Edexcel International GCSE Science Samples by Collins

Student Book EDEXCEL INTERNATIONAL GCSE (9-1) BIOLOGY • Develop your practical skills with investigative tasks • Check your progress and understanding using the end of the topic checklists and in-text questions • Practise your exam technique with exam-style questions in each section, annotated examples and further guidance • Gain insights into the real-life uses of science through the Science in Context sections

Biology Teacher Pack ISBN: 9780008236229

Chemistry Student Book ISBN: 9780008236212

Physics Student Book ISBN: 9780008236205

Chemistry Teacher Pack ISBN: 9780008236243

Physics Teacher Pack ISBN: 9780008236236

EDEXCEL INTERNATIONAL GCSE (9-1) BIOLOGY

Collins Edexcel International GCSE Biology provides all the material you need for your International GCSE 9-1 qualification.

EDEXCEL INTERNATIONAL GCSE (9-1) BIOLOGY Jackie Clegg, Sue Kearsey, Gareth Price and Mike Smith

ISBN 978-0-00-823619-9

9 780008 236199

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Contents Getting the best from the book............................4

Section 1 The nature and variety of living organisms......................8 a) Characteristics of living organisms.................10 b) Variety of living organisms................................15 c) Exam-style questions...........................................25

Section 2 Structure and functions in living organisms..................28 a) Level of organisation............................................30 b) Cell structure..........................................................36 c) Biological molecules.............................................43 d) Movement of substances into and out of cells...............................................................55 e) Nutrition...................................................................68 f) Respiration...............................................................97 g) Gas exchange.........................................................105 h) Transport..................................................................124 i) Excretion....................................................................148 j) Coordination and response................................157 k) Exam-style questions...........................................177

Section 3 Reproduction and inheritance.............188 a) Reproduction..........................................................190 b) Inheritance..............................................................214 c) Exam-style questions...........................................248

Section 5 Use of biological resources......................320 a) Food production....................................................322 b) Selective breeding................................................342 c) Genetic modification (genetic engineering)..........................................350 d) Cloning.....................................................................359 e) Exam-style questions...........................................367

The International GCSE examination....374 Overview.......................................................................374 Assessment objectives and weightings.............375 Examination tips.........................................................375 Answering questions................................................378

Developing experimental skills..............380 Planning and assessing the risk............................380 Carrying out the practical work safely and skilfully......................................................386 Making and recording observations and measurements....................................................390 Analysing the data and drawing conclusions...................................................................393 Evaluating the data and methods used.............400

Mathematical skills....................................404 Glossary.........................................................................406 Answers..........................................................................415 Index...............................................................................434

Section 4 Ecology and the environment................254

a) The organism in the environment..................256 b) Feeding relationships..........................................268 c) Cycles within ecosystems...................................283 d) Human influences on the environment........293 e) Exam-style questions...........................................311

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When we talk about the ‘heart’ of something, in a general way, we mean the centre of something – not only where it is, but also the role it plays. And for good reason: the human heart is not only positioned in the middle of the body; it also plays a central role in maintaining life. The heart and circulatory system function to circulate blood around the body and so deliver oxygen from the lungs, and nutrients from the digestive system, to all cells so that they can respire and carry out all the processes needed for life. The blood then removes waste products from these processes, for example delivering carbon dioxide to the lungs and urea to the kidneys for excretion and removal from the body. The heart plays a central role in staying alive and staying healthy.

STARTING POINTS 1. How is the body organised so that it can carry out the life processes effectively? 2. What do all cells have in common, and how are some cells different from others? 3. What are the basic molecules of life? 4. How do cell membranes control what can get into and out of the cell? 5. How do plants and humans get the food they need for growth? 6. What is cellular respiration and how do the body systems support it? 7. How are gas exchange surfaces adapted for rapid exchange of gases into and out of the body? 8. How are materials transported around the bodies of plants and humans? 9. What are the waste materials of metabolism and how are they removed from the body? 10. How do plants and humans respond to changes in the environment around them?

SECTION CONTENTS a) Level of organisation

f) Respiration

b) Cell structure

g) Gas exchange

c) Biological molecules

h) Transport

d) Movement of substances into and out of cells

i) Excretion

e) Nutrition

k) Exam-style questions

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j) Coordination and response

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Structure and functions in living organisms

∆∆Microscopic view of leaf surface of spiderwort, showing cells.

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Coordination and response INTRODUCTION

US tennis star Andy Roddick can hit a tennis ball so hard that it travels at around 250 km per hour. In order to return the ball successfully, his opponents have only a fraction of a second to work out where to stand and how best to return the ball. Their response is built on years of training, so that they can respond without consciously thinking.

∆∆Fig. 2.110 Professional tennis players serve so quickly that a radar gun is used to measure the speed of the ball.

KNOWLEDGE CHECK ✓✓Plants and animals detect the environment with specialised sense organs. ✓✓Animals respond to changes in the environment using nervous and hormonal systems. ✓✓Plants respond to changes in the environment using their hormonal system. ✓✓Nerve cells are specialised cells adapted to the function of carrying electrical impulses.

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LEARNING OBJECTIVES ✓✓Understand how organisms are able to respond to changes in their environment. ✓✓Understand that homeostasis is the maintenance of a constant internal environment, and that body water content and body temperature are both examples of homeostasis. ✓✓Understand that a coordinated response requires a stimulus, a receptor and an effector. ✓✓Understand that plants respond to stimuli. ✓✓Describe the geotropic and phototropic responses of roots and stems. ✓✓Understand the role of auxin in the phototropic response of stems. ✓✓Describe how nervous and hormonal communication control responses and understand the differences between the two systems. ✓✓Understand that the central nervous system consists of the brain and spinal cord and is linked to sense organs by nerves. ✓✓Understand that stimulation of receptors in the sense organs sends electrical impulses along nerves into and out of the central nervous system, resulting in rapid responses. ✓✓Understand the role of neurotransmitters at synapses. ✓✓Describe the structure and functioning of a simple reflex arc illustrated by the withdrawal of a finger from a hot object. ✓✓Describe the structure and function of the eye as a receptor. ✓✓Understand the function of the eye in focusing on near and distant objects, and in responding to changes in light intensity. ✓✓Describe the role of the skin in temperature regulation, with reference to sweating, vasoconstriction and vasodilation. ✓✓Understand the sources, roles and effects of the following hormones: adrenaline, insulin, testosterone, progesterone and oestrogen. ✓✓Understand the sources, roles and effects of the following hormones: ADH, FSH and LH.

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SENSITIVITY Sensitivity, the ability to recognise and respond to changes in external and internal conditions, is recognised as one of the characteristics of living organisms. A change in conditions is called a stimulus. To produce a coordinated response to that stimulus, there must be a receptor that can recognise the stimulus and an effector, a mechanism to carry out the response. Coordination means detecting and responding appropriately to a particular stimulus.

Coordination and response in flowering plants TROPISMS Plants generally respond to changes in the environment by a change in the way they grow. For example, a shoot grows towards light, and in the opposite direction to the force of gravity, while a root grows away from light, but towards moisture and in the direction of the force of gravity. These growth responses to a stimulus in plants are called tropisms. These responses help the plant produce leaves where there is the most light, and roots that can supply the water that the plant needs.

◁◁Fig. 2.111 The response of growing towards light helps a plant get more light for photosynthesis.

Growth in response to the direction of light is called phototropism. If the growth is towards light, it is called positive phototropism, as in shoots. Roots grow away from light so they are negatively phototropic. Growth in response to gravity is called geotropism. Roots show positive geotropism, but shoots are negatively geotropic. Tropisms are controlled by plant hormones called auxins. These hormones are made in the tips of shoots (and roots) and diffuse away from the tips. Further back along a shoot, the hormones stimulate cells to elongate (grow longer) so that the shoot grows longer.

● 158

SCIENCE IN CONTEXT

GARDENER’S TIP

One effect of the hormone auxin is to inhibit the growth of side shoots. This is why a gardener who wants a plant to stop growing taller and encourage it to become more bushy will take off the shoot tip, so removing a source of auxin.

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The growth of shoots towards light can be explained by the response of auxin to light. • When all sides of a shoot receive the same amount of light, equal amounts of auxin diffuse down all sides of the shoot. So cells all around the shoot are stimulated equally to grow longer. This means the shoot will grow straight up. • When the light on the shoot comes mainly from the side, auxin on that side of the shoot moves across the shoot to the shaded side. The cells on the shaded side of the shoot will receive more auxin, and so grow longer, than those on the bright side. This causes the shoot to curve as it grows, so that it grows towards the light.

light

auxin produced at tip

light

light auxin diffuses away from tip

light

shoot grows more cell elongation on shaded side cells elongate

less auxin

more auxin

with light all around or from above

shoot curves towards the light

with light from the side

∆∆Fig. 2.112 The effect of light and auxin on the growth of shoots.

The hormone is also made in root tips. However, it has the opposite effect on root cells compared with shoot cells, because it reduces how much the cells elongate. • When roots are pointing straight down, all sides of the root receive the same amount of hormone, so all cells elongate by the same amount. • When the root is growing at an angle to the force of gravity, gravity causes the hormone to collect on the lower side. This reduces the amount of elongation of cells on the lower side of the root, so that the root starts to curve as it grows until it is in line with the force of gravity. root curves downwards

auxin concentrated on lower side of root

less cell elongation

∆∆Fig. 2.113 The effect of gravity on the growth of roots.

REMEMBER

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A full understanding of the phototropic responses in stems is needed to gain higher marks. Remember that auxin causes shoots to curve by the elongation of existing cells, not by the production of more cells.

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Developing investigative skills Fig. 2.114 shows apparatus that can be used to investigate the effect of light on the growth of seedlings.

inner walls painted black window to allow light in

Devise and plan investigations ➊➊Describe how the apparatus could be used

for this investigation. ➋➋Describe how you would set up a control for this investigation.

Make observations and measurements ➌➌a) If this investigation were set up correctly, what result would you expect to see in the seedlings from the windowed box, compared with your control? b) Explain your answer.

Evaluate data and methods ➍➍Suggest how this investigation could be

Petri dish with damp paper towel and seeds

∆∆Fig. 2.114 Apparatus for investigating the effect of light on growing seeds.

extended to investigate whether roots also show a phototropic response.

QUESTIONS 1. Describe the term tropism in your own words. 2. Give one example of: a) positive phototropism b) positive geotropism. 3. Describe the action of auxin in a shoot growing in one-sided light.

Coordination and response in humans

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There are two systems involved in coordination and response in humans. • One is the nervous system, which includes the brain, the spinal cord, the peripheral nerves and specialist sense organs such as the eye and the ear. Communication in the nervous system is in the form of electrical impulses and responses may be very rapid.

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• The other is the hormonal (or endocrine) system, which uses chemical communication by means of hormones. Hormones are secreted by endocrine glands and act upon target cells in other tissues and organs. The hormonal system helps to maintain basic body functions including metabolism and growth. It often has more long-term effects than the nervous system and usually its response is less rapid. REMEMBER

For the top marks you must be able to compare and contrast the two systems of coordination in humans. Try also to identify the stimulus, receptor, effector and response in any example of the nervous or hormonal system.

THE NERVOUS SYSTEM In the human nervous system: • Specialised sense organs that contain receptor cells sense stimuli (changes in conditions). • Information about these stimuli is sent as electrical impulses from the receptor cells through nerves to the central nervous system. • The central nervous system (brain and spinal cord) processes the electrical impulses and coordinates the response. • The response passes as electrical impulses along nerves to effectors, which are often muscles but may be endocrine glands. • The effectors produce the response to the stimulus.

brain peripheral nerves spinal cord cerebrum

cerebellum medulla

spinal nerve

∆∆Fig. 2.115 The human central nervous system.

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∆∆Fig. 2.116 The nervous system.

