understand the structure of the atom. There is still a lot we do not know about atoms. Scientists continue to work to improve our understanding of the structure of the atom. For example, scientists from all over the world are using the Large Hadron Collider in Switzerland to further understand the structure of matter. Explain how Thompson’s model of the atom is different from the one scientists use today. Who discovered the electron and when did they discover it? Who proved that the neutron existed and when did they do this it? What two things did Rutherford discover about the structure of the atom? 10 How is Rutherford’s model different from the model scientists use today? M Activity 5.1.1 An atomic timeline SA In a group of three, make a time line of the discoveries that have led to the model of the atom we use today. Do some research on the three scientists J. J. Thompson, Ernest Rutherford and James Chadwick. Find out where and when they worked and some personal details; add this to your time line. How does the use of a model help me to understand the structure of the atom? Summary checklist I can describe the structure of the atom I can list the particles found in an atom I can describe some of the properties of the particles found in an atom I can describe some of the discoveries that have helped to create the model of the atom that is used today. 151 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 5 Materials and their structure 5.2 Purity In this topic you will: explain what is meant by purity • calculate percentage purity • describe how it is difficult to get a pure product Getting started PL E • Answer the three questions on your own and then check with a partner. Be ready to share your answers with the class. 1 What does it mean if a substance is pure? 2 Which of these items are pure substances? Key words carat suggest translucent sodium chloride; oxygen; sea water; gold; orange juice; copper oxide; silver nitrate; soil; black ink; potassium. Of the items in question 2, which are elements, mixtures and compounds? SA M 3 152 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 5.2 Purity Pure elements If an element is pure; it means that every one of its atoms is exactly the same and made of just one type of atom. For example, pure gold is made of gold atoms. However, an alloy of gold may contain other metals such as copper or silver. PL E When you buy gold it is usually marked to state if it is pure gold (24 carat) or an alloy such as 18 carat or 9 carat. This is a measure of its purity. The more gold it has, the higher its purity. 18 carat gold has 18 parts out of 24 that are gold; the rest (6 parts out of the 24) is made up of other metals such as silver or copper. 18 carat gold has a purity of 75%. To calculate this: 18 × 100 = 75% __ 24 SA M The photograph shows samples of 8 carat, 14 carat, 18 carat, and 24 carat gold. You can see that the colour changes from slightly coppery to yellow-gold. When silver is sold, it is usually marked with the number of parts per thousand that are silver. So, silver marked 925 has 925 atoms out of 1000 that are silver and 75 atoms of some other metal. You can see this mark in the photograph of the silver ring. Silver marked 900 is of lower purity than that marked 925. This silver ring has the mark 925. The ring contains 925 parts silver out of 1000 parts. 925 × 100 = 92.5% ____ 1000 So, it is 92.5% pure silver. 153 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 5 Materials and their structure Diamonds are made from the element carbon. The carbon atoms are arranged in a particular way. If they are pure, diamonds contain no other elements. Pure diamonds are colourless and translucent (lets the light through). A yellow diamond SA M A pure diamond PL E If diamonds have other elements mixed in with the carbon atoms, they can be different colours. For example, if a few carbon atoms per million are replaced with nitrogen, the diamond will be yellow. If some carbon atoms are replaced by atoms of the element boron, then the diamond will be blue. The rarest of all is a green diamond, formed when one atom per 1000 of carbon atoms is replaced by nitrogen, nickel or hydrogen. A blue diamond A green diamond Questions 1 What percentage of 9 carat gold is gold? 2 What percentage of silver is in silver marked 900? 3 Which element mixed with carbon in diamonds makes them blue? 4 Which elements may cause a diamond to be green? 154 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 5.2 Purity Seawater PL E Seawater is made up of water and various salts such as sodium chloride. If you want to obtain sodium chloride from seawater you can evaporate off the water. In some countries this is done by letting seawater fill flat and shallow areas called beds, and allowing the water evaporate in the heat from the Sun. If you are trying to obtain pure sodium chloride this will be a problem because sodium chloride is not the only salt that is dissolved in seawater. If you take 1000 g Workers carrying salt in Nha Trang, Vietnam of seawater, about 350 g of it is made up of salts. Of this 350 g, about 68% is sodium chloride, the rest is made up of magnesium chloride, sodium sulfate, calcium chloride and some other salts. If you want pure sodium chloride, you need to do some work to remove the other salts. Salts are compounds made from acids. The names tell you which acid has been used to form them. For example, sodium chloride from hydrochloric acid and sodium sulfate from sulfuric acid. M seawater water 96.5% sodium chloride 68% SA salt 3.5% salt from seawater magnesium chloride 14.6% sodium sulfate 11.4% calcium chloride 3.1% other salts 2.9% The sodium chloride that is obtained from this seawater is only 68% pure. The mass of sodium chloride in 1000 g seawater is: ____ 35 × 68 = 23.8 g 1000 Questions 5 Draw up a table to show the percentage of salts found in seawater. 6 What mass of magnesium chloride would you expect to find in the seawater sample? 155 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 5 Materials and their structure Think like a scientist Finding the mass of salts in seawater You will need: • an evaporating basin • safety glasses • tongs • Bunsen burner • tripod • pipe-clay triangle • access to a top pan balance • seawater sample PL E Method 1 Read through the method and think very carefully about any risks there may be when you carry out this task. Write a risk assessment. 2 Place an evaporating basin on a top pan balance and record the mass. 3 Add some seawater and find the mass of the seawater. 4 Heat the seawater until it begins to spit. Remove from the heat and allow the rest of the water to evaporate. 5 When there is no longer any water remaining and the basin is cool, find the mass of the salts. FPO Questions 2 3 SA 4 5 What mass of salts did you obtain from the seawater? What percentage of the seawater is this? About 68% of the salt in seawater is sodium chloride. Estimate the mass of sodium chloride in your sample. Is this about what you expected? If not, why not? What difficulties did you have carrying out this investigation? How did you try to overcome them? What safety measures did you have in place whilst carrying out this investigation? M 1 6 Pure products When a chemical reaction takes place and a product is formed from the reactants, it is often very important that the product is pure. For example when medicines are being made, the product needs to be free from any impurities that may upset the way the medicine works or that do the patient harm. When there is a simple reaction there is only one product. magnesium + oxygen magnesium oxide 156 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 5.2 Purity In other reactions there may be more than one product. When there is more than one product they are mixed up together. These products will need to be separated and purified to produce whichever pure product you want. The products may also be mixed up with some of the reactants if they have not all been used up in the reaction. sodium nitrate + silver chloride sulfuric acid + sodium hydroxide sodium sulfate + water barium chloride + sodium sulfate barium sulfate + sodium chloride PL E silver nitrate + sodium chloride potassium nitrate + lead iodide copper carbonate + hydrochloric acid copper chloride + water + carbon dioxide SA M lead nitrate + potassium iodide 157 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 5 Materials and their structure Think like a scientist Reactions with more than one product You will need: • safety glasses • test tubes • test tube racks • universal indicator solution • conical flask • measuring cylinder • burette • boiling tube • delivery tube with bung • clamp stands • safety glasses • limewater Safety PL E • chemical reactants as in the examples above You must wear safety glasses to carry out all these reactions. Wash your hands after handling any chemicals. Method Use the equations above as examples of chemical reactions you could carry out. You can try other reactions if your teacher prefers. Remember than if you are going to do a burette neutralisation reaction you will need to measure the reactants carefully. Carry out a risk assessment for each reaction you attempt. M Reaction 1 sulfuric acid Silver nitrate is an irritant. Take care when you use it. SA Half fill a test tube with silver nitrate solution. Place some silver nitrate solution in a test tube and slowly add some sodium chloride solution. Reaction 2 Sulfuric acid and sodium hydroxide are irritants take care when you use them. Fill the burette carefully using a small funnel. conical flask sodium hydroxide and universal indicator Your teacher may want to do this as a demonstration as a burette can be difficult to use. Place a measured 20 cm3 volume of sodium hydroxide in a conical flask. Add a few drops of universal indicator solution. Put sulfuric acid in the burette and add to the flask until the alkali is neutralised. Take care when you use the burette and ask for help if you have not used one before. 158 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 5.2 Purity Continued Reaction 3 Barium chloride is harmful if swallowed. Half fill a test tube with barium chloride solution and add sodium sulfate solution. Reaction 4 Reaction 5 delivery tube PL E Place lead nitrate in a test tube and add potassium iodide. Wash your hands after handling lead compounds. Copper carbonate is harmful so wash it off you skin if you spill any. rubber bung boiling tube hydrochloric acid test tube limewater Place a few spatulas of copper copper carbonate carbonate in a boiling tube and add hydrochloric acid. Place the delivery tube bung in the mouth of the boiling tube and allow the gas to be passed into water or limewater. Questions Record each reaction you carry out. For each one, write the word equation and your observations. 8 For each reaction suggest or offer ideas on how the products could be separated and purified. 9 What safety measures did you have in place whilst carrying out these reactions? SA M 7 What does ‘pure’ mean? When chemical reactions take place how can you be sure you have a pure product? Summary checklist I can explain what is meant by purity I can calculate percentage purity I can explain why it is difficult to obtain a pure product. 159 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 5 Materials and their structure 5.3 Weather and climate In this topic you will: learn the difference between weather and climate • make observations of the weather Getting started Key words PL E • atmosphere climate climatology humidity meteorology statistics visibility weather SA M With a partner, write down as many words about the weather as you can. Be prepared to share them with the class. You must be ready to explain the meanings of the words you write down. 160 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 5.3 Weather and climate What is weather? When you look out of the window, what is the weather like? What people mean by weather is the state of the atmosphere and its changes from minute to minute, hour to hour, day to day, or week to week. In some places, the weather is very similar each day but in others the weather changes frequently. PL E When people talk about the weather they say things such as, ‘What is the weather like today?’, ‘How hot is it today?’ or ‘Will it rain tomorrow?’ They are thinking in the short term. People generally think about weather as the combination of temperature, humidity, precipitation, cloudiness, visibility and wind. M Countries all over the world take careful measurements of the weather to help predict what will happen next, to see patterns in the weather and to provide information about the weather over time. For example, it is important to be prepared for snowstorms or heat waves as they can affect the transport systems, production of food, how much power people need to run their homes, and even what they want to buy in the shops. SA Scotland Namibia New Zealand Canada Republic of Ireland Bangladesh 161 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 5 Materials and their structure Questions 1 Describe the weather in each of the photographs. Use as many of the words from the Getting started task as you can. 2 Why do scientists take careful measurements of the weather? Activity 5.3.1 Recording the weather PL E In this activity you will record the details of the weather over a period of at least a week. Method 3 In your group, discuss which weather features you will be able to measure and/or observe. Share these ideas with the class. 4 After the discussion make a list of the weather features that you will measure and/or observe. 5 Decide how your group will collect this information. What equipment will you need? You may need to do some research to decide this. You may need some laboratory equipment. A camera might also be useful as you could take photographs to record cloud cover. M Remember that the readings should be taken at the same time each day. The temperature should be taken in the shade, not in full sun. The bulb of the thermometer should not be touching anything other than the air. 6 Prepare a results table to record your findings. 7 Record your findings each day for at least a week. Questions Why should the readings be taken at the same time each day? SA 1 2 Why are the temperature readings always taken in the shade? 3 Write a report about the changes in the weather over the week. In this report you should present your observations in an appropriate way. 4 Plot a graph to show the changes in temperature over the week. 5 Compare your readings with someone else in your class. Are there any differences and, if so, can you give reasons for the differences? Is this comparison a fair comparison? 6 Compare your readings with those that are recorded nationally. You could use the internet to find these. Are yours different and, if so, explain why yours are different. Is this comparison a fair one? 162 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 5.3 Weather and climate Activity 5.3.2 Finding out about the weather. In this activity you will find out information about the weather in a particular place and evaluate the information you find. Work with a partner. Choose a particular place anywhere in the world. Perhaps it is somewhere you might like to go on holiday, to have a beach holiday, to go skiing or to learn how to sail a boat. 2 Find as much information as you can about the weather in that place. For example: you may need to know: What is the average number of hours of sunshine? How much rain is expected? How windy is it? How much snow there will be? PL E 1 Make sure you find information from different sources. You might look at web sites such as; travel agents, the national weather information or local weather watchers. You could also look at past weather records over a few years and compare them. • Is the information you find from all sources exactly the same? • Can you suggest why this is? • Which source of information do you think is more reliable? • Could some sources be biased? Perhaps someone wants to give the best view of the weather to encourage you to go there. Present your findings, as a poster or a talk, and suggest the best time of year to visit your chosen place. Use the suggested questions as a starting point to explain which sources of information you have used and how much you feel able to trust the information. SA 4 Think about these questions and discuss them with your partner. M 3 How can I explain the difference between the weather and the climate where I live? 163 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 5 Materials and their structure Weather or climate? What is the difference between weather and climate? When people talk about climate, they mean the weather of a place over a much longer time, usually more than 30 years. Weather can change in a few hours or even in minutes. PL E Climate is the average weather in an area and takes several years to change. Climate information includes the statistics of weather information that tells us about the normal weather as well as the range of extreme weather at that place. Weather is affected by factors such as temperature, humidity, cloudiness and precipitation. Climate is affected by two key factors: temperature and precipitation. The study of weather is called meteorology. The study of climate is called climatology. Climate zones SA M The map below shows the main climate zones on Earth. The key shows the names of these zones. Key polar tundra mountains temperate mediterranean arid tropical 164 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 5.3 Weather and climate Each zone has a characteristic climate. Description of climate Polar very cold and dry all year Temperate cold winters and mild summers Arid hot and dry all year Tropical hot and wet all year Mediterranean mild winters and hot, dry summers Mountains/tundra/taiga Questions PL E Climate zone very cold all year Which climate zone do you live in? 4 Name two countries that are in the arid zone. (You may need to use an atlas to help you.) 5 Name two countries that have areas with a Mediterranean climate but are not near the Mediterranean Sea. 6 Name three countries that are in the tropical zone. 7 What is the difference between the climate in the arid zone and the tropical zone? 8 What are the differences between the climate in the temperate zone and the Mediterranean zone? M 3 SA What do I notice about how the climate zones are distributed? Summary checklist I can explain the difference between weather and climate I can make observations and take measurements of the weather 165 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 5 Materials and their structure 5.4 Climate and ice ages In this topic you will: learn about how the Earth’s climate has changed in past • find out about ice ages, glacial periods and interglacial periods • look at some of evidence that the Earth’s climate cycles between colder and warmer periods. Getting started PL E • boulder cycled glacial period glaciers ice ages interglacial period peat bog M The photgraph shows the body of a baby mammoth, which has been named Yuka. Her frozen body was discovered in 1977 in eastern Siberia. In that part of the world, it is so cold that the lower layers of the soil stay frozen solid all year round. Scientists think that Yuka lived and died about 39 000 years ago, when the temperature was even colder than it is now. Key words SA With a partner, discuss why Yuka’s body has been preserved for so long. Be ready to share your ideas with the rest of the class. 166 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 5.4 Climate and ice ages Ice sheets PL E Look back at the photograph in the Getting started section. When Yuka was alive, and for thousands of years afterwards, the Earth was much colder than it is now. The map shows the parts of the world that were covered by ice sheets 25 000 years ago. Key M ice sheet Activity 5.4.1 SA Where in the World is there ice? Working in a group of three or four, use an atlas to find out which parts of the Earth are covered with ice today. Compare this with what the Earth looked like 25 000 years ago. Be ready to share your ideas. Questions 5 Name a part of the Earth that was covered with ice 25 000 years ago, but is no longer covered with ice. 6 When you look at the parts of the Earth that are covered with ice today what do they have in common? 167 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 5 Materials and their structure Glacial and interglacial periods The very cold period when Yuka lived lasted until about 10 000 years ago. Because so much of the Earth was frozen, it is called a glacial period. ‘Glacial’ means ‘frozen’. Today, the Earth is in an interglacial period. ‘Inter’ means ‘between’. Over the last 450,000 years, the Earth’s climate has cycled or swung between glacial and interglacial periods. In an interglacial period, there is permanent ice close to the North and South Poles. • In a glacial period, the ice spreads much further south from the North Pole and further north from the South Pole. PL E • Ice ages When Yuka was alive, the Earth was in a glacial period. Much more of the Earth was frozen than now. Looking even further back in time, scientists have found that this cycle of glacial periods and inter-glacial periods did not always happen. There were long periods of time when Earth was so warm that there was no permanent ice on its surface, not even at the North Pole or South Pole. M In between these warm periods, there were cold periods, with glacials and interglacials. These cold periods are called ice ages. SA The graph in below shows when scientists think the ice ages happened on Earth. They think the second one, which began about 850 million years ago, was the coldest. Some scientists think that the whole Earth was covered with ice and snow then. The Earth was like a giant snowball. 25 ice age ice ice ice age age age ice age 20 Average global temperature 15 in °C 10 5 2500 2000 1500 1000 Millions of years ago 5 500 today 0 Temperature at a site a little North of the -5 South Pole in °C -10 interglacial periods glacial periods 400 000 300 000 200 000 100 000 today Years ago 168 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 5.4 Climate and ice ages Questions 1 How many ice ages do scientists think there have been on Earth? 2 Is the Earth in an ice age now? Explain why you think that. 3 Explain the difference between a glacial period and an ice age. 4 Is the Earth in a glacial period now? PL E How do scientists know the Earth was colder in the past? The photograph shows some boulders (big rocks) in California, USA. People have often wondered how rocks like this got into their strange positions. The best explanation is that they were carried there by ancient glaciers. Glaciers are rivers of ice that move slowly downhill (they are formed from snow that over many years becomes compressed into thick masses of ice). The glaciers carry rocks with them. If the glacier melts, the rocks are left behind. Sometimes, scientists can see scratches on the rock surfaces, where the moving ice dragged other rocks across them. These rocks are in Yosemite National Park, in California. Scientists think they were left behind when a glacier melted, thousands of years ago. SA M Boulders like this were the first clue that glaciers used to be present in parts of the Earth that are much warmer now. Later, other evidence was found that supports this idea. For example, in places that are now quite warm, it is possible to find fossils of animals and plants that were adapted to live in very cold places. Questions 5 Use an atlas or the internet to identify and list glaciers nearest to where you live. 6 When rivers run through rock, they wear the rock away. This sometimes creates very deep valleys, such as the Grand Canyon in Arizona. When glaciers moved millions of years ago, they left their mark on the landscape. Find out about and describe the effect that glaciers had on the land. A glacier in Iceland 169 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 5 Materials and their structure Pollen evidence for glacial and interglacial periods Scientists can use pollen to find out what kind of plants lived long ago. SA M PL E In New Zealand, a scientist extracted a core of soil from a peat bog. When plants die they normally decay. In some conditions, without oxygen and slightly acid, the decay is very slow and a peat bog may be formed. The different layers of peat represent different periods of history, the deeper the peat, the older it is. Scientists can take samples of the peat bog by using an instrument called an auger and remove a core of the peat bog. They must be careful to remove the core and keep it in the correct order so that they know which part is oldest. This scientist is using an auger to extract a core sample. A core sample from a peat bog showing different layers. The deepest level of the soil in the core was formed 237 000 years ago. The scientist collected pollen from different parts of the core. He identified the plants from which the pollen came. Because he knew the type of climate that each kind of plant can live in, he was able to work out what the climate was like between years ago and now. 170 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 5.4 Climate and ice ages Depth (cm) Core 0 Years ago 400 500 interglacial 11 000 14 500 17 300 27 280 48 000 75 000 600 700 800 900 127 000 1000 Summary checklist Climate warms, ice retreats, lake becomes a bog. cold climate, subalpine vegetation glacial Climate cools, grassland increases, forest decreases. PL E 300 Climate cycle mainly lowland forest 100 200 Environment Warm climate forest expands. interglacial cold climate vegetation with glacier nearby glacial SA M I can describe how the Earth’s climate has changed in the past I can explain the difference between ice ages, glacial and interglacial periods I can give some evidence that the Earth’s climate cycles between colder and warmer periods. 171 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 5 Materials and their structure 5.5 Atmosphere and climate In this topic you will: learn about the atmosphere of the Earth • learn how a change in the atmosphere can affect the climate • learn about renewable resources PL E • Check your understanding Key words What is an ice age? What evidence is there to show that the Earth’s climate was different in the past? analogy biodegradable bioplastics deforestation emissions fossil fuels global warming greenhouse effect locked up photosynthesis recycled renewable resources SA M Think about the two questions. Write down your ideas. Then discuss them with a partner. Together sort your ideas out and be prepared to share them with the class. 