Combined and Co-ordinated Sciences for Cambridge IGSCE by Cambridge International Education

Original material © Cambridge University Press & Assessment 2022. This material is not final and is subject to further changes prior to publication.

are working with Cambridge Assessment International Education towards endorsement of this resource. SAMPLE

• Cambridge IGCSE Combined Science (0653) or Cambridge IGCSE Co-ordinated Sciences (Double Award) (0654) • only the Core part of the syllabus, or the Supplement as well.

CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: COURSEBOOK ii

All the Biology topics come first, followed by Chemistry and then Physics. However, you almost certainly won’t follow this sequence in your lessons. Where possible, the book follows the order of topics in the syllabus. Some topics have been merged or moved where concepts are closely related. You will probably find that you study Biology, Chemistry and Physics alongside each other, so you will use different parts of the book in different lessons.

Core Supplement Core Supplement

There are sidebars in the margins of the coursebook to show which material relates to each syllabus. If there is no sidebar, it means that everyone will study this material.

You will study the material: You will study the material: You will study the material: You will study everything. This includes the material: Without a sidebar Without a sidebar Without a sidebar Without a sidebar

SAMPLE

With a dashed blue sidebar With a solid blue sidebar With a solid blue sidebar With a dashed black sidebar With a dashed black sidebar With a dashed blue sidebar With a solid black sidebar With a dashed black sidebar

Introduction

This book has been written to help you obtain the knowledge and skills required for your Cambridge IGCSE™ Combined Science (0653) or Cambridge IGCSE™ Co-ordinated Sciences (Double Award) (0654) course. We hope that you enjoy using it.

Cambridge IGCSE Combined Science (0653) is a single award syllabus. This means that your final qualification is the equivalent to one Cambridge IGCSE subject. Cambridge IGCSE Co-ordinated Sciences (0654) is a double award syllabus. In this case, your final papers are the equivalent of two Cambridge IGCSE subjects.

Core and Supplement

Your teacher will tell you whether you are studying:

Original material © Cambridge University Press & Assessment 2022. This material is not final and is subject to further changes prior to publication.

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

Use this table to ensure that you study the right material for your syllabus: Cambridge IGCSE Combined Science (0653) Cambridge IGCSE Co-ordinated Sciences (0654)

If you study Core content only for either syllabus, you will be entered for Papers 1 (Multiple Choice (Core)) and 3 (Theory (Core)) and either Paper 5 (Practical Test) or 6 (Alternative to Practical). If you also study the Supplement, you may be entered for Papers 2 (Multiple Choice (Extended)) and 4 (Theory (Extended)), and either Paper 5 (Practical Test) or 6 (Alternative to Practical).

Remember, though, that these are only very short summaries and you will need to know more detail than this for your course.

Summary At the end of each chapter, there is a short list of the main points covered in the chapter.

SAMPLE

There are two possible papers aimed at testing your practical skills, Paper 5 and Paper 6 (Practical Test and Alternative to Practical, respectively). Your teacher will tell you which of these you will be entered for. You should try to do the activities in this coursebook no matter which of these papers you are entered for.

Projects You will find a project at the end of every chapter, which give you the opportunity to work in groups, exercise your creativity, and develop your research and critical thinking skills.

Questions

Each chapter has several sets of questions within it. Most of these require quite short answers and simply test if you have understood what you have just read or what you have just been taught.

Workbooks

Introduction iii

There are three workbooks to go with this coursebook – one for each science. If you have the workbooks, you will find them really helpful in developing your skills, such as handling information and solving problems, as well as some of the practical skills.

Original material © Cambridge University Press & Assessment 2022. This material is not final and is subject to further changes prior to publication.

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

Activities Each chapter contains activities. These will help you to develop the practical skills you will need in your course. There are further activities online on Cambridge GO.

At the end of each chapter, there are some longer questions testing a range of material from the chapter. Some of these are similar in style to Cambridge Assessment International Education past paper questions.

Original material © Cambridge University Press & Assessment 2022. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this resource.

These set the scene for each chapter, help with navigation through the coursebook and indicate the important concepts in each topic. They will begin with the header 'In this chapter you will:' and will list the key topics of the chapter for all students.

• learn about the seven characteristics of living organisms • find out how the binomial system is used to name organisms

SAMPLE

This contains questions and activities on subject knowledge you will need before starting this chapter.

SELF/PEER ASSESSMENT

CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: COURSEBOOK iv

Command words that appear in the syllabus and might be used in exams are highlighted in the practice questions. In the margin, you will find the Cambridge International definition. You will also find these definitions in the Glossary at the back of the book with some further explanation on the meaning of these words.

COMMAND WORDS

EXPERIMENTAL SKILLS

BEFORE YOU START

This feature focuses on developing your practical skills. They include lists of equipment required and any safety issues, step-by-step instructions so you can carry out the experiment, and questions to help you think about what you have learnt. ACTIVITY Activities give you an opportunity to check and develop your understanding throughout the text in a more active way, for example by creating presentations, posters or role plays. Where activities have answers, teachers can find these for free on the Cambridge GO site.

How to use this book

KEY WORDS Key vocabulary is highlighted in the text when it is first introduced, and definitions are given in boxes near the vocabulary. You will also find definitions of these words in the Glossary at the back of this book.