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spinal cord

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Nerve cells Nerves connect the sense organs to the central nervous system, and the central nervous system to effectors. Nerves, the brain and the spinal cord are all made of specialised cells called neurones. Neurones are specially adapted for their function because they have many endings that connect with other neurones for passing electrical impulses, and long cell extensions, called axons and dendrons, that carry the electrical impulses. • Neurones that link sense organs to the central nervous system are called sensory neurones. • Neurones within the central nervous system may be very short, and are called relay (sometimes intermediate dendrites or connecting) neurones. • Neurones that connect the central nervous system to an effector, such as a muscle, are called motor neurones.

neurones

nerve (nerve surrounded by fibrous sheath)

∆∆Fig. 2.117 Nerves are large bundles of many neurones.

Motor neurone

nucleus

axon

insulating sheath

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Synapses cell body Sometimes impulses may have to pass electrical impulse along several neurones. The place where an impulse passes from one neurone to another is called a synapse. This is a very small gap between the ends of two neurones. sac containing The electrical impulse itself does not neurotransmitters neurotransmitter travel across the gap, but instead causes chemicals called neurotransmitters to be released from the end of one electrical electrical neurone which diffuse across the impulse impulse synapse. When the neurotransmitters reach the next neurone they cause a new electrical impulse to be sent. Although the neurotransmitters travel by diffusion, because the synapse is so ∆∆Fig. 2.118 When an electrical impulse arrives at a synapse, are released which start a new impulse in the narrow (about 1/50,000th of a mm), the neurotransmitters next neurone. whole process happens very quickly. Synapses mean that impulses can only travel in one direction from one neurone to another. They also allow one neurone to pass impulses to several others at the same time, or to receive impulses from several others. SENSE ORGANS Different sense organs contain different specialised receptor cells that respond to different stimuli. The table shows the different sense organs in humans.

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Sense organ Skin

Sense Touch

Tongue Nose Eyes

Taste Smell Sight Hearing Balance

Ears

Stimulus Pressure, pain, hot/cold temperatures Chemicals in food and drink Chemicals in the air Light Sound (vibrations in air) Movement/position of head

∆∆Table 2.9 Sense organs in humans.

The eye In humans, the eye is the sense organ that responds to changes in light. The specialised light-sensitive receptor cells are found in the retina at the back of the eye. Light passing through the eye and reaching the retina causes changes in these cells, sending electrical impulses to the brain along the optic nerve. Other structures of the eye support this process. • The cornea, lens, aqueous and vitreous humour are all transparent, to let light pass through. The cornea and lens refract (bend) light to form an image on the retina. The jelly-like aqueous and vitreous humour maintain the shape of the eyeball. • The pupil is a hole in the iris that controls how much light enters the eye. • The inside of the eye is very dark, to stop light reflecting and so cause multiple images. choroid layer (contains dark pigment to absorb light) sclera (protective white outer layer) retina (contains lightsensitive receptor cells) fovea (the most sensitive part of the retina) optic nerve (carries electrical impulses to the brain)

pupil (hole in centre of iris, to let light into eye) lens (helps focus image) suspensory ciliary muscle ligament

to the brain

vitreous humour

∆∆Fig. 2.119 Structure of the human eye.

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blind spot (where the optic nerve attaches to the retina, there are no light-sensitive cells)

ciliary muscle (circular muscle around lens which helps to change its shape) cornea (refracts light) aqueous humour suspensory ligament (attaches lens to ciliary muscle) iris (controls amount of light entering the eye)

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There are two different kinds of light-sensitive cells in the retina. • Cone cells respond to light of different wavelengths, and therefore respond to different colours. They only work well in bright light, so we only see colour images when the light is bright enough. The cone cells are mostly clustered at the fovea on the retina, where most light falls. • Rod cells respond to differences in light intensity, not wavelength. They are more sensitive at low light intensities than cone cells, so we use these mostly in low light conditions. They can not distinguish different colours. Rod cells are found all over the retina.

● SCIENCE IN CONTEXT

DARK ADAPTATION

In bright light the rod cells lose their ability to respond. This is because the coloured pigment in the cells that responds to light is changed into another form. As the light becomes dimmer, the pigment slowly changes back into the form that detects light. However, it can take up to half an hour for the rods to fully recover. This is known as dark adaptation and explains why, if you move from a bright place to a darker place, it takes a while for your eyes to adjust and see clearly again.

Changing light conditions The light-sensitive cells in the retina only respond to the stimulus of light above a certain light intensity. When it is so dark that the cells are not stimulated, we cannot see. Since vision is an important sense, at low light intensities our eyes need to gather as much light as possible. However, rod and cone cells are easily damaged by high light intensity – which is why you should NEVER look directly at a bright light source such as the Sun. circular muscle relaxed

radial muscle contracted

circular muscle contracted

pupil dilated

radial muscle relaxed

pupil constricted

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∆∆Fig. 2.120 The pupil response to light. Left: in dim light. Right: in bright light.

The iris (ring-shaped, coloured part of the eye) controls the amount of light entering the eye by controlling the size of the hole in the centre, the pupil. The iris contains circular and radial muscles. In bright light

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the circular muscles contract and the radial muscles relax, making the pupil smaller. This prevents damage to the cells in the retina by reducing the amount of light entering the eye. The reverse happens in dim light, when the eye has to collect as much light as possible to see clearly.

most refraction occurs here

light from distant object

Focusing light muscles relax and the suspensory In order to see clear images of our ligaments pull on the lens to make it thin and wide surroundings, the light that enters our eyes needs to be focused properly on the rays are spread out so retina. need more refraction The thick clear cornea bends light rays as they enter the eye in order to focus them on the retina. The lens provides fine focus to sharpen the image. light from near object Rays of light from distant objects are almost parallel when they enter the eye. They require less refraction (bending) to come to a focus on the retina – the cornea can manage most of this without muscles contract, reducing the tension on help from the lens. The ciliary muscles, the suspensory ligaments and the lens which bulges to a fatter shape and which are circular, relax and the lens is refracts the light more pulled into a thinner shape by the suspensory ligaments. This provides the ∆∆Fig. 2.121 How the eye focuses light from distant correct focusing power. and near objects. Rays of light from near objects are diverging when they enter the eye. They need much more powerful refraction to bend them to a focus on the retina. The ciliary muscles contract, which means they pull less on the suspensionary ligaments. This allows the elastic lens to return to a more rounded shape. This refracts light more to achieve a focused image on the retina.

QUESTIONS 1. Explain how the following structures are adapted to support the role of the eye in sensing light:

a) cornea b) pupil c) retina. 2. Explain how the eye responds to changing light intensity. is near to the person.

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3. Explain how the eye produces a focused image of an object that

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REFLEX RESPONSES The simplest type of response to a stimulus is a reflex. Reflexes are rapid, automatic responses to a specific stimulus that usually protect you in some way, for example blinking if something gets in your eye or sneezing if you breathe in dust. The pathway that nerve impulses travel along during a reflex is called a reflex arc: stimulus → receptor → sensory neurone → relay neurone in CNS → motor neurone → effector → response

Simple reflexes are usually spinal reflexes, which means that the impulses are processed by the spinal cord, not the brain. The spinal cord sends an impulse back to the effector. Effectors are the parts of the body that respond, either muscles or glands. Examples of spinal reflexes include responses to standing on a pin or touching a hot object. stand on pin → pain receptors → sensory neurone → spinal cord → motor neurone → leg muscles → leg moves

When the spinal cord sends an impulse to an effector, other impulses are sent on to the brain so that it is aware of what is happening. It also allows the brain to over-ride the reflex response. For example, if you were holding a large bowl of hot food that you were looking forward to eating, you might look around quickly for somewhere to put it down rather than drop it immediately and risk breaking the bowl. message is also passed to the brain

4. relay neurone

5. motor neurone central nervous system (spinal cord) synapse

6. effector (biceps muscle)

7. response (hand moves)

3. sensory neurone

2. pain receptor in skin

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1. cooker (stimulus – heat)

∆∆Fig. 2.122 A spinal reflex to touching a hot object.

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REMEMBER

For higher marks you will need to understand the structure and functioning of the reflex arc, and be able to interpret diagrams and describe what happens at each step.

QUESTIONS 1. What is meant by the term reflex response and why are these responses important for survival?

STIMULUS (any change in our surroundings)

RECEPTORS (senses) sensory neurone impulses

2. Describe the reflex response that occurs when you put

HOMEOSTASIS For our cells to carry out all the life processes properly, they need the conditions in and around them, such as the temperature and amount of water and other substances, to stay within acceptable limits. Keeping conditions within these limits – that is, keeping the internal environment constant – is called homeostasis.

CENTRAL NERVOUS SYSTEM (brain / spinal cord)

motor neurone impulses

EFFECTORS (muscles / glands)

Temperature control RESPONSE The temperature in the core of your body is about 37 °C, (we do something) regardless of how hot or cold you may feel on the outside. This core temperature may naturally vary a little, but it never varies a lot unless you are ill. ∆∆Fig. 2.123 A diagrammatic reflex arc. Heat energy is constantly released by cells as a result of respiration and other chemical reactions, and is transferred to the surroundings outside the body. To maintain a constant body temperature these two processes must balance. The temperature of the blood from the core of the body is monitored by the hypothalamus in the brain. If the temperature varies too much from 37 °C, the hypothalamus causes changes to happen that bring the temperature back to about 37 °C. The hypothalamus also receives electrical impulses from heat sensor cells in the skin surface. If core temperature rises too far: • Sweat is released on to the surface of the skin from glands. Sweat is mostly water, and this water evaporates. Evaporation needs heat energy, so heat energy is removed from the skin surface as the sweat evaporates, cooling the skin. • Blood vessels carrying blood near the surface of the skin dilate (get wider) so more blood flows through them. This is known as vasodilation, and it is what makes light-skinned people look pink when they are hot. Vasodilation makes it easier for heat energy to be transferred to the skin surface and from there to the environment by radiation and conduction.

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your finger on something hot.

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If core temperature falls too far: • Blood vessels carrying blood near the surface of the skin constrict (get narrower), which reduces the amount of blood flowing through them. This is known as vasoconstriction. As the warm blood is kept deeper in the skin, this reduces the rate of heat transfer by conduction to the skin surface and from there to the environment. • Body hair may be raised by muscles in the skin. This has little effect in humans (often called goose bumps) but is more effective in mammals with fur and in birds, because the fur or feathers trap air next to the skin. Air is not a good conductor of heat energy, so this still layer of air acts as insulation. • Muscles may start to ‘shiver’. This means they produce rapid, small contractions. Cellular respiration is used to produce these contractions, releasing heat energy at the same time which heats the blood flowing through the muscles. A coldAday cold day

A hot A day hot day

air trapped between hairs –hairs insulation layer layer air trapped between – insulation

less airless between hairs –hairs heat–escapes from body easilyeasily air between heat escapes from more body more sweatsweat evaporating evaporating blood blood vessels close close to the to skin dilate dilate vessels thesurface skin surface

blood blood vesselsvessels close to the to skin constrict close thesurface skin surface constrict

∆∆Fig. 2.124 The skin responds to maintain body core temperature.

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Control of body water content Our bodies gain water through: • food – most foods contain water • drink • respiration and other chemical reactions – water is one of the waste products of respiration. Our bodies lose water through: • breathing • sweating • egestion – faeces contains water • excretion of urine. Although we are constantly gaining and losing water, it is important that our overall water content does not vary too much. If we contain too little water, and are in danger of dehydrating, we can drink more, and we produce less, more concentrated urine. (We still have to produce some urine to excrete urea.) If we contain too much water, and are in danger of overhydrating, we produce a larger volume of more dilute urine. The amount and concentration of urine produced is controlled by the hypothalamus in the brain, which monitors the body’s water content by monitoring the concentration of the blood.

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1. Describe the term homeostasis in your own words. 2. Give two examples of homeostasis in the human body. 3. Explain the role of skin blood vessels in maintaining core body temperature.

Developing investigative skills You can use a test tube of warm water wrapped in wet paper towel as a model to investigate whether sweating really does cool the body, measuring how the temperature of the water changes over time.

Devise and plan investigation ➊➊Explain how the tube models sweating in a human. ➋➋How would you set up the control for this investigation? Explain your answer.