172 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 5.5 Atmosphere and climate The atmosphere The atmosphere is a layer of gas above the Earth’s surface. It is very different today from the atmosphere when the Earth formed billions of years ago. Earth’s atmosphere PL E Scientists think that the Earth was formed about 4600 million years ago. The Earth was very hot and it was molten for millions of years. Then, as the Earth cooled, a solid crust formed. There was a lot of volcanic activity, much more than there is now. The volcanoes produced gases, which formed the early atmosphere. Water vapour was produced by the volcanoes and, as the Earth cooled, this water vapour condensed into liquid water. The water fell as rain and formed the first lakes and oceans. About 4000 million years ago, scientists think that the atmosphere contained mainly carbon dioxide, little or no oxygen, small amounts of the gases methane and ammonia, and some water vapour. This early atmosphere on Earth was like the atmosphere on Venus is today. The temperature on Venus is very high – on the surface, it is which is hot enough to melt lead. 4% water vapour Earth’s atmosphere today M Earth’s early atmosphere traces of nitrogen, ammonia, methane 21% oxygen 78% nitrogen average surface temperature above 400 °C average surface temperature 20 °C SA 95% carbon dioxide traces of carbon dioxide, water vapour, ammonia, methane Questions 1 Where did the early atmosphere on Earth come from? 2 Give at least two differences between the early atmosphere on Earth and the atmosphere today. 3 Explain why the Earth’s early atmosphere was not suitable for us or any other animals. 173 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 5 Materials and their structure Changes to the atmosphere PL E About 3500 million years ago, micro-organisms developed on Earth. They lived in the oceans and used the carbon dioxide in the atmosphere to make food. They produced oxygen as a waste product of this process. As plants developed over millions of years, they began to grow on land. Plants use carbon dioxide to produce food (glucose, a sugar) by the process of photosynthesis. carbon dioxide + water glucose + oxygen The levels of oxygen in the atmosphere continued to rise. Scientists know this because there was enough oxygen to combine with iron in the rocks to form iron oxide. These rocks in Dallo, Ethiopia have bands of red iron oxide and date from about 2.1 to 2.0 billion years ago. By 200 million years ago there was very little carbon dioxide left in the atmosphere. Most of the carbon had been used to make the chemicals, which are part of all living things. M When the organisms die and rot, the carbon in them is released back into the environment. It is recycled. Some organisms do not rot when they die and are turned into fossil fuels such as oil or coal. The carbon is locked up in the fossil fuels until they are burned them. SA Many organisms with shells evolved around 600 to 400 million years ago. The shells are made from calcium carbonate, CaCO3. When these shelled animals died and fell to the bottom of the oceans as sediment the many layers of shells pressing down on each other formed rocks, such as limestone. So carbon is also locked up in these rocks. Fern fossil in coal This limestone is full of fossils of animals with shells. 174 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 5.5 Atmosphere and climate Questions What are fossil fuels? 5 How did the carbon dioxide in the atmosphere get used up? 6 What evidence is there that the levels of oxygen rose? 7 What two elements are present in carbon dioxide? 8 What three elements are present in calcium carbonate? 9 Limestone is a sedimentary rock. How is it formed? PL E 4 10 When did carbon first start to be locked up? Atmospheric changes today The amount of carbon dioxide in the atmosphere fell until about 200 years ago. Then the levels of carbon dioxide began to rise. Where is the carbon dioxide coming from? Humans caused this rise because they started to release the carbon that had been locked up in the Earth for millions of years. They burn fossil fuels, such as oil and coal, to keep themselves warm. carbon + oxygen carbon dioxide SA M As humans developed industry and transport, they have burned more and more oil and coal. So there are greater emissions of carbon dioxide. Humans use a lot of fossil fuels to generate electricity in power stations. A container ship burning dieselBrick factories producing waste gases from fossil fuel Cars burning petrol 175 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 5 Materials and their structure M PL E Humans also make the situation worse as they cut down forests of large established trees that use a lot of carbon dioxide in photosynthesis. This deforestation is done for many reasons: to use the wood for building or to make things, to get to resources such as minerals which are mined, to produce crops for profit such as palm oil, to grow more food crops, or to provide pastures for animals such as cattle. Because there are fewer trees, less of the carbon dioxide is being used up, so the level in the atmosphere increases. Cattle eat the grass and produce carbon dioxide and gases such as methane in their intestines. This also changes the atmosphere. This forest is being cut down to provide wood. Many of the trees in this forest have been cut down to grow palm oil plants This forest is being cut down to provide more land for agriculture. SA When limestone, which consists of calcium carbonate, is used to make other products such as building cement, the carbon in the calcium carbonate is released into the atmosphere. calcium carbonate calcium oxide + carbon dioxide All these things lead to a change in the atmosphere and an increase in carbon dioxide levels. Atmospheric changes and climate There is evidence that the carbon dioxide and other gases, such as methane, act like a blanket around the Earth. This is an analogy. The ‘blanket’ represents the gases that keep the Earth warm. Another analogy is that the gases are like putting the Earth in a greenhouse. A greenhouse lets in light and heat from the Sun, but heat energy is trapped inside. 176 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 5.5 Atmosphere and climate Think about how an analogy can help you to understand an idea? 5 atmosphere PL E The layers of gases produce the greenhouse effect. This is a natural effect; without it, the Earth would be much colder. However, increasing the levels of greenhouse gases, such as carbon dioxide, methane and water vapour, increases the greenhouse effect. So, as the levels of carbon dioxide, methane and water vapour increase, the amount of heat escaping decreases, and so the Earth’s climate becomes warmer. This is known as global warming. 2 4 Earth 3 Sun SA M 1 177 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 5 Materials and their structure Think like a scientist The greenhouse effect You will need: • • • three large plastic bottles, such as 2 litre drinks bottles with lids, with a hole in each lid three thermometers a means of fixing the thermometers in place (such as modelling clay) carbon dioxide supply PL E • °C thermometer modelling clay 100 100 100 90 90 80 80 80 70 70 70 60 60 60 50 50 50 40 40 40 30 30 30 20 20 20 10 10 10 0 0 0 extra carbon dioxide extra water normal air SA Method °C 90 M plastic bottle °C 1 Place a thermometer in each of the bottles so that the bulb does not touch the bottle in any way. 2 Add some carbon dioxide to one bottle. 3 Add about 5 cm3 of water to another bottle. 4 Leave the third bottle with normal air. 5 Label the bottles. 6 Place the bottles alongside one another outside. If this is not possible, you can leave them in the classroom near the window. 7 Take the temperatures in each bottle at the start. 8 Record the temperatures in the three bottles over the next few days. You decide when and how often. 178 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 5.5 Atmosphere and climate Continued Questions What did you consider when deciding when and how often to take readings? 2 Present your findings in a table. 3 What do your results show? 4 Why did you have one bottle with normal air in it? 5 Can you explain why you got these results? 6 How could you improve the investigation? PL E 1 Reducing global warming You have seen that humans contribute to global warming by burning fossil fuels. One way to reduce this impact is to use renewable resources. A renewable resource is one that does not deplete (run out) or can be replenished within a human’s life time. Examples include wind, tidal and solar power. M A non-renewable resource is a resource that cannot be replaced after it is used. Examples include coal, petroleum, and natural gas. Renewable resources SA When fossil fuels are burned to generate electricity, carbon dioxide is produced. This adds to the problem of global warming. The more electricity is produced, the more carbon dioxide adds to the problem. To reduce global warming people need to generate more of their electricity from renewable energy resources. These energy resources will become more important as the supplies of fossil fuels run out. 179 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 5 Materials and their structure Wind PL E People have been using the power of the wind for hundreds of years. They used windmills to grind wheat into flour and to pump water. Now they use wind turbines to generate electricity. You need a lot of wind turbines to generate as much electricity as a power station so wind turbines are grouped together to form wind farms. No harmful waste product, such as carbon dioxide, is produced when electricity is generated in this way. The problem with wind-generated power is that electricity is only produced when the wind blows. This windmill in France was used to grind wheat. Tidal This wind farm, made up of many wind turbines, is used to generate electricity in China. M This wind pump is used to pump water on this farm. SA Tides make water rise and fall twice every day. This happens as a result of the pull of the Moon’s gravity as the Earth spins. It is possible to use this movement to generate electricity. To do this you need to trap the water, in river estuaries, behind a barrier and then generate electricity by releasing the water to flow through electricity generator turbines as the tide goes out. The problem is you can only generate electricity at certain times each day and the barrier may interfere with wildlife habitats. A hydroelectric turbine at a tidal farm in Brest, North West France Solar The energy from the Sun can be used to generate electricity. Photovoltaic cells can convert solar energy to electrical energy. This can only happen when the Sun is shining. These photovoltaic cells are part of a large solar energy farm in Mexico. 180 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 5.5 Atmosphere and climate Using other renewable resources Bioplastics The use of plastics has developed over the past hundred years. Plastics are very useful materials but they have one very big problem: they do not break down easily and cause many problems for wildlife when they are thrown away. The waste builds up on land and in the oceans. Humans produce a lot of plastic waste, especially from plastics that are only used once. M PL E Bioplastic is a biodegradable material that comes from renewable sources (biomass, such as vegetable oils, sawdust or food waste) unlike conventional plastics that are made from petroleum. Plastic waste on a beach in Indonesia This cutlery is made from biodegradable bioplastic. SA The use of bioplastics from renewable sources will help to reduce the use of fossil fuels and to prevent damage to the environment caused by disposal of single-use plastics. What can I do to reduce my use of single-use plastics? Summary checklist I can describe how the Earth’s climate has changed in the past I can explain the difference between ice ages, glacial and interglacial periods I can give some evidence that the Earth’s climate cycles between colder and warmer periods. 181 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 5 Materials and their structure Check your progress 5.1 a Copy the diagram of a helium atom and label it, using these labels. proton neutron electron nucleus − PL E + + − b [4] Name the subatomic particle that: i has a positive charge [1] ii has no charge [1] iii has the least mass [1] iv is made up of protons and neutrons [1] a M 5.2 Gold jewellery is marked to tell you how pure the gold is. Which is the marking that has the most gold? b 15 carat gold 9 carat gold [1] c 18 carat gold [1] 5.4 Match the terms, A–E, with the meanings, 1–5. [5] SA 5.3 Pure diamond is made up of carbon atoms arranged in a particular way. How do pure diamonds differ from diamonds that contain other elements? A weather 1 a measure of the amount of water vapour in the atmosphere B climatology 2 the state of the atmosphere in a particular place C climate 3 the study of weather D meteorology 4 the weather conditions prevailing in an area in general and over a long period E humidity 5 the study of climate 182 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. Check your progress 5.5 The graph shows the average global temperatures over the past 400 million years. 25 20 Average global temperature in °C 15 5 400 a PL E 10 300 200 100 Millions of years ago today What was the average global temperature between 350 and 260 million years ago? [1] b What is this period of time known as? [1] c What was the average global temperature 100 million years ago? [1] [2] 5.7 What evidence is there that the Earth is getting warmer? [2] M 5.6 How does the study of ice cores from deep in the ice, from places that have been frozen for a long time, such as Greenland, help us to understand how our atmosphere has changed over time? 5.8 The atmosphere has changed since the Earth formed. For each of these statements write true or false. a The atmosphere now has more carbon dioxide than the earlier atmosphere [1] The early atmosphere had little or no oxygen [1] c The atmosphere was formed from the gases produced by volcanoes [1] d The atmosphere today contains about 50% nitrogen [1] e The atmosphere today contains about 0.04% carbon dioxide. [1] 5.9 a Much of the electricity you use is generated using fossil fuels. Name three ways electricity can be generated without using these fuels. [1] SA b b What is meant by the term ‘global warming’? c Explain how using fossil fuels adds to the problems of global warming. 5.10 a What is an analogy? Give an example. [2] [2] 183 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 5 Materials and their structure Project: Global warming and climate change debate Background In June 2019, the average world temperature was . It was an increase of 1.1 oC above the average global temperature for the whole of the twentieth century. During this worldwide heat wave there were: wildfires in the Arctic with millions of hectares burning in Northern Russia • heat waves and severe water shortages in India • more than 5000 people in Japan taken to hospital for treatment due to the heat wave • a huge impact on the growth of crops. PL E • July 2019 was the hottest on record in Europe. People died of heat stroke. Overhead power cables expanded in the heat and failed. Crops were damaged so food production was affected. Scientists say it is the latest sign that the Earth is experiencing a huge increase in global warming. There is a wide sense amongst scientists that the rise in carbon dioxide emissions from human activities is altering the temperature. A climate researcher from the European Union’s Copernicus Climate Change Service, said in a television interview: M ‘This particular month has been very warm, but to me this is not the main point. All the months of 2019 have been warm in comparison to other years. And that trend is not likely to stop unless we do something about reducing the emission of greenhouse gases.’ SA However, some people think that the change in temperatures is just part of the Earth’s normal cycle and there is no need to reduce the emissions of greenhouse gases as there is no proof it is these gases that cause climate change. Your task In your group (no more than four), draw up two lists of evidence and give your reasoning; one in support of the idea that humans are contributing to climate change and one that does not support that idea. Your teacher will select which point of view each group will represent. During the debate your group must stick to the point of view you have been given. 184 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 6 Light In this topic you will: PL E 6.1 Reflections • describe how light is reflected from a plane surface • understand the law of reflection • be able to draw ray diagrams to show reflection of light. Getting started Work in groups to discuss answers to these questions. Does light travel in straight lines or in curved paths? 2 Describe the evidence to support your answer to question 1. SA M 1 Key words angle of incidence angle of reflection incident ray law of reflection normal perpendicular plane mirror protractor ray diagram rays reflection set square 185 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 6 Light Reflection PL E When you think of reflection you probably think of using a mirror. Most of the mirrors you use are plane mirrors. ‘Plane’ means flat. To see what reflection looks like from a surface that is not plane, you can look at your own reflection from a spoon. The reflection is distorted. Remember that light travels in straight lines called rays. When drawing light rays, always use a ruler and put an arrowhead on the ray to show its direction. A light ray arriving at a mirror is called an incident ray. An incident ray is the ray coming onto a surface. The incident ray makes an angle with the surface of the mirror. Measure this angle from a line perpendicular to the mirror and not from the mirror 1 itself. The line perpendicular to the mirror is called the normal. In physics incident and maths, ‘normal’ means perpendicular or at right angles to something. 1 The diagram shows how to do this. M 1. Draw the incident ray and the mirror. Sometimes, this is done for you. 2. Use a ruler to make the incident ray meet the mirror. SA 3. Use a protractor or set square to draw the normal. The normal is perpendicular to the mirror where the incident ray meets the surface. The normal is usually a dashed line so it is not confused with the light ray. 4. Use a protractor to measure the angle between the incident ray and the normal. We call this angle the angle of incidence or ???. 5. Measure an angle equal to the angle of incidence on the other side of the normal. This angle is called the angle of reflection or ???. Draw a reflected light ray coming away from the mirror at this angle. Remember to put an arrowhead on the reflected ray. ray 1 incident ray incident 1 ray incident 1 ray incident 2 ray incident 2 ray 2 incident ray incident 2 ray incident 2 ray incident 3 ray incident 3 ray 3 incident ray incident 3 ray incident 3 ray incident 4 ray incident 4 ray 4 incident ray incident 4 ray incident 4 ray incident 5 ray incident 5 ray 5 incident ray incident 5 ray incident 5 ray incident ray mirror mirror mirror mirror mirror mirror mirror mirror normal mirror normal normal mirror normal mirror normal mirror mirror normal mirror normal i normal normal i i normal i normal i normal i r normal normal i r i r normal i r i r mirror mirror mirror mirror reflected ray reflected ray reflected ray reflected ray reflected ray mirror mirror mirror mirror mirror mirror mirror 186 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 6.1 Reflections These diagrams are called ray diagrams because they show what happens to the light rays during reflection. What we have drawn obeys the law of reflection. Which is that the angle of reflection is equal to the angle of incidence. PL E In physics, a law is something that always applies. We can use the law of reflection in everyday situations. For example, mirrors can be used to see behind us. The driver of the car can see the cyclist by using this mirror. In this picture, light from the Sun is reflected from the cyclist. This is the incident ray on the mirror. The reflected ray from the mirror goes to the driver’s eye. SA M The ray diagram shows how this works. 187 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 6 Light Questions 1 Which of the angles in this diagram is the angle of reflection? Write the letter. A B mirror C 2 3 Copy this ray diagram. PL E D a Extend the incident ray to meet the mirror. b Draw a normal where the incident ray meets the mirror. c Measure and write down the angle of incidence. d Draw a reflected ray in the correct place. incident ray mirror Sofia looks at a candle in the mirror. Copy and complete the diagram to show how light from the candle reflects from the mirror to Sofia. M You do not have to measure the angles. Draw and label: the incident ray • the normal • the reflected ray • the angle of incidence, • the angle of reflection, SA • 4 Marcus drops a pencil. The pencil rolls under his bed. Marcus cannot see the pencil. The diagram shows a light ray coming from the pencil. Marcus can use a mirror to see the pencil. FPO Copy and complete the diagram by adding a mirror and a reflected light ray to show how Marcus can see the pencil. You do not have to measure the angles. 188 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 6.1 Reflections Activity 6.1.1 Mirrors and reflections Work in pairs. Make a list of places where mirrors are used. In each of your examples, describe why a mirror is used. PL E Reflections can also be seen from some surfaces that are not mirrors. Make a list of some of these surfaces. What do these surfaces have in common? Think like a scientist Measuring angles of incidence and reflection In this investigation, you will investigate the law of reflection. Work in pairs or groups of three. You will need: • ray box with power supply M • Make the room as dark as possible for this activity. • plane mirror and support to hold it vertical • plain paper • pencil • ruler • protractor Method Set up the equipment as shown in the diagram. mirror modelling clay white paper pencil protractor 110 80 90 100 90 100 110 80 70 120 60 0 01 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 180 180 170 16 0 170 0 ruler 130 50 14 50 40 70 16 0 0 15 20 10 0 10 20 120 40 2 60 50 0 13 0 30 to power supply 14 SA 1 17 18 19 Place the plane mirror vertically at one side of the white paper. Mark the position of the front of the mirror on the paper using a pencil. 20 21 22 23 24 25 26 27 28 29 30 Continued 189 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 6 Light Continued Place the plane mirror vertically at one side of the white paper. Mark the position of the front of the mirror on the paper using a pencil. 4 Use the protractor to draw a normal line at the surface of the mirror. 5 Use the ray box to direct a ray of light onto the mirror. Where the normal meets the mirror surface.' 6 Use a pencil to make marks on the paper for the positions of the incident and reflected rays as shown in the diagram. 7 Turn the ray box off, remove the mirror and use the pencil marks to construct a ray diagram. Use the protractor to draw the normal. 8 Measure the angle of incidence, i and the angle of reflection, r from your diagram and record the angles. 9 Repeat this for at least four more different angles. Use a new piece of paper or a new area on the same piece of paper each time. M PL E 3 Questions 1 Record your results in a table with two columns: angle of incidence and angle of reflection. Remember to include the unit. 2 State: the independent variable b the dependent variable in this experiment. SA a 3 Draw a graph of your results. Put the independent variable on the x-axis. Complete your graph with a straight line of best fit. 4 Describe the pattern in your results. 5 a Describe some of the things that were difficult to do accurately in this experiment. b Suggest some ways to improve the accuracy of this experiment. 190 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 6.1 Reflections Continued Self-assessment For each of these statements, decide on how well you agree. Give yourself five if you agree very much and one if you do not agree at all. I can recall the law of reflection. • I can draw ray diagrams to show reflection. • The experiment on reflection helped my understanding. Summary checklist PL E • SA M I can understand and describe how light is reflected from a plane mirror I can recall the law of reflection I can draw ray diagrams to show reflection of light from a plane mirror. 191 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 6 Light 6.2 Refraction In this topic you will: describe how light is refracted at the boundary between air and glass or air and water • describe how light changes speed when it passes between different substances • draw ray diagrams to show how light is refracted. Getting started PL E • Work in groups to discuss answers to these questions. be ready to share your ideas with the rest of the class. 1 Why do you think you cannot see clearly when looking through a glass of water? angle of refraction away from the normal bent distorted lenses medium refraction towards the normal SA M 2 List as many transparent materials as you can. Try to include solids, liquids and gases. Key words 192 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 6.2 Refraction Refraction When you look through a glass of water or through a wet window, you cannot see clearly. PL E Look carefully at the picture, which shows a glass of water on a table. The background, through the glass of water, appears distorted. Distorted means changed to be less clear. The background appears distorted because of refraction. The material that light passes through is called a medium. Air, glass and water are each examples of a medium for light to pass through. This glass of water is refracting the light passing through it. You will remember that light travels very fast. The speed of light in air is 300 000 kilometres per second. When light passes from air into water or glass, the light travels more slowly. The table shows how the speed of light changes according to the medium. Speed of light in kilometres per second air 300 000 water 225 000 glass 200 000 M Medium SA The change of speed can cause the light to change direction. Imagine you are on roller skates. You are moving at a constant speed on a hard surface. The roller skate on one foot goes onto grass. What happens? You will change direction because one roller skate is moving slower than the other. This is what happens when a ray of light passes from air into glass or water. One side of the ray of light slows down first, causing it to change direction. Refraction of light is defined as the change in direction of light on passing from one medium to another because of change in speed. 