Questions Appearing throughout the text, questions give you a chance to check that you have understood the topic you have just read about. The answers to these questions are accessible to teachers for free on the Cambridge GO site.

LEARNING INTENTIONS

IN THIS CHAPTER

YOU WILL:

Throughout this book, you will notice lots of different features that will help your learning. These are explained below.

At the end of some activities and experimental skills boxes, you will find opportunities to help you assess your own work, or that of your classmates, and consider how you can improve the way you learn.

SAMPLE

The summary checklists are followed by ‘I can’ statements which relate to the Learning intentions at the beginning of the chapter. You might find it helpful to rate how confident you are for each of these statements when you are revising. You should revisit any topics that you rated ‘Needs more work’ or ‘Almost there’. I can See topic... moreNeedswork thereAlmost Ready to move on PRACTICE QUESTIONS Questions at the end of each chapter provide more demanding practice questions, some of which may require use of knowledge from previous chapters. The answers to these questions are accessible to teachers for free on the Cambridge GO site. These boxes tell you where information in the book is extension content, and is not part of the syllabus.

SUMMARY CHECKLIST

Worked examples are used to demonstrate the stops you should take to answer a specific type of question. They are followed by opportunities for you to practise the techniques for yourself. These activities ask you to think about the approach that you take to your work, and how you might improve this in the future. TIP These contain advice to help you avoid common misconceptions and provide support for answering questions.

SUMMARY There is a summary of key points at the end of each chapter.

REFLECTION

WORKED EXAMPLES

How to use this book

P1 Motion IN THIS CHAPTER YOU WILL: • learn how to take measurements of length, volume and time • calculate density • perform experiments to determine the density of an object • define speed and calculate average speed • plot and interpret distance–time and speed–time graphs • work out the distance travelled, from the area under a speed–time graph • understand that acceleration is a change in speed and the gradient of a speed–time graph • distinguish between scalar and vector quantities • define and calculate acceleration, and understand deceleration as a negative acceleration • use the gradient of a distance–time graph to calculate speed, and the gradient of a speed–time graph to calculate acceleration • discover the differences between mass and weight • describe how forces may change the size, shape and motion of a body • find the resultant of two or more forces acting along the same line • find out about the effect of friction (or air resistance or drag) on a moving object. Original material © Cambridge University Press & Assessment 2022. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this resource. SAMPLE

SCIENCE IN CONTEXT

SAMPLE

AROUND THE WORLD IN 80 DAYS

The first known circumnavigation (trip around the world) was completed by a Spanish ship on 8 September 1522. It took more than three years. The French writer Jules Verne wrote the book Le tour du monde en quatre-vingts jours (which means Around the World in Eighty Days) in 1873. In honour of the writer, the Jules Verne Trophy is a prize for the fastest circumnavigation by a yacht. The award is currently held by the yacht IDEC Sport, which completed the journey in just under 41 days in 2017. In 2002, the American Steve Fossett was the first to make a solo circumnavigation in a balloon, without stopping, taking just over 13 days. In 2006, he flew the Virgin Atlantic GlobalFlyer, the first fixed-wing aircraft to go around the world without stopping or refuelling. It took him just under three days. Hypersonic jets are being developed that could fly at 1.7 km/s. At this speed, they could circumnavigate the globe in an incredible six and a half hours.

Figure P1.02: The Virgin Atlantic GlobalFlyer passes over the Atlas Mountains.

Original material © Cambridge University Press & Assessment 2022. This material is not final and is subject to further changes prior to publication. are working with Cambridge Assessment International Education towards endorsement of this resource.

Figure P1.01: What is the volume of liquid that fits into this cup?

P1 Physics 3 BEFORE YOU START Working in pairs, measure: • the length, width and thickness of this book and work out its volume • the thickness of a sheet of paper that makes up this book • the length of a journey (for example, on a map) that is not straight • the volume of liquid which fits into the cup shown in Figure P1.01. CONTINUED • learn how force, mass and acceleration are related • investigate the effect of forces on a spring • describe and calculate the turning force • investigate and apply the principle of moments • describe the conditions needed for an object to be in equilibrium • perform an experiment to find the centre of mass • describe how the centre of gravity of an object affects its stability • relate pressure to force and area, and recall the associated equation p FA=

KEY WORD acceleration: the rate of change of an object’s velocity. Calculating acceleration Picture an express train setting off from a station on a long, straight track. It may take 300 s to reach a velocity of 300 km/h along the track. Its velocity has increased by 1 km/h each second, and so we say that its acceleration is 1 km/h per second.

Discussion questions

Original material © Cambridge University Press & Assessment 2022. This material is not final and is subject to further changes prior to publication.

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

2 What could cause the fastest boat to not win a round-the-world yacht race?

These are not very convenient units, although they may help to make it clear what is happening when we talk about acceleration. To calculate an object’s acceleration, we need to know two things: • its change in velocity (how much it speeds up) • the time taken (how long it takes to speed up).