Make observations and measurements The table shows the results of an investigation like the one described above. Time (min) 0 Temperature of Wet towel 56 water in tube (°C) Dry towel 56

2 50 52

4 46 49

6 42 46

8 39 44

10 36 44

12 34 41

14 32 40

16 31 39

➌➌Use the results to draw a suitable graph. Analyse and interpret data ➍➍Describe any pattern shown in your graph. ➎➎Draw a conclusion from the graph. ➏➏Explain your conclusion using your scientific knowledge. HORMONES Hormones are chemical messengers. They are made in the endocrine glands. Endocrine glands do not have ducts (tubes) to carry away the hormones they make: the hormones are secreted directly into the blood to be carried around the body in the plasma. (There are other types of glands, called exocrine glands, such as salivary and sweat glands, that do have ducts.) Most hormones affect several parts of the body; others only affect one part of the body, called the target organ. The changes caused by hormones are usually slower and longer-lasting than the changes brought about by the nervous system.

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ating

QUESTIONS

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Adrenaline The adrenal glands produce adrenaline. This hormone is released in times of excitement, anger, fright or stress, and prepares the body for ‘flight or fight’: the crucial moments when an animal must instantly decide whether to attack or run for its life. The effects of adrenaline are: • increased heart rate • increased depth of breathing and breathing rate • increased sweating • hair standing on end (this makes a furry animal look larger but only gives humans goose bumps) • glucose released from liver and muscles • dilated pupils • paling of the skin as blood is redirected to muscles.

pituitary gland

adrenal glands ovaries (female)

(male) testes

pancreas

∆∆Fig. 2.125 The position of some endocrine glands in the human body.

ADH (Antidiuretic hormone) ADH (antidiuretic hormone) is made by the hypothalamus but then stored and released by the pituitary gland in the brain. It helps regulate the body’s water content. It causes the kidney tubules to reabsorb more water into the blood by increasing the permeability of the collecting ducts (see page 152). The pituitary gland also produces many other hormones which control other processes in the body, such as growth.

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Insulin Insulin is secreted by the pancreas, which is also part of the digestive system. Insulin controls the concentration of glucose in the blood, which must remain within a small range. If it rises or falls too much, you can become very ill. After a meal containing carbohydrates, the blood glucose concentration rises rapidly as glucose is absorbed from digested food in the small intestine. This rise is detected by the pancreas, and causes the pancreas to release insulin. The insulin travels in the blood to the liver. Here it causes any excess glucose to be converted to glycogen, another carbohydrate, which is insoluble and is stored in the liver. Between meals, glucose in the blood is constantly diffusing into cells for use in cellular respiration. So the blood glucose concentration falls. When a low level of glucose is detected by the pancreas, the pancreas stops secreting insulin and secretes the hormone glucagon instead. Glucagon converts some of the stored glycogen back into glucose, which is released into the blood to raise the blood glucose concentration again.

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EXTENSION

People with one kind of diabetes (called Type I) are unable to produce insulin. This means that their blood glucose concentration may become so high or so low that it damages cells, which in extreme cases may lead to unconsciousness and death. These people may need to inject insulin to help prevent this damage. 1. Control of blood glucose concentration is an example of homeostasis. Explain what this means. 2. Describe the role of insulin in controlling blood glucose concentration. 3. Patients need to check their blood glucose concentration with a simple blood test before deciding how much insulin to inject. Explain why this is important. 4. The amount of exercise that a person with diabetes does will affect the amount of insulin they inject. Explain why.

â&#x2C6;&#x2020;â&#x2C6;&#x2020;Fig. 2.126 A portable kit for instant testing of blood glucose. People with Type I diabetes use this to check their blood glucose before and after meals, and throughout the day.

Testosterone Testosterone is the male sex hormone and is secreted from the testes. Testosterone causes secondary sexual characteristics in boys (see page 203) and is needed for the production of sperm. Progesterone and oestrogen The ovaries produce the female sex hormones progesterone and oestrogen. Oestrogen is responsible for the development of secondary sexual characteristics in girls (see page 203), and together with progesterone it helps control the menstrual cycle (see page 204). FSH and LH FSH (follicle-stimulating hormone) and LH (luteinising hormone) are both produced by the pituitary gland in the brain. They work together with progesterone and oestrogen to control the menstrual cycle (see page 204).

QUESTIONS 1. Explain the meaning of the following terms: a) hormone b) endocrine gland c) target organ. are produced in the body, and what effects they have: adrenaline, insulin, testosterone, progesterone and oestrogen.

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2. Draw up a table to show the following hormones, where they

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End of topic checklist ADH (antidiuretic hormone) is a hormone produced in the hypothalamus but stored and released by the pituitary gland. It is involved in regulating water content in the blood by changing the permeability of the collecting duct of kidney nephrons. Adrenaline is a hormone produced by the adrenal glands that is responsible for the â&#x20AC;&#x2DC;fight or flightâ&#x20AC;&#x2122; response. Auxins are plant hormones that control phototropism and geotropism. The central nervous system is the part of the nervous system that coordinates and controls responses, consisting of brain and spinal cord. An effector carries out the response to a stimulus; in animals these are muscles or glands. Electrical impulses are the form in which information is sent along nerves. The endocrine glands are a collection of cells that secrete hormones into the blood. FSH (follicle-stimulating hormone) is a hormone produced by the pituitary gland that helps control the menstrual cycle. Geotropism is a growth response in plants affected by the direction of the force of gravity. Homeostasis is the maintenance of a constant internal environment. A hormonal system is a chemical response system in humans where hormones produced by the endocrine glands are carried in the blood to target organs where they affect the cells. Insulin is a hormone produced by the pancreas that causes muscle and liver cells to take glucose from the blood. LH (luteinising hormone) is a hormone produced by the pituitary gland that helps control the menstrual cycle. Nerves are bundles of neurones that connect receptors to the central nervous system, and the central nervous system to effectors. A neurone is a nerve cell, which is specially adapted for carrying electrical nerve impulses.

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Neurotransmitters are chemicals that pass from one neurone to another across a synapse. The nervous system is a response system in humans that uses electrical impulses between receptor cells, neurones and effector cells to produce a response to a stimulus.

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Oestrogen is a hormone produced by the ovaries that helps to control the menstrual cycle and produces secondary sexual characteristics in girls. Phototropism is a growth response in plants affected by light. Progesterone is a hormone produced in the ovaries that helps to control the menstrual cycle. Receptor cells detect a stimulus, for example cells in the retina detect light. A reflex arc is the pathway that nerve impulses travel along during a reflex. Sense organs are organs containing receptor cells adapted for the receiving of a particular type of stimulus. A stimulus is a change in the environment that triggers a response in an organism. A synapse is a small gap between two neurones across which neurotransmitters travel. A target organ is an organ of the body containing cells that respond to a particular hormone. Testosterone is a hormone produced by the testes that produces secondary sexual characteristics in boys. Vasoconstriction means narrowing of blood vessels. Vasodilation means widening of blood vessels.

The facts and ideas that you should know and understand by studying this topic:

❍❍Organisms respond to changes in their environment. ❍❍A coordinated response requires a stimulus that is sensed by receptor cells, which ❍❍Plants respond to stimuli by growth responses called tropisms, which are controlled by plant hormones called auxins.

❍❍Plant shoots show positive phototropism when they grow towards light. ❍❍Plant roots show positive geotropism when they grow towards the force of

gravity. Plant shoots show negative geotropism when they grow in the opposite direction to the force of gravity.

❍❍Rapid responses in humans are coordinated through nervous impulses in the

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nervous system, and longer-term responses are coordinated through chemicals (hormones) in the hormonal system.

COORDINATION AND RESPONSE

results in a change in the organism brought about by a receptor (usually muscles or glands in an animal).

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End of topic checklist continued ❍❍The central nervous system consists of the brain and spinal cord, which coordinate and control responses.

❍❍Stimulation of receptor cells in sense organs causes electrical impulses to travel along nerves to the central nervous system.

❍❍Neurotransmitters travel across synapses allowing an electrical impulse in one neurone to start another impulse along the next neurone.

❍❍The reflex arc is a connection of sense organ, nerves and spinal cord, and effector, which allows rapid responses without thinking, such as when you rapidly pull your finger away after touching a hot object.

❍❍The eye has many adaptations for its function in sensing light, including the light- sensitive cells in the retina, and the cornea and the lens for focusing light.

❍❍Contraction or relaxation of the muscles in the iris change the size of the pupil in

response to changes in light intensity, to control the amount of light entering the eye.

❍❍Contraction or relaxation of the ciliary muscles supporting the suspensory

ligaments attached to the lens change the shape of the lens to aid fine focusing of images on the retina.

❍❍Homeostasis is the control of the internal environment of the body within narrow limits so that cells can function well.

❍❍Examples of homeostasis in humans includes the regulation of blood water concentration and temperature regulation.

❍❍Core body temperature is regulated by vasodilation near the skin surface and

sweating when too hot, and vasoconstriction near the skin surface and muscle shivering when too cold.

❍❍ADH is the hormone made in the hypothalamus and released by the pituitary gland, which controls the amount of water reabsorbed from urine passing through the collecting ducts in the kidney.

❍❍Adrenaline is the hormone that is made in the adrenal glands and prepares the body in many ways for action, including increasing heart rate.

❍❍Insulin is the hormone made in the pancreas that causes blood glucose concentration to be reduced when it is too high.

❍❍Testosterone is the male sex hormone made in the testes that controls the

development of secondary sexual characteristics in boys and is needed for sperm production.

❍❍Progesterone and oestrogen are the female sex hormones made in the ovaries

that help control the menstrual cycle; oestrogen also controls the production of secondary sexual characteristics in girls.

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❍❍FSH and LH are hormones made in the pituitary gland that help control the menstrual cycle.

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End of topic questions 1. Some sprouting tomato seedlings are placed in a dimly lit room near to a brightly lit window. a) Which of these statements best describes the seedlings over the next few weeks? Explain your choice. (2 marks) i) The seedlings wilt and bend towards the light.

∆∆Sprouting tomato seedlings.

ii) The seedlings grow towards the brightest light. iii) The seedlings grow straight up. iv) The seedlings bend towards the light. b) What is meant by the term positive phototropism?

(1 mark)

c) Explain the survival advantage to plants of having shoots that are positively (2 marks) phototropic. d) What is meant by positive geotropism?

(1 mark)

e) Explain the survival advantage to plants of having roots that are positively (2 marks) geotropic. 2. a) What is the purpose of the nervous and hormonal systems in humans?

(1 mark)

b) Use the following table headings to compare the nervous and hormonal (6 marks) systems in humans. System

Cells of system

Method of transmission

Speed of response

(5 marks)

3. a) Describe the sequence of sensing and response in the nervous system of one (4 marks) of Andy Roddick’s opponents who returns a serve successfully. (2 marks)

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b) Is this a reflex action? Explain your answer.

COORDINATION AND RESPONSE

c) Explain as fully as you can why it is advantageous to have both systems.

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End of topic questions continued 4. Explain the following. a) A student visiting a coal mine could not see anything in the mine when the (2 marks) lights were turned off. b) A cataract is a clouded lens in the eye, caused by many conditions. A patient (2 marks) with cataracts cannot see clear images. c) A person who is long-sighted needs to wear spectacles with converging lenses (2 marks) in order to read something near to them. 5. One example of homeostasis in humans is the control of core body temperature. a) Identify the receptors, monitoring area, and effectors in the response to (6 marks) a change in external temperature. b) Explain why changes in skin blood flow affect the rate of heat loss from (2 marks) the body. c) Explain why homeostasis of core body temperature is important for survival.

(4 marks)

6. For each of the following hormones, name the gland that produces it, one target organ, and describe its effect on that target organ: (3 marks)

b) adrenaline.

(3 marks)

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a) insulin

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Student Book EDEXCEL INTERNATIONAL GCSE (9-1) CHEMISTRY • Develop your practical skills with investigative tasks • Check your progress and understanding using the end of the topic checklists and in-text questions • Practise your exam technique with exam-style questions in each section, annotated examples and further guidance • Gain insights into the real-life uses of science through the Science in Context sections

Chemistry Teacher Pack ISBN: 9780008236243

Physics Student Book ISBN: 9780008236205

Biology Student Book ISBN: 9780008236199

Physics Teacher Pack ISBN: 9780008236236

Biology Teacher Pack ISBN: 9780008236229

EDEXCEL INTERNATIONAL GCSE (9-1) CHEMISTRY

Collins Edexcel International GCSE Chemistry provides all the material you need for your International GCSE 9-1 qualification.