193 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 6 Light Light passing from air into water or glass This ray diagram shows what happens when light passes from air into glass or water. The light slows down when it passes from air into glass or water. This causes it to change direction. normal angle of incidence air glass or water angle of refraction PL E The light passing from air into glass or water is bent towards the normal. That means the refracted ray is closer to the normal than it would be if the incident ray just carried on in a straight line. incident ray Notice also from the ray diagram that, when light passes from air into glass or water, the angle of incidence is greater than the angle of refraction. Both of these angles are measured from the normal. refracted ray Light passing from air into glass or water is bent towards the normal. Light passing from water or glass into air The ray diagram in Figure 6.2.4 shows what happens when a ray of light passes from water or glass into air. refracted ray normal The light speeds up when it passes from glass or water into air. This causes it to change direction. M We say that the light passing from glass or water into air is bent away from the normal. That means the refracted ray is further away from the normal than it would be if the incident ray just carried on in a straight line. SA You will also notice from the ray diagram that when light passes from glass or water into air the angle of refraction is greater than the angle of incidence. Both of these angles are measured from the normal. air glass or water angle of refraction angle of incidence incident ray Light passing from glass or water into air is bent away from the normal. Refraction in everyday life Refraction can be a nuisance. It can stop you from seeing clearly through wet windows. Each individual drop of water on the window refracts light in a different direction, making it very difficult to see. This is why many vehicles have windscreen wipers. The windscreen wipers remove the water drops. It is then easier to see clearly as all the refraction from the glass is in the same direction. Drops of water on glass make it difficult to see because of refraction. 194 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 6.2 Refraction PL E Refraction can also be useful. Lenses are used in our eyes, in cameras and in glasses that people wear, to cause refraction of light. A lens is a curved piece of glass that is designed to refract light in a known way. This phone has a lens to refract light for a photograph. Questions 1 2 Different glasses refract light in different ways to help people to see more clearly. Complete the sentences, using ‘faster’ or slower. a Light travels … in water than it does in air. b Light travels … in air than it does in glass. Complete the sentence to describe refraction correctly. 3 M Refraction of light happens when light … direction because of a change in … . ray of light This ray diagram shows a ray of light in air. Copy and complete the ray diagram to show what happens when the ray of light enters the glass. Include on your diagram: the normal • the angle of incidence • the refracted ray • the angle of refraction. SA • 4 air glass This diagram shows a ray of light in water. Copy and complete the ray diagram to show what happens when the ray of light enters the air. Include on your diagram: • the normal • the angle of incidence • the refracted ray • the angle of refraction. air water ray of light 195 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 6 Light Activity 6.2.1 Refraction effects This activity shows three effects of refraction. Effect 1: The appearing coin Place a coin or small piece of metal at the bottom of an opaque container, such as a cup. PL E Position yourself so that the coin is just out of view behind the edge of the container as shown in the diagram. view from here Now pour water into the cup until it is almost full. Pour the water in carefully so the coin does not move. The coin comes into view. cup coin Can you use a ray diagram to explain why? You need to think about how a light ray travels from the coin, up through the water and out into the air. Effect 2: Broken pencil in water Pour water into a transparent drinking glass until it is about three-quarters full. Set a pencil into the glass so it is resting at an angle. M View the glass and pencil from the side. The pencil appears to be broken at the surface of the water. glass water SA Can you use a ray diagram to explain why? You need to think about how light travels from the pencil, through the water and out through the side of the glass. Effect 3: Broken pencil in water and oil Repeat the demonstration in Effect 2: Broken pencil in water, but this time put water into the glass until it is only half full. Now, gently pour cooking oil on top of the water until the glass is about three-quarters full. View the glass and the pencil from the side again. How does the pencil appear this time? What can you conclude about the speed of light in water and in cooking oil? 196 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 6.2 Refraction Think like a scientist Drawing accurate ray diagrams In this investigation, you will make accurate ray diagrams from rays of light. Work in groups of three or four. You will need: • ray box and power supply Method • plain paper • pencil • ruler • Make the room as dark as possible for this activity. PL E • protractor • glass block Set up the equipment as shown in the diagram. 2 Use the pencil to draw around the glass block. 3 Switch on the ray box and position it so the light ray makes an angle with the glass surface. 4 Use the pencil to mark the position of the incident ray in two places: about 5 cm away from the glass block and where it meets the glass block. 5 Do the same for the ray that emerges from the glass block on the other side. 6 Switch off the ray box and lift the glass block off the paper. 7 Use the ruler to join up the light rays. 8 Use the protractor to draw a normal at both surfaces. 9 Measure the angle of incidence and angle of reflection at both surfaces. SA M 1 10 Repeat steps 2–9, using different angles and a new piece of paper each time. Make sure to include an angle of incidence of zero. 197 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 6 Light Continued Questions 1 What did you notice about the pairs of angles at each surface each time? 2 Plot a graph of your results for the first glass surface where the light ray goes into the glass. PL E Put angle of incidence on the horizontal axis and angle of refraction on the vertical axis. Join your points with a line that passes through all of the points. 3 Describe the trend shown in the graph. 4 What do you observe when the angle of incidence is zero? Self-assessment Answer these questions about the group work. What did you do in the group? • Did you make sure everyone in the group had a role? • Would you feel confident to lead a group activity next time? M • Summary checklist SA I can describe how light changes speed between air and either water or glass I can recall that a change in speed can make a light ray change direction I can recall which way light changes direction when it passes from air into glass or water I can recall which way light changes direction when it passes from glass or water into air. 198 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 6.3 Making rainbows 6.3 Making rainbows In this topic you will: learn how white light is made from many colours • discover how dispersion of white light can be done with a prism • be able to recall the colours of white light in the correct order. Getting started PL E • Work in groups to discuss the answer to these questions. Do you ever see a rainbow at night? • Does the Sun have to be shining to enable you to see a rainbow? • Does there have to be rain or recent rain to enable you to see a rainbow? • What colours can you see in a rainbow? dispersion prism spectrum triangular SA M • Key words 199 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 6 Light Newton’s discovery about light The name Newton is often associated with forces, but Isaac Newton made many other important discoveries. PL E In the year 1666, Newton showed that white light could be split into different colours. The picture shows Newton using light from the Sun, coming through a hole. Newton is using a glass block in the shape of a triangle to split the light into its colours. He is shining the colours onto a screen. The next picture shows what the colours look like when seen on a screen. The spectrum The colours that make up white light The range of colours that can be seen in white light is called a spectrum. In the spectrum, the colours are not separate but they merge from one to another. M Some people think Newton originally saw five or six colours, but most people now agree that there are seven. In the order that they appear in the spectrum, these seven colours are: red orange yellow green blue indigo violet You can remember the order of the colours using a made-up person’s name: ‘ROY G. BIV’. SA Dispersion Dispersion means splitting light into different colours. Dispersion happens because light is refracted. Each of the different colours of light that make up white light is refracted through a slightly different angle. This can be shown by using a triangular prism. ‘Triangular’ means in the shape of a triangle. A prism is a solid shape such as the one that Newton used. When a ray of white light passes through the prism, the ray is refracted. Violet light is refracted through the largest angle and red light is refracted through the smallest angle. You can see this in the picture. Dispersion of white light, using a triangular prism 200 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 6.3 Making rainbows Rainbows A rainbow is formed when drops of water in the air cause dispersion of light. The light is also reflected from inside the drops of water. That means that, for you to see a rainbow: the Sun must be shining, to provide bright light • there must be rain or small drops of water in the air, to cause dispersion of light • the Sun must be behind you, because the water drops reflect the light inside them. PL E • M The drops of water from the hosepipe in Figure 6.3.4 are making a rainbow. The Sun is shining and the Sun is behind the camera. SA Drops of water on a sunny day can cause a rainbow. Questions 1 What name is given to white light being split into different colours? refraction 2 dispersion reflection conduction The diagram shows a glass block being used to separate white light. What name describes this piece of equipment? Write one letter. A round glass cylinder B square glass prism C triangular glass prism D hexagonal glass prism 201 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 6 Light 3 The diagram shows white light being separated into different colours. The colours are seen on a white screen. white light A a Which letter shows the position of red light on the screen? b Which letter shows the colour of light that is refracted through the smallest angle? c What word describes the range of colours seen on the screen? B glass prism screen C PL E refraction reflected separated spectrum 4 Explain why drops of water are needed for a rainbow to be seen. 5 When looking at a rainbow, some people see indigo and violet as the same colour. How many colours will these people say they can see in the rainbow? Think like a scientist Making a rainbow In this activity, you will change variables and describe how observations change. Work in groups of two or three. M You will need: • a ray box and suitable power supply • a triangular glass prism • a piece of white paper or card to use as a screen SA Safety Do not put your eye closer to the prism than about  metre. The light will become very bright and could cause damage to your eye. Make the room as dark as possible for this activity. Set up the equipment as shown in the diagram. incident ray glass prism ray box screen Method: Part 1 1 2 Adjust the positions of the ray box and the screen until you see the colours of the rainbow on the screen. Move the screen closer to the prism. 3 Move the screen further away from the screen. 202 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 6.3 Making rainbows Continued Questions 2 3 a How many colours can you see on the screen? b List the colours in order starting from red. Name the colour that is refracted: a through the smallest angle b through the largest angle. Describe two things that happened to the colours when: a the screen was moved closer to the prism b the screen was moved further away from the prism. Method: Part 2 1 2 3 4 5 Remove the screen and stand about 1 metre from the prism, in the same direction as the screen had been. Move so that you are looking into the refracted rays with one eye. You may find it easier to cover the other eye. Move from side to side so that you can see the different colours. Increase the distance between your eye and the prism to about 2 metres. Again, move from side to side so that you can see the different colours. Describe two differences in the observations when you moved further away. Describe one advantage and one disadvantage of Method: Part 1 and Method: Part 2 for observing the colours. This activity is an analogy for how rainbows form. Describe one strength and one limitation of this analogy. SA 3 M Questions 1 2 PL E 1 Self-assessment Different people see different numbers of colours in this activity. The numbers of colours usually vary from 5 to 7. Did you see the same number as everyone else in the class? Suggest reasons why people see different numbers of colours. Summary checklist I can recall that white light is made from different colours of light I can describe how to use a prism to produce dispersion of white light I can list the seven colours in order starting from red. Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 6 Light 6.4 Colours of light In this topic you will: discover what happens when colours of light are added • discover what happens when colours of light are subtracted • discover why we see different colours. Getting started Work in pairs. PL E • Make a list of all the colours you can see in this picture of flowers. absorbed coloured filters cyan magenta non-luminous primary colours subtraction transmit SA M How many did you get? How does this number compare with other groups? Key words 204 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 6.4 Colours of light Primary colours Topic 3.3 explained that there are seven colours in white light. These are the colours that can be seen in the rainbow. However, there are three colours of light from which all other colours of light can be made. These are called the primary colours. The primary colours cannot be made by mixing any other colours of light. The primary colours of light are: red • green • blue. PL E • The primary colours of light are different from the primary colours in paints. The colours in light mix differently from the colours in paint. Adding colours of light The diagram shows what happens when three beams of light, each of a different primary colour, overlap. You can see the effect of adding the primary colours: • • • red + green = yellow red + blue = magenta blue + green = cyan red + green + blue = white. magenta yellow white blue M • red The different colours that you see on a mobile phone, computer or television are all produced from combinations of the three primary colours of light. cyan green Colours formed by overlapping the three primary colours of light SA When you look very closely at some types of computer monitor, television or phone screen, you can see the individual sources of red, green and blue light. The colours on this phone display are made by adding the three primary colours of light. Close-up of a television screen showing the sources of the primary colours of light. 205 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 6 Light When you look at a television or phone screen, you see far more colours than just red, green, blue, cyan, magenta, yellow and white. Most screens can display 256 different colours. Changing the brightness of the primary colours makes all these different colours. For example, orange is made by adding red and green, but with the red brighter than the green. Research has shown that 256 is the maximum number of colours that most people can see. Subtracting colours of light PL E You have probably used a filter in your chemistry lessons. Filters are used to remove something from a mixture. You can also use coloured filters to remove colours from light. If a transparent piece of coloured glass or plastic is placed in front of a white light, then only light of that colour will be transmitted (get through). All the other colours will be absorbed. A common example of coloured filters is in traffic lights. The traffic lights use three identical white lamps. In front of each lamp is a coloured filter for red, yellow or green. Take the red filter as the example to see how this works. M White light, from the lamp, is made from the seven colours of light: red, orange, yellow, green, blue, indigo and violet. These traffic lights use coloured filters. SA When these seven colours arrive at the red filter, only red is transmitted. The other six are absorbed. This is shown in the diagram. Figure 6.4.3: A coloured filter works by absorbing the colours of light that are different from the colour of the filter. This is an example of subtraction of light. White light has had six colours subtracted to leave only red. In the traffic lights, the yellow and green filters work in exactly the same way. Each of them absorbs six colours and only transmits one colour. 206 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 6.4 Colours of light The blue stage light in the picture has a white lamp and a blue filter. If you look carefully, you can see where the white lamp is inside the black case. The colours of the filters in stage lights can be changed to produce different colours. M PL E Photographers sometimes use coloured filters on a camera to get different effects. This stage light is using a white lamp and a blue filter. What colour was the filter used in taking this photograph? As with numbers, it is possible to subtract colours of light until the end result is zero. SA For example, if white light shines on a green filter, only green light will get through. The other colours of the white light are absorbed. If this green light then shines on a red filter then no light will get through. Green is one of the colours that a red filter absorbs. white light only green light passes through green filter no green light passes through red filter The result of using two different coloured filters 207 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 6 Light Seeing colours When you look at a non-luminous object, you see the light that is reflected from the object. ‘Non-luminous’ means the object does not emit its own light. Look at the flower in the picture. PL E The flower is seen in white light. The flower looks yellow because it reflects only yellow light. The flower absorbs the other six colours in white light. This is shown in the diagram. white light coming in yellow light yellow surface M The flower appears yellow because it reflects yellow light and absorbs the other colours. A white object reflects all the colours in white light equally. A black object absorbs all the colours in white light and does not reflect any. SA These three balls appear black, red or white, according which colours of light they reflect and which they absorb. 208 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 6.4 Colours of light Look at the two cubes in Figure 6.4.7. One is red and the other is blue. The cubes are shown in different colours of light. The red cube appears black when seen in green light. This is because red objects only reflect red light. They absorb all other colours. Here, the red cube is absorbing the blue light and not reflecting any light. Questions 1 List the three primary colours of light. 2 Name the colour produced when 4 blue and red cubes seen in blue light C blue and red cubes seen in red light a blue and red cubes in white light; b the same cubes in green light; c the same cubes in red light. a red light and blue light are added together b red light and green light are added together c red, green and blue lights are added together. A stage light uses a white lamp. What colour of light will be seen when: a a yellow filter is used b an orange filter is used. a A green ball appears green. What colour of light could be shining on the green ball? Choose two. blue green red white magenta A blue ball appears black. What two colours of light could be shining on the blue ball? SA b blue 5 B M 3 blue and red cubes seen in white light PL E The blue cube appears black when seen in red light for the same reason. It absorbs the red light and does not reflect any light. A green red white A T-shirt looks red. What could explain this? Write three letters. A the T-shirt is red and is seen in white light B the T-shirt is red and is seen in red light C the T-shirt is blue and is seen in green light D the T-shirt is white and is seen in red light E the T-shirt is yellow and is seen in blue light 209 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 6 Light Activity 6.4.1 Making colours on the screen Many computer applications, such as those for word-processing and slide-making, have colour options. In the ‘more colours’ options of these there are RGB tools to customise colours. • R at maximum • G at zero • B at zero. Bright yellow has: • R at maximum • G at maximum • B at zero. Try making: magenta • cyan • white • black. M • PL E The letters RGB stand for ‘red’, ‘green’ and ‘blue’, the primary colours of light. You can adjust these to make whatever colour you want. For example, bright red has: Now make some other colours of your choice. SA In each case, write down the RGB settings for each colour. Think like a scientist Identify the colour In this investigation, you will make predictions about colours and light. Work in groups of two or three. You will need: • white paper and coloured paper • coloured pens • flashlights • coloured filters • a room that can be darkened 210 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 6.4 Colours of light Continued Method 1 Write the names of some colours on a piece of coloured paper. Use different coloured pens to write each word. The colours do not have to match correctly. For example, on yellow paper, write: ‘blue’ with blue pen • ‘red’ with green pen • ‘green’ with blue pen. PL E • 2 Use the flashlight and a red filter to illuminate the paper. 3 Ask someone from a different group to identify: 4 • the colour of the paper • the words that are written in the correct colours • the colours of pen used to write the other words. Vary the words, the colours of the pens, the colours of the paper and the colours of the filters, and repeat steps 1–3. Questions Which colour combinations were easiest to get correct? 2 Which colour combinations were most difficult to get correct? M 1 Self-assessment What parts of this topic are easiest to understand? 2 What parts of this topic are most difficult to understand? 3 What part of this topic could you teach to someone else? SA 1 Summary checklist I can recall the three primary colours of light I can recall the colours that are made when these primary colours are added together I can understand that filters work by subtracting light I can predict what will happen when light of different colours shines on filters of different colours I can understand why coloured objects appear coloured when seen in white light I can predict the colours that objects will appear to be, when seen in light of different colours. 211 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 6 Light 6.5 Galaxies In this topic you will: discover that galaxies contain dust, gas, stars and other solar systems. Getting started Work in pairs. PL E • Key words Arrange these objects in order from smallest to largest. solar system planet galaxy moon SA M star elliptical galaxy irregular spiral stellar dust universe 212 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 6.5 Galaxies The Milky Way PL E If you look at the sky on a clear night, far away from any lights, you can see a milky band across the sky. This milky band is part of the galaxy where we live, called the Milky Way. The photograph shows what this looks like through a camera set for very low light conditions. This is part of our own galaxy, the Milky Way. M The word ‘galaxy’ comes from a Greek word for ‘milky’. Shapes of galaxies SA The reason why our own galaxy looks like a band across the sky is because of the shape of the galaxy. The Milky Way is a spiral galaxy. If you were to look at the Milky Way from far away, it would appear as a spiral. Because we live in a spiral galaxy, we can only see one ‘arm’ of the spiral, which is that band across the sky. In fact, most of the stars we see at night are in our own galaxy. There are an estimated 250 000 000 stars in the Milky Way including our Sun. This is what the Milky Way would look like from far away. There are other galaxies in the universe besides our own. The word ‘universe’ is used to describe all of space and everything in it. These other galaxies have different shapes, and they are classified according to shape. They are called elliptical galaxies or irregular galaxies. 