SAMPLE

CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: COURSEBOOK 4 1.5CONTINUEDUnderstanding

Sometimes these epic adventures inspire those who do them to campaign for a better world. The British sailor Ellen MacArthur is just such a person. She held the world record for the fastest solo circumnavigation, achieved on 7 February 2005. However, she retired from competitive sailing to set up the Ellen MacArthur Foundation, a charity that works with businesses and in education to accelerate the transition to a circular economy. A circular economy is one in which things should be designed to last a long time and be easy to maintain, repair, reuse or recycle. Therefore, a circular economy would create less waste.

1 What were the speeds of the six journeys mentioned in the first paragraph? Assume that the Earth’s circumference is 40 000 km.

The acceleration of the object is defined as the change of an object’s velocity per unit time. acceleration change in velocity time taken = We can write the equation for acceleration in symbols. We use Δv for change in velocity and Δt for time taken. So we can write the equation for acceleration like this: a v t = ∆ ∆ KEY EQUATION acceleration change in velocity time taken = =a v t ∆ ∆

Acceleration is an increase in speed. Deceleration is a decrease in speed. If an object speeds up quickly we say it has a high acceleration. Some cars, particularly high-performance ones, are advertised according to how rapidly they can accelerate. An advert may claim that a car goes ‘from 0 to 100 km/h in 5 s’. This means that, if the car accelerates at a steady rate, it reaches 20 km/h after 1 s, 40 km/h after 2 s, and so on. We could say that it speeds up by 20 km/h every second. In other words, its acceleration is 20 km/h per second. So, we say that an object accelerates if its speed increases. Its acceleration tells us the rate at which its speed is changing, that is, the change in speed per unit time. When an object slows down, its speed is also changing. We say that it is decelerating. Instead of an acceleration, it has a deceleration.

acceleration

Figure P1.03: Ellen MacArthur celebrates after completing her record solo round the world journey on 7 February 2005 in Falmouth, England.

P1.22 A train, initially moving at 15 m/s, speeds up to 39 m/s in 120 s. What is its acceleration?

P1.21

Figure P1.26 shows a speed–time graph for a bus. The graph frequently drops to zero because the bus stops to let people on and off. Then the line slopes up, as the bus accelerates away from the stop. Towards the end of its journey, the bus is moving at a steady speed (horizontal graph), as it does not have to stop. Finally, the graph slopes downwards to zero again as the bus pulls into the terminus and stops.

Original material © Cambridge University Press & Assessment 2022. This material is not final and is subject to further changes prior to publication.

Speed–time graphs can show us a lot about an object’s movement. Was it moving at a steady speed, or speeding up, or slowing down? Was it moving at all?

WORKED EXAMPLE P1.6 An aircraft accelerates from 100 m/s to 300 m/s in 100 s. What is its acceleration?

Graphs of different shapes

Step 1: Start by writing down what you know, and what you want to know. initial velocity u = 100 m/s final velocity v = 300 m/s time t = 100 s acceleration a = ? Step 2: Now calculate the change in velocity. change in velocity = 300 m/s 100 m/s = 200 m/s Step 3: Substitute into the equation. acceleration change in velocity time taken 200m/m/s = = = 20100 s .ss 2 Alternatively, you could substitute the values of u, v and t directly into the equation. a vu t = = = ∆ 23001001002m/s Answer The aircraft’s acceleration is 2.0 m/s2. Questions P1.20 Which of the following could not be a unit of km/sacceleration?2mph/s km/s m/s2

Time Speed

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

Just as we can represent the motion of a moving object in a distance–time graph, we can also represent it with a speed–time graph. A speed–time graph shows how the object’s speed changes as it moves. Always check any graph by looking at the axes to see the labels. A speed–time graph has speed on the vertical axis and time on the horizontal axis.

A car sets off from traffic lights. It reaches a speed of 21 m/s in 10 s. What is its acceleration?

The slope of the speed–time graph tells us about the bus’s acceleration: • the steeper the slope, the greater the acceleration • a negative slope means a deceleration (slowing down) • a horizontal graph (slope = 0) means a constant speed.

Figure P1.26: A speed–time graph for a bus on a busy route. At first, it has to stop frequently at bus stops. Towards the end of its journey, it maintains a steady speed.

Units of acceleration In Worked example P1.6, the units of acceleration are given as m/s2 (metres per second squared). These are the standard units of acceleration. The calculation shows that the aircraft’s velocity increased by 2 m/s every second, or by 2 metres per second per second. It is simplest to write this as 2 m/s2, but you may prefer to think of it as 2 m/s per second, as this emphasises the meaning of acceleration.

Speed–time graphs

P1 Physics 5 In the example of the express train, the train increases in speed by 300 km/h and time taken is 300 s. So, for the train, acceleration a = 300300km h s / = 1 km/h per second.

SAMPLE

Time B C D ASpeed

EB D F0 0 605040302010

0 100 20 Time / s shaded area = distance travelled m/s/Speed

• C: sloping downwards, so the speed decreases and the train is decelerating.

• D: horizontal, so the speed has decreased to zero and the train is stationary.

CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED

Figure P1.29: Speed–time graph.

To understand this equation, consider Worked examples P1.7, P1.8 and P1.9. WORKED EXAMPLE P1.7

Calculate the distance you travel when you cycle for 20 s at a constant speed of 10 m/s (see Figure P1.29).