EDEXCEL INTERNATIONAL GCSE (9-1) CHEMISTRY Sam Goodman and Chris Sunley

ISBN 978-0-00-823621-2

9 780008 236212

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Contents Getting the best from the book �� 4

Section 1 Principles of chemistry �� 8 a) States of matter ��10 b) Elements, compounds and mixtures ��22 c) Atomic structure ��30 d) The Periodic Table ��38 e) Chemical formulae, equations and calculations ��48 f) Ionic bonding ��72 g) Covalent bonding ��80 h) Metallic bonding ��89 i) Electrolysis ��94 j) Exam-style questions �� 104

Section 2 Inorganic chemistry �� 108

Section 4 Organic chemistry ��242 a) Crude oil ��244 b) Alkanes ��259 c) Alkenes ��269 d) Alcohols ��275 e) Carboxylic acids ��286 f) Esters ��290 g) Synthetic polymers ��295 h) Exam-style questions ��303

The International GCSE examination ��308 Overview ��308 Assessment objectives and weightings ��309 Examination tips ��309 Answering questions ��312

Developing experimental skills ��314

a) Group 1 (alkali metals) – lithium, sodium and potassium �� 110 b) Group 7 (halogens) – chlorine, bromine and iodine �� 117 c) Gases in the atmosphere �� 126 d) Reactivity series �� 134 e) Extraction and uses of metals �� 143 f) Acids, alkalis and titrations �� 158 g) Acids, bases and salt preparations �� 167 h) Chemical tests �� 178 i) Exam-style questions �� 188

Planning and assessing the risk ��314 Carrying out the practical work safely and skilfully ��318 Making and recording observations and measurements ��320 Analysing the data and drawing conclusions ��324 Evaluating the data and methods used ��327

Section 3 Physical chemistry

Glossary ��332 Answers ��336 Index ��347

196

Mathematical skills ��331

a) Energetics �� 198 b) Rates of reaction �� 212 c) Reversible reactions and equilibria �� 230 d) Exam-style questions �� 238

Periodic Table ��330

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Organic chemistry is one of the ‘branches’ of chemistry and is seen as distinct from other branches, such as inorganic and physical chemistry. It can be described as the chemistry of living processes (often referred to as biochemistry) but extends beyond that. It focuses almost entirely on the chemistry of covalently bonded carbon molecules and, as well as life processes, it includes the chemistry of other types of compounds, including plastics, petrochemicals, drugs and paint. The early chemists didn’t think they would ever be able to make the sort of chemicals involved in living processes but they were wrong. For example, today very complex chemicals used in the manufacture of drugs can be made and then their structures modified to achieve improvements in their effectiveness. An understanding of organic chemistry can be developed from a knowledge of the structure of a carbon atom and how it can combine with other carbon atoms by forming covalent bonds. In this section you will be introduced to a few of the ‘families’ or series of organic compounds. This knowledge will provide a sound basis for further work in chemistry or biology.

STARTING POINTS 1. Where is carbon in the Periodic Table of elements? What can you work out about carbon from its position? 2. What is the atomic structure of carbon? How are its electrons arranged? 3. How does carbon form covalent bonds? Show the bonding in methane (CH4), the simplest of organic molecules. 4. You will be learning about series of organic compounds which are hydrocarbons. What do you think a hydrocarbon is? 5. You will be learning about methane. Where can methane be found and what it is used for? 6. You will also be learning about ethanol, which belongs to a particular series of organic compounds. Do you know where you could find ethanol in everyday products?

SECTION CONTENTS a) Crude oil

e) Carboxylic acids

b) Alkanes

f) Esters

c) Alkenes

g) Synthetic polymers

d) Alcohols

h) Exam-style questions

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Organic chemistry

â&#x2C6;&#x2020;â&#x2C6;&#x2020;Many paints contain hydrocarbons, which are organic chemicals.

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INTRODUCTION

Alcohols are another homologous series of organic compounds with ethanol as the most common alcohol. There are many more uses for ethanol than for other alcohols, and so its manufacture is very important. Ethanol may be produced by a ‘natural’ method starting with sugar, and by a ‘synthetic’ method starting with a product of crude oil.

∆∆Fig. 4.26 The ethanol being made here could be used as a disinfectant in hospitals or as a fuel in cars.

International GCSE: Chemistry

Alcohols

KNOWLEDGE CHECK ✓✓Understand the term ‘homologous series’. ✓✓Know the typical physical properties of compounds that exist as simple molecules. ✓✓Know what isomers are.

ALCOHOLS Alcohols are molecules that contain the –OH functional group, which is responsible for their properties and reactions. Alcohols have the general formula CnH2n+1OH and belong to the same homologous series, part of which is shown below. It is important to be able to name alcohols with up to six carbon atoms. For example, C6H13OH is hexanol.

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LEARNING OBJECTIVES ✓✓Know that alcohols contain the functional group –OH. ✓✓Be able to name alcohols with up to six carbon atoms, using the rules of the International Union of Pure and Applied Chemistry (IUPAC). ✓✓Be able to to draw structural and displayed formulae for methanol, ethanol, propanol (propan-1-ol only) and butanol (butan-1-ol only), and name each compound. ✓✓Know that ethanol can be oxidised by: • burning in air or oxygen (complete combustion) • reaction with oxygen in the air to form ethanoic acid (microbial oxidation) • heating with potassium dichromate(VI) in dilute sulfuric acid to form ethanoic acid. ✓✓Know that ethanol can be manufactured by: • reacting ethene with steam in the presence of a phosphoric acid catalyst at a temperature of about 300 °C and a pressure of about 60–70 atm • the fermentation of glucose, in the absence of air, at an optimum temperature of about 30 ºC and using the enzymes in yeast. ✓✓Understand the reasons for fermentation, in the absence of air, and at an optimum temperature.

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INTERNATIONAL GCSE: CHEMISTRY

Alcohol

Formula

Methanol

CH3OH

Displayed formula

Boiling point (ºC) 65

H H

Ethanol

C2H5OH H

Propanol

C3H7OH H

Butanol

C4H9OH H

97 OH

118 OH

∆∆Table 4.7 Properties of alcohols.

ETHANOL – THE MOST COMMON ALCOHOL Ethanol, commonly just called ‘alcohol’, is the most widely used of the alcohol family. Its major uses are given in Table 4.8. Use of ethanol Solvent, such as disinfectants and perfumes Fuel, such as for cars

Alcoholic drinks, such as wine, beer, spirits

Reason The –OH group allows it to dissolve in water, and it dissolves other organic compounds. It releases fewer pollutant gases than petrol (less NOx and SO2). It is a renewable resource because it comes from plants, for example sugar beet and sugar cane. Alcohol is a depressant and slows down reactions. Some people like this effect. However, alcohol can potentially damage the liver and other organs in the body.

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∆∆Table 4.8 Uses of ethanol.

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QUESTIONS 1. What would be the formula of the alcohol butanol, which has

INTERNATIONAL GCSE: CHEMISTRY

▷▷Fig. 4.28 Brazilians use alcool as vehicle fuel. It is made from the fermented and distilled juice of sugar cane.

four carbon atoms?

2. What are the advantages of using ethanol as a fuel in a motor car?

3. Ethanol is commonly used as a solvent. What is a solvent? MANUFACTURING ETHANOL BY FERMENTATION Ethanol is made by fermentation. This involves mixing a sugar solution with yeast and maintaining the temperature between 25 and 30 °C in the absence of air. The yeast contains enzymes, which catalyse (speed up) the breaking down of the sugar. Enzymes are not effective if the temperature is too low, and they are destroyed (denatured) if the temperature is too high. Fermentation of sugar takes place in large vats. However, even with the yeast as a catalyst, the process is slow and it takes several days to be completed. As the concentration of the ethanol increases, the activity of the yeast decreases, so eventually fermentation stops. The chemical reaction for fermentation is: sugar

yeast

  → yeast

ethanol

+ carbon dioxide

C 6 H 1 2 O 6 (aq)   → 2C 2H 5 OH (l) +

2C O 2 (g)

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Fermentation takes time because it is an enzymic reaction (yeast) and a batch process. At the end, a more concentrated solution of ethanol is extracted by fractional distillation. The mixture is boiled and the ethanol vapour reaches the top of the fractionating column, where it condenses back to a liquid.

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INTERNATIONAL GCSE: CHEMISTRY

thermometer

water out

condenser

water in

fractionating column containing glass beads

almost pure ethanol

ethanol + water heat

∆∆Fig. 4.29 Laboratory apparatus for fractional distillation of an ethanol and water mixture. In large-scale manufacture different equipment would be used but the principles of separation are the same.

QUESTIONS 1. What does the word ‘fermentation’ mean? 2. What is the optimum temperature for fermentation? 3. Why is yeast needed in the fermentation process? 4. What other compound (as well as ethanol) is produced in the

278

fermentation process?

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A student needed to carry out the fermentation of sugar in the laboratory to make some ethanol for fuel. The student set up the apparatus as shown in the diagram below. At first there seemed to be nothing happening, but by the next morning the reaction had started. When the reaction had finished, the student used fractional distillation to obtain some ethanol. (Note: ethanol is highly flammable.)

reaction flask containing sugar + yeast + water

water bath at 25–30°C (the best temperature for the enzymes in yeast to break down the sugar molecules).

INTERNATIONAL GCSE: CHEMISTRY

Developing investigative skills

lime water containing bubbles of CO2

∆ Fig. 4.30 Fermentation apparatus.

Devise and plan investigations ➊➊How could the student have tried to maintain the temperature of the water

279

bath while the reaction was proceeding? ➋➋What was the purpose of the lime water? ➌➌What would the student have observed to indicate that a reaction had started? ➍➍How would the student know when the reaction was complete? ➎➎In the fractional distillation process, which liquid would be collected first, ethanol or water? Explain your answer.

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MANUFACTURING ETHANOL FROM ETHENE On an industrial scale, ethanol is also made from ethene, which is obtained from crude oil. The reaction is: ethene

steam

300°C, 70 atm

ethanol

phosphoric acid as catalyst H

H C

300°C, 70 atm (g) +

H2O(g)

phosphoric acid as catalyst

OH(g)

∆∆Fig. 4.31 Reaction of ethene and steam to make ethanol.

These are quite extreme conditions in terms of energy (300 ˚C) and specialist plant equipment (to generate 70 atmospheres), so the process is expensive. Unlike fermentation, this process is continuous and produces ethanol at a fast rate. THE CHOICE OF METHOD IN THE MANUFACTURE OF ETHANOL The best method for making ethanol depends on local circumstances: for example, how much sugar cane or crude oil is available. Fermentation Ethene + steam

Advantage Uses renewable resources. Produces flavour of alcoholic drinks. Fast continuous processes. Large amounts of ethanol produced.

Disadvantage Slow ‘batch’ process. Only small amount of ethanol produced. Uses non-renewable resource.

∆∆Table 4.9 Advantages and disadvantages of methods of making ethanol.

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Ethanol undergoes oxidation reactions and, depending on the reaction conditions can produce different products. 1. Combustion in air or oxygen When the combustion is complete (with sufficient oxygen) the products are carbon dioxide and water. C2H5OH(l) + 3O2(g) → 2CO2(g) + 3H2O(l) 2. Microbial oxidation In the fermentation process to make ethanol from sugar, if the yeast is contaminated by other microbes the ethanol produced can be oxidised into ethanoic acid (CH3COOH, acetic acid, vinegar). Most microbial action takes place when wine is exposed to air after fermentation. This can happen in the wine making process and makes the wine undrinkable.

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ethanoic acid

H(l)

2[O]

H H

O (aq)

H2O(l)

∆∆Fig. 4.32 Oxidising ethanol to make ethanoic acid.