213 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 6 Light a b c PL E The three different shapes of galaxy a: Spiral, b: Elliptical, c: Irregular The closest known galaxy to the Milky Way is called the Canis Major Dwarf Galaxy. It is elliptical in shape and a distance of away from us. What are galaxies made of? Galaxies are made from stellar dust, gas, stars and solar systems held together by gravity. Stellar dust is the dust that is found in space. The Earth is travelling through a cloud of stellar dust that is estimated to contain an average of one dust particle in every million cubic metres of space! M The gravity holding a galaxy together is very strong because galaxies are very large and have very large mass. Even if you could travel at the speed of light (300 000 kilometres per second), it would take you more than 100 000 years to cross from one side of the Milky Way to the other! Scientists estimate the mass of the Milky Way to be 1 500 000 000 000 times the mass of the Sun. SA How many galaxies are there? Scientists have counted the galaxies in one part of space. The scientists then multiplied this number up to estimate the number of galaxies in the universe. The answer they got was 100 000 000 000 galaxies! Estimates such as this may not be accurate. There could actually be more or fewer galaxies in the part of space that the scientists counted compared with the rest of the universe. Also, the scientists may not know the total volume of the universe accurately. 214 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 6.5 Galaxies Questions 1 List the three different shapes of galaxies. 2 Which of these are found in galaxies? Choose all that are correct from the list. planet star universe stellar gas Name the force that holds the parts of a galaxy together. 4 Explain why most of the stars we see in the night sky are from our own galaxy and not from other galaxies. 5 Suggest why scientists can only estimate the number of stars in the Milky Way and not know the number accurately. Think like a scientist PL E 3 Estimating large numbers In this investigation, you will use an analogy for estimating the number of stars in a galaxy. Work in groups of two or three. You will need: M • one large cup or other container filled with coarse sand or fine gravel, for the whole class • a hand lens (magnifying glass) for each group • a piece of white paper for each group SA • small container for the whole class • access to laboratory equipment for measuring masses and volumes • a calculator for each group Scientists cannot count the number of stars in a galaxy because there are too many. However, scientists can estimate the number of stars in a galaxy. You are going to estimate the number of grains of sand in your container. There are too many to count them all, so this activity is an analogy for how scientists estimate numbers of stars. Method 1 Put a small quantity of sand from the large container onto the white paper and separate the grains. You should only put out the quantity you can count easily. Continued 215 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 6 Light Continued Count the grains, record the number, and put the grains into the small container. 3 Do the same again: count some grains from the large container and then add them to the small container. 4 Write down the total number of grains your group put in the small container. 5 Now decide as a class whether you want to work in mass or in volume for the last two steps. 6 Measure the total mass or volume of the grains in the small container. 7 Now put these back into the large container and measure the total mass or volume of sand in that. Questions PL E 2 What was the total number of grains the class put in the small container? Call this value G for grains. 2 What was the total volume or mass of the grains in the small container? Call this value S for small. 3 What was the total volume or mass of the grains in the large container? Call this value L for large. 4 Calculate the value of G × __ L S This number is an estimate of the total number of grains in the large container. a Explain the advantage of this method compared to counting all the grains in the large container. b Give reasons why the estimate may not be accurate. SA 5 M 1 c Suggest some ways that the estimate could be made more accurate. 6 Suggest how working as a whole class is an analogy for how scientists studying the Milky Way work. 7 Knowing roughly how long it took you to count your grains in step 2, estimate how long it would take you to count all the grains in the large container. 8 Suggest how you could estimate the number of grains of sand on a beach. Self-assessment Decide how confident you are about each of these: • understanding how this method of estimating works • whether you could apply this method to estimating some other large quantity. 216 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 6.5 Galaxies Summary checklist SA M PL E I can understand what galaxies are I can recall the three shapes of galaxies I can recall that galaxies contain stellar dust and gas, stars and solar systems I can understand that gravity holds all the parts of a galaxy together in space. 217 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 6 Light 6.6 Rocks in space In this topic you will: discover that asteroids are rocks that are smaller than planets • know that scientists believe asteroids to be rocks left over from the formation of the Solar System Getting started Work in groups. PL E • asteroid belt asteroids craters impacts SA M Make a list of different types of objects in the Solar System. Key words 218 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 6.6 Rocks in space Asteroids Asteroids are objects made from rock that orbits the Sun. Asteroids range in size up to 975 km across. The smallest asteroid that has been studied is 2 m across. Most asteroids are not regular shapes, just as rocks on Earth are not regular shapes. PL E Scientists describe the shape of most asteroids as being similar to the shape of potatoes. Most of the asteroids in the Solar System orbit the Sun between the orbits of Mars and Jupiter. This part of the Solar System is called the asteroid belt. There are millions of asteroids. Some that have been studied have been given names. The largest asteroid is called Ceres and was discovered in the year 1801. When Ceres was discovered, scientists thought it was a new planet. As Ceres looked much smaller than a planet, the term asteroid was introduced. This photograph of Ceres, was taken by a spacecraft in 2015. Ceres looks like a small planet. It is round, with a diameter of 975 km, and covered with craters. M Ceres also has a core, a mantle and a crust like some planets. Scientists think that Ceres would have become a planet if it had continued to grow during the formation of the Solar System. The next photograph shows asteroid Itokawa, which is one of the smallest asteroids to be visited by a spacecraft. SA Asteroid Itokawa is about 530 m long and about 250 m wide. In the year 2005, a spacecraft collected samples from the surface of Itokawa. It was the smallest asteroid to be visited at that time. Ceres is an unusual asteroid and also the largest. Study of the samples has given scientists more evidence about how the Solar System formed. Itokawa appears to be made from lumps of rock. These lumps of rock appear to have come from other small planets or moons which have been broken by impacts. The force of gravity holding the lumps of rock together is weak because the asteroid is a relatively small object. When an asteroid such as Itokawa passes a large object such as a planet, tidal forces can change the shape of the asteroid. Some asteroids are made from a single piece of rock. Scientists know this because these asteroids are small and spin quickly. The force of gravity in these asteroids would be too weak to hold separate pieces of rock together. Itokawa is an asteroid that has been studied by spacecraft. 219 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 6 Light Asteroids and Earth Scientists think that a large asteroid impacts the Earth on average every 130 000 years. Smaller asteroids impact with Earth very frequently. PL E The map in Figure 6.6.3 shows where asteroids impacted Earth between the years 1994–2013. These smaller asteroids were less than diameter and broke apart in the atmosphere, so never reached the Earth’s surface. The map shows the positions of asteroid impacts on Earth between 1994 and 2013. There are two reasons why asteroids impact with Earth. • • The Earth exerts a strong force of gravity on passing objects such as asteroids. Many asteroids have orbits that pass relatively close to Earth. Questions Describe what is meant by the term ‘asteroid’. 2 Some asteroids have diameters between and . M 1 Explain why these asteroids are classed as small objects in the Solar System. The asteroid Ceres is covered with craters. Suggest how these craters were formed. 4 Describe where the rocks came from to form asteroids. SA 3 Activity 6.6.1 Making a model asteroid In this activity, you will make a model of an asteroid. You will need: • a selection of small rocks • black acrylic paint • some coarse sand • glue suitable for stone • white acrylic paint • trays for mixing paint • paint brushes 220 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 6.6 Rocks in space Continued Method Use an internet search engine or the pictures in this topic to plan what your model will look like. 6 Choose a small rock and, if necessary, attach sand onto the surface with glue to give a rough texture. 7 When the glue has dried, you can paint your asteroid. 8 Mix the black and white paints to achieve the colours of grey that you want. 9 Together with the other models in your class, you could make a model of part of the asteroid belt. Questions PL E 5 Asteroids are different from planets. Describe one way that your model shows this difference. 2 Some large asteroids that your model could represent have a diameter of 200 km. The planet Jupiter has a diameter of  . Calculate how many times larger Jupiter is than these asteroids. 3 a Use a ruler to measure the length of your model asteroid. b Use your answer to question 2 to calculate the size of model you would need to make for the planet Jupiter on the same scale. M 1 Think like a scientist What happened at Tunguska? SA In this investigation, you will look at evidence that supports or contradicts hypotheses. Work in groups of two or three. Method 1 Read these facts. • Tunguska is in northern Russia, far from any towns or cities. There is forest there, with many trees. • In the morning of 30 June 1908 there was a very large explosion at Tunguska, between 5 km and 10 km above the ground. • People living over 800 km away could see and hear the explosion. • Vibrations from the explosion were recorded almost 5000 km away. • The explosion flattened trees over an area of 2000 km2. Continued 221 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 6 Light Continued 3 Read these five hypotheses of what caused the explosion. 1 A comet impacting the Earth. 2 A type of volcano erupting. 3 Testing of a new type of bomb. 4 An alien spacecraft crashing. 5 An asteroid impacting the Earth. Consider the evidence. • All the trees that fell are pointing outwards from a central position. • People discovered how to make very powerful bombs in 1945. • No bomb this powerful has ever been made. • Tunguska is very far from tectonic plate boundaries. • Most comets break up higher than  • A small part of a comet is made from rock. • Small rocky fragments have been found that show the signs of falling through the atmosphere at very high speed. • No metal parts have been found at Tunguska. in the atmosphere. M Questions 1 PL E 2 Use the evidence to decide whether each of the five hypotheses can be supported or contradicted. You can also use facts given in this topic as evidence. SA Write about each hypothesis in turn. 2 3 Decide, using this evidence: a which of the hypotheses are most likely b which of the hypotheses are most unlikely. Explain some of the limitations of the conclusions you have made. Peer-assessment Find another group whose answers to question 2 are different from yours. 1 Are you convinced by their conclusions? 2 If not, can you understand why they made these conclusions? 222 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 6.6 Rocks in space Summary checklist SA M PL E I can describe what is meant by the term asteroid I can recall where most asteroids in the Solar System are found I can know that asteroids are formed from rocks left over from the formation of the Solar System I can know that some asteroids pass close by Earth and can, from time to time, impact Earth. 223 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 6 Light Check your progress 6.1 A plane mirror is a type of mirror. Which of these words describes the meaning of plane? [1] flat irregular round smooth PL E 6.2 Copy and complete the sentence that describes how light is reflected from a plane mirror. The angle of reflection is … to the angle of … . [2] 6.3 Copy and complete the diagram to show how light is reflected from the plane mirror. You do not have to measure angles. Label the reflected ray and the angles of incidence and reflection. [3] M normal plane mirror 6.4 The motorcycle in the picture is fitted with mirrors. SA The motorcycle rider can see objects that are behind the motorcycle by using these mirrors. 224 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. Check your progress Draw a ray diagram to show how the rider can see a ray of light that is coming from behind. [4] 6.5 State the name given to light changing direction when the light passes from air into water. [1] 6.6 Copy and complete each of these sentences with either the words ‘speeds up’ or the words ‘slows down’. When light passes from air into glass, the light … . b When light passes from air into water, the light … . c When light passes from glass into air, the light … . PL E a [1] 6.7 Copy these sentences. [2] Write T or F after each one to show if it is true or false. In a ray diagram, the angle of incidence is measured between the light ray and the surface. In a ray diagram, the angle of refraction is measured between the light ray and the normal. M In a ray diagram, the normal is a line at 90° to the surface. 6.8 Copy these ray diagrams to show what happens to the light rays. On each diagram, draw and label: the normal • the refracted ray • the angles of incidence and refraction. • You do not have to measure any angles. SA • a air [4] b air water [4] glass 225 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 6 Light 6.9 Complete the sentences by using words from the list. Copy and complete word can be used once, more than once or not at all. [5] dispersion prism colours spectrum orange violet blue reflection White light can be split into its component … . PL E This is called … and can be done with a … . The range of colours is called a … . The range starts with red and ends with … . 6.10 Describe the light that will emerge at points A, B and C when white light shines on each of these filters. • If coloured light will emerge, write the colour. • If white light will emerge, write ‘no change’. • If no light will emerge, write ‘no light’. a [1] A M white light red filter b white light [1] [1] SA C blue filter c white light red filter B green filter 226 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. Check your progress 6.11 A theatre uses coloured lights to make objects appear different. Write the colour that each of these objects will appear. A red book in white light. [1] b A green door in green light. [1] c A white T-shirt in blue light. [1] d A blue ball in green light. [1] PL E a 6.12 Two different coloured lights of the same brightness shine onto a white wall. The two colours of light overlap. Write the colours that will be seen at the points X, Y and Z. a white wall red light X b blue light Y SA Z [1] blue light white wall red light d M white wall green light c [1] [1] green light State the colour that would be seen if red, green and blue lights of the same brightness all overlapped on the white wall. [1] 227 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 6 Light 6.13 a List the four things that make up a galaxy. [2] b Name the galaxy that contains the Earth. [1] [2] SA M PL E 6.14 Asteroids are different from planets. State two features of asteroids that make them different from planets. 228 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. Project Project: Investigating refraction Refraction is all around you every day. Refraction is generally what allows you see transparent objects. Dissolve some white sugar or salt in water. Make sure it is all dissolved so you have a transparent solution. Describe what you see. PL E Now take a transparent container holding some water. Look at the water from the side and slowly pour your sugar or salt solution into the water. How can you see both liquids if they are both transparent? Your task You will do experiments that will help you explain what you see when you pour the sugar or salt solution into water. Work in groups. You can use equipment such as: a ray box and power supply • glass or plastic containers with smooth, flat sides • water • other transparent liquids • sugar and salt to dissolve in water. Safety M • Remember to keep liquids away from the power supply and the ray box. SA Carry out experiments using the method in Think like a scientist: Drawing accurate ray diagrams in Topic 6.2. Investigate how each substance refracts light. When you dissolve sugar or salt in water, does it change how the light is refracted? Does the concentration of the sugar or salt affect the refraction? Which substance refracts the light through the largest angle? Which substance refracts the light through the smallest angle? Record all your results and present them in the most effective way. Can you now explain what you see when you pour the sugar or salt solution into water? 229 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 7 Diet and growth In this topic you will: PL E 7.1 Nutrients • learn about the six types of nutrient that everyone needs to eat • find out why they need these nutrients • learn about some good sources of these nutrients. Getting started Everyone needs energy to stay alive and to do things. They get their energy from the food that they eat. Think about the answers to these two questions on your own. M Then turn to your partner and discuss your ideas about each question. Be ready to share your ideas with the rest of the class. Which kinds of food are best for giving you energy? • What happens to your food after you have swallowed it, before it gives you energy? SA • Key words anaemia carbohydrate fat minerals nutrients oil protein starch vitamin A vitamin C vitamin D vitamins 230 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 7.1 Nutrients Carbohydrates, fats and proteins The photograph shows a plate of food. There are several different kinds of food on the plate. How does each of these foods help the body to stay healthy, and to have energy? SA M PL E The rice contains a lot of starch. Starch is a type of carbohydrate. After you have eaten starch, the body breaks it down to make a sugar called glucose. You may remember that glucose is the fuel that your cells use for respiration, to release energy. So starch, sugar and other carbohydrates are needed to give you energy. The chicken and beans contain a lot of protein. Protein is important for making new cells in the body. So you need protein to help the body to grow, or to repair itself if it gets damaged. Protein is also needed to make haemoglobin and antibodies. The avocado contains fats and oils. Fats and oils are very similar, but fats are solid at normal temperatures and oils are liquid. Fats and oils give you energy. They are also needed to make cell membranes 231 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 7 Diet and growth PL E Protein, carbohydrate and fat are nutrients. Nutrients are substances found in food, that you need to stay healthy. These three photographs some of the kinds of food that you can eat to get these nutrients. These foods are good sources of protein. These foods are good sources of starch (a type of carbohydrate Energy stores These foods contain a lot of fat. You do not eat all the time, but you need energy all the time. You get almost all of your energy from the carbohydrates and fats that you eat. You can also get energy from protein if you run out of carbohydrates and fats. M You store a little bit of carbohydrate, and quite a lot of fat, in your body. These energy stores provide you with energy whenever you need it. You store a small amount of carbohydrate in your cells, especially in the liver and muscles. These are short-term energy stores. SA For long-term stores, your body stores fat in special cells under-neath the skin and around some of the body organs. Fat stores in the body also provide heat insulation. Animals that live in cold places, like this seal, have a lot of fat stores underneath their skin, to help to stop them losing heat from their body. 232 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 7.1 Nutrients Activity 7.1.1 Protein and carbohydrate in food Work with a partner for this activity. Think about what both of you have eaten so far today. Make a list. Which foods do you think contain a lot of protein? In your list, draw a green circle around each one. PL E Which foods do you think contain a lot of carbohydrate? In your list, draw a blue circle around each one. Use the internet or a reference book to see if you are right. Make changes to your list and circles if you were not correct. Think like a scientist Testing foods for starch You are going to try to find out which types of food contain starch. You can use iodine solution to find out if a food contains starch. Iodine solution is orange-brown. When it mixes with starch, it becomes very dark blue-black. M You will need: at least six different kinds of food • some paper plates or other place to put the pieces of food, keeping them separate • a white tile • a bottle of iodine solution, with a dropper SA • Method 1 Collect six different kinds of food. Try to include some foods that come from plants, and some that come from animals. Make sure you keep them completely separate from one another. 2 Draw a results table like this: Food Colour of iodine solution after adding to the food Does the food contain starch? Continued 233 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 7 Diet and growth Continued Method Take a small piece of the first food. Put it onto a white tile. 4 Add a few drops of iodine solution. Record the colour that you see in your results table. 5 Clean the white tile. Now repeat steps 2 and 3 for the other foods, making sure to clean the tile each time. 6 Complete the last column in your results table. Questions 1 Explain why it was important to keep all the foods separate from one another. 2 Suggest why it is a good idea to use a white tile for this experiment. 3 In your results table, which column shows your results? Which column shows your conclusions? 4 Did any of the foods that came from plants contain starch? 5 Did any of the foods that came from animals contain starch? Questions Copy and complete this table. M 1 PL E 3 Nutrient Examples of foods that contain a lot of this nutrient Why the body needs this nutrient SA Protein Carbohydrate Fat 2 Explain the difference between the meanings of the words ‘food’ and ‘nutrient’. 234 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 7.1 Nutrients Vitamins Vitamins are nutrients that are needed in only small amounts, but if you don’t eat them you can get ill. There are lots of different kinds of vitamin. Each kind is given a letter. Vitamin A Vitamin C PL E Vitamin A is needed to help your eyes to work well, so that your vision is good. It is particularly important for helping us to see when it is quite dark. People who don’t have enough vitamin A in their diet may not be able to see anything at night. It also helps your white blood cells to fight pathogens. You get vitamin A by eating green vegetables, carrots and squash (such as pumpkin), fruit, foods made from milk (such as cheese) and some kinds of fish. SA M Vitamin C helps the skin to stay strong and to heal quickly if it is damaged. It keeps blood vessels and bones healthy. People who don’t eat enough vitamin C can get an illness called scurvy. A person with scurvy feels weak and may have swollen, bleeding gums. You get vitamin C by eating fresh fruit and vegetables. Citrus fruits are particularly rich in vitamin C. Potatoes and colourful berries are also good sources of vitamin C. In the past, before anyone knew about vitamin C, sailors on long sea voyages often got scurvy. This was because they had no fresh fruit or vegetables to eat. Vitamin D Vitamin D is needed for strong bones and teeth. It helps the body to absorb calcium from the food that you eat. There are not many kinds of food that contain vitamin D. Oily fish is probably the best source. But for most people, most vitamin D does not come from the food that you eat. Instead, vitamin D is made in the skin when sunlight falls onto it. People who never go outdoors, or who never get any sun on their skin, may not get enough vitamin D. This is most likely to happen if you live in a country far from the equator, or where there is not much sunshine. In children, lack of vitamin D can stop their bones growing normally. This illness is called rickets. 235 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 7 Diet and growth Activity 7.1.1 Vitamins poster Work in a group of three for this activity. You will need a big piece of paper, and some coloured pens or pencils. Divide the sheet of paper into three equal areas. Label the areas Vitamin A, Vitamin C and Vitamin D. PL E Use the information in this book, the internet and/or the library to find out which foods contain a lot of each vitamin. Draw pictures of the foods in each space. If you like, you could also cut out some pictures of foods from packaging or magazines, and stick the pictures onto your poster. Minerals There are several different kinds of mineral that you need to eat. Two of the most important ones are calcium and iron. Calcium SA Iron M Bones and teeth contain calcium, so you need to eat plenty of calcium to make them strong. Foods made from milk are excellent sources of calcium. Seeds and some types of nut (for example, almonds) also contain a lot of calcium. Iron is needed to make haemoglobin. If you don’t eat enough iron, you don’t make enough haemoglobin, so not enough oxygen is transported around the body. This causes an illness called anaemia, which makes a person feel very tired. Good sources of iron include meat (especially red meat), dark green vegetables, many kinds of fish and shellfish and some nuts and seeds. 