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

• A: sloping upwards, so the speed increases and the train is accelerating.

SCIENCES: COURSEBOOK 6 Figure P1.27 represents a train journey. The graph is in four sections. Each section illustrates a different point:

• B: horizontal, so the speed is constant and the train is travelling at a steady speed.

Finding distance travelled from a speed–time graph A speed–time graph represents an object’s movement. It tells us about how its speed changes. We can also use the graph to deduce (work out) how far the object travels. To do this, we have to make use of the equation: distance = area under speed–time graph

Figure P1.28: Speed–time graph for question P1.23. Name the sections that represent: i steady speed ii speeding up (accelerating) iii being stationary iv slowing down (decelerating). P1.24 A car is travelling at 20 m/s. The driver sees a hazard. After a reaction time of 0.7 s, she performs an emergency stop by applying the brakes. The car takes a further 3.3 s to come to a stop. Sketch a speed–time graph for her journey from the moment she sees the hazard to the moment she brings her car to a stop. Label the graph with as many details as you can.

Original material © Cambridge University Press & Assessment 2022. This material is not final and is subject to further changes prior to publication.

Figure P1.27: An example of a speed–time graph for a train during part of its journey.

Step 1: Distance travelled is the same as the shaded area under the graph. This rectangle is 20 s wide and 10 m/s high, so its area is 10 m/s × 20 s = 200 m.

The fact that the graph lines are curved in sections A and C tells us that the train’s acceleration was changing. If its speed had changed at a steady rate, these lines would have been straight. Questions P1.23 Look at the speed–time graph in Figure P1.28. Time / minutes km/h/Speed A G 10 20 30 40 50 60 70 80 H C

Step 2: Check using the equation: distance travelled = speed × time = 10 m/s × 20 s = 200 m Answer You would travel 200 metres.

SAMPLE

P1 Physics 7

Subject Measurement instrumentMeasuring Picture Units technologyFood Volume of milk Measuring jug Litres

Original material © Cambridge University Press & Assessment 2022. This material is not final and is subject to further changes prior to publication.

PROJECT: MAKING MEASUREMENTS

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

Many subjects in school involve taking measurements. Your task is to survey the measurements needed in your subjects and identify the measuring instruments which are used. You will then produce a students’ guide to measurement. You can present this as a short video, or as a table like the one shown here. You should include: • a range of measuring instruments, including those for measuring length, volume and time • reference to the units for each of the measurements • hints on how to ensure the measurements are accurate and precise. You could extend your project by adding other measurements such as angles or electric current. or millilitres

C10 Chemistry IN THIS CHAPTER YOU WILL: • learn how to describe the composition of clean dry air • investigate common air pollutants and their adverse effects • describe how carbon dioxide and methane are greenhouse gases linked to global warming and climate change • consider strategies to reduce climate change • consider strategies to reduce the effects of acid rain • explain how oxides of nitrogen form in car engines and are removed by catalytic converters • understand how greenhouse gases cause global warming • describe the tests for the presence of water, and why distilled water is used in experiments • describe tests for the purity of water • describe the main steps needed to purify the domestic water supply. Original material © Cambridge University Press & Assessment 2022. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this resource. SAMPLE

of carbon monoxide from vehicles, a catalytic converter is fitted. This converts carbon monoxide into carbon dioxide, as shown in the equation above.

Particulates are linked to increased respiratory disease and there is also evidence that they can cause cancer.

KEY WORDS greenhouse gas: a gas that absorbs heat reflected from the surface of the Earth, stopping it escaping the atmosphere. Release of carbon dioxide into the atmosphere Carbon dioxide (CO2) is produced during the complete combustion of fossil fuels. Fossil fuels are used to produce electricity and are the basis of many forms of transport. For example, methane (natural gas)

Greenhousechange gases

C10.5 Give a balanced symbol equation to show how a catalytic converter can remove carbon monoxide (CO) and nitrogen oxide (NO) from the exhaust gases to produce only nitrogen and carbon dioxide.

C10 Chemistry 9

KEY WORDS incomplete combustion: a type of combustion reaction in which a fuel is burnt in a limited supply of oxygen; the incomplete combustion of hydrocarbon fuels produces carbon, carbon monoxide and water. complete combustion: a type of combustion reaction in which a fuel is burnt in a plentiful supply of oxygen; the complete combustion of hydrocarbon fuels produces only carbon dioxide and water. Particulates Like carbon monoxide, carbon particulates (‘soot’ particles) are formed as a result of incomplete combustion of fuel. The incomplete combustion of octane to form particulates is shownoctaneby: + oxygen → particulate (soot) + water 2C8H18 + 9O2 → 16C + 18H2O

Original material © Cambridge University Press & Assessment 2022. This material is not final and is subject to further changes prior to publication.