3. Oxidation by potassium dichromate(VI)

281

If ethanol is heated with potassium dichromate in the presence of dilute sulfuric acid the ethanol is oxidised to ethanoic acid. This is the reaction that is commonly used to prepare ethanoic acid in the laboratory. Ethanoic acid belongs to an important homologous series of carboxylic acids (see the next topic). The carboxylic acids are important starting materials for making esters and polyesters (see later topics).

INTERNATIONAL GCSE: CHEMISTRY

oxidation ethanol

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SCIENCE IN CONTEXT

ETHANOL AS A FUEL

The development of ethanol as a fuel for cars has a long history. In the USA cars made by Ford (especially the Model T) used ethanol as a fuel until 1908. Now most cars in the USA can run on blends of petrol/ethanol containing up to 10% ethanol. Petrol in the European Union has up to 10% ethanol.

∆∆Fig. 4.33 In the USA, the ethanol in gasohol is made from maize.

Brazil and the USA are the world’s top producers of ethanol. In Brazil about one-fifth of all cars can use 100% ethanol fuel, known as E100; many other cars use petrol/ethanol blends. Brazil makes its ethanol mostly from fermented sugar obtained from sugar cane; in the USA corn is used as the source of the sugar. Starting from sugar cane is much more efficient, and so ethanol is much cheaper to produce in Brazil than in the USA. One problem with using ethanol as a fuel is that it readily absorbs water from the atmosphere. This causes some problems when transporting the fuel and makes it more expensive than petrol to transport.

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A key question is, should food be used to make a fuel? Is it better to use fuel made from crude oil? Some people argue that the food is needed for people to eat and should not be used to run cars. They say that using so much land for growing sugar cane and corn to make ethanol means that less land is available for growing food. This leads to food shortages and increases in the price of food. What do you think?

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Ethanol is an alcohol with the formula C2H5OH. It is used for a wide range of purposes, from producing medicine, synthesising chemical products, as a fuel as well as a beverage. Fermentation of sugar into ethanol was one of the earliest organic reactions carried out and distillation was well known by the early Greeks. Ethanol is now manufactured from the products of oil. For the questions below use your knowledge of organic chemistry and the work you have studied on rates and equilibria to understand the different factors affecting the manufacture of ethanol in today’s society. 1. Ethanol can be produced by the direct hydration of ethene. The conditions for the manufacture are 300 oC, 60–70 atmospheres and phosphoric(V) acid as a catalyst. a) The reaction of ethene and steam in the formation of ethanol is reversible and the reaction is exothermic. Write a balanced symbol equation to show this and describe what is meant by exothermic.

INTERNATIONAL GCSE: CHEMISTRY

EXTENSION

b) Consider the temperature. In order to produce the maximum possible amount of ethanol in the equilibrium mixture an ‘optimum temperature’ or ‘compromise temperature’ is needed. Explain why the manufacturers do not use a very high temperature. c) Consider the pressure. Use your knowledge of the effects of changing the pressure on the equilibrium position and the need to consider pressure when constructing a manufacturing plant to give reasons why a pressure of 60–70 atmospheres is used in the reaction between ethene and steam.

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d) Consider the catalyst. The phosphoric(V) catalyst has no effect on the position of equilibrium, so describe why is it needed.

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End of topic checklist Fermentation is the process by which ethanol is made from a solution of sugar and yeast. Fractional distillation is a process used to separate liquids with different boiling points.

The facts and ideas that you should know and understand by studying this topic:

❍❍Know that alcohols have a functional group –OH. ❍❍Know that ethanol is the most common alcohol. ❍❍Know the structural and displayed formulae for methanol, ethanol, propanol (propan-1-ol only) and butanol (butan-1-ol only).

❍❍Be able to describe the fermentation process used to manufacture ethanol from sugars, such as glucose, including the importance of the absence of air, an optimum temperature (30 °C) and the enzymes in yeast.

❍❍Be able to describe the manufacture of ethanol using ethene and steam passed over a catalyst of phosphoric acid, with a temperature of 300 °C and pressure of 60–70 atmospheres.

❍❍Know that ethanol can be oxidised by: burning air or oxygen (complete combustion)

●●

reaction with oxygen in the air to form ethanoic acid (microbial oxidation)

●●

by heating with potassium dichromate(VI) in dilute sulfuric acid to form ethanoic acid.

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●●

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1. What is the general formula for an alcohol? (1 mark) 2. EXTENDED Pentanol is an alcohol with five carbon atoms. a) What is the molecular formula of pentanol? (1 mark) b) Draw the displayed formula for pentanol. (1 mark) 3. What are the two main sources of sugar used in the manufacture of ethanol by fermentation? (2 marks) 4. In the laboratory fermentation experiment to make ethanol from sugar using yeast, explain the importance of the following: a) The reaction temperature is kept between the range 25–30 °C. (2 marks) b) Oxygen from the air cannot enter the reaction flask. (2 marks)

INTERNATIONAL GCSE: CHEMISTRY

End of topic questions

5. In the industrial manufacture of ethanol from ethene: a) What is the source of the ethene? (1 mark) b) What is the function of the phosphoric acid? (1 mark) c) What conditions of temperature and pressure are used? (2 marks) d) Write a balanced symbol equation for the reaction. (1 mark) 6. Ethanol can be oxidised to ethanoic acid. a) Explain why this can be a problem when making ethanol by the fermentation of glucose. (2 marks)

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b) In the laboratory the oxidation of ethanol can be achieved using potassium dichromate(VI). What reaction conditions are needed for this reaction? (2 marks)

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Carboxylic acids INTRODUCTION

∆∆Fig. 4.34 Carboxylic acids can be made into esters, which provide the smell and flavour of some sweets.

The first member of the carboxylic acid homologous series is methanoic acid, which ants produce when they sting an animal or attack another insect. The most common carboxylic acid is ethanoic acid, or acetic acid as it used to be called, which is the main constituent of vinegar. As well as having properties similar to those of common acids, such as hydrochloric acid and sulfuric acid, the carboxylic acids have some very different properties.

KNOWLEDGE CHECK ✓✓Understand the term homologous series. ✓✓Know some of the typical properties of common acids such as hydrochloric acid and sulfuric acid. LEARNING OBJECTIVES O

✓✓Know that carboxylic acids contain the functional group C OH. ✓✓Understand how to draw structural and displayed formulae for unbranched-chain carboxylic acids with up to four carbon atoms in the molecule, and name each compound. ✓✓Describe the reactions of aqueous solutions of carboxylic acids with metals and metal carbonates. ✓✓Know that vinegar is an aqueous solution containing ethanoic acid.

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WHAT ARE CARBOXYLIC ACIDS? Carboxylic acids are molecules that contain the –COOH functional group, which is responsible for their properties and reactions. The carboxylic acids have the general formula CnH2n+1COOH (although n can be equal to zero in the case of methanoic acid).

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Formula

Structural formula

Methanoic acid

HCOOH

O O H H

C C OH OH

Ethanoic acid

CH3COOH

H H H H

O O

C C

C C OH OH

H H

Propanoic acid

C2H5COOH H H

Butanoic acid

C3H7COOH H

H H

C C

H H

O O C C OH O C OH

INTERNATIONAL GCSE: CHEMISTRY

Acid

∆∆Table 4.10 Some common carboxylic acids.

Ethanoic acid is a weak acid because it is only partially ionised when dissolves in water. CH3COOH(aq)

L CH3COO–(aq) + H+(aq)

THE REACTIONS OF CARBOXYLIC ACIDS Aqueous ethanoic acid behaves as a typical acid. It has a pH lower than 7 and will react with alkalis and carbonates to form salts. For example, aqueous ethanoic acid will react with sodium carbonate as follows: +

ethanoic acid

H 2H

C H

sodium carbonate

sodium ethanoate

water

O C

(aq)

Na2CO3(aq)

carbon dioxide

O + H2O(l)

+ CO2(g)

ONa(aq)

∆∆Fig. 4.35 The reaction of aqueous ethanoic acid with sodium carbonate.

The reaction will not be as vigorous as with dilute hydrochloric acid of the same concentration. Ethanoic acid is a weak acid and has a lower concentration of hydrogen ions, H+(aq). In the same way carboxylic acids will react with metals such as magnesium to produce hydrogen gas. + magnesium → magnesium ethanoate

2CH3COOH(aq) + Mg (s)

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→ (CH3COO)2Mg(aq)

hydrogen

+ H2(g)

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ethanoic acid

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The facts and ideas that you should know and understand by studying this topic:

❍❍Know that carboxylic acids contain the functional group –COOH. ❍❍Know the names, structural and displayed formulae of methanoic, ethanoic, propanoic and butanoic acids.

❍❍Be able to describe the reactions of aqueous solutions of carboxylic acids with metals and metal carbonates.

❍❍Know that vinegar is an aqueous solution containing ethanoic acid.

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End of topic checklist

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1. What is the functional group in a carboxylic acid? (1 mark) 2. a) What is the name of the carboxylic acid with three carbon atoms in the molecule? (1 mark) b) Draw the structural formula of this carboxylic acid with three carbon atoms. (1 mark) 3. a) What would you observe when solid sodium carbonate is added to an aqueous solution of ethanoic acid? (3 marks)

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b) Write a balanced equation for this reaction. (2 marks)

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End of topic questions

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Esters INTRODUCTION

Esters are a homologous series of organic compounds made by the reaction between an alcohol and a carboxylic acid. Esters are volatile substances (readily form a vapour), have distinctive smells and are commonly used as food flavourings and in perfumes. The ester grouping is also an important grouping in some synthetic polymers as you will see in the next topic. ∆∆Fig 4.36 Oils from plants, such as olive oil, are esters of long-chain carboxylic acids and the alcohol propan-1,2,3-triol.

KNOWLEDGE CHECK ✓✓Know the functional group of the alcohol homologous series. ✓✓Know the functional group of the carboxylic acid homologous series. LEARNING OBJECTIVES O

✓✓Know that esters contain the functional group C O ✓✓Know that ethyl ethanoate is the ester produced when ethanol and ethanoic acid react in the presence of an acid catalyst. ✓✓Understand how to write the structural and displayed formulae of ethyl ethanoate. ✓✓Understand how to write the structural and displayed formulae of an ester given the name or formulae of the alcohol and carboxylic acid from which it is formed and vice versa. ✓✓Know that esters are volatile compounds with distinctive smells and are used as food flavourings and perfumes. ✓✓Be able to prepare a sample of an ester such as ethyl ethanoate.

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O WHAT ARE ESTERS? Esters contain the functional group C O and have the general formula CnH2n+1COOCmH2m+1 where typically m and n are numbers from 1 upwards. The structural and displayed formulae for ethyl ethanoate are shown in Table 4.11.

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Displayed formula H

∆∆Table 4.11 Structural and displayed formulae of ethyl ethanoate.

Ethyl ethanoate can be made by the reaction between ethanol and ethanoic acid in the presence of concentrated sulfuric acid acting as a catalyst. H H

C H

O C

(l) O

H (l)

+ H2O (l) ethanol

ethanoic acid

ethyl ethanoate

water

INTERNATIONAL GCSE: CHEMISTRY

Structural formula CH3COOC2H5

∆∆Fig.4.37 Reaction of ethanol and ethanoic acid to form an ester, ethyl ethanoate, and water.

Other esters can be made in the same way. For example: carboxylic acid

+ alcohol L ester

+ water

propanoic acid

propyl propanoate

ethyl propanoate

+ water

propanoic acid

propanol

+ ethanol L

water

The name of the ester identifies which carboxylic acid and which alcohol has been used to make it. For example: Name of ester

Name of alcohol

methyl ethanoate ethyl methanoate

methanol ethanol

Name of carboxylic acid ethanoic acid methanoic acid

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Esters are sweet-smelling substances. They are commonly used as constituents of perfumes, essential oils, food flavourings (e.g. in pear drop sweets) and in cosmetics.

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A sample of ethyl ethanoate was made by mixing some ethanol and ethanoic acid in a boiling tube. A few drops of concentrated sulfuric acid were added and then the boiling tube was warmed up to 60 °C in a water bath heated by a hot plate. After 3 or 4 minutes the contents of the boiling tube were poured into another beaker containing cold water. The smell of the ethyl ethanoate could then be clearly detected coming from the beaker of cold water.

Evaluate data and methods ➊➊What safety precautions should you take when using concentrated sulfuric

acid? ➋➋Why do you think the boiling tube was heated in a beaker of water on a hot plate rather than directly in a Bunsen burner flame? ➌➌If you wanted a pure sample of ethyl ethanoate what procedure could be used to separate the ethyl ethanoate that has formed from any unreacted ethanol, ethanoic acid and water? ➍➍Adding the reaction mixture to cold water made the ethyl ethanoate smell more apparent rather than that of any ethanoic acid that had not reacted. Can you explain why this approach might work?

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International GCSE: chemistry

Developing investigative skills

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An ester is a compound formed by the reaction between an alcohol and a carboxylic acid in the presence of an acid catalyst.

The facts and ideas that you should know and understand by studying this topic: O

❍❍Know the functional group of the ester homologous series is C O . ❍❍Know that esters are volatile compounds with distinctive smells and are used in food flavourings and in perfumes.

❍❍Know the structural and displayed formula for ethyl ethanoate. ❍❍Be able to describe how ethyl ethanoate can be made from ethanol and ethanoic acid.

INTERNATIONAL GCSE: CHEMISTRY

End of topic checklist

❍❍Understand how to identify which acid and which alcohol are needed to made a

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particular ester and vice versa.

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1. Draw the displayed formulae for the following esters: a) methyl methanoate. (1 mark) b) propyl ethanoate. (1 mark) 2. a) Copy and complete the following table: Name of ester ethyl ethanoate propyl methanoate methyl propanoate

Name of alcohol

Name of carboxylic acid (2 marks) (2 marks) (2 marks)

b) What catalyst would be needed in each of the above reactions? (1 mark)

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End of topic questions

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Synthetic polymers INTRODUCTION

Polymers exist in nature; two examples are cellulose and starch. Synthetic polymers are manufactured, often using starting materials made from crude oil. Many synthetic polymers are commonly known as plastics and have a wide range of uses in daily life. Other synthetic polymers are used as fabrics – look for ‘polyester’ or ‘polyamide’ next time you look at a label on clothes. Plastics are useful because of their resistance to other chemicals. This is also the reason why disposal of plastic material is such a big environmental issue: they do not break down (degrade) easily.

∆∆Fig. 4.38 Most tennis racquets have carbon fibre reinforced polymer frames.

KNOWLEDGE CHECK ✓✓Know that alkenes are unsaturated hydrocarbons and contain C=C double bonds. ✓✓Know that alkenes can be used to make a wide range of plastic materials. ✓✓Know how esters are made from carboxylic acids and alcohols.

ADDITION POLYMERISATION Alkenes can be used to make polymers, which are very large molecules made up of many identical smaller molecules called monomers. Alkenes are able to react with themselves. They join together into long chains, like adding beads to a necklace. When the

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LEARNING OBJECTIVES ✓✓Know that an addition polymer is formed by joining up many small molecules called monomers. ✓✓Understand how to draw the repeat unit of an addition polymer, including poly(ethene), poly(propene), poly(chloroethene) and (poly)tetrafluoroethene. ✓✓Understand how to deduce the structure of a monomer from the repeat unit of an addition polymer and vice versa. ✓✓Be able to explain problems in the disposal of addition polymers, including: • their inertness and inability to biodegrade • the production of toxic gases when they are burned. ✓✓Know that condensation polymerisation, in which a dicarboxylic acid reacts with a diol, produces a polyester and water. ✓✓Understand how to write the structural and displayed formula of a polyester, showing the repeat unit, given the formulae of the monomers from which it is formed including the reaction of ethanedioic acid and ethanediol. ✓✓Know that some polyesters, known as biopolyesters, are biodegradable.

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monomers add together like this, the material produced is called an addition polymer. Poly(ethene) or polythene is made this way. By changing the atoms or groups of atoms attached to the carbon–carbon double bond, a whole range of different polymers can be made. The double bond within the alkene molecule breaks to form a single covalent bond to a carbon atom in an adjacent molecule. This process is repeated rapidly as the molecules link together. H

H H C

H H

H C

H H

∆∆Fig. 4.40 Poly(ethene) from ethene H

Cl H C

H H

Cl C

H H

many small molecules

ethene

catalyst and heat

poly(ethene)

one large molecule

∆∆Fig. 4.39 Ethene molecules link together to produce a long polymer chain of poly(ethene).

∆∆Fig. 4.41 Poly(chloroethene) from chloroethene

Name of monomer

Displayed formula of monomer

ethene

H propene

H H H H C H C CC C H H

propene

tetrafluoroethene

poly(ethene)

H H

chloroethene (vinyl chloride)

H C

F C

Name of polymer

C F

poly(propene)

C H

poly(chloroethene) (polyvinylchloride) poly (tetrafluroethene) or PTFE

Displayed formula of polymer H

CH3 H C

Uses of polymer buckets, bowls, plastic bags packaging, ropes, carpets plastic sheets, artificial leather non-stick coating in frying pans

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∆∆Table 4.12 Monomers and their polymers.

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◁◁Fig. 4.42 This pan is coated with PTFE non-stick plastic. How is PTFE made?

QUESTIONS 1. In what way is a polymer like a string of beads? 2. Name the polymer used extensively to make plastic bags. 3. The diagram shows the structural formula of chloroethene. H

Cl C

C H

a) Show how two molecules of chloroethene join together to form part of the polymer poly(chloroethene).

b) Draw the structure of the repeat unit of the polymer.

CONDENSATION POLYMERISATION Polymers can also be made by joining together two different monomers so that they react together. When they react, they expel a small molecule. Because the molecule is usually water, the process is called condensation polymerisation and the products are condensation polymers.

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∆∆Fig. 4.43 Condensation polymerisation.

INTERNATIONAL GCSE: CHEMISTRY

4. What type of polymer is poly(chloroethene)?

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INTERNATIONAL GCSE: CHEMISTRY

∆∆Fig. 4.44 This surfboard is made from a condensation polymer called polyurethane.

Polyesters are condensation polymers and, as the name suggests, just like esters they are made from an alcohol and a carboxylic acid. However, so that ester links can be formed between a large number of carboxylic acid and alcohol monomers each monomer needs to have two functional groups. The alcohol is known as a diol and the acid as a dicarboxylic acid. How these combine together is shown in the diagram below.

ethanediol

ethanedioic acid

ethanediol

(diol)

(dicarboxylic acid)

(diol)

ester

2H2O

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∆∆Fig.4.45 Reaction of a diol and a dicarboxylic acid to produce an ester linkage and water.

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1. Polyester is an example of a condensation polymer. How is this type of polymer different from an addition polymer?

2. Why is it important that the monomers which join together to make polyester have reactive groups at each end of the molecule?

Many of the plastics in common use are addition polymers. The pollution caused by plastics is a growing problem, particularly as plastics are durable and inexpensive. Many plastics are nonbiodegradable and so cannot be broken down naturally by bacteria in the environment. Living organisms, particularly marine animals, can be affected through entanglement, direct ingestion of plastic waste or through exposure to chemicals within the plastics. In the UK alone 5 million tonnes of plastic are consumed each year, and it is estimated that less than one-quarter of this enters recycling systems. This leaves large amounts of plastic waste destined for burial in landfill sites or for burning. Burning plastics generates highly toxic fumes. Recycling is also not without significant challenges. Different plastics have to be carefully separated to identify those that can be recycled (see the section on thermoplastics and thermosetting plastics).

INTERNATIONAL GCSE: CHEMISTRY

QUESTIONS

Recently bioplastics and biopolyesters, made from renewable biomass sources, such as vegetable fats and oils and starch, have been developed and a number of these are biodegradable.

299

◁◁Fig. 4.46 Some plastic bags are biodegradable. They are made from polythene and starch. When buried, the starch breaks down and leaves tiny fragments of polythene.

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● Science in Context

The challenges of recycling plastics

∆∆Fig. 4.47 Waste plastics are lightweight but very bulky.

Some types of plastic can be melted down and used again. These are called thermoplastics. Other types of plastic harden or decompose when they are heated. These are called thermosetting plastics. Recycling them is difficult because the different types of plastic must be separated. polymer chain

thermoplastic plastic polymer chain strong cross-links

thermosetting plastic

300

▷▷Fig. 4.48 Thermoplastics have weak intermolecular forces that break on heating, which allows them to be melted and re‑moulded. In thermosetting plastics, the intermolecular bonds are strong interlinking covalent bonds. The whole structure eventually breaks down when these bonds are broken by heating.

weak intermolecular forces

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End of topic checklist A monomer is a molecule that can combine with other molecules to form a polymer. An addition polymer is made when molecules of a single monomer join together in large numbers. A condensation polymer is formed when two monomers react together and eliminate a small molecule such as water Biopolyesters are biodegradable.

The facts and ideas that you should know and understand by studying this topic:

❍❍Understand that an addition polymer is formed by joining up many small molecules called monomers.

❍❍Be able to draw repeat units of addition polymers from the structural formula of the monomer, such as poly(ethene), poly(propene), poly(chloroethene) and poly(tetrafluroethene).

❍❍Be able to deduce the structural formula of a monomer from the repeat unit of an addition polymer, and do the same in reverse.

❍❍Be able to explain that addition polymers are hard to dispose of as their inertness means that they do not easily biodegrade, and they produce toxic gases when burnt.

❍❍Understand that some polymers, such as polyester, form by a different process called condensation polymerisation.

❍❍Know that when dicarboxylic acid reacts with a diol, this produces a polyester and water and so is condensation polymerisation.

❍❍Given the formulae of the monomers from which it is formed, be able to draw the

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structural and displayed formula of a polyester showing the repeat unit, including the reaction of ethanedioic acid and ethanediol.

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End of topic questions 1. Explain what is meant by the following words: a) monomer (1 mark) b) polymer. (1 mark) 2. This question is about addition polymers. a) What is an addition polymer? (1 mark) b) What structural feature do all monomers that form addition polymers have in common? (1 mark) c) Use displayed formulae to show how propene molecules react together to form poly(propene). (2 marks) d) Explain why a polymer poly(propane) does not exist. (2 marks) 3. Addition polymers are not biodegradable. Explain what this means. (2 marks) 4. This question is about condensation polymers. a) In what ways is a condensation polymer different to an addition polymer? (2 marks) b) Name an example of a condensation polymer. (1 mark) c) Show how a polyester is formed by the reaction between a diol and a dicarboxylic acid. (1 mark)

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5. A headline in a newspaper states ‘Plastics – the problem must be solved’. Discuss the problem referred to and how you think it should be solved. (6 marks)

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Student Book EDEXCEL INTERNATIONAL GCSE (9-1) PHYSICS • Develop your practical skills with investigative tasks • Check your progress and understanding using the end of the topic checklists and in-text questions • Practise your exam technique with exam-style questions in each section, annotated examples and further guidance • Gain insights into the real-life uses of science through the Science in Context sections

Physics Teacher Pack ISBN: 9780008236236

Chemistry Student Book ISBN: 9780008236212

Biology Student Book ISBN: 9780008236199

Chemistry Teacher Pack ISBN: 9780008236243

Biology Teacher Pack ISBN: 9780008236229

EDEXCEL INTERNATIONAL GCSE (9-1) PHYSICS

Collins Edexcel International GCSE Physics provides all the material you need for your International GCSE 9-1 qualification.

EDEXCEL INTERNATIONAL GCSE (9-1) PHYSICS Steve Bibby, Malcolm Bradley and Susan Gardner

ISBN 978-0-00-823620-5

9 780008 236205

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Contents Getting the best from the book �� 4

Section 1 Forces and motion �� 8 a) Units ��10 b) Movement and position ��12 c) Forces, movement, shape and momentum ��29 d) Exam-style questions ��70

Section 2 Electricity ��76 a) Units ��78 b) Mains electricity ��79 c) Energy and voltage in circuits ��92 d) Electric charge �� 117 e) Exam-style questions �� 129

Section 3 Waves �� 134 a) Units �� 136 b) Properties of waves �� 137 c) The electromagnetic spectrum �� 148 d) Light and sound �� 158 e) Exam-style questions �� 183

Section 4 Energy resources and energy transfers �� 186 a) Units �� 188 b) Energy �� 189 c) Work and power �� 212 d) Human influences on the environment �� 227 e) Exam-style questions �� 238

Section 5 Solids, liquids and gases �� 244

a) Units ��294 b) Magnetism ��295 c) Electromagnetism ��306 d) Electromagnetic induction ��320 e) Exam-style questions ��333

Section 7 Radioactivity, fission and fusion ��336 a) Units ��338 b) Radioactivity ��339 c) Fission and fusion ��362 d) Exam-style questions ��372

Section 8 Astrophysics �� 374 a) Units ��376 b) Motion in the Universe ��377 c) Stellar evolution ��386 d) Cosmology ��393 e) Exam-style questions ��401

The International GCSE examination ��403 Overview ��403 Assessment objectives and weightings ��404 Examination tips ��405 Answering questions ��407

Developing experimental skills ��409 Planning and assessing the risk ��409 Carrying out the practical work safely and skilfully ��412 Making an recording observations and measurements ��413 Analysing the data and drawing conclusions ��416 Evaluating the data and methods used ��418

Mathematical skills ��422 Glossary ��424 Answers ��430 Index ��443

a) Units �� 246 b) Density and pressure �� 247 c) Change of state �� 265 d) Ideal gas molecules �� 277 e) Exam-style questions �� 289

Section 6 Magnetism and electromagnetism ��292

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From simple viewing of the night sky to breathtaking images from the Hubble Space Telescope, humans have tried to make sense of what they see beyond the Earth. Many theories have been developed and many have been questioned and discarded as new evidence comes to light. This progress has been partly driven by new technologies from telescopes to space travel. But humans are very curious about our sky and that curiosity is unlikely to diminish. You have met forces before and we will consider their effects on the movement of the planets, including Earth, and other celestial bodies. The vast amounts of energy released by nuclear fusion in stars must come to an end when temperatures and pressures are no longer great enough to sustain fusion reactions, and so a starâ&#x20AC;&#x2122;s life cycle must come to an end. The wavelengths of light emitted by stars and the microwave radiation coming from every direction in space provide evidence for how the Universe began.

STARTING POINTS 1. What is the Solar System made of? 2. What are the differences between galaxies and stars, a red giant and a white dwarf? 3. What is the Universe and how might it have started? 4. What is meant by the life cycle of a star?

CONTENTS a) Units b) Motion in the Universe c) Stellar evolution d) Cosmology e) Exam-style questions

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Astrophysics

∆∆More than 100 years ago in 1901, an ordinary star suddenly became one of the brightest stars in the sky. This image combines data from NASA’s Chandra X-ray Observatory with radio and optical telescope data to look at the supernova it left. These pictures give insight into how scientists can study the birth, life and death of stars. Even stars that exploded years ago.

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Stellar evolution INTRODUCTION

∆∆Fig. 8.6 Cassiopeia A, a star in the constellation Cassiopeia, is a remnant of a supernova and appears as a shell of expanding material.

When you look at the stars on a clear night you can see up to about 5000 without a telescope or binoculars. Most stars are larger than our Sun despite being visible only as tiny specks of light. Our Sun is much closer to the Earth than any other star so it seems larger. It takes about 8 minutes for light to reach us from the Sun. Our next nearest star is about 4 light years away. This is the distance that light travels in four years. Given that light travels at 300 000 000 metres every second, the nearest star is about 60 × 60 × 24 × 365.25 × 4 × 300 000 000 m away from us, or about 3 × 1016 m.

The sky and its stars stay much the same for long periods of time. But the sky does change and some stars are being made and some are ending their existence – sometimes in spectacular fashion. KNOWLEDGE CHECK ✓✓Know that the energy in stars is produced by nuclear fusion. ✓✓Know that the Universe is massive and consists mainly of space. ✓✓Know that the Universe changes over time.

386

LEARNING OBJECTIVES ✓✓Understand how stars can be classified according to their colour. ✓✓Describe the evolution of stars of similar mass to the Sun through the following stages: • nebula • star (main sequence) • red giant • white dwarf. ✓✓Describe the evolution of stars with a mass larger than the Sun. ✓✓Understand how the brightness of a star at a standard distance can be represented using absolute magnitude. ✓✓Draw the main components of the Hertzsprung–Russell diagram (HR diagram).

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COLOURED STARS When we first look at stars, they all seem white. If you look for a while longer, you will see that some are slightly blue or red. When we heat a metal bar with a Bunsen burner it will glow red-hot. This indicates the frequency of the radiation that is emitted at this temperature. If we heated the bar with an acetylene torch it would become hotter and the light from it would be slightly blue. This relationship between the metal bar’s colour and its temperature is also shown by stars. Cool stars appear red as most of the radiated energy is in the red to infrared range of the electromagnetic spectrum. Hot stars appear white or blue as most of their radiated energy is in the blue to ultraviolet range of the electromagnetic spectrum. The colour of a star is related to its surface temperature and scientists use this to group stars into different types. Our Sun is a G type star. Type of star

Colour

O B A F G K M

blue blue blue white to blue yellow to white red to orange red

Approximate surface temperature (K) > 25 000 11 000–25 000 7500–11 000 6000–7500 5000–6000 3500–5000 < 3500

QUESTIONS 1. Stars can be classed as anything between blue ➔ white ➔ yellow ➔ orange ➔ red.

a) Explain and describe what causes the different colours of the stars.

b) Draw a table showing the type, colours, and approximate

387

surface temperature in K for stars.

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INTERNATIONAL GCSE: PHYSICS

BRIGHTNESS OF STARS The colours of stars are important as we have seen. It is also important to look at the brightness of stars. The two main ways of describing the brightness of a star or galaxy are apparent magnitude and absolute magnitude. The apparent magnitude is how bright the object is when seen by an observer on Earth. This can depend on two factors: 1. the amount of energy the star radiates per second (its luminosity) 2. the distance of the star from Earth. The distance of stars from the Earth varies greatly. Therefore, very bright but distant stars can have a lower apparent magnitude than a less bright, nearby star. The absolute magnitude of a star depends only on its luminosity. Absolute magnitude is the apparent magnitude of an object if it was a standard distance from the Earth. In this way, we can compare the actual brightness of stars regardless of how distant they are. The standard distance for absolute magnitude is 32.6 light years (about 3 × 1017 m). There is no need to travel to a distance of 3 × 1017 m from a star to measure its luminosity as there is a formula which relates the apparent magnitude to absolute magnitude, if its distance is known. This is based on the fact that light follows an inverse square law. This law simply means that when the light source is twice as far away, it will appear four times less bright. EVOLUTION OF A STAR A star is formed from a huge cloud of dust and gas called a nebula.

∆∆Fig. 8.7 The Tarantula Nebula is a star-forming region in the Large Magellanic Cloud, the nearest galaxy to our own Milky Way. The most dense areas of gas and dust will be the birthplace of future generations of stars.

388

The gas clouds in a nebula contain hydrogen gas. The gas particles are gradually pulled in towards the centre of the nebula by gravitational attraction. The nebula becomes a much more dense structure called a proto-star. Compression causes the gas molecules to increase speed and the gas becomes very hot, up to about 15 million °C. Eventually, the great pressures involved also force the hydrogen nuclei together. This initiates a nuclear fusion reaction, fusing hydrogen nuclei to form helium. A very large amount of thermal energy is released. The thermal energy generated prevents the proto-star shrinking any more.

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The star then continues fusing hydrogen into helium for many millions of years until the hydrogen starts to run out. What happens next depends on the star’s mass. Our Sun is in this steady phase of fusion (main sequence star) and it has about 5 billion years left before the next stage. When stars with a similar mass to our Sun start to run out of hydrogen they start fusing helium. The core of the star gets much hotter and expands. The star is no longer on the main sequence. The star appears red because the observed surface temperature of the star decreases as the outer layers spread out, so it is called a red giant. When fusion ends, the outer layers are pushed away and the hot, small core of the star collapses to become a white dwarf. The Sun, although it appears large to us, is in fact a relatively small star. When stars with a mass larger than the Sun run low on hydrogen they start fusing helium to carbon. The star gets hotter and hotter and expands, leaving the main sequence. It becomes a red supergiant. Eventually this massive star explodes as a supernova. The explosion blows the outer layers of the star into space. The remaining core of the star contracts and may form an extremely dense neutron star or, if the original star was massive enough, even a black hole. Black holes are small, very dense massive concentrations of matter. Their gravitational pull is huge. The gravity is so great that even light cannot escape from it. a huge hydrogen gas cloud in space gravity pulls gas cloud together making a proto-star the high pressures and temperatures cause nuclear fusion long stable period of normal life, main sequence – energy released by fusion of hydrogen to helium for a very long time

hydrogen runs out – next stage depends on the mass of the star

medium mass star (like our Sun)

outer part of star becomes cooler and forms a red giant

the core shrinks to form a white dwarf

high mass star (a few times more massive than our Sun) carries on fusing helium to other elements

star forms a red supergiant then explodes forming a supernova

superheavy star (many times more massive than our Sun)

star forms a red supergiant then explodes forming a supernova

core contracts to form a black hole core contracts to form a neutron star

389

∆∆Fig. 8.8 Stars are ‘born’, have a finite ‘life’ and eventually ‘die’. This is the life-history of a star.

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supergiants

Betelgeuse

Rigel

Spica

red giants Aldebaran

Sirius A

Sun

a -m

ce en qu se in

Absolute magnitude

e pr

INTERNATIONAL GCSE: PHYSICS

HERTZSPRUNG-RUSSELL (HR) DIAGRAM

Sirius B 10

white dwarfs

50000 20000

10000

5000

2500

spectral class

Surface temperature / K

∆∆Fig. 8.9 The Hertzsprung-Russell diagram, showing examples of different types of star.

The Hertzsprung–Russell (HR) diagram is a graph that shows the luminosity of a star plotted against its surface temperature. When the data for many stars are plotted, they are not randomly scattered but fall into distinct groups. The majority of stars are shown as a curved band. These are the main sequence stars. Stars on the main sequence towards the lower right are cooler (reddish) and dimmer and stars at the upper left are hotter (blue) and more luminous. Other groups are the red giants and white dwarfs. The HR diagram is useful to scientists as it shows what stage a star is at in its life cycle, from its position on the diagram.

QUESTIONS 1. Black holes and neutron stars are not shown on the HR diagram. Suggest a reason why.

2. a) Where are hot, bright stars found on the HR diagram? b) What will happen to these hot, bright stars in the future? c) Where will these hot bright stars move to on the diagram in the future?

3. Our Sun is a medium temperature and brightness star. What will

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happen to the Sun and its position on the diagram in the future?

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End of topic checklist A nebula is a huge gas cloud in space that is pulled together by gravity to form a star. Nuclear fusion is the energy source for all stars. In the main sequence stage of a star it spends a long time in a stable state undergoing fusion of hydrogen and producing a steady output of energy. A red giant forms from a low mass star after the energy output from fusion of hydrogen ends and the star expands to a much greater size. A white dwarf forms from a low mass star after a red giant cools and contracts. High mass stars can explode as a supernova after which they can form a neutron star or black hole. A Hertzsprung–Russell (HR) diagram is a diagram that shows the luminosity of a star plotted against the surface temperature. The absolute magnitude is the apparent magnitude of an object if it was a standard distance from the Earth.

The facts and ideas that you should understand by studying this topic:

❍❍Understand how the temperature of stars can affect their colour. ❍❍Know how stars are formed and how they end. ❍❍Describe the differences in the life cycle of a star similar in size to our Sun and of a star much larger than our Sun.

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❍❍Understand how fusion drives the energy output of stars.