236 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 7.1 Nutrients Questions 3 Look back at question 1. Draw a similar table, but include vitamin A, vitamin C, vitamin D, calcium and iron instead of protein, carbohydrate and fats. Then complete your table. Use your knowledge about respiration to explain why a person with anaemia does not have much energy. 5 These bell peppers are stuffed with beef mince and vegetables, and topped with cheese. They contain a lot of iron and calcium. PL E 4 What other nutrients do you think this meal contains? Explain your answer. Water There is one more nutrient to add to the list of what you need to take into your body each day. This is water. SA M Water is needed for many different purposes in the body. Cells and blood contain a lot of water. Almost 90% of a person’s body weight is made up of water. Water in cells allows all the different chemicals inside them to dissolve, so that they can react together. These reactions keep us alive. Water in blood allows it to flow easily, transporting substances all over the body. Summary checklist I can list the six types of nutrient that I need in my diet. I can explain why I need each of these nutrients. I can list some foods that contain each of these nutrients. 237 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 7 Diet and growth 7.2 A balanced diet In this topic you will: find out what is meant by a balanced diet • think about the nutrients you should try to eat each day • learn why you should try not to eat too much of some nutrients. Getting started PL E • Try to answer these questions on your own. Can you name the six nutrients that you need to eat? • Which three nutrients can give you energy? • Which two groups of nutrients are needed in only small amounts? balanced diet constipation fibre SA M • Key words 238 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 7.2 A balanced diet Diet Your diet is the food that you eat each day. Your diet should provide you with some of all the different kinds of nutrients. It should also give you the right amount of energy. A diet that provides all the different kinds of nutrients, and the right amount of energy, is called a balanced diet. PL E How much energy? Each day, the energy in the food you eat should be approximately equal to the energy that you use up. Most of your energy comes from the carbohydrates and fat that you eat. Different people use different amounts of energy. For example: • • • • M • If you do a lot of sport, or walk or run a lot each day, you use more energy. If you don’t move around much, you use less energy. Some people’s genes mean that their body uses up energy more quickly than other people doing the same thing. If you are growing fast, you need extra energy to help your cells to divide. Tall people use more energy to move their body around than small people. The bar chart shows some examples of the energy that different people need each day. A megajoule is one million joules. SA 12 10 8 Number of megajoules of energy needed each day 6 4 2 0 baby aged 3 months child aged 8 years boy aged 15 years girl aged 15 years man aged 50 years woman aged 50 years Person 239 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 7 Diet and growth Questions Use the bar chart in Figure 7.2.1 to answer these questions. 2 3 4 5 How many megajoules of energy does an eight-year-old child need, on average? Explain why some eight-year-old children might need more energy than this. Explain why some eight-year-old children might need less energy than this. Suggest why a man aged 50 years needs to take in less energy in his diet than a boy aged 15 years. Suggest why most 15-year-old girls need less energy in their diet than most 15-year-old boys. Different diets PL E 1 Everyone is different. Different people need different diets. Everyone needs plenty of minerals and vitamins, but people vary in how much protein and carbohydrate they need. Here are some examples. SA M Young people who are still growing need a lot of protein to make new cells. If they use a lot of energy, then they need to eat enough carbohydrate to give them plenty of energy. They need to eat a little bit of fat, for energy and also for making the membranes on the new cells. People who have to sit down for a lot of the day don’t use up as much energy as people who are very active. So they don’t need to eat as much carbohydrate or fat as someone who has a job that involves moving around, or who does a lot of sport. A pregnant woman needs to eat plenty of protein to help to build her growing baby’s new cells. She also needs lots of iron in her diet, to make haemoglobin in her own blood and her baby’s blood. She should eat plenty of calcium, for building her baby’s bones. 240 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 7.2 A balanced diet Fibre As well as the six nutrients you need in your diet, you also need to eat plenty of fibre. PL E Fibre is not actually a nutrient. This is because, when you eat it, you cannot digest it. So it does not go into the blood or to your cells. Instead, it just travels all the way through the digestive system. It leaves the body as faeces. You might think this means that it is no use to you, but in fact fibre is very important to keep the digestive system healthy. It helps to prevent constipation, when the digestive system slows down and faeces collect inside it, instead of being passed out. Fibre is mostly cellulose. Remember that plant cell walls are made of cellulose, so foods made from plants are a good source of fibre. Cereal grains, seeds and fresh fruit and vegetables are all excellent sources of fibre. And the good thing about this is that these foods usually contain lots of different minerals and vitamins, too. Question M Copy and complete each of these sentences. Choose the correct words from the brackets. a I need protein for (growth/energy). b There is a lot of protein in (sugar/fish). c Starch and (sugar/fat) are carbohydrates. SA 6 d I get energy from carbohydrate and (calcium/fat). Food groups It can be quite difficult to think about which nutrients are in each kind of food that you eat. To make it easier, it sometimes helps to think about food groups. 241 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 7 Diet and growth The picture shows some different kinds of food arranged in a triangle. The bigger the area in the triangle, the greater the proportion of your diet that kind of food should make up. PL E Not too many sweets or fried foods Quite a lot of meat, fish, eggs, pulses or dairy products, for, protein. M Lots of fresh fruit and vegetables, for minerals, vitamins and fibre. Plenty of rice, bread, pasta – preferably whole grain – for starch and fibre. SA Not too much Although you should try to include every different kind of nutrient in your diet, there are some things that you should not eat too much of. • Too much sugar (a kind of carbohydrate) can make your teeth decay. It also increases the risk of developing an illness called diabetes. • Too much fat, oil or carbohydrate can make you put on weight. This can put a strain on your joints, heart and other body organs. • Eating too many fats that come from animals can increase the risk of developing heart disease. 242 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 7.2 A balanced diet Activity 7.2.1 Advice on a healthy diet Work with a partner for this activity. M PL E These five learners are all giving good advice about eating a balanced diet. Think about what each person is saying. SA Match each of the pieces of advice with one of these reasons. 1 This means that you will get some of each kind of nutrient, including all the different vitamins and minerals. 2 These contain fibre and lots of vitamins. 3 This often contains a lot of fat from animals, and very few vitamins or minerals. 4 Not eating enough food will prevent the cells, tissues and organs in your body having enough energy to keep healthy. 5 It can increase the risk of getting heart disease when you get older. 243 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 7 Diet and growth Questions 8 Look at the picture of the food triangle. a Explain why sweets and fried foods are at the top of the triangle. b Explain why it is better to eat whole-grain bread, or brown rice, rather than white bread or rice. c Suggest how you can make sure you get enough protein in your diet, if you don’t like eating meat or fish. PL E 7 Your little brother’s favourite meal is a burger and fries, with a sweet milky drink. a What nutrients does he get from this meal? b What else should he include in his diet? c Explain to him why he should not eat his favourite meal too often. Summary checklist SA M I can explain what is meant by a balanced diet. I can explain why different people need different diets. I can explain why no one should eat too much sugar or fat. 244 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 7.3 Growth, development and health 7.3 Growth, development and health In this topic you will: learn how growth takes place • find out about the difference between growth and development • think about how your diet and the amount of exercise you take affects your growth, development and health • learn how smoking affects health. Getting started PL E • Most people know that doing plenty of exercise and not smoking help you to stay healthy. With a partner, think about these questions. How does doing plenty of exercise help to keep you healthy? 2 How does not smoking help to keep you healthy? carbon monoxide development embryo nicotine particulates tar SA M 1 Key words 245 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 7 Diet and growth Growth Every person on Earth began their life as a single cell. This cell divided to produce two cells. Each of these cells got bigger, then divided again. Each cell grows. The cells divide again. Each cell grows. PL E A single cell divides into two. To begin with, the cells are all the same. They produce a little ball of cells called an embryo, and eventually a baby. This all happens inside the mother’s body. By the time the baby is born, it is a miniature human being. It continues to grow until it is about 18–20 years old. Cells contain a lot of protein. Energy is needed to make cells divide. A pregnant woman and a growing child need plenty of protein in their diet, as well as enough energy to help cells to divide. Development SA M The change from a single cell to an adult human involves more than just growth. As the tiny embryo grows into a baby, all its different tissues and organs are formed. As the baby grows into a child, its leg muscles and bones become stronger, so that it can walk and then run. Its brain develops, as it learns to talk and to play with toys. These changes are called development. Each person is an individual, and everyone grows and develops at different rates, and in slightly different ways. But everyone goes through the same stages in development. These are shown in the chart in. Notice that each stage blends gradually into the next one – there are no sharp divisions between them. baby age in years 0 toddler 1 2 3 4 5 6 child 7 8 adolescent 9 10 11 12 13 14 15 adult 16 17 18 19 20 Questions 1 Growth means getting bigger. Explain what happens as a person grows, to make their body get bigger. 2 Some young children do not get enough protein or energy in their diet. Explain why they may not grow very tall. 246 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 7.3 Growth, development and health Exercise and health Topic 7.2 described some of the ways in which your diet can affect your health. There are other ways in which the decisions you make about your lifestyles can affect how healthy you are. Smoking PL E Taking regular exercise is a really good thing to do. This helps to use some of energy in the food you eat each day, stopping you from storing too much as fat. It also makes the heart and muscles work hard, so that they become strong. Exercise can also make people feel more cheerful and positive about life. Smoking cigarettes damages the smoker’s health. It also damages the health of people around them, who accidentally breathe in cigarette smoke. Tobacco contains many different harmful substances. Nicotine Tobacco smoke contains nicotine. Nicotine can help someone to stay alert. Nicotine is addictive. This means that it is difficult to manage without it, once you are used to smoking. This is why smokers find it so difficult to stop smoking. Tar M Nicotine damages the blood vessels in a smoker’s body. It makes them get narrower, so it is harder for blood to get through them. Smokers are more likely than non-smokers to develop heart disease. SA Tobacco smoke contains a mixture of dark, sticky substances called tar. Some of the chemicals in tar cause cancer. Cancer happens when cells start dividing out of control and spread to other parts of the body. Smoking increases the risk of getting many different kinds of cancer, including lung cancer. Carbon monoxide Carbon monoxide is a poisonous gas. When it gets into the body, it combines with haemoglobin inside red blood cells. This stops haemoglobin doing its normal job, which is to combine with oxygen and transport it to all the body cells that need it. So a smoker’s cells don’t get enough oxygen. They cannot carry out enough respiration, so don’t have enough energy. Particulates Tobacco smoke contains tiny particles of carbon and other materials, called particulates. They get trapped inside the smoker’s lungs. This makes the walls of the alveoli break down. Instead of having millions of tiny alveoli in the lungs, the smoker has a lot of big spaces. This is makes it difficult for them to get enough oxygen into their blood. 247 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 7 Diet and growth Activity 7.3.1 Why do people smoke? PL E Work in a group of three for this activity. Until the 1960s, no one realised that smoking was bad for your health. Today, everyone knows how harmful it is. In your group, discuss these questions. You might need to do some research to find the answers to some of them. • Why do people choose to smoke? Do you think the reasons are different for older people and younger people? • Why is it difficult to give up smoking, once you have started? • Why did it take so long for people to realise that smoking was harmful? In the 1940s and 1950s some cigarettes were advertised as being medically approved and good for you. Find some data about smoking from the 1950s. Where did the data come from? Was some of it biased? Why might tobacco companies have tried to hide the dangers? • Is the government in your country trying to reduce the number of people smoking? If so, what are they doing? Be ready to share your ideas. 10 Questions SA M The bar chart in Figure 7.3.2 shows the percentages of babies with a birthweight lower than normal, born to mothers who smoked different numbers Percentage of of cigarettes per day while they were pregnant. babies born with low Use the information in the bar chart to answer birthweight these questions. 3 4 5 What percentage of babies born to mothers who do not smoke have a low birthweight? Calculate the percentage of babies born to non-smoking mothers that do not have a low birthweight. Describe how smoking during pregnancy affects the chance of having a baby with a low birthweight. 8 6 4 2 0 none less than 15 15 or more Number of cigarettes per day smoked by mother during pregnancy Summary checklist I can describe how organisms grow. I can explain what is meant by development. I can explain why exercise is good for a person’s health. I can explain how smoking damages health. 248 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 7.4 Moving the body 7.4 Moving the body In this topic you will: learn about hinge joints and ball-and-socket joints • find out how a pair of muscles moves the arm at the elbow. Getting started PL E • Some bones protect parts of the body. Look at the diagram of the skeleton on the next page. Which bones do you think are important for protection? What do they protect? 2 Some bones are important in movement. Which bones do you think are important for movement? antagonistic muscles ball-and-socket joints biceps contraction exoskeleton hinge joints joints muscles relax skeleton tendons triceps SA M 1 Key words 249 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 7 Diet and growth The skeleton cranium Animals’ bodies are supported by a skeleton. Insects and other arthropods have a skeleton on the outside of their body. This is called an exoskeleton. clavicle scapula sternum rib humerus PL E Your skeleton is inside your body. It is made of bones. You do not need to remember the names of all of these bones, but you may know some of them already. vertebral column Bones are hard and strong. They contain a lot of calcium. If you do not have enough calcium in your diet, your bones may not grow properly. Bones contain living cells, so you also need protein in the diet to build strong bones. Joints ulna radius carpals femur Bones cannot bend. Movement in the skeleton can only take place where two bones meet one another. These places are called joints. tibia fibula M Some joints work like the hinges on a door. They let the bones move back and forth in one direction, in the same way that a door opens and closes. These are called hinge joints. pelvic girdle The human skeleton SA Some joints let the bones move in a complete circle. At these joints, one of the bones has an end shaped like a ball. The other bone has a cup, or socket, that the ball fits into. These are called ball-and-socket joints. Activity 7.4.1 Identifying different kinds of joint Work with a partner. Look at the diagram of the skeleton. If you have a model of a skeleton, you could look at that as well. Can you find at least two different hinge joints on the skeleton? (You may be able to find many more than two.) Try moving your own joints at these places. Which bones meet at the hinge joints? Now try to find two different ball-and-socket joints on the skeleton. Try moving your own joints at these places. Which bones meet at the ball-and-socket joints? Write down your ideas, and be ready to share them with the rest of the class. 250 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 7.4 Moving the body Questions 1 Explain what a joint is. 2 These pictures show a man hitting a golf shot. Which hinge joints is he moving? b Which ball-and-socket joints is he moving? PL E a M Joints in the arm You have several different joints in your arms. These include the shoulder joint, the elbow joint, the wrist joint and all the joints in the fingers. SA The photo is an X-ray of someone’s arm. Can you pick out the humerus, radius and ulna? You should also be able to find the hinge joint at the elbow, and the ball-and-socket joint at the shoulder. scapula (shoulder blade) ball-and-socket joint humerus wrist bones, with many joints between them radius hinge joint at elbow hinge joints in fingers ulna finger bones hand bones 251 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 7 Diet and growth Muscles PL E Bones and joints cannot move themselves. You use muscles to move bones at joints. Muscles are made of specialised cells. These cells are able to make themselves shorter. This is called contraction. Muscles use energy to contract. Like all cells, they get this energy from nutrients, especially glucose. The energy is released from glucose by respiration. The more you ask your muscles to contract, the more energy they use, and therefore the more glucose they use. Muscles can produce a strong pulling force when they contract. Many of your muscles are attached to bones, by tough cords called tendons. When the muscle contracts, it pulls on the tendon, which pulls on the scapula bone. This makes the bone move at a joint. This diagram shows the muscles that move the arm bones at the elbow joint. three tendons First, look at the biggest muscle in the diagram. triceps muscle This is the biceps. (Biceps is an unusual word, because it ends in an s even though it is singular. humerus One biceps, two biceps.) ‘Bi-‘ means two. This muscle is called the biceps because it has two tendons that attach it to the scapula. two tendons biceps muscle radius M ulna The longer, thinner muscle in the diagram is the triceps. Questions 3 6 Tendons are not stretchy. Suggest why. SA 4 5 The biceps is attached to the scapula at one end. Which bone is the other end attached to? Which bones is the triceps attached to? Tri- means three. Suggest why the triceps has this name. 252 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 7.4 Moving the body Bending the elbow joint Activity 7.4.2 Feeling your muscles To bend the arm, the biceps contracts (gets shorter) and the triceps relaxes. The contracting biceps pulls on the tendon, so the radius moves upwards. pulling force PL E Think about what happens when you bend your arm at the elbow. When you decide to bend your arm, your brain sends an electrical impulse along a neurone, to your biceps muscle. The cells in the biceps muscle respond to this electrical impulse by contracting. This makes the whole muscle get shorter. The biceps muscle is firmly fixed to the scapula at one end and the radius at the other end. So when it gets shorter, these bones are pulled closer together. The elbow bends, as shown in the diagram. You can do this activity on your own. Rest your arm on the table in front of you, keeping it straight. M Put the fingers of your other hand on your upper arm, where your biceps muscle is. Slowly and steadily, bend your arm upwards. Do this several times. What can you feel happening in your upper arm, when you do this? SA Be ready to share your ideas. Straightening the elbow joint Now think about how you straighten your arm at the elbow joint. It’s important to remember that muscles can only pull. They cannot push. Muscles can generate a force by getting shorter, or contracting. But they cannot generate a force by getting longer. So the biceps cannot push the arm straight again. You need another muscle to pull the arm straight. The muscle that does this is the triceps muscle. This diagram shows how it does this. When a muscle is not contracting, it relaxes. This is all that muscles can do – they can either contract or relax. To straighten the arm, the triceps contracts and the biceps relaxes. The contracting triceps pulls on the tendon, so the ulna moves downwards. 253 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 7 Diet and growth Antagonistic muscles You can see that the biceps muscle and the triceps muscle work as a team. • To bend the arm, the biceps contracts and the triceps relaxes. • To straighten the arm, the triceps contracts and the biceps relaxes. Think like a scientist PL E Two muscles that work together like this are called antagonistic muscles. When one of them contracts, it moves the bones at a joint in one direction. When the other muscle contracts, it moves the bones in the other direction. Using a model arm to investigate how the biceps muscle works You are going to investigate how the size of the force produced by the biceps muscle differs, if it is attached at different positions on the radius. You will need: • a model arm, like the one in the diagram • a newton meter • some masses on a hanger M Topic 3.4 showed that the arm acts like a lever. In this investigation, you are going to try attaching the ‘biceps muscle’ at different points along the ‘radius’, to find out the force needed to lift a weight. Set up your model arm like this. SA support masses hooks at 10 cm intervals ‘humerus’ firmly attached to support 0 10 20 30 40 piece of wood or strong cart to represent the humerus bone 50 60 70 80 90 100 newton meter ‘radius’ attached to ‘humerus’ with freely moving pivot piece of wood or strong card to represent the radius bone 254 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 7.4 Moving the body Continued Method Read through the method. Then construct a results chart to fill in your results. 2 Put some masses on the hanger. Start with just one or two masses. (Make sure you record these masses in your results table.) 3 Attach the newton meter to hook 1. Pull gently and steadily vertically upwards until the ‘radius’ makes a right angle with the ‘humerus’. Record the force reading on the newton meter as you keep the radius in this position. 4 Now attach the newton meter to hook 2, and repeat. 5 Repeat again, with the newton meter attached to hook 3 and then hook 4. 6 Put some more masses on the hanger. Repeat steps 4 to 6. Questions PL E 1 What does the newton meter represent in this model? 2 What happened to the force needed to keep the radius horizontal, as you moved the newton meter further away from the elbow joint? 3 Use what you have learnt about turning forces (moments) in your physics lessons to explain your answer to question 2. 4 What happened to the force needed to move the radius, when you added extra masses to the hanger? 5 Use what you have learnt about turning forces (moments) in your physics lessons to explain your answer to question 4. 6 Which position – 1, 2, 3 or 4 – matches the position where the real biceps is attached to the real radius? SA M 1 7 Muscles can produce very strong forces when they contract. But they cannot make themselves very much shorter. Suggest why the real biceps is attached in this position. Summary checklist I can name the bones in the arm. I can identify some hinge joints and ball-and-socket joints in the body. I can describe how muscles produce a force when they contract. I can explain how the biceps and triceps work as antagonistic muscles to move the arm at the elbow. 