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

SAMPLE

Carbon monoxide Incomplete combustion occurs when a hydrocarbon fuel is burned in a limited supply of oxygen. When this happens, one possible product is the pollutant carbon monoxide (CO). The incomplete combustion of octane (an important constituent of petrol) is shown by: octane + oxygen → carbon monoxide + water 2C8H18 → 17O2 → 16CO + 18H2O This should be compared to complete combustion of hydrocarbon fuels. Complete combustion occurs in a plentiful supply of oxygen and releases only carbon dioxide and water. Carbon monoxide is toxic to humans because it binds very strongly with haemoglobin in red blood cells. This prevents the blood cells from carrying oxygen around the body. Carbon monoxide can be produced when insufficient oxygen is taken into an engine. It can also be made when the air inlets get blocked in a gas central heating system, because this prevents oxygen from entering Tothe system.reduceemissions

Carbon dioxide, methane and climate

Although carbon dioxide is produced naturally by respiration, it is considered a particularly important pollutant. It is one of the greenhouse gases and increased amounts in the atmosphere have resulted in global warming. Global warming causes an increase in average temperatures and, because of this, is leading to climate change. There are several greenhouse gases including water vapour, carbon dioxide, methane, nitrous oxide, sulfur hexafluoride and chlorofluorocarbons (CFCs). In this section we will only look at two main greenhouse gases: carbon dioxide and methane.

An important source of particulates is from diesel vehicles. The particulates are produced when insufficient oxygen is drawn into the engine. To reduce particulate emissions, diesel vehicles are fitted with particulate traps (fine mesh filters) that remove the particles from the exhaust gas. Questions C10.1 What are the percentages of nitrogen, argon and oxygen in clean dry air? C10.2 Describe some of the problems caused by acid rain. C10.3 Fuels undergo either complete or incomplete combustion in oxygen. a State the word equation for the incomplete combustion of methane to produce carbon monoxide and water. b Balance this symbol equation: ___C6H14 + ___O2 → ____CO + ____H2O C10.4 Explain how oxides of nitrogen are formed and give some of the problems they are linked to.

EARTH Some energy is radiated back into space as light and heat. radiatedenergybytheSun Energy radiated by the Sun

The greenhouse gases allow high-energy, short wavelength radiation from the Sun to pass through the atmosphere and reach the Earth’s surface. Some of this thermal energy is absorbed and heats the oceans and land, and some is radiated (reflected) back into the atmosphere. The heat radiated by the Earth has a lower energy and a longer wavelength. The actual wavelength of this reflected radiation falls within the infrared part of the electromagnetic spectrum. The greenhouse gases, such as carbon dioxide and methane, can absorb this infrared radiation and then reradiate (re-emit) it in all directions. As it is re-emitted in all directions, some comes back towards the Earth’s surface. This reduces the heat loss to space and increases the temperature of the lower atmosphere. This phenomenon is called the greenhouse effect because the absorption and reflection of heat that warms the atmosphere works in a similar way to a greenhouse (Figure C10.4).

Burning fossil fuels, forest fires, industry and human activities produce various ’greenhouse gases‘. As these increase, more and more of the Sun’s energy is trapped. The Earth warms up.

10 produces carbon dioxide when burnt in a plentiful supply + oxygen → carbon dioxide + water CH4 + 2O2 CO2 + 2H2O

Scientists(climate change).havelinked global warming to increased levels of greenhouse gases because of the strong correlations between the concentration of the gases in the atmosphere and the average recorded temperatures.

Greenhouse effect

KEY WORDS greenhouse effect: the natural phenomenon in which thermal energy (heat) from the Sun is ‘trapped’ at the Earth’s surface by certain gases in the atmosphere (greenhouse gases).

CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: COURSEBOOK

of oxygen:methane

Like carbon dioxide, methane (CH4) is a greenhouse gas with levels in the atmosphere increasing over recent years. Some of the reasons for rising levels of methane in the atmosphere are linked to increased cattle farming and more waste being generated by larger populations. Cattle emit large amounts of methane as part of their digestive system. A single cow can produce over 1000 times the mass of methane compared with a human. The decomposition of food waste under anaerobic conditions by bacteria at landfill sites also releases large amounts of methane into the atmosphere. Global warming Carbon dioxide and methane occur naturally in the atmosphere and play an important role in maintaining a constant temperature on Earth. This relatively constant temperature is due to a natural phenomenon that scientists call the greenhouse effect. By trapping thermal energy reflected from the Earth’s surface, the greenhouse gases maintain an average surface temperature of around 15 °C. Without the greenhouse effect the average temperature would be much lower, possibly only −18 °C. At this temperature, life of the type we know would not exist. Over the last 200 million years, levels of greenhouse gases have remained relatively constant, but because of human activity this is now starting to change. Increased use of fossil fuels and changes in farming have caused levels of carbon dioxide and methane to rise. This, in turn, has resulted in an increase in the average surface temperature of the Earth. The increase is known as global warming and it has resulted in changing weather patterns

Some energy is absorbed in atmosphere.the

→

An important impact of climate change is that the increase in average temperature has caused quicker rates of melting of the Earth’s polar ice caps and glaciers. This has led to rising sea levels and so there has been increased flooding in

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

Release of methane into the atmosphere

Figure C10.4: The greenhouse effect. Climate change Global warming has brought about a range of consequences for the Earth’s climate. The impacts of global warming differ from country to country and general changes in weather patterns are known collectively as climate change.

Original material © Cambridge University Press & Assessment 2022. This material is not final and is subject to further changes prior to publication.

SAMPLE

Reducing the amount of methane released into the atmosphere Methane is released by both rotting vegetation and livestock.