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End of topic questions 1. Describe the life cycle of a small star about the size of our Sun. 2. Describe the life cycle of a star with a mass much greater than the Sun. 3. Why are black holes difficult for scientists to detect? 4. Describe, using a diagram, the nuclear fusion reaction that takes place in stars. 5. Explain how a HR diagram can be useful to scientists. 6. What is meant by the term â&#x20AC;&#x2DC;apparent magnitude of a starâ&#x20AC;&#x2122;?

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7. Explain why the absolute magnitude of a star can often be more useful to scientists than its apparent magnitude.

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Cosmology INTRODUCTION

Cosmology is the study of the Universe. So you might think that it covers all topics in physics, chemistry and biology. If that was the case cosmology would be the biggest subject of them all. The Universe itself being infinite would mean that its subject matter would be infinite too! Luckily cosmology confines itself to the big picture view of the Universe: how it began, how it has evolved and how it will change in the future. ∆∆Fig. 8.10 This image from NASA’s Hubble space telescope shows one of the most distant galaxies we know. It dates from 750 million years after the Big Bang that created our Universe. The light took 12.9 billion years to reach us.

LEARNING OBJECTIVES ✓✓Be able to describe the past evolution of the Universe and the main arguments in favour of the Big Bang. ✓✓Be able to describe evidence that supports the Big Bang theory (red-shift and cosmic microwave background (CMB) radiation). ✓✓Be able to describe that if a wave source is moving relative to an observer there will be a change in the observed frequency and wavelength. ✓✓Be able to use the equation relating change in wavelength, wavelength, velocity of a galaxy and the speed of light:

change in wavelength velocity of a galaxy = reference wavelength speed of light l − l 0 l v = = l0 l0 c

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✓✓Be able to describe the red-shift in light received from galaxies at different distances away from the Earth. ✓✓Be able to explain why the red-shift of galaxies provides evidence for the expansion of the Universe .

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KNOWLEDGE CHECK ✓✓Know about the Doppler effect and how movement of a light source relative to an observer can affect the wavelength and frequency of waves detected by the observer. ✓✓Know that theories and models change as scientists to try to explain new evidence.

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THE BIG BANG One theory which tries to explain the origin of the Universe is known as the Big Bang theory. The basic idea is that all the matter in the Universe was originally concentrated in one extremely small, dense place. This matter began to expand very rapidly because of a very hot explosion. In time the Universe continued to expand but also cooled down. The matter in the Universe then started to group together or coalesce into many large gas clouds. These were then subject to gravitational forces and then galaxies, stars and planets were eventually formed. The Universe is older now but it is still expanding today. But what is the evidence that supports this theory? Without evidence to back it up it would just be an idea or an opinion and few would be convinced by it. Supporting evidence: Red-shift Scientists can observe the Universe as it is today. They look at other galaxies in space. Scientists observe light from other galaxies and they notice that it seems to be of a longer wavelength than expected. It appears to be red-shifted. We know from our work on waves (section 3) that when a sound source is moving towards us, the sound waves from it are reduced in wavelength and increased in frequency. This causes the pitch of the sound to increase as the source (such as an ambulance siren) approaches. This is known as the Doppler effect. The Doppler effect also occurs for moving light sources. There will be a change in the observed frequency and wavelength of light from a star that is moving towards or away from the Earth.

observer

• Source moving towards observer • Wavelength decreased; frequency increased • Observer sees light blue-shifted

observer

• Source moving away from observer • Wavelength increased; frequency decreased • Observer sees light red-shifted

∆∆Fig. 8.11 The Doppler effect for light waves.

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The Sun produces helium by nuclear fusion. Atoms of helium in the atmosphere of the Sun absorb particular wavelengths of light emitted by the core of the Sun. This top spectrum in the diagram is the spectrum of the light from our Sun. The black lines show where helium

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spectrum produced by light from the Sun

each line is red-shifted

spectrum produced by light from a distant galaxy

∆∆Fig. 8.12 The whole pattern of lines from a distant galaxy has been red-shifted compared with light from the Sun.

If we compare the Sun’s spectrum with that of a star from another galaxy we can see that the absorption lines due to helium gas in the star’s atmosphere are there but they have moved towards the red coloured part of the spectrum. The red light has a longer wavelength than blue and so we can say that the absorption lines have been redshifted. This is like the increase in frequency of sound waves of an ambulance that moves away from us at speed. This shows that the star is moving away from us.

INTERNATIONAL GCSE: PHYSICS

has absorbed light of particular wavelengths. Less light escapes from the Sun at these wavelengths – that part of the spectrum is dark.

QUESTION 1. Most galaxies that have been observed show red-shift. A few galaxies show blue-shift.

a) Use the Doppler effect to explain how some galaxies show blue-shift.

b) Why is it a relief to know that the great majority of galaxies show red-shift rather than blue-shift?

Using red-shift It is possible to work out the speed of a moving ambulance by measuring the frequency (or wavelength) of sound waves heard by a stationary observer. It is also possible to calculate the speed at which a star is moving away from Earth by looking at how much the wavelength of the light has shifted towards the red end of the spectrum. The equation for the relationship between the change in wavelength, wavelength, velocity of a galaxy and the speed of light is:

l − l0 l v = = c l0 l0

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change in wavelength ve l ocity of a galaxy = reference wavelength speed of light

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Where: l = wavelength observed l0 = reference wavelength v = velocity of galaxy c = velocity of light

WORKED EXAMPLE A spectral line for hydrogen on Earth has a wavelength of 760 nm. The same spectral line for hydrogen observed from a distant quasar is 645 nm. (Quasars are very distant, extremely bright objects that drown out the light from all the other stars in the same galaxy). The velocity of light in free space, c = 3.0 × 108 m/s. Calculate the velocity at which the quasar is moving away from the Earth. Give your answer in m/s. Write down the equation: change in wavelength ve l ocity of a galaxy = reference wavelength speed of light l − l0 l v = = c l0 l0 change in wavelength: Δl = 760 – 645 = 115 nm l × c rearranging the equation: v = l0 115 × 3 × 108 substitute the values: v= 645 v = 53 488 372 m/s Velocity of the quasar is 5.35 × 107 m/s

(to 3 significant figures)

QUESTION 1. A spectral line for hydrogen on Earth is 760 nm. The same spectral line for hydrogen for a distant quasar is 680 nm.

The velocity of light in free space, c = 3.0 × 108 m/s.

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Calculate the velocity of the quasar relative to the Earth. Give your answer in m/s.

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● SCIENCE IN CONTEXT

THE UNIVERSE

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How red-shift provides evidence for the Big Bang Scientists have measured the red-shift from many galaxies and found that: • most galaxies show red-shift, hence most galaxies are moving away from Earth. • distant galaxies show greater red-shift, hence distant galaxies are l v = ). moving away from us more quickly that nearby ones (since c l Edwin Hubble was the first astronomer to show the relationship between the recession velocity of galaxies and their distance, and to deduce that the Universe is expanding. If the Universe is expanding now, then in the past it must have been smaller. Ultimately, the idea goes back to the Universe starting at a single point in a violent ‘explosion’ – the Big Bang theory.

In the 1920s, the astronomer Edwin Hubble (1889–1953) was trying to answer the question of how big the Universe is. Was the Milky Way, our own galaxy, everything there is, or were there other objects outside it? Using the Mount Wilson telescope in California, Hubble studied small ‘fuzzy’ objects in the sky. Building on the work of Henrietta Leavitt (1868–1921), which described how to measure the distance to a type of star called a Cepheid Variable, Hubble discovered that these ‘fuzzy’ objects were complete galaxies of their own, clearly outside the Milky Way. This settled the argument and showed that the Universe (everything there is) was much bigger than anybody previously thought. Hubble also discovered, through observations of red shift (a process where the frequency of light waves changes depending on whether the object is moving), that distant galaxies are all moving away from us – the Universe is expanding. If the Universe is expanding now, then in the past it must have been smaller. Ultimately, the idea goes back to the Universe starting at a single point in a violent ‘explosion’. This is the Big Bang theory. It is also supported by observations of the cosmic microwave background radiation – the ‘echoes’ of the Big Bang that can still be detected. Ever since then, gravity has been acting to slow down the expansion. It is unclear whether the Universe will expand forever or not.

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However, observations in the past 20 years have suggested that the Universe has expanded faster we would expect from our current theories. There appears to be much more to the Universe than we have previously detected. Only when we add in factors called dark matter and dark energy do the observations make sense. At this time, the exact nature of these materials is not known and they have not been detected directly.

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From the rate of expansion scientists have calculated that the Universe started from a single point about 13.8 billion years ago. This is the estimated age of the Universe. Supporting evidence: Cosmic microwave background radiation In the 1960s scientists detected a low energy, low frequency electromagnetic radiation coming from all parts of the Universe. It is detected by using radio telescopes on Earth and is not associated with any star, galaxy or other object. Radio telescopes are very large and can collect and concentrate the electromagnetic waves that come from space. Unlike optical telescopes, radio telescopes are not affected by clouds in the Earth’s atmosphere. Clouds do not block radio waves as they do for visible light. So radio telescopes can be used day and night regardless of the weather conditions on Earth. This background radiation is in the microwave range of the electromagnetic spectrum and is called the cosmic microwave background (CMB) radiation. The CMB radiation is very uniform – it comes from all directions in space. The COBE satellite was launched in 1989 by NASA to measure CMB radiation. The evidence from COBE also supports the uniformity of the CMB detected on Earth. In 1948 the Big Bang theory predicted that this microwave radiation should exist as a relic of the thermal radiation from the original Big Bang explosion. The theory also predicted that the observed wavelength of the radiation today would be much greater than the wavelength of the light emitted shortly after a hot Big Bang. This is due to the expansion of the Universe, which stretches the wavelength of the light. The Big Bang theory predicted that the present-day radiation should be equivalent to a temperature slightly above absolute zero at 2.7 K. That is about 270 °C. In the 1960s this background radiation was detected and the temperature was confirmed as 2.7 K. The COBE satellite has also confirmed these predictions. The thermal radiation from shortly after the Big Bang 13.8 billion years ago has been travelling through space ever since that time. Big Bang theorists continue to interpret this evidence.

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The future of the Universe Scientists are unsure how the Universe will progress. It depends on two things: • how quickly the galaxies are moving apart • how much mass there is in the Universe.

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The cosmic microwave background (CMB) radiation is microwave radiation left over from the thermal radiation of the Big Bang. The Doppler effect is how the wavelength or frequency of waves changes if the source of the waves is moving relative to the observer. Red-shift occurs when stars are moving away from us at great speeds. This movement increases the wavelength of the light that is emitted by the star. Observations of red-shift and CMB radiation provide evidence to support the Big Bang theory.

The facts and ideas that you should understand by studying this topic:

INTERNATIONAL GCSE: PHYSICS

End of topic checklist

❍❍Know that if a wave source is moving relative to an observer there will be a change in the observed frequency and wavelength.

❍❍Use an understanding of the Doppler effect to explain red-shift. ❍❍Know and use the relationship between change in wavelength, wavelength, velocity of a galaxy and the speed of light:

change in wavelength ve l ocity of a galaxy = reference wavelength speed of light l − l0 l v = = c l0 l0

❍❍Describe the past evolution of the Universe and the main arguments in favour of the Big Bang.

❍❍Describe evidence that supports the Big Bang theory (red-shift and cosmic microwave background (CMB) radiation).

❍❍Describe the red-shift in light received from galaxies at different distances away from the Earth.

❍❍Explain why the red-shift of galaxies provides evidence for the expansion of the

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Universe.

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1. Explain the difference between red-shift and blue-shift.

(5 marks)

2. The Big Bang theory predicted the existence of cosmic microwave background radiation today at an equivalent temperature of 2.7 K. a) Describe how this radiation can be detected on Earth and in space.

(2 marks)

b) Describe how scientists confirmed these predictions.

(5 marks)

3. â&#x20AC;&#x2DC;Distant galaxies show more red-shift than nearby onesâ&#x20AC;&#x2122;. a) What does this say about the speeds and directions of distant and nearby (3 marks) galaxies? b) How does this evidence support the idea that the Universe started at a point in (1 mark) the past?

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End of topic questions

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