255 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 7 Diet and growth Check your progress 7.1 A weightlifter asks his trainer for advice on his diet. The trainer gives this advice. • Eat some protein with every meal. • Eat plenty of starch or other carbohydrates. a Copy and complete the sentences. Choose words from the list. contract fat relax glucose respiration PL E constriction The weightlifter uses his muscles to lift weights. The muscles to make the weights move. This uses energy. The muscles get the energy by breaking down in a reaction called . [3] Explain why the weightlifter needs to eat plenty of protein. [2] c Explain why the weightlifter needs to eat plenty of carbohydrate. [2] d List four other nutrients the weightlifter should include in his diet as well as protein and carbohydrate. [2] SA M b 256 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. Check your progress 7.2 The graph shows the mean mass of girls at different ages. 60 PL E 50 40 Mean mass / kg 30 20 a b d 4 6 8 10 12 Age / years 14 16 18 20 What is the mean mass of girls when they are two years old? [1] By how much does the mean mass increase between two years and 10 years old? [1] Between which ages does growth happen most rapidly? [1] Does the graph show that most girls have stopped growing by the age of 20? Explain your answer. [1] SA c 2 M 10 257 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 7 Diet and growth 7.3 The diagram shows the skeleton of a cat. Cats have the same bones as humans, but their sizes are different. D PL E A S R P C B Q b Which joints, A, B, C or D, are hinge joints and which are ball-andsocket joints? Choose from P, Q, R and S. c [1] Where should the two ends of a muscle be attached to move the cat’s front leg as shown by the arrow? M a [1] Where should the two ends of a muscle be attached to move the cat’s front leg back to its original position? Choose from P, Q, R and S. [1] What name is given to two muscles like the ones you have described in b and c? [1] Explain why two muscles are needed to move a bone in one direction and then back again. [2] f Name one mineral needed for the cat to form strong bones. [1] g Cats are predators. They eat other animals. Suggest where cats get this mineral from, in their diet. [1] SA d e 258 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. Project Project: A diet for Mars explorers In this project, you will evaluate issues that require scientific understanding. Your task You are going to work with everyone else in your class to produce a display about feeding astronauts as they travel to Mars and back. PL E The National Aeronautics and Space Administration, NASA, is hoping to send people to Mars by the 2030s. They have many problems to solve if they are going to achieve this. One problem is how to feed the astronauts so that they stay healthy and strong during the long trip. It would take up to three years to go to Mars and back. Here are some problems and suggestions that are being discussed by scientists and others. NASA could send a spaceship loaded with five years’-worth of food to arrive on Mars before the astronauts arrive. Would that work better than the astronauts taking all their food with them? • It would take up less space if the food could just be pills, instead of ‘real’ food. Would that work? • The bones and muscles of astronauts get smaller and weaker when they are in space for a long time. Are there any kinds of food that might help to reduce this problem? • To get fresh vitamins, astronauts need to eat fresh plant-based foods. Could they grow plants on their spaceship? Could they grow plants on Mars? M • SA Work in a group of four or five. Choose one or two of these problems – it would be good if different groups choose different ones. Use the internet to find other people’s ideas for solving them. You might also have your own ideas. Work with the other groups in your class to produce a display about how to feed the Martian astronauts. 259 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 8 Chemical reactions In this topic you will: PL E 8.1 Exothermic reactions • learn about chemical reactions that give out energy • plan and carry out an investigation Getting started Key words This word equation shows the reaction between carbon and oxygen that takes place when carbon burns: combustion dissipate exothermic reaction carbon oxygen + carbon dioxide fuel oxidation reaction • Name a reactant. preliminary work • Name a product. • How many atoms make up a particle of carbon dioxide? • How many of these atoms are carbon? • How do you know that burning releases energy to the environment? SA M Answer these questions and then compare answers with a partner. Be prepared to share answers with the class. 260 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 8.1 Exothermic reactions Burning ox yg at Fuels have a store of chemical energy. Charcoal, wood, coal, natural gas and oil are examples of fuels. fuel PL E When the fuel burns, the chemical energy is changed to thermal, light and sound energy. The thermal, light and sound energy dissipate (spread out) into the surroundings. he en When something burns, a chemical reaction takes place. Burning is a chemical reaction in which a substance combines with oxygen. In a burning reaction, there are energy changes. The substance that reacts with oxygen is called a fuel. M Burning requires oxygen, fuel and heat (thermal energy) SA Combustion is another term for burning. Look back at the equation in Getting started. You can see that, during the reaction, the atoms of carbon and oxygen join together in new ways. When this happens, chemical energy is changed to thermal energy and the temperature rises. A chemical reaction in which thermal energy is given out is called an exothermic reaction. Questions 1 What is needed for combustion to take place? 2 What is an exothermic reaction? 3 How can you tell that burning is an exothermic reaction? 261 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 8 Chemical reactions Burning other substances Hydrogen can be used as a fuel in a model rocket. The combustion of hydrogen is an exothermic reaction. The hydrogen and the oxygen combine to form water. hydrogen + oxygen water PL E hydrogen + oxygen water When the atoms of hydrogen and oxygen rearrange themselves and combine together, energy is given out. This chemical energy is changed into kinetic, thermal, sound and light energy. bent paperclips M stopper string to spark generator plastic bottle mixture of hydrogen and air Burning hydrogen can propel a plastic bottle like a rocket. SA In this experiment, a large plastic soda bottle filled with hydrogen and air is attached to a string across the room. The stopper in the bottle has wires that allow a spark to be generated. The hot spark provides the energy to start the reaction. The hydrogen and oxygen react together. The reaction gives out a lot of energy and the stopper is pushed out. This energy makes the bottle shoot (move very quickly) along the string. 262 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 8.1 Exothermic reactions The reactions of other substances burning in air are also exothermic reactions. An example is burning magnesium, which produces magnesium oxide. Energy is given out as heat and light as the magnesium and oxygen atoms rearrange themselves. Mg O Mg Mg O O Mg O oxygen + magnesium oxide PL E magnesium When a substance burns, it combines with oxygen and a new substance called an oxide is formed. Any reaction in which a substance combines with oxygen is an oxidation reaction. Burning magnesium ribbon An exothermic reaction with water This is the equation for the reaction between potassium and water. K H O H K H O H + water O H K O H potassium hydroxide H + H hydrogen M potassium K SA Water is made up of particles containing atoms of hydrogen and oxygen. In the potassium and water reaction, the bonds between the atoms of oxygen and hydrogen in the water break. The atoms rearrange to form the products potassium hydroxide and hydrogen. Stored chemical energy is changed to thermal energy, which dissipates into the environment. 263 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 8 Chemical reactions An exothermic reaction with acid If you add magnesium to dilute hydrochloric acid the test tube gets hot. This reaction is an exothermic one. °C 100 90 80 70 60 50 40 H 30 Cl 20 10 0 Mg + Cl Mg Cl Cl hydrochloric acid H magnesium chloride + H hydrogen PL E magnesium H Measuring the rise in temperature during a reaction Sofia and Marcus each measured 10 cm3 of dilute hydrochloric acid into a test tube and measured the temperature. Then they each added an identical piece of magnesium ribbon to their test tube of acid. When the reaction stopped, they each measured the temperature again. °C °C 100 100 90 90 80 80 70 70 60 60 50 50 4 40 4 40 30 30 20 20 10 10 0 M 0 SA Measuring the rise in temperature when magnesium reacts with hydrochloric acid. Sofia’s results Marcus’s results Start temperature in °C End temperature in °C Start temperature in °C End temperature in °C 18 42 21 45 Questions °C 4 What are the products when magnesium and hydrochloric acid react? 5 How did Sofia and Marcus know when the reaction had finished? 6 Marcus thought that more chemical energy had been changed to thermal energy by his reaction because, in his experiment, the end temperature was higher. Sofia thought that both reactions changed the same amount of chemical energy to thermal energy. Whose idea is correct? Explain why? 100 90 80 70 60 50 40 30 20 10 0 264 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 8.1 Exothermic reactions 7 Explain why it is a good idea to wear safety glasses whilst carrying out this investigation. 8 Sofia and Marcus wondered how they could produce a higher temperature change. Their ideas included adding more magnesium, using a different metal and using a different acid. Think like a scientist PL E Write each of these three ideas as a scientific question to be investigated. Planning and carrying out an investigation into the reaction between acid and magnesium Method Choose one of the scientific questions to be investigated from question 8 (or write one of your own) and write a plan for your investigation. • Before you write your plan, try out the reaction between magnesium and an acid. In this preliminary work you should practise measuring the temperature change. • Decide what equipment you will need and make a list. • You also need to find out how big a change in the variable (for example, the length of the magnesium ribbon) is needed to make a change in the temperature that you can measure. • When the reaction takes place and chemical energy is changed to thermal energy, the thermal energy dissipates (spreads out) into the environment. • • M 1 Are you sure that you are measuring the temperature change accurately? What could you do to reduce this heat loss? Decide how you will record and present your results. • Carry out a risk assessment. SA • 2 Ask your teacher to check your plan. 3 Carry out your plan. You may find that you want to make changes to it once you begin doing the investigation. If so, write down the changes that you have made and explain why you made them. Questions 1 What can you conclude from your results? 2 Compare your results with others from the class. Are your results in agreement with others who carried out the same investigation? 3 How could you improve your investigation? 265 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 8 Chemical reactions How can preliminary work help me to improve my investigation? Summary checklist SA M PL E I can describe what happens in an exothermic reaction. I can plan an investigation. I can carry out an investigation safely. 266 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 8.2 Endothermic reactions 8.2 Endothermic reactions In this topic you will: learn about chemical reactions that absorb energy • distinguish between exothermic and endothermic reactions and processes • learn about the use of exothermic and endothermic reactions and processes PL E • Key words Getting started When you make any scientific measurements, you are told that you need to be accurate and precise. endothermic process What do you think this means? Discuss it with your partner. endothermic reactions • Look at these three archery targets. C If you are being accurate, where should your arrows hit the target? SA • B M A • If you are being precise, should all your arrows be near to one another or spread out? • Which archer has been precise but not accurate? • Which archer has been neither precise nor accurate? • Which archer has been both accurate and precise? Share your answers and ideas with the class. 267 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 8 Chemical reactions Endothermic reactions Some chemical reactions absorb thermal energy from their surroundings and change it to chemical energy stored in the chemical bonds. These are called endothermic reactions. When an endothermic reaction takes place, the temperature at the end of the reaction is lower than that at the start of the reaction. Think like a scientist You will need: • a test tube PL E Carrying out an endothermic reaction • test tube rack • stirring rod • lemon juice or citric acid Method 1 • thermometer • sodium hydrogen carbonate • spatula • safety glasses Place some citric acid or lemon juice in a test tube so that it is about half full. 2 Measure and record the temperature. 3 Add three spatulas of sodium hydrogen carbonate and stir. Do not use the thermometer to do this. 80 60 40 30 What was the difference between the temperature at the start and the end of the experiment? Is thermal energy given out to the surroundings or taken in from the surroundings during this reaction? SA 2 90 50 Questions 1 100 70 Measure and record the temperature. M 4 °C 20 10 0 Looking at endothermic reactions This is the word equation for the reaction between sodium hydrogen carbonate and citric acid: sodium hydrogen carbonate + citric acid sodium citrate + water + carbon dioxide During this reaction, thermal energy is absorbed from the surroundings and stored in the form of chemical bonds. So, if this reaction was carried out in a test tube, the surroundings will have a lower temperature and the test tube will feel cooler. 268 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 8.2 Endothermic reactions If you eat sherbet sweets, this reaction takes place in your mouth. The sherbet is a mixture of dry citric acid and sodium hydrogen carbonate. When you eat the sweets, these substances dissolve in your saliva, and react together. This gives a cool ‘fizzy’ feeling in your mouth (the surroundings), which is refreshing. Questions What are the reactants in the reaction shown in the word equation above? 2 Which are the products in the reaction shown in the word equation above? 3 What is an endothermic reaction? 4 Explain why eating sherbet sweets makes your mouth feel cooler. 5 You may also get a ‘fizzy’ feeling in your mouth when you eat sherbet. Why is this? PL E 1 Another way to cool down M If you place about of water in a beaker and then stir in three spatulas of potassium chloride, you will find that the beaker gets cold. In this case, no chemical reaction has taken place. No new products are formed. The potassium chloride has just dissolved. A solution of potassium chloride has been formed. Potassium chloride is the solute and water is the solvent. SA When potassium chloride dissolves in water, thermal energy is absorbed from the surroundings. This is why the beaker feels cold. This is an endothermic process. Ice melting is another endothermic process. Thermal energy is absorbed from the surroundings as the solid ice changes to liquid water. Think about what happens to the particles when water changes state. The particles in the ice are lined up in rows and can only vibrate about fixed positions – they cannot move around inside the ice. The forces between the particles are strong. °C 100 90 80 potassium chloride 70 60 50 thermometer 40 30 glass rod 20 10 0 water energy taken in As the particles absorb thermal energy from the surroundings, they vibrate more and more. The ice begins to melt. When the particles have enough energy, they can move and overcome the forces holding them in place. The particles can now slide past one another. The water is now in a liquid state. 269 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 8 Chemical reactions Questions 7 8 9 Why is ice melting called an endothermic process and not an endothermic reaction? Suggest a change of state, other than ice melting, that is an endothermic process. When you have been swimming and you come out of the pool, you may feel cold. Use your understanding of endothermic processes to explain why. Suggest whether water freezing is an endothermic or exothermic process. Can you explain your suggestion? PL E 6 Endothermic or exothermic? In exothermic reactions and processes, thermal energy is given out. In endothermic reactions and processes, thermal energy is taken in. °C °C 100 100 90 90 °C 80 80 100 70 50 40 70 90 60 60 80 heat given out 70 50 60 40 heat taken in 50 30 M boiling water cooling 30 40 20 10 20 30 ice melting 20 10 10 0 0 0 SA Exothermic processes give out energy to the surroundings (left). Endothermic processes absorb energy from the surroundings (right). Think like a scientist Endothermic or exothermic? In this series of experiments, you will try some of reactions and processes and decide if the reaction or process gives out energy to the surroundings or absorbs energy from the surroundings. You will need: • beakers or polystyrene cups or other insulated containers • stirring rod • thermometer (do not use the thermometer for stirring the solutions) • chemicals as listed below • safety glasses 270 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 8.2 Endothermic reactions Continued Suggested reactions and processes to try 1 Sodium hydroxide and dilute hydrochloric acid. 2 Potassium chloride and water. 3 Melting ice cubes. 4 Copper sulfate solution and magnesium powder. °C 100 90 80 thermometer 70 Ammonium nitrate and water. 6 Boiling water until steam comes off. 7 Steam from a kettle directed at a cold surface. 8 Dilute hydrochloric acid and magnesium ribbon. 9 Sodium hydrogen carbonate and citric acid. 40 PL E 5 60 50 Method 30 20 10 0 polystyrene cup containing liquid Carry out some or all of the reactions or processes suggested. Make sure you do a risk assessment for each test that you do. Construct a results table. 2 Place one of the solutions in the beaker or polystyrene cup. 3 Measure and record the temperature. 4 Add the other substance. 5 Allow the substances to react, dissolve or change. 6 Measure and record the temperature. 7 Clean the thermometer and the glass rod before using them for the next test. 8 For each test you did, say if it is endothermic or exothermic and if it is a reaction or process. SA M 1 Questions 3 What advantage is there if a polystyrene cup is used rather than a glass beaker? 4 Which reaction gave out the most energy to the surroundings? 5 Which reaction absorbed the most energy from the surroundings? 6 Did you have difficulty measuring the temperature with any of these reactions or processes? Explain how you could decide if the reaction or process was exothermic or endothermic if you could not measure the temperature. 271 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 8 Chemical reactions Using exothermic reactions Some exothermic reactions are used to produce self-heating cans of food or drink. For example, a can of self-heating food contains two chemicals, which are in separate compartments. When you open the can, the two chemicals mix with each other and react. The reaction warms up the food or drink. opening system seal for water and calcium oxide compartments water waterproof separator calcium oxide heat insulator PL E The chemicals used are calcium oxide and water. When the water and calcium oxide are mixed together they react, and heat is given off. calcium oxide + water calcium hydroxide These cans can be very useful if you are in a remote area, or in an emergency when there is no power, or when you are camping. A self-heating can. When the can is opened, the seal between the water and the calcium oxide compartment is broken and the reaction takes place. Thermal energy is given out and transferred to the food. The cans are expensive to produce because the compartments must be sealed from one another and from the food, so that it does not become contaminated. There have also been problems with the food not being heated evenly. Using endothermic processes SA M People sometimes use ice packs when they injure themselves. These packs are stored in a fridge or freezer until they are needed. When the ice pack is placed on the injured area, heat from this area is transferred to the ice pack and the ice melts. This is an endothermic process. not an endothermic reaction as no new substances are formed It means that the injured area is cooled and this often prevents it from swelling up. After it has been used, the ice pack can go back into the freezer to be used again. Some ‘ice’ packs are made from substances that undergo an endothermic process when they mix together. A chemical icepack being used to treat an injury. These packs can be used even when you don’t have fridge or freezer. The pack has two compartments inside, each with a different substance. These are usually ammonium nitrate and water. When you push on the pack and break the compartment containing ammonium nitrate, the water mixes with it and the ammonium nitrate begins to dissolve. This is an endothermic process, so the temperature drops. 272 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 8.2 Endothermic reactions Questions 7 Explain why self-heating cans are very expensive. 8 Explain why a self-heating food container can only be used once. 9 Describe one advantage and one disadvantage of each of the two types of icepack described above. Summary checklist PL E What exothermic and endothermic reactions do I use in my everyday life? SA M I can list some chemical reactions that are endothermic. I can explain the difference between an endothermic reaction and an exothermic process. I can carry out an investigation to distinguish between exothermic and endothermic reactions and processes. I can describe some uses of exothermic and endothermic reactions and processes. 273 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 8 Chemical reactions 8.3 Metals and their reactions with oxygen In this topic you will: describe the reactions of some metals with oxygen • carry out an investigation • compare how reactive some metals are with oxygen Getting started PL E • collapses inert prevent reactive rusts SA M Think about what you learned about the properties of metals in Stage 7. In one minute, write down all the properties you can remember. Compare your list with a partner and add any new ones to your list. Then compare your new list with another pair and add any more properties. Be prepared to share your list with the class. Key words 274 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 8.3 Metals and their reactions with oxygen Metals and oxygen In Stage 7 you learned about the properties of metals. Now you are going to investigate how different metals react with oxygen. Think like a scientist Heating metals in air PL E In this activity, you will heat several different metals in air. Air contains oxygen, and some metals will react with it. Read though the instructions and decide on the safety precautions you will need to take. Discuss these in your group and then with the class before you carry out your investigation. You will need: • safety glasses • Bunsen burner • heatproof mat • tongs • small pieces of metal such as magnesium, zinc, iron and copper Method Take a small piece of one of the metals. 2 Place it in the tongs and heat it in a Bunsen flame. 3 Record your observations in a table and explain what happened. 4 Repeat steps 1–3 for each of the other metals provided. M 1 Questions Which was the most reactive metal that you used? What evidence do you have for this? 2 What safety precautions did you take? 3 Suggest why were you not given metals such as sodium or potassium to heat. 4 Suggest why were you not given metals such as gold or silver to heat. SA 1 275 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 8 Chemical reactions Looking at the reactions of metals with oxygen Many metals react with oxygen if they get hot enough. When you look carefully at the reactions of metals with oxygen, it is possible to identify which metals are more reactive. For example, magnesium is more reactive than iron because magnesium reacts more quickly than iron. This reaction between metals and oxygen is an oxidation reaction. SA M PL E Some metals react very quickly with oxygen without even being heated. When pieces of sodium, potassium or calcium are taken from their containers, they appear dull. When the pieces are cut, the surface is shiny. The shiny surface soon becomes dull because the metal reacts with the oxygen in the air. The surface becomes covered with a new substance – the oxide of the metal. These metals are so reactive that they have to be stored under oil to prevent them reacting. The layer of metal oxide on the surface prevents any more of the metal from reacting with the air or water vapour. A scientist cuts a piece of sodium metal with a scalpel. The general word equation for this reaction is: metal + oxygen metal oxide Some metals, such as gold, do not react with oxygen. They are generally unreactive. They are described as inert. Silver reacts slowly with the air and if a silver object is not cleaned it goes black over time, as silver oxide is formed. 276 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 8.3 Metals and their reactions with oxygen Questions 1 Which property for sodium and potassium is not typical of a metal? 2 Why is the scientist in the photograph wearing gloves to cut this piece of sodium? 3 Write a word equation for the reaction between sodium and oxygen. The reaction between iron and oxygen PL E When iron is left in damp air it rusts. The iron reacts with oxygen to form an orange-brown solid, called iron oxide, otherwise known as rust. iron + oxygen iron oxide This is not a very useful reaction because it means that the iron changes and no longer has the same properties. A strong iron girder can become rusted and fall apart. This could mean that a building collapses. SA M The reaction between iron and oxygen only takes place when both water and oxygen are present. The water is not part of the equation, but it is needed for the reaction to happen. The reaction takes a long time to happen – iron is not very reactive with oxygen. This new iron spanner, nuts and bolts are shiny. The iron sheets in this old barn have rusted. 