Reducing the amount of carbon dioxide released into the atmosphere

Original material © Cambridge University Press & Assessment 2022. This material is not final and is subject to further changes prior to publication.

The problems linked to climate change are not limited to increased temperatures. For many countries, climate change means more frequent, more extreme weather patterns. For some this has included more severe storms and associated flooding and landslides.

renewable (resources): sources of energy and other resources that cannot run out provided they are managed sustainably, or that can be made at a rate faster than our current rate of use.

C10.9 The greenhouse gases allow short wavelength, high-energy radiation from the Sun to pass through the atmosphere. What do they do to the longer wavelength radiation reflected into space from the Earth’s surface?

C10.8 What are some of the problems linked to climate change and the melting of the ice caps? List some of the strategies that could be used to reduce these environmental issues.

While the effects of climate change can be disruptive to human ways of living, they can be catastrophic for animals and plants. Many living organisms are extremely sensitive to even slight changes in average temperature. For example, changes in temperature can lead to differences in the seasons when plants bud and produce fruit, which then has consequences for the wildlife whose life cycles depend on these plants. Changes in sea temperature can lead to bleaching of coral reefs and the associated loss of marine life.

In the short term, a more realistic option for reducing methane emissions from cattle is to better educate people about the harmful effects of an excessively meat-rich diet.

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

REFLECTION How easy do you find it to apply your scientific understanding to issues such as global warming and climate change? Could you explain these environmental issues to someone else? Are there any other factors you would need to consider?

C10 Chemistry 11 some low-lying countries and faster rates of coastal erosion.

How can the scientific knowledge you have learnt benefit people and the environment?

There is evidence that encouraging greater dependence on plant-based food is being successful, with increasing numbers of vegetarians and vegans around the world. Questions C10.6 Name two greenhouse gases and give a source for each. C10.7 Why are levels of carbon dioxide in the atmosphere increasing?

The melting of ice caps is also causing changes to the life cycles and migratory patterns of animals and birds. Polar bears, who rely on sea ice as they travel between different hunting grounds, have been particularly badly affected.

There are many steps that can be taken to reduce the release of greenhouse gases at an individual, national and global level. In recent years, governments from around the world have tried to take steps together to reduce their greenhouse gas emissions. There have been important climate change conferences where agreements have been made, including the Kyoto Protocol of 2005 and the Paris Agreement of 2016. Increased public awareness of the impact of climate change and a stronger presence of environmental groups has placed pressure on governments to react.

KEY WORDS

An important step towards decreased greenhouse gas emissions of carbon dioxide is to reduce our reliance on fossil fuels for transportation and electricity generation. This can be done by turning to renewable sources of energy such as wind and solar. Many countries have started to remove coal power stations and replace them with renewable energy sources. Methods of transport are starting to change, and several countries have committed themselves to phasing out diesel engines. There is significant interest in moving away from petrol cars to electric cars, although there are still issues about how the electricity used to power these vehicles is created. Some manufacturers are also looking at developing fuel cell vehicles. Hydrogen fuel cells are of particular interest because the only chemical product is water (Chapter 6). An alternative method being used by many countries is to plant additional trees (afforestation) which will capture the carbon dioxide through photosynthesis.

An increase in temperature can also lead to more severe droughts. With higher temperatures, the soil dries out more quickly, and this is then compounded by changes in rainfall. Very dry soil and low rainfall increase the chances of crop failure. In the longer term, arable land can become so arid it turns to desert. In regions such as California and parts of Australia, drying out of grasslands as a result of climate change has increased the frequency and severity of wildfires.

Innovative approaches have been considered to reduce methane emissions from livestock, including changes in their diet and even trying to capture the gases they produce.

B7 Biology IN THIS CHAPTER YOU WILL: • learn about the functions of xylem and phloem, and where they are found • investigate the movement of water through stem and leaves • find out what transpiration is, why it happens, and conditions that affect its rate • learn about translocation of sucrose and amino acids in plants. • find out about the human circulatory system • learn about the structure and function of the heart • think about factors that increase the risk of developing heart disease • investigate how exercise affects heart rate • compare the structure and function of arteries, veins and capillaries • find out about the components of blood, and what they do • explain how the structures of arteries and veins are related to their functions • explain how the structures of capillaries are related to their functions. Original material © Cambridge University Press & Assessment 2022. This material is not final and is subject to further changes prior to publication. We are working with Cambridge Assessment International Education towards endorsement of this resource. SAMPLE

Figure B7.14: A potometer with a reservoir, which makes it easy to refill.

It is not easy to measure how much water is lost from the leaves of a plant. It is much easier to measure how fast the plant takes up water. The rate at which a plant takes up water depends on the rate of transpiration. The faster a plant transpires, the faster it takes up water.

If the temperature is high, it is windy and the air is very dry, then transpiration will happen very quickly. The plant may lose water from its leaves faster than it can take it up from its roots. The individual cells in the plant lose so much water that they become flaccid (Chapter 3, Topic 3.2). The tissues in the leaves are no longer supported by the turgid cells pushing outwards against one another. The leaves become soft and floppy. This is called wilting (Figure B7.13).

