Cambridge Primary Science 6 Learners Book 2nd Edition 2021 PDF

CAMBRIDGE Primary Science Learner’s Book 6 Fiona Baxter & Liz Dilley 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 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/9781108742726 © 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 2014 imprints to be updated 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 ISBN 978-1-108-74272-6 Paperback Additional resources for this publication at www.cambridge.org/delange Cambridge University Press has no responsibility for the persistence or accuracy of URLs for external or third-party internet websites referred to in this publication, and does not guarantee that any content on such websites is, or will remain, accurate or appropriate. Information regarding prices, travel timetables, and other factual information given in this work is correct at the time of first printing but Cambridge University Press does not guarantee the accuracy of such information thereafter. NOTICE TO TEACHERS IN THE UK It is illegal to reproduce any part of this work in material form (including photocopying and electronic storage) except under the following circumstances: (i) where you are abiding by a licence granted to your school or institution by the Copyright Licensing Agency; (ii) where no such licence exists, or where you wish to exceed the terms of a licence, and you have gained the written permission of Cambridge University Press; (iii) where you are allowed to reproduce without permission under the provisions of Chapter 3 of the Copyright, Designs and Patents Act 1988, which covers, for example, the reproduction of short passages within certain types of educational anthology and reproduction for the purposes of setting examination questions. Introduction Introduction Welcome to Stage 6 of Cambridge Primary Science. We hope you will enjoy using this book and find out how interesting and exciting Science can be. People have always asked questions about things they observed and looked for answers to their questions. For example, in Stage 6 you will find the answers to these questions: Why does our heart beat? How do huge ships manage to float How does our body protect us on the ocean? against diseases? What is the difference between a series How can people harm food chains? circuit and a parallel circuit? How can we tell if a chemical reaction What causes rainbows? has taken place? Why does the Moon look different at How do rocks and fossils form? different times of the month? How does the Moon stay in orbit around the Earth? You will work like a scientist to find the answers to these questions. You will also ask your own questions to investigate. We have included a variety of different activities and exercises for you to try. Sometimes you will work with a partner or work in a group. You will be able to practise new skills such as drawing and interpreting circuit diagrams, presenting results on a scatter graph and interpreting food webs. As you practise these new skills, you can check how you are doing and also challenge yourself to do better. You will be able to reflect on how well you have worked and what you could do differently next time. We use science in our lives every day. You will see how science knowledge is important when we discuss issues such as pollution and the spread of diseases. You will learn about some of the things that scientists in the past discovered and invented and how scientists today are still improving on these designs. You will also see how people use science to divide the year up into months. We hope you enjoy thinking and working like a scientist. Fiona Baxter and Liz Dilley iii Contents Contents Page Unit Science strand Thinking Science in Context and Working Scientifically strand viii Working like a scientist 2 1 The human body Biology Models and Describe how scientific Structure and representations knowledge and function Scientific enquiry: understanding changes purpose and planning over time through the use of Life processes evidence gained by enquiry Carrying out scientific enquiry Analysis, evaluation and conclusions 35 2 Materials: properties Chemistry Scientific enquiry: Identify people who and changes Properties of purpose and planning use science, including materials Carrying out professionally, in their area scientific enquiry and describe how they use Changes to science materials Analysis, evaluation and conclusions Describe how science is used in their local area 63 3 Rocks, the rock cycle Earth and Models and Identify people who and soil Space representations use science, including 3.1 Igneous rocks Planet Earth Scientific enquiry: professionally, in their area purpose and planning and describe how they use 3.2 Sedimentary rocks Cycles on science. and fossils Earth Carrying out 3.3 Metamorphic rocks scientific enquiry and the rock cycle 3.4 Soil 97 4 Food chains and Biology Models and Discuss how the use of food webs Ecosystems representations science and technology can Carrying out have positive and negative scientific enquiry environmental effects on their local area. Analysis, evaluation and conclusions Use science to support points when discussing issues, situations or actions. iv Contents Page Unit Science strand Thinking Science in Context and Working Scientifically strand 112 5 Forces and electricity Physics Models and Describe how scientific 5.1 Mass and weight Forces and representations knowledge and energy Scientific enquiry: understanding changes 5.2 The effects of forces purpose and planning over time through the use of 5.3 Floating and sinking evidence gained by enquiry. Carrying out 5.4 Different circuits Electricity and scientific enquiry and circuit diagrams magnetism Analysis, evaluation and conclusions 142 6 Light and the Solar Physics Models and Describe how science is System Light and representations used in their local area. 6.1 Reflection sound Scientific enquiry: 6.2 Refraction purpose and planning 6.3 The Solar System Earth and Carrying out Space scientific enquiry Earth in Space Analysis, evaluation and conclusions 168 New science skills 174 Glossary 180 Acknowledgementts v How to use this book How to use this book In this book you will ﬁnd lots of different features to help your learning. What you will learn in the unit. Questions to find out what you know already. 4 Living Things Important function support words and protect muscles their meanings. organs length An investigation to carry out with a partner or in groups. These questions help you track your progress. A fun activity about the science you are learning. vi 14 How to use this book Questions to help you think about how you learn. This is what you have learnt in the unit. At the end of the unit, there is a project for you to carry out, using what you have learnt. You might make something or solve a problem. Questions that cover what you have learnt in the unit. If you can answer these, you are ready to move on to the next unit. vii Working like a scientist Working like a scientist We can work like scientists and use the five different types of scientific enquiry to find answers to different kinds of science questions. Research Sometimes we cannot find the answer to a scientific question in a direct way, such as by doing an investigation. This might be because it is impossible or unsafe to do. Instead, we can do research to find the information we are looking for. We can use books, use the internet or watch videos. These are called secondary sources of information. We can use this type of scientific enquiry to: find out about new scientific discoveries, such as how the coronavirus virus is spread, or discoveries made in the past, for example how scientists first invented batteries build on our knowledge of a topic, such as finding out about the respiratory systems of different vertebrates compare information from different sources and decide which answer is best, for example finding out how different factors can affect pulse rate, or the effects of harmful substances in food chains help us realise that sometimes there are questions that scientists don’t yet know the answers to. For example, why does the force of gravity only pull and not push? Fair testing In a fair test we change one factor or variable and keep all the others the same, to try to answer a scientific question. By changing only one variable, we know that no other variable will affect the results of the test. For example, if we investigate the question in Unit 2, ‘does water temperature affect the rate of dissolving?’ then: the water temperature is the independent variable that we change viii Working like a scientist the time it takes the solute to dissolve is the dependent variable that we measure the amounts of water and solute and number of times we stir the solution are the control variables that we keep the same. Observing over time In investigations we often need to observe changes caused by things we do. How often we need to observe depends on the changes we are looking at. We can see some changes straight away, such as the formation of a gas when we mix vinegar and baking soda. If we observe what happens to our breathing rate when we exercise, we can see the change in a few minutes. Observing changes in nature can often take longer. We will need a month to observe the changes in the Moon’s appearance as it orbits the Earth. ﬁrst quarter waxing waxing gibbous cresent C sunlight D B Earth full E A new F H waning G waning gibbous cresent third ix quarter Working like a scientist Identifying and classifying igneous rocks Identifying is the process of naming can you see the crystals something, for example the different types with the naked eye? of blood vessels in the human body. We can name them because they have features we recognise, such as the thickness of the blood yes no vessel wall. We classify objects, materials and living things in groups by observing the rock is an intrusive rock is an ways in which they are different. We can igneous rock, e.g igneous rock, e.g usually classify these things by asking a basalt series of ‘yes or no’ questions. For example, we can use a key to find out the type of igneous rock in a sample we have found. Pattern seeking Pattern seeking involves observing, recording and analysing data. The patterns we observe can help us to identify a trend or relationships between one or more things. We often find patterns in nature where we cannot easily control the variables. For example: a pattern linking mass of an object with its weight a pattern between the time a planet takes to travel around the Sun and its distance from the Sun. Mercury Saturn Venus Neptune Mars Uranus Earth Jupiter Asteroid belt x 1 The human body 1.1 The circulatory system We are going to... describe the parts of the circulatory system and their functions learn that the circulatory systems of other animals are similar to ours measure pulse rates and record results in tables make a prediction and plan a fair test on the effect of exercise on pulse rate use results to say if the prediction was accurate describe any patterns in results and use results to make a conclusion find information to answer a scientific question ask a question to investigate and find the answer. blood circulation oxygen blood vessels circulatory system pressure carbon dioxide heart pulse 2 1.1 The circulatory system Getting started The parts inside your body are called organs. The body organs do different jobs to keep you alive and healthy. Discuss these questions with a partner. Be prepared to share your ideas with the class. 1 Which organ is found in the head? 2 Which organs are found in the chest? 3 Which organ pumps blood around the body? 4 Name two organs in the digestive system. Parts of the circulatory system The circulatory system carries food and oxygen to all parts of your body. It also carries waste substances that your body does not need. The circulatory system has three main parts: the heart blood vessels blood. to body blood The heart carrying oxygen Put your hand on your chest. Can you feel your to lungs heart beating? Why does your heart beat? Make a fist with your hand. That’s how big your heart is. Your heart is found inside your from lungs chest, slightly to the left. It is protected by the ribs. Your heart is a special muscle. Its job is to pump blood through your body. This process is called circulation. Every time the heart blood muscle contracts to pump blood, you can without oxygen feel a heartbeat. It takes less than a minute to pump blood to every part of your body. The heart does this all the time and never stops. from body 3 1 The human body Why must the The heart has two sides. The left side pumps blood that contains oxygen heart pump blood around all around the body. The right side the body? pumps blood without oxygen to the lungs only. The drawing shows the flow of blood in the heart. When you look at the drawing, remember that the left side of the drawing shows the right side of the heart and the right side of the drawing shows the left side of the heart. Blood vessels and blood Blood is a red liquid that flows around the body. heart lungs The blood carries food particles and oxygen to all parts of the body. It also picks up waste products, such as carbon dioxide, from the body and carries them to organs which can get rid of them. Carbon dioxide is a waste gas that the body must get rid of. The kidneys and lungs are body organs that help the body get rid of waste products. Blood moves through the body in the blood vessels. Look at the inside of your wrist. Sometimes you can see the blood vessels through your skin. There are three kinds of blood vessels: arteries veins blood carrying capillaries. blood oxygen without from the oxygen lungs 4 1.1 The circulatory system Each kind of blood vessel has a Capillaries – joins arteries and veins. Very narrow different structure and function with thin walls to allow in the body. Artery – carries blood substances like oxygen and containing food and The blood vessels run from the oxygen away from food to move through them heart to the lungs, around the the heart to the body Small artery body and back to the heart. Small vein Blood always moves along the same pathway in the blood vessels. The heart pumps blood in arteries to the lungs to pick up oxygen. The oxygen-rich blood travels Thick elastic back in veins from the lungs muscular wall Thin elastic muscular wall to the heart. These are the only veins that carry blood with oxygen. Vein – carries blood containing The heart pumps the oxygen-rich wastes, such as carbon dioxide, blood in other arteries to the rest from the body towards the heart of the body. The blood from the rest of the body, which is now low in oxygen, travels back to the heart in veins. Questions 1 a What does the heart do? b Why does it do this? 2 What is a heartbeat? 3 Why does the heart pump blood to the lungs before it pumps blood to the rest of the body? 4 Why do we need three different types of blood vessels? 5 Describe to your partner the pathway of blood around the body. Make a cycle diagram to show this pathway. 5 1 The human body Circulatory systems of other animals Many vertebrates have a similar circulatory system to ours. The pictures show the circulatory systems of a fish, a frog and bird. FISH FROG BIRD gill capillaries lung and skin capillaries lung capillaries artery artery artery heart vein vein heart vein heart body capillaries body capillaries body capillaries Activity 1 Compare circulatory systems of some vertebrates Work with a partner. Look at the drawings of the circulatory systems of different vertebrate animals, then discuss the questions. 1 Which parts of the animal circulatory systems are the same as the human circulatory system? 2 How are the animal circulatory systems are different to the human circulatory system? Explain this to a partner. How am I doing? Answer ‘well’, ‘okay’ or ‘I need help’ to each of the questions below. How well can I: identify the parts of the circulatory system in humans and other vertebrates? explain how the animal circulatory systems are different to the human circulatory system? 6 1.1 The circulatory system Heartbeat and pulse Your heart beats about 90 times a minute. When you are grown up it will beat about 70 times a minute. When you run around, your body needs a lot more food and oxygen. The more active you are, the more often your heart needs to beat to supply enough food particles and oxygen from the blood. You can count your heartbeats by feeling your pulse. Your pulse is caused by the pressure of the blood as the heart pumps it to the rest of the body. Two good places to find your pulse are on the side of your neck and the inside of your wrist. When you find your pulse you will feel a small beat under your skin. Each beat is caused by the contraction of your heart muscle. Think like a scientist 1 Measuring pulse rate You will need: a watch or timer that can time seconds 1 Find your pulse on your wrist or neck. 2 Count how many beats you feel in one minute. Repeat this three times. 3 Record the results in a table. Is the number of beats the same each time? 4 Compare your measurements with others in your class. 7 1 The human body Continued I could feel my heart beating faster after I ran Questions to catch the school bus 1 What is the difference this morning. between heartbeat and pulse? 2 Did everyone in your group have the same pulse rate? Why do you think this is? 3 Work out your average pulse rate from the measurements you made. 4 Which type of scientific enquiry did you use in the investigation? How am I doing? Choose a card to answer the questions. How well can I: measure pulse rate? explain the difference between heartbeat and pulse? I get it! I can even explain to others. I need a little more help. I don’t understand it. I need a lot of help. 8 1.1 The circulatory system Think like a scientist 2 How does exercise affect pulse rate? Plan a fair test investigation to find out how doing exercise affects our pulse rate. 1 a Make a prediction to answer the question you are going to investigate. Say why you made this prediction. b How will you test your prediction? 