277 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 8 Chemical reactions What causes iron to rust? A new iron nail is placed in each of four test tubes, as in the diagram. tube 1 tube 2 tube 3 PL E After a few weeks the experiment looks like this. tube 4 tube 1 tube 2 tube 3 tube 4 Test tube 1 contains nothing, apart from the nail, and is open to the air. Test tube 2 contains water and the nail is half in the water. The tube is open to the air. So, this tube has air and water. Test tube 3 has calcium chloride in the bottom. The calcium chloride absorbs water so the air inside the tube is dry. The tube is stoppered. Test tube 4 has water that has been boiled to remove as much dissolved gas as possible. On top of the boiled water is a layer of oil. This stops any air entering the water. The tube is stoppered. 1 2 3 Result moist air nail is rusted water and air nail is very rusty dry air no rust boiled water covered with oil, no air small amount of rust SA 4 M Tube number Contains Questions 4 What conditions are needed to prevent iron from rusting? 5 Which test tube and which conditions caused the iron to rust most quickly? 6 Why is the same type of nail used in all test tubes? 7 How is the air in tube 3 dried? 8 How is the air in tube 4 kept out of contact with the nail? 278 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 8.3 Metals and their reactions with oxygen How can iron be protected? PL E There are ways that iron can be protected so that it does not rust. The iron can be painted. This stops the oxygen in the air The iron can be galvanised. This means covering the iron reaching the iron. with a layer of zinc. This again prevents the oxygen reaching the iron. Why do we need to reduce the rusting of iron? M Summary checklist SA I can describe the reactions of some metals with oxygen. I can carry out an investigation safely. I can compare how reactive some metals are with oxygen. 279 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 8 Chemical reactions 8.4 Reactions of metals with water In this topic you will: describe the reactions of some metals with water • carry out an investigation • compare how reactive of some metals are with water Getting started PL E • reactivity sandpaper SA M Think back to the reactions of metals with oxygen, that you studied in Topic 8.3. Write down the name of the most reactive metal you learnt about and try to make a list of the other metals in order of how reactive they are. Compare your list with a partner and make one list to share with the class. Key words 280 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 8.4 Reactions of metals with water Think like a scientist Reactions of metals with water It can be difficult to see how some metals react with water because they may be covered in a surface layer of metal oxide if they have reacted with the oxygen in the air. In the investigations, you may need to use sandpaper to clean the surface of the metals so that the metal can come in direct contact with the water. • test tubes PL E You will need: • test tube rack • sandpaper • forceps • small pieces of metals such as magnesium, zinc, iron and copper Method Take a small piece of one of the metals you have been given. Use sandpaper to clean the surface of the metal. 2 Place the metal into a test tube of water. 3 Record your observations in a table and explain what happened. You may need to leave the metal to react for some time. If nothing happens, you could try testing the metal again, this time using hot water. 4 Repeat steps 1–3 for each of the other metals you have been given. M 1 Questions Which was the most reactive of the metals you were given? What evidence do you have for this? 2 Use the results of your experiment to arrange the metals in order of their reactivity, starting with the most active. 3 Suggest why some metals will react with hot water but not cold. SA 1 281 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 8 Chemical reactions Reactions of sodium and potassium with water PL E Some metals are too reactive for you to test in water. Sodium and potassium react very vigorously. They have to be stored under oil to prevent them from reacting with the water vapour in the air. M Sodium reacts vigorously with water.Potassium is even more reactive than sodium. So much thermal energy is generated that the hydrogen gas produced in the reaction catches fire. In these two reactions the metal reacted with water to produce hydrogen and the metal hydroxide. metal hydroxide + hydrogen SA metal + water Questions 1 Write the word equation for the reaction between sodium and water. 2 What safety precautions must be taken when these reactions take place? 3 Explain why these metals are stored under oil. 282 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 8.4 Reactions of metals with water Reactions of other metals with water Some other metals react less vigorously with water – for example, calcium and magnesium. In the experiment shown in the diagram, a piece of calcium has been placed at the bottom of a beaker and covered with water. A filter funnel has been placed upside down over the metal. The gas given off is collected in a test tube by the displacement of water. PL E Questions bubbles of gas 4 What is the gas that is given off ? How would you test for it? 5 How could you tell if calcium or magnesium is more reactive? 6 What factors should you take into account to make this a fair test? 7 Write the word equation for the reaction between calcium and water. metal (calcium) Some of the metals that do not react with water may react with steam. Even magnesium will react more rapidly with steam than with water. hydrogen gas burning M In the reaction shown here, magnesium is heated. From time to time, the heat is directed at the ceramic wool. The ceramic wool has been soaked in water, which when heated produces steam. In this reaction the magnesium reacts with water, which is in the form of a gas. Magnesium oxide and hydrogen are formed. The hydrogen gas that is given off can be burnt. magnesium ribbon ceramic wool heat Heating magnesium The word equation for this reaction is: magnesium oxide + hydrogen SA magnesium + water (g) In the equation above the (g) after water indicates it is water in the form of a gas, in this case steam. Steam is formed by boiling water and is very hot whereas water vapour is made up of water particles in the air at lower temperatures. Some metals, such as gold, do not react with water at all. Questions 8 Explain using particle theory, why the reaction between steam and magnesium is more vigorous than between water and magnesium. 9 Which metals do not react with water? Name three. 10 If an element is said to be inert, what does it mean? 283 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 8 Chemical reactions Summary checklist SA M PL E I can describe the reactions of some metals with water. I can carry out an investigation safely. I can compare how reactive some metals are with water. 284 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 8.5 Reactions of metals with dilute acids 8.5 Reactions of metals with dilute acids In this topic you will: describe the reactions of some metals with dilute acid • plan an investigation • carry out an investigation safely • compare how reactive some metals are with dilute acid Getting started PL E • You have 2 minutes to write down and complete as many of these word equations as you can. oxygen + sodium • oxygen + magnesium • oxygen + iron • water + potassium • water + calcium • magnesium + steam reagents salt M • Key words SA Check your partner’s work. Be prepared to share your answers with the class. 285 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 8 Chemical reactions A familiar reaction You will probably remember the reaction of magnesium with dilute hydrochloric acid. This is the word equation for this reaction: magnesium chloride + hydrogen magnesium + hydrochloric acid Magnesium chloride is an example of a salt. When a metal reacts with an acid, the products are a salt and hydrogen. PL E The general equation for this reaction is: metal + acid Questions salt + hydrogen 1 Write the word equation for the reaction between magnesium and sulfuric acid. 2 What is the salt produced in the reaction in question 1? 3 Describe what you would observe if this reaction took place in a test tube. 4 Write the word equation for the reaction between zinc and nitric acid. Think like a scientist M An investigation into the reaction of metals in acid Sofia and Marcus have been asked to investigate the reactivity of metals with acids. They need to decide on which of the equipment and reagents that are available in the laboratory they need, to enable them to carry out the investigation as shown below. cm3 100 °C 90 100 80 90 70 80 SA 70 60 cm3 10 50 9 5:00 40 30 hr min start stop 20 10 0 00.00 g ? 8 7 6 5 4 3 2 60 50 40 30 20 10 1 ? safety screen gloves safety glasses face protector Metals etals such as sodium, potassium, nesium, calcium, zinc, zin copper,rr, and iiron zinc ron magnesium, in the form of blocks, s, filings or powder 286 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 8.5 Reactions of metals with dilute acids Continued Part 1: Planning the investigation Use the information and ideas above to plan the investigation for Sofi a and Marcus. Choose which of the items in the diagrams they need to use. Some of the items are not appropriate to use. Discuss in your small group how you will answer these questions. What will they change? • What will they keep the same? • How will they measure the reactivity and decide which is the most or least reactive metal? • How will they keep safe? • What equipment will they use? PL E • Remember to include a results table and an idea of what they should be looking for in order to identify which are the most reactive metals. Write your plan and show it to your teacher. Questions Which of the metals shown, should not be used by Sofia and Marcus? Explain why. 2 Explain which measuring cylinder they should use to measure out enough acid to use in this investigation. M 1 Part 2: Carrying out the investigation SA Your task is to find the order of reactivity of the metals you are given, remember to work in a methodical way and keep an accurate record of your results. Method 1 Follow the plan you have written, once you have had it checked by your teacher. Remember to work carefully and to keep an accurate record of your results. 2 Select the appropriate equipment. A B C D E Questions 3 Which metal was the most reactive in dilute acid? 4 Which metal was the least reactive in dilute acid? 287 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 8 Chemical reactions Activity 8.5.1 Reactivity order PL E On seperate sticky notes, write the name of each of the metals you used when carrying out the investigation into the reaction of metals in acid. Stick these on to the table in the order of reactivity, with the most reactive at the top. Use the information from the investigation above. Compare your order with other groups. Are they the same or similar? Use the class results to make an order you all agree on. Does this order tie in with the results from the investigations of the reactions of metals with oxygen and water? Now write sticky notes for the metals you could not use (sodium, gold, silver, calcium and potassium) and fit those into your list. When you are happy with your order, make a poster to show your list and illustrate it with diagrams to show the various reactions with oxygen, water and/or dilute acids. Questions Which was the most reactive of the metals you used? 6 How did you decide which of the metals in the list was the least reactive? SA M 5 How did the three investigations help me to decide in which order to put the metals? Summary checklist I can describe the reactions of some metals with dilute acid. I can plan an investigation. I can carry out an investigation safely. I can compare how reactive some metals are with dilute acid. 288 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. Check your progress Check your progress 8.1 Match these words or phrases to the descriptions, a, b, c, d and e. Each word or phrase may be used once, more than once or not at all. burning evaporation decreases melting ice endothermic increases exothermic magnesium ribbon placed in hydrochloric acid a PL E sodium hydrogen carbonate added to citric acid An example of a chemical reaction where thermal energy is given out to the surroundings [1] b An example of an endothermic reaction [1] c The temperature in an endothermic reaction [1] d An example of an endothermic process [1] e The type of reaction between calcium and water [1] a b Which variable will Marcus change? d Explain what he must do in order to be able to identify which fuel gave out the most thermal energy to the surroundings. [2] Name one safety precaution he should take whilst carrying out this investigation. [1] b sodium hydroxide + … c … + oxygen d potassium + water carbon dioxide sodium chloride + … magnesium oxide …+… 40 thermometer 30 20 0 water spirit burner 8.3 Copy and complete the following word equations. carbon + … 50 10 [2] a °C [1] Name two variables Marcus must keep the same. SA c M 8.2 Burning is a chemical reaction where thermal energy is given out to the surroundings. Marcus has four fuels to investigate to find out which gives out the most thermal energy to the surroundings. He uses apparatus like this: fuel in spirit burner [1] [2] [1] [2] 289 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 8 Chemical reactions 8.4 Zara and Arun are carrying out an investigation into the heat given off when they add pieces of calcium to water. They both use water and add pieces of calcium. These are Zara’s results. Start temperature in°C Final temperature in °C 1 19 20 19 21 19 22 19 23 Start temperature in°C Final temperature in °C 21 22 21 22 21 24 21 25 2 3 4 Temperature change in °C PL E Mass of calcium added in g These are Arun’s results. Mass of calcium added in g 1 2 M 3 4 a Temperature change in °C What trend is shown by both sets of results? [1] Predict what would happen if of calcium were added. [1] Complete the table for both of the student’s results. [2] Construct a summary table to show the mean temperature change for each mass of calcium used. (Your table does not need to show the start and final temperatures). [2] Zara and Arun plot a graph of their results. Which variable and unit should they put along the horizontal axis? [1] f Which variable and unit should they put on the vertical axis? [1] g Zara and Arun carried out a third set of experiments, using water instead of . Could they use these results to add to the first two sets, to calculate the mean temperature change? Explain your answer. [2] b SA c d e 290 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. Project Background PL E Project: Working with chemicals safely Each day you make decisions about how to keep safe and minimise the risks that you take. It might be when you cross a street, when you make a hot drink, head a football, cook a meal or use a knife to cut vegetables. You probably don’t even realise you are doing it, but you are carrying out a risk assessment for most tasks. Your task M In the laboratory there are a number of hazardous situations and there are rules about how you should behave and what you should do to stay safe. In the picture above there are lots of things happening that are unsafe. People should never behave like that in a laboratory, so look carefully at the picture and identify as many things that are unsafe as you can. You should be able to explain why a thing is unsafe. Work in a group of three or four and make a list, with reasons. SA Your main task is to provide guidance to learners starting the secondary science course, to help them keep safe. You could write a poem or a song that could be on every laboratory wall or in every child’s notebook; you could write a guide book; write and perform a short play or make a poster that could be in every laboratory. You should try to come up with some original way of getting the safety message across. Your work will be shared with the whole class. 291 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 9 Magnetism In this topic you will: PL E 9.1 Magnetic fields • describe a magnetic field • understand that magnetic fields surround magnets • understand how magnetic fields interact Getting started compass like poles magnet magnetic magnetic field magnetic field lines SA M Work in pairs. Make a list of places where magnets are used. Key words 292 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 9.1 Magnetic fields The magnetic field A magnet is something that will attract magnetic materials. Magnetic materials include the metals iron, steel, nickel and cobalt. You will probably have used a magnet to attract paperclips. Magnets have two poles, north and south. They are shown with the letters N and S on diagrams. The paperclips are made from steel, which is a magnetic material. PL E When a paperclip is close to one of the poles of a magnet, the paperclip will be attracted to the magnet. As you move the paperclip further away, it stops being attracted. The paperclip is attracted to a magnet when it is in the magnetic field of that magnet. A magnetic field is the area around a magnet where the effects of the magnet can be detected. A magnetic field surrounds all magnets. The magnetic field of a magnet is strongest at the poles. paperclip M magnet The paperclip is outside the magnetic field of this magnet, so will not be attracted. SA You can detect a magnetic field in two ways. You can see whether a magnetic object moves because of attraction. You can also use a compass. A compass contains a magnetised needle that is free to turn. The needle will turn and point in the direction of a magnetic field. The picture shows a compass. Some mobile devices such as phones have compass apps. Magnetic field lines You can draw magnetic field lines around a magnet to represent the magnetic field. The rules are that • magnetic field lines join opposite poles • the magnetic field lines have arrows that point N S • magnetic field lines must not touch each other • magnetic field lines must not cross each other. A compass can be used to detect a magnetic field. 293 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 9 Magnetism Following these rules, the magnetic field lines around a bar magnet look like this: PL E and the magnetic field lines around a horseshoe magnet look like this: M You can tell by looking at magnetic field lines where the magnetic field is strongest. The magnetic field is strongest where the lines are closest together. If one magnet is stronger than another, the magnetic field of the stronger magnet will be different in two ways. • All the field lines will be closer together. • The field lines will extend further away from the magnet. SA You can also tell, by looking at magnetic field lines, in what direction a compass will point. When it is in a magnetic field, a compass will point in the direction of the lines. The five small compasses are pointing in the direction of the magnetic field lines. 294 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 9.1 Magnetic fields Magnetic fields interacting You probably already know about the forces between two magnets. • Two north poles repel. • Two south poles repel. • A north and a south pole attract. This force is due to the magnetic fields from each magnet. PL E Look at the field lines between two magnets when their opposite poles are together. The magnetic field lines between the two magnets are all pointing in the same direction. This means there will be a force of attraction between the magnets. Now look at the field lines between two magnets when their like poles are together. The magnetic field lines in the space directly between these two magnets are all pointing in opposite directions. This means the magnets will repel, or try to move away from each other. M Questions 1 Describe what is meant by the term ‘magnetic field’. 2 The magnetic field of magnet A extends further than the magnetic field of magnet B. SA State what can be concluded about the strengths of these two magnets. 3 Copy this diagram of a bar magnet. Draw the magnetic field lines around your diagram. S N Draw a total of eight lines and put arrows on each line. 4 a Draw magnetic field lines to show how a north and a south pole attract. b Draw magnetic field lines to show how two south poles repel. 295 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 9 Magnetism Activity 9.1.1 Showing a magnetic field pattern Work in pairs. PL E You will need: • a bar magnet • a horseshoe magnet (optional) • a piece of A4 size paper • piece of thick card, up to, but not thicker than, the thickness of the magnet • iron filings Safety Be careful not to get the iron filings on your skin. They can be sharp and get stuck in your skin. Be careful not to get the iron filing on the magnet. They are very difficult to remove and other people will get the iron filings on their skin. Method 2 3 SA 4 Cut a hole in the middle of the thick card, just large enough to put the bar magnet in. Put the bar magnet into the hole so it lies flat in the card. The card is to support the paper and keep the paper level. Put the paper on top of the card so the magnet is under the middle of the paper. Gently and evenly sprinkle the iron filings over the paper. Tap the paper gently to allow the iron filings to move into position. You should see a pattern like the one in the picture. M 1 Questions 1 2 3 a Where is the magnetic field strongest? b How can you tell this from the pattern of iron filings? a Can you tell by looking at the pattern of iron filings, which is the north or south pole? b Explain your answer. Look closely at the iron filings that are on top of the poles of the magnet. What do you observe? When you have finished, carefully lift the paper vertically away from the magnet. Bend the paper to form a slight ‘U’ shape and use this as a channel to pour the iron filings back into the container. 296 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 9.1 Magnetic fields Continued Extension If you have time, you could use two magnets, first arranged with like poles facing and then with opposite poles facing. In each case, try to explain the pattern of iron filings. PL E Think like a scientist Detecting a magnetic field In this investigation, you will investigate ways of detecting a magnetic field. Work in pairs or groups of three. You will need: See the diagram. You could also choose some other different types of magnets to investigate. Method 1 Set the magnet, ruler and paperclip on the smooth surface as shown in the diagram. ruler paperclip M bar magnet cm 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 smooth surface Record whether the north or south pole of the magnet is facing the paperclip. Slowly move the paperclip toward the pole of the magnet. Record the distance from the pole of the magnet when the paperclip becomes attracted to the magnet. Call this value d for distance. Repeat another two times and record all your measurements of d. Turn the magnet around so the other pole is facing the paperclip. Repeat steps 3–5 for this pole. If you have time, repeat the investigation with other, different, magnets. Continued SA 2 3 4 5 6 7 8 297 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 9 Magnetism Continued Questions 1 Calculate the average of your 2 Explain how the value of 3 Explain what your results show about the strength of the magnetic field from the north and south poles of the same magnet. 4 Explain why: is related to the strength of the magnetic field. PL E 5 values for each pole of each magnet you tested. a the surface needs to be as smooth as possible b the paperclip needs to be as small as possible. Suggest how you could improve this investigation to get more accurate values of d. Self-assessment For each of these statements, decide on how well you agree. Give yourself 5 if you agree very much and 1 if you do not agree at all. I understand what is meant by a magnetic field. • I can draw the magnetic field lines around a bar magnet. • I can draw the magnetic field lines between two opposite poles of different bar magnets. • I can draw the magnetic field lines between two like poles of different bar magnets. M • Summary checklist SA I can describe what is meant by the term magnetic field. I can explain how to detect a magnetic field. I can draw magnetic field lines around a magnet. I can draw magnetic field lines between two magnets. 298 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 9.2 The Earth as a giant magnet 9.2 The Earth as a giant magnet In this topic you will: discover that the Earth has a magnetic field • learn that the core of the Earth acts as a magnet Getting started PL E • Work in groups to discuss the answers to these questions. Where are the terms ‘north pole’ and ‘south pole’ used, in addition to their use with magnets? • What is a magnetic compass used for, apart from science experiments in school? geographic north pole magnetic north naturally occurring navigate SA M • Key words 299 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 9 Magnetism The Earth’s magnetic field SA M PL E Around 4000 years ago, a Greek shepherd called Magnes was looking after his sheep. The story of Magnes says that iron nails in his shoes stuck to one particular type of rock. The rock was called lodestone and contained a substance that was later named magnetite, which is a naturally occurring magnet. ‘Naturally occurring’ means it is not made by people. Both the Greeks and the Chinese started to investigate magnetic properties. The Chinese discovered that a small needle of lodestone, split off the rock, could be made to float on water. When allowed to float, the needle of lodestone always turned to point in the same direction. One end of the needle pointed toward the north and the other end pointed toward the south. This was the invention of the magnetic compass. It was soon discovered that the compass needle pointed to a position close to the Earth’s north pole, but not exactly to the geographic north pole. This point is now called The first compasses, in 200 BCE, looked like this. magnetic north. Magnetic north moves very slowly, and is currently in the Arctic Ocean, north of Alaska. The invention of the compass was very important because it allowed people to navigate in places such as oceans and deserts, with less chance of getting lost. With a compass, you will always know what direction you are facing. Even today with satellite navigation (satnav), ships and aeroplanes still use magnetic compasses. Satellite navigation, or satnav, systems do not use the Earth’s magnetic field. Some animals, such as the birds in the photograph, use the Earth’s magnetic field to navigate over long distances. The compass on this modern ship is the bowlFigure 9.2.2 shows what the Earth’s magnetic field lines shaped object near the centre of the picture. look like compared with a bar magnet. These birds are using the Earth’s magnetic field to navigate. spin axis The Earth’s magnetic field is similar to that of a bar magnet. 