Figure B7.13: These pictures, taken over a period of one hour, show a plant that is gradually losing more water by transpiration than it can take up into its roots.

The higher the temperature, the greater the kinetic energy of water molecules. This means that water evaporates faster from the surface of the mesophyll cells, and the water vapour diffuses out of the leaf into the air

rate is also affected by humidity. Humidity means the moisture content of the air. The higher the humidity, the less water vapour will diffuse out from the leaves. This is because there is not much of a diffusion gradient for the water between the air spaces inside the leaf, and the wet air outside it. Transpiration decreases as humidity increases.

EXPERIMENTAL SKILLS 7.2

Transpirationmore quickly.

Conditions that affect transpiration rate

Original material © Cambridge University Press & Assessment 2022. This material is not final and is subject to further changes prior to publication.

The rate at which water vapour diffuses out of a plant’s leaves is affected by the environment. Transpiration happens faster when the temperature is high.

B7 Biology 13

KEY WORDS humidity: how much water vapour is present in air. wilting: (of a plant): losing more water than it can take up, so the cells lose their turgidity.

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

SAMPLE

Figure B7.14 illustrates apparatus which can be used to compare the rate of transpiration in different conditions. rulermeniscusair/watercapillary tube screwreservoirclip containing water rubber tube with airtight seal transpiring branch of the twaterdrawingplant,upfromhepotometer

14CONTINUED

3 If you have submerged your potometer in water, take it out of the water and stand it on the bench. Check that your potometer is airtight and that there are no air bubbles. (If you suspect it is not airtight, you can smear petroleum jelly over anywhere that you think might be leaking)

In this investigation, you will use a potometer to measure how fast a plant shoot takes up water in different conditions. You will practise handling apparatus carefully, making accurate measurements, recording results and drawing conclusions. You will also evaluate your method and think about possible improvements.

CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: COURSEBOOK

airtightrubbercapillarymeniscusair/waterrulertubetubewithseal

• a potometer, like the ones in Figure B7.14 or B7.15

SAMPLE

You will need:

1Method

A capillary tube is a glass tube with a very narrow hole. There are many different kinds of potometer, so yours might not look like Figure B7.14. The simplest kind is just a long glass tube which you can fill with water. A piece of rubber tubing slid over one end allows you to fix the cut end of a shoot into it, making an air-tight connection (Figure B7.15). This works just as well as the one in Figure B7.14 but is much harder to refill with water.

Fill the potometer with water. If you have a potometer like the one in Figure B7.14, you can simply open the clip and then close it once the tubes are all full of water. If your potometer is like the one in Figure B7.15, submerge it in a big container of water (such as a big sink).

It is called a potometer, which simply means ‘water measurer’. By recording how fast the air/water meniscus moves along the capillary tube, you can compare how fast the plant takes up water in different conditions.

Safety Take care with the sharp blade. In step 2, put the plant shoot onto a non-slip surface such as a cork board to cut it. Cut away from you, not towards you.

Figure B7.15: A simpler potometer without a reservoir. This one can be refilled by taking it apart and submerging the tube in water.

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

5 When the air/water meniscus reaches the scale, begin to record the position of the meniscus every two minutes for ten minutes.

Before you start Look carefully at your potometer and check you know how it works and how to use it.

• a retort stand, boss and clamp to support the potometer • a fresh, leafy shoot • a sharp blade to cut the end of the shoot so that it fits into the potometer • a timer • a fan • access to places with different temperatures –for example, a warm room and a fridge.

Original material © Cambridge University Press & Assessment 2022. This material is not final and is subject to further changes prior to publication.

2 Cut a plant shoot, making a slanting cut. Push the shoot into the potometer. If your potometer is like the one in Figure B7.15, do this while the tube is still completely under water.

4 Now leave the apparatus in a light, airy place. Fix the ruler close to the tube, to act as a scale. As the plant transpires, the water it loses is replaced by water taken up through the cut end of the stem. Air will be drawn in at the end of the capillary tube.

Leaves make carbohydrates by photosynthesis. They also use some of these carbohydrates to make amino acids, proteins, fats and oils and other organic substances.

source: part of a plant that releases sucrose or amino acids, to be transported to other parts. sink: part of a plant to which sucrose or amino acids are being transported, and where they are used or stored.

2 Explain why the air/water meniscus moves along the scale.

KEY WORDS

The part of a plant from which sucrose and amino acids are being translocated is called a source. The part of the plant to which they are being translocated is called a sink.

When a plant is actively photosynthesising and growing, the leaves are generally the major sources of translocated material. They are constantly producing sucrose, which is carried in the phloem to all other parts of the plant. These ‘receiving’ parts – the sinks – include the roots and flowers. The roots may change some of the sucrose to starch and store it. The flowers use the sucrose to make fructose (an especially sweet-tasting sugar found in nectar). Later, when the fruits are developing, sucrose may be used to produce sweet, juicy fruits ready to attract animals.

B7 Biology 15

CONTINUED

SAMPLE

Some of the substances made in the leaves, especially sucrose and amino acids, are transported to other parts of the plant in the phloem tubes. This is called translocation Sources and sinks

6 Repeat the investigation, but with the apparatus in a different situation. You could try each of these: • blowing it with a fan • putting it in a refrigerator.

But many plants have a time of year when they wait in a state of reduced activity for harsh conditions to end. In a hot climate, this may be during the hottest, driest season.

If so, explain what you think caused the difficulties.

3 Use your results to draw line graphs, so that you can easily compare the rate of movement in different conditions.

1QuestionsaDid you have any difficulties setting up the potometer and getting the meniscus to move?

b Did you manage to overcome the difficulties? If so, describe how you did this.

translocation: the movement of sucrose and amino acids in phloem from sources to sinks.

In temperate countries, it may be during the winter. During these difficult times, the plant does not photosynthesise. It survives by using its stores of starch, oils and other materials in its roots. The stored materials are converted to sucrose and transported to other parts of the plant. So, these storage areas have now become sources.

Original material © Cambridge University Press & Assessment 2022. This material is not final and is subject to further changes prior to publication.

Translocation

Figure B7.16a: Baobab trees in the wet season, when the leaves are sources of sucrose. b: In the dry season, the stems and roots store starch, ready to supply the leaves with sucrose when they begin to grow in a few months’ time. a b

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

Transport in animals

right side of heart left side of heart

frombloodOxygenatedcells.iscarriedthelungs.

B7.14 Explain how, and where, blood becomes deoxygenated.

16 For example, baobab trees (Figure B7.16) grow in tropical countries such as Madagascar. In the wet season, their leaves photosynthesise and make sucrose. This is transported to the trunk and roots, where it is stored as starch. In the dry season, the baobab drops its leaves. When it rains again, the stores of starch are changed to sucrose, and transported to the growing buds, helping them to grow and form new leaves. You can see from this example that phloem can transfer sucrose in either direction – up or down the plant. This is not true for the transport of water in the xylem vessels.

The main transport system of all mammals, including humans, is the blood system. It is also known as the circulatory system. It is a network of tubes, called blood vessels. A pump, the heart, keeps blood flowing through Figurethe vessels.B7.17 shows the general layout of the human blood system. The arrows show the direction of blood flow.

the blood becomes deoxygenated. The deoxygenated blood is brought back to the right-hand side of the heart. It then goes to the lungs, where it becomes oxygenated once more.

bodycellstocarriedbloodOxygenatedisalltheinthefromtheleftsideoftheheart.oftherbloodDeoxygenatediseturnedtorightsidetheheart.

Oxygen diffuses from the blood to the body

CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: COURSEBOOK

Oxygen diffuses into the blood from the lungs. tobloodDeoxygenatediscarriedthelungs.

7.2

Figure B7.17: The general layout of the circulatory system of a human, as seen from the front.

SAMPLE

Put your finger on the position of the lungs, at the top of the diagram, and then follow the arrows. You can see that blood flows from the lungs into the left-hand side of the heart, and then out to the rest of the body. It then flows back to the right-hand side of the heart, before travelling to the lungs again. The blood in the left-hand side of the heart has come from the lungs. It contains oxygen, which was picked up in the capillaries surrounding the alveoli. It is called oxygenated blood This oxygenated blood is then sent around the body. Some of the oxygen is taken up by the body cells, which need oxygen for respiration. When this happens,

B7.11 As the dry season comes to an end, suggest which part of a baobab becomes a source, and which parts are sinks. B7.12 Phloem tubes can transport sucrose both up and down a plant. Explain why xylem can only transport water up a plant and not down it.

Water can only go upwards, because transpiration always happens at the leaf surface, and it is this that provides the ‘pull’ to draw water up the plant. Questions B7.10 In the wet season, suggest which part of a baobab is a source, and which parts are sinks.

KEY WORDS circulatory system: a system of blood vessels with a pump and valves to ensure one-way flow of blood. oxygenated blood: blood containing a lot of oxygen. deoxygenated blood: blood containing only a little oxygen. Questions B7.13 Look at Figure B7.17. Which side of the heart contains oxygenated blood, and which contains deoxygenated blood?

Circulatory systems

B7 Biology 17

The circulatory system shown in Figure B7.17 is a double circulatory system. This means that the blood passes through the heart twice on one complete circuit of the body.

KEY WORDS

Original material © Cambridge University Press & Assessment 2022. This material is not final and is subject to further changes prior to publication.

SAMPLE

We can think of the double circulatory system being made up of two parts. The blood vessels that take the blood to the lungs and back are called the pulmonary system. The blood vessels that take the blood to the rest of the body and back are called the systemic system.

double circulatory system: a system in which blood passes through the heart twice on one complete circuit of the body. Double circulatory systems have some advantages over single circulatory systems. When blood flows through the tiny blood vessels in a fish’s gills or a mammal’s lungs, it loses a lot of the pressure that was given to it by the pumping of the heart. In a mammal, this low-pressure blood is delivered back to the heart, which raises its pressure again before sending it off to the rest of the body. In a fish, the low-pressure blood just continues around the fish’s body. This means that blood travels much more slowly to a fish’s body organs than it does in a mammal. This is particularly important when you think about the delivery of oxygen for respiration. Any tissues that are metabolically very active need a lot of oxygen delivered to them as quickly as possible, and this delivery is much more effective in a mammal than in a fish.

Double circulatory systems

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