2 Identify the variables in your investigation that you will: measure change keep the same. 3 Identify the equipment you will need. 4 Decide how you will record and present your results. 5 Carry out your investigation and present your results. Questions 1 Was your prediction correct? 2 Describe any pattern you could see in the results. 3 What conclusion could you make from your results? 4 Which two types of scientific enquiry did you use in the investigation? Explain your answer. How are we doing? As a group, choose one the faces as your answer to each of or or the questions. Could we make a prediction with reasons? Could we identify the different variables in the investigation? Could we choose suitable materials and equipment to use? Could we say how to record and present our results? Did we work together to plan and carry out the investigation? 9 1 The human body Activity 2 Identify other factors that affect pulse rate You have found out that exercise affects pulse rate. What other factors can affect pulse rate? How do these factors affect pulse rates? Do some research to find the answer. Report back to the class on your findings. Think like a scientist 3 Ask and investigate a question You have investigated how exercise affects pulse rate. With a partner, think of another question about heartbeats and pulse rates that you would like to find the answer to. Decide on the type of investigation you will use to answer your questions; for example, a fair test, doing research or observing over time. Find out the answer to your question. Make a presentation to share with the class about your findings. What did I do to help my group in the practical tasks? Why did I choose to help them in this way? 10 1.1 The circulatory system Look what I can do! I can describe the parts of the circulatory system and their functions. I can say how the circulatory systems of other animals are similar to ours. I can measure pulse rates. I can record results in tables. I can plan a fair test on the effect of exercise on pulse rate. I can make a prediction about how exercise affects pulse rate. I can use results to say if the prediction was accurate. I can describe any patterns in results. I can draw a graph of results. I can use results to make a conclusion. I can find information to answer a scientific question. I can ask a question to investigate and find the answer. 11 1 The human body 1.2 The respiratory system We are going to... describe how the respiratory system works make and explain a model of breathing show that breathing involves two different stages, breathing in and breathing out measure breathing rate do practical work safely record results in a table draw a line graph of results use results to make a conclusion find information to answer a scientific question. Getting started 1 Draw a picture of the lungs. 2 Tell a partner the following: why you drew the lungs that way what happens to the lungs when we breathe in and out. breathing breathing rate diaphragm lungs windpipe 12 1.2 The respiratory system Parts of the respiratory nose system windpipe The human respiratory system contains these parts: lung two lungs air tubes leading from the mouth and nose to the lungs muscles in the chest that allow air to move in and out of the lungs. The lungs and breathing diaphragm muscle We use our lungs for breathing. We need to breathe to stay alive. We breathe in and breathe out. The lungs are in the chest. They are protected by the ribs. The lungs are like stretchy sponges that fill up with air. Activity 1 Investigate breathing You will need: a balloon 1 Put your hands on your rib cage. 2 Breathe in. What do you feel? 3 Now breathe out. What do you feel? 4 Breathe in again. Hold the balloon to your mouth and breathe out. What happens to the balloon? What does this show you? 13 1 The human body Continued Questions 1 When you breathe in, does your chest get bigger or smaller? Why do you think this is so? 2 When you breathe out, does your chest get bigger or smaller? Why do you think this is so? 3 Explain how we are able to blow up a balloon. Breathing We need oxygen to live. When we breathe in, oxygen gas from the air moves into the blood vessels in the lungs. Blood carries the oxygen to the heart and then to the other parts of the body. As your body uses up oxygen, it makes carbon dioxide. The blood carries the carbon dioxide back to the lungs. We get rid of carbon dioxide in the air we breathe out. Air enters the body through the Air leaves the body nose or mouth through the nose or mouth The air goes down Air from the lungs the windpipe and windpipe moves up the into the lungs windpipe The ribs move The ribs move upwards and downwards outwards and inwards The chest gets The chest gets diaphragm smaller and air is bigger and the pushed out of lungs ﬁll with air the lungs The diaphragm The diaphragm muscle contracts muscle relaxes and moves and moves downwards upwards breathing in breathing out 14 1.2 The respiratory system Think like a scientist 1 Make a model to explain breathing You will need: a plastic bottle, a narrow plastic tube or straw, an elastic band, scissors, two balloons, electrical tape, sticky putty or plasticine play dough® 1 Cut the bottom off the plastic bottle. Safety: Take care not to cut yourself with the scissors or sharp edge of the cut bottle. 2 Tie a knot in the narrow end of one balloon and cut off the other end. 3 Stretch the newly cut end of the balloon around the bottom of your plastic bottle. Use the electrical tape to fix the balloon in place. 4 Put a plastic tube or straw in the neck of the other balloon and fix it in place with the elastic band. Be sure not to make the elastic band so tight that it crushes the straw. The air must ﬂow through, so blow gently through the straw to see if the balloon inﬂates. 5 Put the straw and the balloon into the neck of the bottle. Put the play dough around the neck of the bottle to seal the bottle. Again, make sure that you don’t crush the straw. 6 a Pull on the bottom balloon and observe what happens. b Let go of the balloon. What happens? Questions 1 Which part of model represents the following parts of the human respiratory system: a lungs? c the windpipe? b the chest cavity? d the diaphragm muscle? 2 Which parts of the chest that are also involved in breathing are not shown by the model? 3 Explain how your model shows the breathing process. 15 1 The human body Do other animals get Activity 2Find out how other animals get oxygen oxygen the same way Use books and the internet to find out as we do? the answer to Sofia’s question. Find information about two animals that get oxygen in a different way to humans. Make a poster to show the class what you find out. We breathe in and out about 16 times every minute. The number of times we breathe in and out in one minute is called our breathing rate. Our breathing rates changes depending on how much oxygen our body needs. Think like a scientist 2 Investigate breathing rate You will need: a timer or watch with a second hand 1 Count the number of breaths you take per minute, while at rest. Record the measurement in a table. 2 Run on the spot for two minutes and then stop. Count and record the number of breaths per minute. 3 Run on the spot for another two minutes and then stop. Count and record the number of breaths per minute. 4 Wait two minutes and measure and record your breathing rate again. Do this again after another two minutes. 5 Draw a line graph of your breathing rate. 6 a When was your breathing rate lowest? b How did exercise affect your breathing rate? Suggest a reason for this. c Use your graph to work out how long it would take for your breathing rate to get back to normal after you stopped exercising. 16 1.2 The respiratory system Continued 7 Use your results to write a conclusion for the investigation. 8 Suggest another factor that could affect a person’s breathing rate. Think about athletes and sports players. 9 Which type of scientific enquiry did you use in the investigation? 10 Name another body system you have learnt about that is also affected by exercise. How am I doing? Was I able to measure my breathing rate accurately? Was I able to draw line graph of my results? Was I able to use my results to make a conclusion for the investigation? Do I know how exercise affects breathing rate? How have the practical activities helped me to learn about the respiratory system? 17 1 The human body Look what I can do! I can describe how the respiratory system works. I can make and explain a model of breathing. I can show that breathing involves two different stages, breathing in and breathing out. I can measure breathing rate. I can do practical work safely. I can record results in a table. I can draw a line graph of results. I can use results to make a conclusion. I can find information to answer a scientific question. 18 1.3 The reproductive system 1.3 The reproductive system We are going to... describe body changes that happen during puberty name the parts of the reproductive system. Getting started Think about what you already know about reproduction and write down your answers to these questions. 1 What is reproduction? 2 Why do living things need to reproduce? 3 Reproduction is part of the life cycle of all living things. Look at the picture of the human life cycle. a Which stage of the life cycle are you in now? b Which stage or stages are your family members in? fertilisation hormones menstruation ova puberty reproductive system sperm 19 1 The human body Growing and developing When you were born you were very small. You couldn’t walk or talk or do anything for yourself. Now you are much bigger and can do many things for yourself. Throughout your childhood you continue to grow and develop. You not only grow taller and heavier, but your body changes in other ways too. Some of the changes mean that you are becoming an adult and will be able to reproduce. This stage in your life is called puberty. Puberty starts at different ages in boys and girls. In boys, puberty usually starts when they are about 13 years old. In girls, puberty often happens from the age of 11. The changes that happen during puberty don’t happen all at once, but in stages. These changes are caused by chemicals in your body called hormones. The first change you will notice is that you grow very fast. Boys can easily grow 10 cm in a year. Girls can grow up to 12 cm in a year as puberty starts. One of the other changes you will notice is that your body grows more hair. In boys, hair begins to grow on the face, armpits and other parts of the body. In girls, hair begins to grow in the armpits and other parts of the body. Your skin can also get oily. Many boys and girls get pimples during puberty. A boy’s shoulders and chest will get broader as his body muscles develop. His voice will change and become deeper. A girl’s hips will get wider and she will start to develop breasts. Her voice will also become a little deeper. 20 1.3 The reproductive system Activity What do you know or want to know about puberty? 1 Write one or two sentences to explain in your own words what puberty is. 2 Make a table to compare your body before puberty with the changes you can expect in your body during puberty. 3 Write down a question you have about puberty on a piece of paper. Fold up the paper and give your question to your teacher. In the next lesson, your teacher will discuss answers to the questions your class has asked. How am I doing? Answer ‘Very well’, ‘Quite well’ or ‘I need help’ to these questions: How well can I explain what puberty is? How well can I identify the body changes that happen during puberty? Changes in the reproductive system There are also important changes that take place inside the bodies of boys and girls during puberty. These changes happen in the reproductive system and make it possible for a boy to become a father and for a girl to become a mother when they are older. The main job of the reproductive system is to make special cells called sex cells that are needed for reproduction. In males, the sex cells are called sperm. In females, the sex cells are called eggs or ova (one egg is called an ovum). During reproduction, a sperm and an egg join together to form a new living being that will grow into baby. This process is called fertilisation. A boy’s body starts to make sperm during puberty. In girls, ova start to develop. Menstruation in girls starts about a year after puberty begins. This is when an unfertilised egg is released from the body together with the lining of the uterus, which causes some bleeding. Menstruation happens about once a month but is often not regular until a girl is older. 21 1 The human body The male reproductive system The male reproductive organs include: two testes, which produce the sperm (one is called a testis) the sperm duct, which carries the sperm to the penis the penis, which transfers the sperm into the female’s body. The diagram shows the parts of the sperm duct male reproductive system. testis penis The female reproductive system The female reproductive organs include: ovaries, which produce the ova or egg cells oviduct the uterus or womb, where the baby develops oviducts, where fertilisation takes place ovary uterus uterus lining the birth canal, which receives the sperm from the male and through which the baby is born. birth canal The diagram shows the parts of the female reproductive system. 22 1.3 The reproductive system Questions 1 What is the main job of the reproductive system? 2 a What are the male sex cells called? b What are the female sex cells called? 3 Which part of the male reproductive system has the following functions? a makes sex cells b carries sex cells to the penis c where the sperm leave the body 4 Which part of the female reproductive system has these functions? a makes sex cells b where fertilisation takes place c where the baby develops d where the sperm enters the body What did I learn about myself in the different activities? Have I changed any ideas I used to have about puberty and the reproductive system? Look what I can do! I can describe body changes that happen during puberty. I can name the parts of the reproductive system. 23 1 The human body 1.4 Diseases We are going to... find out about types of living things that cause diseases find information about diseases find out how our body stops us from getting infectious diseases find out about things we can do to prevent diseases from spreading group methods to prevent diseases draw a dot plot of results learn how to avoid being bitten by insects. Getting started Write down the answers to the questions, then discuss your ideas with a partner before sharing them with the class. 1 The boy in the picture has chicken pox. Have you ever had chicken pox or any other similar disease? 2 What were the signs that you were ill? 3 Chicken pox is an infectious disease. What does this mean? barrier defence host hygiene mucus parasite repellent vector 24 1.4 Diseases Living things that cause disease Diseases stop our bodies from working properly. There are different kinds of living things that cause disease. They infect other living things and grow and reproduce on or in the body of the living thing that they infect. Any living thing that lives on or in the body of another living thing is called a parasite. The living thing that a parasite infects is called the host. Bacteria are very small living things that we can only see using a microscope. Bacteria cause diseases such as cholera and pneumonia. Not all bacteria are harmful. Viruses are even smaller than bacteria. All viruses are harmful and cause diseases in humans, animals and plants. Some viruses even infect bacteria! Humans get flu, chicken pox and measles from viruses. The yeast that we use to make bread rise is a fungus. Mushrooms that we eat are also fungi. But some fungi are parasites that cause diseases. Ringworm in humans and animals, athlete’s foot in humans and rusts in plants are caused by fungi. There are other kinds of parasites that also cause infectious diseases. Malaria and dysentery are two diseases caused by these parasites. Questions 1 a What is a parasite? b Why are viruses and some bacteria and fungi parasites? 2 Make a table of the different kinds of living things that cause diseases and name two examples of a disease that each one causes. 25 1 The human body Activity 1 Find information about diseases Do some research to find out the following: the word we use to describe any living thing that causes a disease the names of the parasites that cause malaria and dysentery how the parasites that cause malaria and dysentery are spread. The body’s defences against diseases Our body has different ways to stop us There are bacteria from being infected with diseases. and other living organisms We call these the body’s all around us that defences against diseases. cause disease. So why are we not ill all the time? Tears - our tears contain a chemical substance that kills some bacteria Mucus - sticky mucus in our noses, windpipe and other air passages traps germs Skin - the skin acts as a barrier to stop germs from getting into the body Acid - acid in the stomach kills any germs in food we have eaten 26 1.4 Diseases Controlling the spread of diseases Diseases can be spread by body contact and in food, in water and in the air. There are different ways we can help to control the spread of diseases. Good hygiene Many diseases are spread in food, water and body fluids. We can help prevent the diseases from spreading by good hygiene. This means keeping yourself and the things around you clean. These are some of the things we can do: Wash your hands with soap and water before eating or working with food and after going to the toilet. Also dry your hands well on a clean towel. Wash your hands after handling animals, cleaning up animal wastes or gardening, Wash raw unpeeled fruits and vegetables before eating them. Keep food covered. Do not leave food at room temperature, especially when the weather is hot, as bacteria and fungi grow faster when it is warm. Keep the kitchen, toilet and surroundings clean. Wash knives and working surfaces in the kitchen with hot soapy water after you have used them. Only drink safe, clean water. Boil water from rivers or reservoirs, or treat it with bleach to kill germs. Do not use rivers or other types of water as a toilet. Cover your nose and mouth with a tissue when you cough or sneeze. If you do not have a tissue, cough or sneeze into your elbow, not your hand. Keep wounds covered with a plaster and do not touch other people’s open wounds. 27 1 The human body Activity 2 Group methods to prevent diseases We use different methods to prevent the spread of different types of diseases. Sort and group the hygiene methods you have learnt about into these groups: Ways to prevent diseases spread in food. Ways to prevent diseases spread in water Ways to prevent diseases spread in body ﬂuids Present your answer in the form of a table. Think like a scientist Analyse hygiene methods that people use Class 5 did a survey of people in their local community to find out which hygiene methods people used. These are their results. Method to prevent infectious diseases Number of people who use the method wash hands after going to toilet 10 wash hands before working with food 5 wash hands after working with food 4 keep the kitchen, toilet and surroundings clean 12 cover nose and mouth when coughing or sneezing 7 1 Draw a dot plot of the results. 2 a Which hygiene method do most people use? b Which hygiene method do fewest people use? 3 Why do you think people should wash their hands with soap and water and not just water? 4 Why should people wash their hands before and after working with food? 5 Why should we cover our nose and mouth when we cough or sneeze? 6 Why do you think it is important to dry our hands well with a clean towel? 28 1.4 Diseases Continued How are we doing? Ask your partner these questions: Can you draw a dot plot of results? Can you say why we should use the different hygiene methods to prevent diseases spreading? Preventing insect bites Some serious diseases, such as malaria, yellow fever and sleeping sickness, are spread by insects. Malaria and yellow fever are spread by mosquitoes. Sleeping sickness is spread by the tsetse fly. The insects don’t cause the disease, but they spread the disease parasite when they bite you. The insects also do not get the disease themselves. We say the insects are vectors. The best way to prevent a disease spread by insects is not to get bitten. These are some of the ways you can prevent insect bites: sleep under bed nets wear long sleeves and long trousers keep doors and windows closed at night when mosquitoes are active use insect repellents on your skin to keep insects away burn mosquito coils to keep insects away. How can I use what I have learned in the future? Did I learn anything that can help other people? 29 1 The human body Look what I can do! I can name types of living things that cause diseases. I can find information about diseases. I can say how our body stops us from getting infectious diseases. I can describe things we can do to prevent diseases from spreading. I can group methods to prevent diseases. I can draw a dot plot of results. I can say how to avoid being bitten by insects. Project: The circulatory system Part 1: Discovery of how the circulatory system works People have tried to explain how the circulatory system works for more than two thousand years. One of the main books of Chinese medicine, written 2600 years ago, stated that ‘all of the blood in the body is pumped by the heart, completes a circle and never stops moving’. Galen was a surgeon and doctor who lived in what is now modern-day Turkey about 1900 years ago. At that time, scientists already knew that there two types of vessels in the body – arteries and veins. Galen thought that the liver produced blood that was then carried to the rest of the body in the veins. The body then used up the blood for energy as it flowed to the different organs. Galen also stated that the arteries contained blood, not air, which was what earlier scientists had thought. He understood that blood went from one side of the heart to the other side of the heart, but he didn’t know how that happened. He thought there were tiny holes in a wall between two sides of the heart. 30 Project Continued Ibn al-Nafis was an Arab physician from Syria who lived 800 years ago. In about the year 1240 he discovered that blood moves from the right side of the heart to the lungs and back to the left side of the heart. He was the first person to challenge Galen’s idea that blood could pass directly from the right side of the heart to the left side of the heart. William Harvey was an English doctor who lived 400 years ago. At that time doctors and scientists thought that the lungs moved the blood around the body. They also thought the heart’s job was to control our feelings. Harvey observed water pumps in London which gave him the idea that the heart pumped blood around the body. He studied the heart and blood vessels and carried out experiments. He was very thorough in his work and spent many hours repeating experiments and going over every detail. He also read the work of early doctors to help him build up his own ideas. Harvey’s results showed him that the heart works by muscle contraction to pump blood to body organs and that blood is carried away from heart by arteries and returns to heart through veins. He observed that in one hour the heart pumps more than the body’s weight in blood. This showed him that the body did not use up the blood that flowed to body organs. In 1628 Harvey explained how blood flows in one direction throughout the body and that gases enter and leave the blood in the lungs. Just over 30 years later, in 1661, an Italian scientist called Marcello Malpighi used a microscope to observe capillaries for the first time. He suggested that capillaries connected the arteries and veins which allowed the blood to flow back through the body in a continuous pathway. We now know that he was correct. Questions 1 a What incorrect ideas did doctors and scientists have about circulation up to 400 years ago? b What correct ideas did doctors and scientists have about circulation before William Harvey’s discoveries? 2 Compare the ideas from the ancient Chinese medical book with Malpighi’s findings two thousand years later. How are they the same? How are they different? 31 1 The human body Continued 3 What observation made William Harvey start to think about how the heart works? 4 a How did Harvey obtain evidence about how the circulatory system works? b Why did he repeat his experiments? 5 a How did Harvey show that the body does not use up the blood that ﬂows to the organs? b Name three other discoveries that William Harvey made about the circulatory system. Part 2 Draw a timeline of discoveries about the circulatory system 1 Draw a timeline to show the discoveries made by different people about the circulatory system. You should include the date and a description of the discovery or event. Think of ways to decorate your timeline to make it look attractive and interesting. 2 Find out who was the first person to do each of the following and when: transplanted the first human heart discovered that humans can have different blood types invented the first stethoscope to listen to the heart beating discovered that a substance in the blood called haemoglobin carries oxygen. Add this information to your timeline. 32 Check your progress Check your progress 1 State whether each of the following statements is true or false. Correct the false statements. a The heart pumps air around the body. b Your heat beats faster when you exercise. c Your pulse rate tells you how fast you are exercising. d Blood moves around the body in special tubes called blood vessels. e The veins carry blood to all parts of the body. 2 Marcus and Arun measured the pulse rate of some of their friends before and after exercising for three minutes. These are their results. Name Pulse rate before exercise Pulse rate directly after exercise Marcus 91 120 Arun 88 122 Jamal 90 128 Kai 89 125 a What equipment did they need to measure the pulse rates? b Draw and label a bar graph of the pulse rates measured. c Use the results to make a conclusion. d Predict what would happen to the pulse rates if they were measured 10 minutes after exercise. Give reason for your prediction. 3 Name each of the following: a the body organs used for breathing b the gas we need to breathe in c the gas our bodies must get rid of d the substance that carries the gases around the body e the muscle that helps us breathe f the part of the skeleton that protects the breathing organs 33 1 The human body Continued 4 a What is puberty? b Describe two body changes that happen in both boys and girls during puberty. 5 a Match each of the body’s defences with the way it helps to protect the body from disease. Body defence How it protects the body from disease tears traps germs mucus stops bacteria entering the body stomach acid contain a chemical substance that kills some bacteria skin kills bacteria in food we have eaten b Explain why we should clean cuts and wounds and cover them with a plaster. 34 2 Materials: properties and changes 2.1 Properties of substances We are going to... learn that the temperature at which a substance changes state is a property of the substance learn about the difference between boiling and evaporation measure temperature collect and record observations and measurements in tables work safely in practical investigations draw graphs of results and measurements and make conclusions plan a fair test and choose materials and equipment to use identify risks and how to work safely when planning a practical investigation find out about the properties of gases use scientific knowledge to make a prediction and use results to say if a prediction was accurate. Getting started Solid, liquid and gas are the three states of matter you have already learnt about. Substances can change from one state of matter to another. 1 In a group, brainstorm what you know about change of state. Write your ideas in a mind map. 2 Choose three things from your mind map to share with another group. boiling point melting point property 35 2 Materials: properties and changes Change of state You should already know that substances change state when they are heated or cooled enough. For example, when we heat ice it melts and becomes liquid water. Ice melts at a temperature of 0 °C. The temperature at which a solid becomes a liquid is the melting point. Gold is also a solid. The melting point of gold is 1064 °C. Melting point is a property of a substance. A property is something about substance that allows us to tell it apart from other substances. This means that each substance has its own melting point. Boiling point is also a property of a substance. Boiling point is the temperature at which particles throughout a liquid have enough energy to change to a gas. Each substance boils at a certain temperature. For example, pure water boils at 100 °C, vinegar boils at 118 °C and liquid gold boils at 2856 °C. Boiling and evaporation Liquids change to gases when they boil and evaporate What’s the difference between those two processess? When a liquid boils, all the particles in the liquid have enough energy to become a gas. This is different to evaporation, which happens when particles on the surface of a liquid change into a gas. Most liquids boil only when they are heated. Evaporation can occur at any temperature. 36 2.1 Properties of substances Activity 1 Compare boiling and evaporation 1 Talk about these questions with a partner: a How do you know a liquid is boiling without measuring the temperature? b How can you tell if a liquid is evaporating? c Which process is faster, boiling or evaporation? Why do you think this? 2 Make labelled drawings to show the difference between boiling and evaporation. Think about what happens to the particle of the liquid in both processes. Think like a scientist 1 Measure and compare melting points You will need: three different solids, three pans, a hotplate, a thermometer, a stopwatch or digital watch This activity is a teacher demonstration. Safety: Do not touch the hot plate or pan: it can burn you. You teacher will do the following: 1 Place a solid in a pan. 2 Heat the solid substance until it melts. Remove the pan from the hot plate as soon as the substance melts. 3 Measure the temperature of the melted substance. You should record the reading in a table. 4 Repeat steps 1–3 with the two other solids. Questions 1 Which substance had: a the highest melting point? b the lowest melting point? 37 2 Materials: properties and changes Continued 2 Draw a bar chart of the results. 3 Write a conclusion for the investigation. Remember a conclusion is what you found out in the investigation. 4 Would the melting points change if you heated more of the substance in each pan? Explain your answer. 5 Why is the melting point of a substance always lower than its boiling point? Think like a scientist 2 Plan a test to compare boiling points of substances Work in a group to plan a fair test to compare the boiling points of different substances. 1 In your test, which variables will you: change? keep the same? measure? 2 What materials and equipment will you need? 3 What will you do to compare the boiling points of the different substances? 4 Are there any dangers or risks in your investigation? How will you work safely? 5 How will you record and present your results? COOKING OIL ORANGE JUICE MILK VINEGAR HONEY 38 2.1 Properties of substances Continued How am I doing? Answer ‘Very well’, ‘Quite well’ or ‘I need help’ to each of the questions. How well can I: identify different variables in a fair test investigation? choose equipment and materials to use in an investigation? identify risks and dangers in an investigation and plan how to work safely? identify the best way to record and present results in an investigation? Properties of gases Air is a mixture of gases. Gas is one of the states of matter. All matter has these properties: It takes up space. It has mass. We can’t feel air unless it is moving. How do we know it’s there? 39 2 Materials: properties and changes Think like a scientist 3 Investigate the properties of gases You will need: two balloons of the same size, two rulers, string, a heavy book, twist ties, scissors, sticky tape, safety goggles Safety: Take care when handling heavy books classroom table 1 Blow up the balloons to the same size and tie book them off tightly with twist ties. two rulers 2 Measure and cut three pieces of string 15 cm long. string 3 Use two pieces of string to tie the balloons onto one of the rulers as shown in the picture. twist ties Keep the balloons the same distance from the end of the ruler. balloons 4 Put the second ruler near the edge of a table and hold down one end with a heavy book. The other end should stick out over the edge of the table. 5 Use the third piece of string to hang the ruler and balloons from the second ruler. 6 Carefully move the balloons so that they are balanced on the hanging ruler. Tape the strings in place so that they cannot move. 7 a You are going to loosen the twist tie on one balloon. Predict what will happen when you do this. Say why. b Loosen the tie and observe what happens. Was your prediction correct? c Make a drawing of your observation. Questions 1 How does the investigation show that gases take up space? 2 How does the investigation show that gases have mass? 3 How did you work safely in the investigation? 40 2.1 Properties of substances How did the practical work help me learn about properties of substances? Has the practical work made me change any of my ideas about gases? Look what I can do! I can understand that the temperature at which a substance changes state is a property of the substance. I can describe the difference between boiling and evaporation. I can measure temperature. I can collect and record observations and measurements in tables. I can work safely in practical investigations. I can draw graphs of results and measurements and make conclusions. I can plan a fair test and choose materials and equipment to use. I can identify risks and how to work safely when planning a practical investigation. I can find out about the properties of gases. I can use scientific knowledge to make a prediction and use results to say if a prediction was accurate. 41 2 Materials: properties and changes 2.2 Thermal and electrical conductors We are going to... learn that conducting heat and electricity are properties of a substance collect and record observations and measurements in tables work safely in practical investigations suggest how to improve an investigation draw graphs of results and measurements and make conclusions group substances according to their properties identify the type of scientific enquiry used in an investigation use scientific knowledge to make a prediction use results to say if a prediction was accurate identify and describe patterns in results. Getting started Have you noticed that when you put a cold, metal teaspoon into a hot cup of tea, the teaspoon handle feels warm after a while? 1 Talk about why this happens. 2 Draw an energy chain to help explain your answer. conduction electrical conductors thermal conductors 42 2.2 Thermal and electrical conductors Substances can conduct heat You should already know that heat can be transferred from one object to another. This type of energy transfer is called conduction. Substances and materials that conduct heat well are called thermal conductors. Why does a metal teaspoon feel hotter than a plastic teaspoon when you put them in a cup of hot tea? Think like a scientist 1 Investigate how well different materials conduct heat You will need: a beaker of hot water, a metal teaspoon, a plastic teaspoon, a glass rod, a pencil, a long, thin piece of polystyrene foam, ﬁve beads, petroleum jelly 1 Put a small bit of petroleum jelly of the same size onto one polystyrene foam pencil end of each of the materials. glass rod bead on Push a bead into the petroleum petroleum jelly metal spoon jelly. plastic spoon 2 Your teacher will pour hot water beaker hot water into a beaker. Put each of the different materials into the beaker. Safety: Don’t touch the hot water. Be careful not knock over the beaker of hot water. 43 2 Materials: properties and changes Continued 3 Which bead do you think will fall off first? Say why. 4 Draw a table to record the order in which the beads fall off the materials. 5 a Which bead fell off first? b Was your prediction correct? 6 a Which bead fell off last? b What did this show you about that material? 7 Write a conclusion for the investigation from your observations. 8 Suggest a way to improve the investigation so that you can draw a graph of your results. 9 Which types of scientific enquiry did you use in the investigation? Explain your answer. How am I doing? Answer ‘Very well’, ‘Quite well’ or I need help’ to each of the questions. How well can I: make a prediction with reasons? record observations in a table? use observations to write a conclusion? suggest how to improve an investigation? Some materials and substances conduct heat better than others. How well a substance can conduct heat is a property of the substance. Metals are good conductors of heat. Silver is the best conductor of heat. Non-metals, such as glass and plastic, are not good conductors of heat. 44 2.2 Thermal and electrical conductors Questions 1 Explain in your own words what a thermal conductor is. 2 Why do you think pots and pans are made from metal? 3 Why do you think the handles of pots and pans are made from plastic? 4 In which cup will your tea stay warm longest: a stainless steel cup, a glass cup or a polystyrene foam cup? Explain why. 5 Find out the name for materials and substances that are not good conductors of heat. Substances can conduct electricity Some materials and substances are able to conduct electricity. They are called electrical conductors. The ability to conduct electricity is a property of materials and substances. You should already know that metals are substances that conduct of electricity. Do other substances also conduct electricity? Think like a scientist 2 Investigate how well different substances conduct electricity You will need: two cells; a cell holder, a 1.5 V lamp, three 15 cm pieces of copper connecting wire, steel paper clip, aluminium foil, tap water, sugar, pencil graphite 1 Set up your circuit as shown in the diagram 45 2 Materials: properties and changes Continued 2 Predict how well each of the substances you are going to test will conduct electricity. Write your predictions in a table. Use ticks to show your prediction and results: 0 ticks lamp doesn’t shine 1 tick ✓ lamp is dim 2 ticks ✓✓ lamp is bright 3 a What substance is the conducting wire made of? b Touch the free ends of the conducting wire together. How brightly does the lamp shine? 4 a Touch the free ends of the wire to the steel paper clip. How brightly does the lamp shine? b If the lamp does not light up, test the substance again to be sure of your result. 5 Repeat Step 4 with all the other substances you are going to test. For each substance, observe the brightness of the lamp. 6 a Record your observations in the table. b Are your results reliable? How can you find out? Questions 1 How well did your results match your predictions? 2 Which of the substances you tested were metals? 3 a Which substance that you tested conducted electricity best? b Which substance that you tested conducted electricity worst or not at all? 4 What can you conclude from your investigation? 5 Group the substances you tested into substances that conduct electricity and substances that do not conduct electricity. 6 Which type of scientific enquiry did you use in the investigation? 46 2.2 Thermal and electrical conductors Activity 1 Compare thermal and electrical conductors The table shows measurements of how well some substances conduct heat and electricity. How well the substance conducts… Substance Heat (W/m−K) Electricity (W/m−K) aluminium 237 37 copper 386 59 graphite 168 1 brass 150 16 steel 80 10 1 Draw a scatter graph of the measurements. Label each data point you plot with the name of the substance. 2 Which substance is: a the best conductor of heat? b the best conductor of electricity? c the worst conductor of heat? d the worst conductor of electricity? 3 Describe the pattern you observe. 4 Identify and describe any measurements that do not fit the pattern. 5 Use the graph to predict the measurement for conducting heat for a substance with a value of 14 for conducting electricity. Plot the value on the graph in a different colour. 6 Suggest a conclusion you can make from the data and your graph. How well did I work in a group? What did I find easy to do? What do I need more help with? 47 2 Materials: properties and changes Look what I can do! I can understand that conducting heat and electricity are properties of a substance. I can collect and record observations and measurements in tables. I can work safely in practical investigations. I can suggest how to improve an investigation. I can draw graphs of results and measurements. I can make conclusions from results and measurements. I can identify the type of scientific enquiry used in an investigation. I can group substances according to their properties. I can use results to say if a prediction was accurate. I can identify and describe patterns in results. 48 2.2 Thermal and electrical conductors 2.3 Reversible changes We are going to... find out about and describe changes to substances that are reversible choose materials and equipment to use identify risks and work safely when doing practical work use the particle model to explain how temperature affects dissolving use scientific knowledge to make a prediction and use results to say if a prediction was accurate collect and record observations and measurements in tables decide if a test is fair make a conclusion from results and measurements ask a question to investigate and choose a type of scientific enquiry to find the answer Getting started You will need: ice cubes, saucer, watch Place the ice cubes in the sun or other warm place for five minutes. 1 a What has happened to the ice after five minutes? b Make a drawing of your observation. 2 What causes the ice to change? 3 What will happen to the ice if you put it back in the freezer? Why? irreversible physical change rate reversible solute solvent uniform 49 2 Materials: properties and changes Changes to substances In a warm place, solid ice melts to become liquid water. This is a change of state. A change of state is a physical change. A physical change alters the how a substance looks or feels. The substance does not change into a new substance. When you put the water back in the freezer it becomes a solid again. We say that the change is reversible. This is because we can change solid ice to liquid water and also change liquid water back to solid ice. Heating causes ice to melt into liquid water. When the water loses heat and cools it becomes solid again. The diagram shows the change of state between ice and water. We can show the change of state in writing like this: Heating Liquid water ⇌ solid ice Cooling What happens when we burn a match? Can the match change back to the way it was? Sometimes the changes to substances cannot be reversed. We call these irreversible changes. Some irreversible changes turn one substance into another substance. This means that there is chemical change. For example, when we burn a match the wood changes into a black substance called carbon. Questions 1 When you mix boiling water with jelly powder it becomes a liquid. In the fridge it becomes solid. Can we make jelly change back to a liquid? Draw a simple flow diagram to explain your answer. 2 Does boiling an egg cause a reversible or irreversible change? Explain why. 50 2.3 Reversible changes Think like a scientist 1 Demonstrate a reversible change 1 Think of a reversible change to a substance. Describe the change. 2 a Decide how you could demonstrate this reversible change. b How will you work safely? 3 Your teacher will put out some materials and equipment. Choose and collect the materials and equipment you will need. 4 a Demonstrate the reversible change you chose to another group. Ask the group to describe the change that takes place. b Explain how to change the substance back to the way it was before you changed it. How are we doing? As a group, point to one of the faces to answer the questions. or or Could we think of reversible change to demonstrate? Could we choose and use suitable materials and equipment? Could we demonstrate that the change is reversible? Dissolving Some substances can dissolve in water or other liquids. For example, sea water is salty because there is dissolved salt in the water. You should remember that the substance that dissolves is called the solute. The substance in which the solute dissolves is called the solvent. Together, the solute and solvent form a solution. 51 2 Materials: properties and changes When a solute dissolves, the particles of the solute move between the solvent particles. The solute particles spread evenly in the solvent. Because of this you cannot see the solute in a solution after it has dissolved. We say that a solution has a uniform appearance. This means that it looks the same throughout. The picture shows how the solute particles spread when they dissolve in water. water particles salt solute dissolves particles, e.g. salt Salt and water particles are evenly spread Activity Describe dissolving The picture shows dissolving. 1 Which substance is the solute? How do you know this? 2 Which substance is the solvent? 3 Draw a picture of the solution after all the solute has dissolved. copper sulfate 4 Describe to a partner what happens when a substance dissolves. water 5 Is dissolving a reversible change? Say why or why not. 52 2.3 Reversible changes Can we make solids Did you dissolve faster? forget to put sugar’ in my coffee? It’s not sweet. I put in two teaspoons like I always do. Why do you think the coffee tasted bitter? How could Marcus make the coffee taste sweeter without adding any more sugar? The coffee and sugar form a solution. The sugar will dissolve faster if Marcus stirs the solution. Stirring is one way to make solid solutes dissolve faster. Stirring causes the particles of the solute to spread out into the spaces between the particles of the solvent more quickly. We say that stirring increases the rate at which a solute dissolves. The rate is how fast something happens. There are other factors that make solids dissolve faster. Have you ever tried to make coffee with water from the fridge? Why do we use hot water? 53 2 Materials: properties and changes Think like a scientist 2 Does water temperature affect the rate of dissolving? You will need: sugar, glass jars, cold water, hot water, teaspoon, a measuring cylinder, a stopwatch or timer Safety: Don’t touch the hot water. Be careful not knock over the jar of hot water. 1 Does sugar dissolve more quickly in hot or cold water? Make a prediction and say why you think this. 2 Stir a teaspoon of sugar into a 100 ml of cold water in a glass jar. 3 Stir a teaspoon of sugar into a 100 ml of hot water in a glass jar. 4 Time how long it takes for the sugar to dissolve in both jars. 5 Record your results in a table. 6 a In which jar did the sugar dissolve quickest? Suggest a reason for this. b Was your prediction correct? 7 How did you make sure your test was fair? 8 Write down what you conclude about the effect of temperature on dissolving a solute. The particles in matter are always moving. When we increase the temperature of a substance, the heat adds energy to the particles of the substance. This energy causes them to move faster and spread out more. In a heated solvent, the particles of the solute also gain energy and move faster than in a cooler solvent. This allows the particles of the solute to spread through the solution more easily, so the solute dissolves faster. Questions 1 What does the rate of dissolving mean? 2 Name two factors that affect the rate of dissolving. 3 a How does heating affect the particles in a solution? b Explain how this affects dissolving. 4 Explain why sugar will dissolve on its own in a cup of cold water if we leave it long enough. 54 2.3 Reversible changes Think like a scientist 3 Ask and investigate a question about dissolving 1 With a partner, think of a question about dissolving that you would like to find the answer to. 2 Decide on the type of scientific enquiry you will use to answer your questions, for example, a fair test, doing research or observing over time. 3 Find out the answer to your question. 4 Make a presentation to share with the class about your findings. Am I happy with the way I worked in this topic? What could I do better? Look what I can do! I can understand and describe changes to substances that are reversible. I can choose materials and equipment to use. I can identify risks and work safely in practical work. I can use the particle model to explain how temperature affects dissolving. I can use scientific knowledge to make a prediction and use results to say if a prediction was accurate. I can collect and record observations and measurements in tables. I can decide if a test is fair. I can make a conclusion from results and measurements. I can ask a question to investigate and choose a type of scientific enquiry to find the answer. 55 2 Materials: properties and changes 2.4 Chemical reactions We are going to... find out that in a chemical reaction, substances react together to form new substances identify reactants and products in chemical reactions observe and describe evidence for chemical reactions record observations in drawings write a conclusion for an investigation measure temperature. Getting started You will need: a candle, a candle holder, matches, a teaspoon Your teacher will light the candle and hold a metal spoon over the flame. Observe what happens after a few minutes. 1 Describe one reversible change you observe when the candle burns. Why does this change happen? 2 What happens to the candle wick? Is this change reversible? 3 Did any new substances form? How do you know this? chemical reaction evidence products react reactants 56 2.4 Chemical reactions Reactants and products When some substances are mixed together, they change and form a new substance. This is called a chemical reaction. We say that the substances react together. The substances that react together are called reactants. The new substances that form are called the products. Think like a scientist 1 Identify reactants and products You will need: vinegar, bicarbonate of soda, a jar with a wide mouth, a spoon 1 Pour some vinegar into the jar. 2 a Put a teaspoon of bicarbonate of soda into the jar. Observe what happens. b Make a drawing of your observations. 3 Try to explain what you observed. 4 Which substances were the reactants? VINEGAR BICARBONATE 5 Which substance was the product? OF SODA 6 a Wait about five minutes. Can you observe any other product? b Describe what you observe. How am I doing? Could I make a drawing of my observations? Could I explain my observations? Could I identify the reactants in the chemical reaction? Could I identify any products formed in the reaction? 57 2 Materials: properties and changes Evidence for chemical reactions Sometimes we can see that a product has formed in a chemical reaction. For example, when vinegar and bicarbonate of soda react, we can see that a gas is produced. The gas is evidence of the reaction. There are also other ways we can tell if a chemical reaction has taken place. Think like a scientist 2 Investigate evidence for chemical reactions A You will need: water, cornstarch, iodine solution, a dropper, a spoon, limewater, a drinking straw, beakers 1 a Pour some water into a beaker. Add three full droppers of iodine solution. b Make a drawing of your observations. c Add a spoon of cornstarch to the beaker and stir. d Make a drawing of your observations. 2 a Pour some limewater into a beaker. b Breathe air into the limewater with a straw. Which gas is in the air you breathe out? c Write one or two sentences to describe your observations. 3 How do you know that a chemical reaction has taken place in this investigation? Safety: Take care not to suck up the limewater into your mouth. It can also irritate your eyes and skin. 58 2.4 Chemical reactions Continued Investigate evidence for chemical reactions B You will need: wire wool, vinegar, a beaker, a thermometer, a timer 1 Loosen up a ball of wire wool and place it in a beaker. Pour vinegar on to the wire wool and let the beaker stand for one to two minutes. Make sure all the wire wool is in contact with the vinegar. 2 Place a thermometer into the middle of the wire wool. VINEGAR Record the temperature reading on the thermometer. 3 Wait five minutes and record the temperature reading on the thermometer again. What do you observe? 4 How do you know that a chemical reaction has taken place in this investigation? 5 Write a conclusion for the investigation. Questions 1 Describe three ways that we can tell that a chemical reaction has taken place and give an example of each. 2 When clear limewater is mixed with carbon dioxide, the reaction forms a substance ca

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