300 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 9.2 The Earth as a giant magnet Notice, in the diagram, that the magnetic field lines around the Earth point towards the Earth’s north pole. You will remember from Topic 9.1 that magnetic field lines point from north to south. This means that the north pole of Earth is actually a magnetic south pole! The term magnetic north, when used in context of the Earth and navigation means the magnetic pole that is close to the geographic north pole. In the same way, magnetic south is the magnetic pole that is close to the geographic south pole. PL E The geographic north and south poles are the parts of the Earth through which the spin axis passes. SA M The Earth’s magnetic field causes the natural appearance of lights visible in the night sky close to the north and south poles. These are caused by particles coming from the Sun arriving into the stronger parts of the Earth’s magnetic field. The needle on this magnetic compass is pointing towards the Earth’s magnetic north. This natural light display is caused by the Earth’s magnetic field. Origin of the Earth’s magnetic field People once thought that the Earth was made almost entirely from magnetic rocks. However, it is now known that the high temperatures deep inside the Earth would cause rocks to lose any magnetism that they had. Scientists also know that the Earth’s magnetic field has reversed in the past. The last change was around 500 000 years ago, when south really was north! 301 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 9 Magnetism PL E It is now known that the Earth’s core is the origin of the magnetic field, but scientists have still to discover the exact reason for this. They think the heat generated in the core, which is mostly made from iron, causes it to continually create a magnetic field. The core also contains some nickel, which is another magnetic metal. The movement in the liquid outer core would explain why the magnetic poles move slowly, and have occasionally reversed. Magnetic north moves at a speed of about 60 km per year. Questions Name the piece of equipment that is used for navigation and uses the Earth’s magnetic field. SA 1 M Airport runways are numbered according to their direction from magnetic north. The numbers sometimes have to be changed due to movement of magnetic north. 2 A bar magnet is allowed to rotate freely. Explain which pole of the bar magnet will point to geographic north. 3 The position of magnetic north on Earth moves at a speed of about per year. Explain why the position of magnetic north can still be used for navigation on a 12-hour journey. 4 a What part of the Earth’s structure causes the Earth’s magnetic field? b 5 Name the magnetic metal that makes up most of this part. a Draw a circle to represent the Earth. With the top of your circle representing geographic north, draw the magnetic field lines around the Earth. Add arrows to show the direction of the field. b State the relationship between the direction of the magnetic field lines and the direction that a magnetic compass will point. 302 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 9.2 The Earth as a giant magnet Think like a scientist Detecting the Earth’s magnetic field In this activity, you will change variables and describe how observations change. Work in groups of two or three. You will need: Method: Part 1 PL E • a needle or thin iron nail • a bar magnet • light string or thread • paper and scissors • adhesive tape • a bowl of water • a wooden clamp stand or non-magnetic support • a piece of cork or polystyrene on which the needle or nail will float Make a paper support for the bar magnet so that the magnet will hang horizontally, as shown in the diagram. 2 Use the light string to hang the magnet, in the paper support, from the wooden clamp stand as shown in the picture. Make sure there are no other magnets or large magnetic objects close by. 3 Allow the magnet to come to rest. Record the direction the magnet is pointing. 4 Move the equipment to another part of the room. Again record the direction the magnet is pointing. M 1 Method: Part 2 Hold the needle or nail and gently stroke the bar magnet along it several times. as shown in the diagram. 6 Record: SA 5 • which pole of the magnet was in contact with the needle • which direction the magnet moved along the needle. 7 Move the magnet away from where you are working. 8 Cut a disc from the cork or a circle from the polystyrene. Set the needle on the disc and float the disc in the water, in a non-magnetic dish as shown. 9 As in Method: Part 1, make sure there are no other magnets or large magnetic objects close by. 10 Allow the needle to come to rest and record the direction it is pointing. 11 Carefully move the equipment to another part of the room and record the direction the needle is pointing. Continued 303 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 9 Magnetism Continued Questions In Method: Part 1 and Method Part 2, the investigation is carried out in two different parts of the room. Explain the reason for this. 2 a In Method: Part 1, which pole of the magnet pointed north? b Explain what this shows about the poles of the Earth’s magnetic field. a In Method: Part 2, state which end of the needle pointed north. b Use your answers to 2 to help you to state which pole of the magnetised needle was pointing north. a Which pole of the magnet was used to stroke the needle or nail? b Which end of the needle was the magnet removed from after each stroking action? c What is the relationship between your answers to 4a and 4b? 3 4 5 PL E 1 In Method: Part 1 and Method Part 2, you made magnetic compasses. Explain why these compasses would not be practical for navigation on a journey. Self-assessment M Answer ‘yes’ or ‘no’ to each of these questions. I understand that the Earth has a magnetic field. • I can explain why the north pole of a magnetic compass points north, even though like poles repel. • I can describe an experiment to show that the Earth has a magnetic field. SA • Summary checklist I know that the Earth has a magnetic field. I can draw a diagram to show the Earth’s magnetic field lines. I can understand why the north pole of a freely rotating magnet points north. I know that the core of the Earth is the origin of the Earth’s magnetic field. 304 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 9.3 Electromagnets 9.3 Electromagnets In this topic you will: describe how to make an electromagnet • recall some applications of electromagnets Getting started PL E • Work in groups to consider applications where it would be useful to have a magnet that could be switched on and off. Key words coil core electromagnet magnetic magnetised SA M permanent magnets 305 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 9 Magnetism Properties of magnetic materials Electromagnets PL E A material is described as magnetic if it is attracted to a magnet. Magnetic materials include the metals iron, nickel and cobalt. Steel is another common magnetic metal. Steel is a mixture that contains a large proportion of iron. Magnetic materials can be magnetised. Magnetised means turned into a magnet. The magnets you have used were all made by magnetising magnetic materials. The magnets you have used are called permanent magnets because they have a magnetic field that is always there. You cannot switch the magnetic field off and on again. One way to magnetise a magnetic material is by using electricity. When this method is used, the magnet is called an electromagnet. M An electromagnet is made by wrapping a wire around a magnetic material, such as iron. The wire that is wrapped around is a called a coil. The material in the middle of the coil is called the core. When current passes through the coil, the magnetic material becomes magnetised. When the current is switched off, the magnetic material loses most of its magnetism. iron nail coiled wire cell – wire + The diagram shows the simplest type of electromagnet. Poles of an electromagnet SA An electromagnet has two poles, similar to a bar magnet. You can find out which pole is which in two simple ways. • • Use a magnetic compass. A magnetic compass points along magnetic field lines, so will point towards the south pole. Use a bar magnet with known poles. Opposite poles attract and like poles repel so, by bringing the bar magnet close to the electromagnet, you can detect which pole is which. You can reverse the poles of an electromagnet in one of two ways. • • Wrap the coil around in the opposite direction. Reverse the connections on the cell or power supply. Applications of electromagnets Electromagnets are used in many applications where a permanent magnet would not be useful. 306 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 9.3 Electromagnets The fire door in the picture is held open with an electromagnet. The electromagnet is connected to the fire alarm. When the fire alarm is switched on, the magnet is switched off and the door closes. When the electromagnet on the wall is switched off, the door will close. PL E Some types of scanners in hospitals use powerful electromagnets. An MRI scanner is used to produce images from inside the human body. MRI stands for magnetic resonance imaging. This MRI scanner uses a powerful electromagnet. M Electromagnets can also be used for sorting scrap metal. The electromagnet will attract iron and steel, leaving other nonmagnetic metals behind. Common non-magnetic metals include copper, aluminium and zinc. When the magnetic metals have been lifted, they can be moved away and then dropped by switching off the magnet. This electromagnet is sorting through scrap metal at scrapyard. SA In a toaster, when the handle is pushed down, an electromagnet holds a metal basket down. A timer turns the electromagnet off and the metal basket then pops up containing the toast. An electric bell uses an electromagnet to make the hammer move. When the electromagnet is on, the hammer is pulled onto the bell. The movement breaks the circuit and the hammer moves away from the bell. The circuit becomes complete again and the hammer is pulled back to the bell. This continues until the power supply is turned off. Electric bells are used in schools, as fire alarms and as door bells. When the electromagnet in the toaster switches off, the toast pops up. The cover has been removed to show the electromagnet inside this electric bell. There are two coils of wire in this electromagnet. Electric motors use electromagnets to change electrical energy into kinetic energy. This is the electromagnet from inside a small electric motor. 307 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 9 Magnetism Questions 1 Which of two of these metals can be magnetised? copper iron aluminium steel silver tin Explain the difference between ‘magnetic’ and ‘magnetised’. 3 State the main difference between an electromagnet and a permanent magnet. 4 Draw a diagram to show how an electromagnet could be made from: • a cell • a switch • a coil of wire • an iron nail. PL E 2 Use circuit symbols for the cell and the switch. a List three applications of electromagnets. b For one of your applications, explain why a permanent magnet would not be suitable. SA M 5 308 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 9.3 Electromagnets Activity 9.3.1 Making an electromagnet Work in groups of two or three. PL E You will need: • a cell • a cell holder or adhesive tape • about 1 m of plastic-coated wire with about 1 cm of insulation removed at each end • leads for use in circuits • a switch • a large iron nail • paperclips Method 7 8 Wrap the insulated wire around the iron nail to form a coil, as shown in the picture. Wrap the turns tightly around the nail and use as much of the length of the nail as you can. Leave enough wire at each end to connect to the cell. Make sure only the plastic coating of the wire is in contact with the nail. Connect the coil into a circuit as shown in the diagram. iron nail Test your electromagnet to see if the end of the nail will pick up paperclips. Use the pointed end of the nail. coil of insulated wire Only switch on your electromagnet for the shortest possible time, otherwise the cell will not last long. M 6 Questions 1 switch Suggest why it is important that only the plastic coating of the wire makes contact with the nail. In this activity, the whole length of the nail becomes magnetised. Suggest why you test the electromagnet by attaching paperclips to the end of the nail and not the middle of the nail. a Describe how you could find out whether the pointed end of the nail was the north pole or south pole of the electromagnet. b State what would happen to this pole if the cell in the circuit were reversed so current flowed in the opposite direction. SA 2 cell 3 Self-assessment Answer these questions after completing the activity. • Could you make an electromagnet by yourself? • If not, what would you need help with? 309 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 9 Magnetism Summary checklist SA M PL E I can understand the difference between an electromagnet and a permanent magnet. I know how to make an electromagnet. I know some applications of electromagnets. 310 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 9.4 Investigating electromagnets 9.4 Investigating electromagnets In this topic you will: discover which factors (or variables) affect the strength of an electromagnet • investigate how these variables affect the strength of an electromagnet Getting started PL E • Work in groups to discuss these questions. What are some differences between the electromagnets used for sorting scrap metal and for working a toaster • keeping a fire door open and for working an electric bell factors soft iron SA M • Key words 311 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 9 Magnetism Strength of electromagnets Topic 9.3 listed the three things that are needed to make an electromagnet: • • • a coil of wire a magnetic core inside the coil an electric current flowing in the coil. These three things are the factors that will affect the strength of an electromagnet. • • The number of turns in the coil. The more turns in the coil, the stronger the electromagnet. The material of the core. Iron and some types of steel in the core make the strongest electromagnets. The current in the coil. The greater the current, the stronger the electromagnet. PL E • A factor is another word for a variable that will affect something. The diagrams show the three ways to increase the strength of an electromagnet. 1 Increase the number of turns on the coil. Keep the current and core the same. Increase the number of turns on the coil. 1 1 Increase the number of turns on the coil. Keep the current and core the same. Increase the number of turns on the coil. Keep the current and core the same. M 15 turns of wire 15 turns of wire 15 turns of wire 2 2 2 Increase the current. Keep the number of turns on the coil and the core the same. Increase the current. Keep the number of turns on the coil and the core the same. Increase the current. Keep the number of turns on the coil and the core the same. SA Use more cells to increase the current. 15 turns of wire 15 turns of wire 15 turns of wire Use a soft iron core in place of a steel core. 3 3 3 20 turns of wire 20 turns of wire 20 turns of wire 15 turns of wire 15 turns of wire 15 turns of wire Change the core to soft iron. Keep the number of turns on the coil and the current the same. Change the core to soft iron. Keep the number of turns on the coil and the current the same. Change the core to soft iron. Keep the number of turns on the coil and the current the same. 15 turns of wire 15 turns of wire 15 turns of wire 15 turns of wire 15 turns of wire 15 turns of wire steel core steel core steel core soft iron core soft iron core soft iron core 312 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 9.4 Investigating electromagnets Soft iron is not soft in the same way as modelling clay is soft. Soft iron is the term used for iron that is easily magnetised and also easily demagnetised. Demagnetised means it has lost its magnetism. In 2019, scientists broke the world record for the strongest electromagnet. They made an electromagnet 4500 times stronger than a school bar magnet. It uses more electricity than three million electric lamps! Questions PL E The strength of an electromagnet can be measured by the force that the electromagnet exerts on a magnetic material. The easiest way to do this is to see how many magnetic objects that the electromagnet can lift and hold. 1 Explain why an electromagnet for sorting scrap metal needs to be stronger than the electromagnet that holds the handle of a toaster down. 2 State the three factors that affect the strength of an electromagnet. 3 The diagrams show circuit diagrams for four electromagnets. Each has the same current and the same number of turns in the coils. The material of the core is shown on each diagram. wood M rubber SA A B nickel aluminium C D Which of the circuit diagrams will make the strongest electromagnet? Write one letter. 4 A science laboratory called CERN in Switzerland uses many very strong electromagnets. The electricity used by CERN is the same as that of a small city. Suggest why CERN uses so much electricity. 313 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 9 Magnetism Think like a scientist Investigating electromagnet strength In this activity, you will carry out investigations and plan further investigations on the strength of electromagnets. Work in groups of two or three. You will need: Safety PL E • three 1.5 V cells or an adjustable d.c. power supply with safety cut-out • leads and connectors • switch • an ammeter • iron nail • paperclips of different sizes • plastic-coated wire at least 1 m long with about 1 cm of plastic removed from each end • selection of similar-sized cores to the iron nail, such as a wooden pencil, roll of paper, plastic pen and at least one other metal Only keep your electromagnet switched on for the shortest possible time, otherwise your cells will not last long. M Check that the wire in the coil is not becoming hot. If the wire becomes hot, switch off immediately and tell your teacher. Method: Part 1 – changing the number of turns in the coil 1 Make an electromagnet. Use the number of cells or the power supply setting that your teacher advises. (You should recall how to make an electromagnet from Topic 9.3.) SA Use the iron nail for the core. Wrap the wire around the core to make five turns. 2 Switch on the electromagnet and see how many paperclips it will hold. Record this result. 3 Switch the electromagnet off and increase the number of turns on the coil by five. 4 Switch on the electromagnet and see how many paperclips it will hold. Record this result. 5 Repeat steps 3–4 until you can’t fit any more turns on the core. 6 Repeat the entire investigation. If any of your results are different, you may need to repeat them a third time. 314 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 9.4 Investigating electromagnets Continued Questions 3 4 Record your results in a table. Calculate the average number of paperclips for each number of turns in the coil. Draw a line graph of your results. Put number of turns in the coil on the horizontal axis. Describe the trend in your results. PL E 1 2 Method: Part 2 – changing material in the core 1 2 3 4 Make an electromagnet. Use the iron nail as the core. Wrap the maximum number of turns in the coil that will fit on the core. Use the number of cells or the power supply setting that your teacher advises. Switch on the electromagnet and see how many paperclips it will hold. Repeat this with other core materials. The other cores should be about the same diameter, so you should not have to unwind the coil each time. As in Method: Part 1, repeat each of your measurements. Questions 7 SA 8 9 Record your results in a table. For each core material, calculate the average number of paperclips for each number of turns in the coil. Draw a bar chart of your results. Put the materials of the core on the horizontal axis. Describe any trends in your results. Explain why a line graph was used in Part 1 and why a line graph would not be suitable in Part 2. M 5 6 Method Part 3 – changing the current in the coil In this part, you will plan the investigation yourself. The aim of this part is to investigate how the current in the coil affects the strength of the electromagnet. 1 Decide which variable to change and how you will change it. Your teacher can help with this. 2 Decide which variables you will control. 3 Draw a circuit diagram for your electromagnet. 4 Make a prediction for your investigation. 5 Decide whether large or small paperclips will give better results. Explain your choice. Continued 315 to publication. Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior We are working with Cambridge Assessment International Education towards endorsement of this title. 9 Magnetism Continued 6 If you have time, carry out your investigation and record your results in a suitable table. Questions 10 Explain whether a line graph or a bar chart is more suitable to display your results. PL E 11 Display your results in the type of graph you have chosen. 12 Explain whether your prediction was accurate. Self-assessment Rate your confidence in each of these statements. • I can recall the three factors that affect electromagnet strength. • I could plan an investigation to test the effect of changing one of these factors. • I can understand whether a line graph or bar chart is more suitable for presenting results. M Summary checklist SA I can recall the factors that affect the strength of an electromagnet. I can predict how a change in any one of these factors will affect the strength of the electromagnet. 316 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. Check your progress Check your progress 9.1 What is a magnetic field? Write one letter. [1] An area where you can use a magnet. B An area where magnetism can be detected. C An area to store magnets. D An area where all magnets are not allowed. PL E A 9.2 What direction do magnetic field lines point? NS SS NN Copy the diagram of a horseshoe magnet. M 9.3 a SN [1] N S Draw the magnetic field pattern of the horseshoe magnet on your diagram. Copy the diagram of two south poles from different magnets. SA b [3] Draw the magnetic field pattern between these two south poles on your diagram. [3] 317 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 9 Magnetism 9.4 Copy this diagram of the Earth on its axis. PL E N S The letters N and S on the diagram show the geographic poles. Draw the pattern of the Earth’s magnetic field on your diagram. [3] 9.5 A soft iron cylinder produces no change in the reading of a magnetic compass. A coil of wire is wrapped around the soft iron cylinder. Electric current is passed through the coil. What change happens in the soft iron cylinder? Write one letter. B C It starts to become a permanent magnet. It starts to become magnetised. It starts to become demagnetised. SA D It starts to become magnetic. M A 9.6 a b [1] State the name given to a magnet that can be switched on and off. [1] Draw a labelled diagram to show how this type of magnet could be made. [4] 9.7 Arun makes an electromagnet using: • one 1.5 V cell • an iron nail 15 cm in length • 10 turns of wire around the nail. a State the effect on the strength of this electromagnet if Arun increases the number of turns of wire around the nail to 20. [1] 318 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 9.4 Investigating electromagnets Arun uses an ammeter to measure the current in the electromagnet circuit. Arun then varies the current. For each current, Arun measures the number of paperclips that the electromagnet will hold. i State the independent variable in this investigation. [1] ii State the dependent variable in this investigation. [1] iii Copy these graph axes and sketch the shape of graph you would predict for the results. PL E b [2] Assume both axes start at zero. Number of paperclips held c M Current in electromagnet Arun wants to investigate the effect of changing the material in the core of her electromagnet. i [2] Which of these materials in the core will make the strongest electromagnet? SA ii List two factors that Arun will need to keep constant when changing the material in the core. Choose one material. paper [1] copper plastic cobalt 319 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this title. 9 Magnetism Project: Investigating magnetism Background Magnetism is all around us in our daily lives. Fridge magnets, computer hard disc drives, electric motors and headphones all use magnetism. Topic 9.2 gave some information about the discovery of magnetism, and a little information about how some animals use the Earth’s magnetic field. Your task PL E Work in groups of three or four. Your group can find out about some of these different aspects of magnetism: • more about the early discoveries in magnetism • more about how animals use magnetism • how the Earth’s magnetic field protects us • magnetic fields around other planets in the Solar System • the strongest known natural magnets in the universe • the many and varied uses of magnets You do not have to include all of these, or you could find out about other aspects of magnetism. M Connect the information you find to tell a story. Present this story in any way you choose, for example: a picture story board • a poem • a stage play SA • • a song. All members of the group should have a role in presenting the story. 320 Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication.