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Tfcs gcse-sci-f-b1


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Tfcs gcse-sci-f-b1

  2. 2. Project Directors EditorsAngela Hall Emma Palmer Emma Palmer Carol UsherRobin Millar Mary Whitehouse Anne Scott Mary Whitehouse Authors Ann Fullick Andrew Hunt Emily Perry Elizabeth SwinbankHelen Harden Neil Ingram Jacqueline Punter Vicky Wong Maria Pack David Sang
  3. 3. ContentsContentsHow to use this book 4 Making sense of graphs 9Structure of assessment 6 Controlled assessment 12Command words 8B1 You and your genes 14 A Same and different 16 F Making ethical decisions 28 B Same but different 18 G Genetic testing 30 C What makes you the way you are? 20 H Can you choose your child? 34 D Male or female? 22 I Cloning 35 E A unique mix of genes Summary 23 38C1 Air quality 42 A The air 44 G Where do all the atoms go? 58 B The story of our atmosphere 46 H How does air quality affect our health? 60 C What are the main air pollutants? 48 I How can air quality be improved? 64 D Measuring an air pollutant 51 Summary 68 E How are air pollutants formed? 54 F What happens during combustion? 56P1 The Earth in the Universe 72 A Time and space 74 G Continental drift 86 B Seeing stars 76 H The theory of plate tectonics 88 C Beyond the Solar System I Earthquakes and seismic waves 78 91 D How big is the Universe? J Using seismic waves 80 96 E How did the Universe begin? 82 Summary 98 F Deep time 84B2 Keeping healthy 102 A Whats up, Doc? 104 F Circulation 118 B Fighting back 106 G Causes of disease – how do we know? 121 C Vaccines 109 H Changing to stay the same 124 D Superbugs 112 I Water homeostasis 126 E Where do new medicines come from? Summary 114 128
  4. 4. C2 Material choices 132 A Choosing the right stuff 134 G Designer stuff 147 B Using polymers 136 H Designer polymers 150 C Testing times 139 I Making crude oil useful 152 D Zooming in 142 J Nanotechnology 154 E The big new idea 144 K Using nanotechnology 156 F Molecules big and small Summary 146 158P2 Radiation and life 162 A Taking a chance with the Sun 164 F Climate change 174 B Radiation models 166 G Changing the future 178 C Absorbing electromagnetic radiation 168 H Radiation carries information 181 D Risky side of the rainbow I Is there a health risk? 170 186 E Heating with microwaves Summary 172 188B3 Life on Earth 192 A The variety of life 194 F Life on Earth is still evolving today 206 B Webs of life 196 G The story of Charles Darwin 208 C Depending on the Sun 198 H The birth of species 214 D Systems in balance 200 I Maintaining biodiversity 216 E Life on Earth has evolved Summary 204 220C3 Chemicals in our lives: Risks & benefits224 A A journey through geological time 226 H Chemicals from salt – a better way 240 B Mineral wealth in Britain 228 I Protecting health and the 242 C Salt: sources and uses 230 environment D Salt in food 232 J Stages in the life of PVC 244 E Alkalis and their uses 234 K Benefits and risks of plasticisers 246 F Chemicals from salt – the foul way 236 L From cradle to grave 248 G Benefits and risks of water treatment 238 Summary 250P3 Sustainable energy 254 Glossary A Why do we need to know about energy? 256 G What happens in a power station? 270 B How much energy do things use? Index 258 H What about nuclear power? 272 C How much energy does a person use? 260 I Renewables – how do they work? 274 Appendices D A national and global problem 262 J How is mains electricity distributed? 276 E How can we use less energy? 264 K Which energy sources should we use? 278 F What are our sources of energy? 266 Summary 280Glossary 284 Appendices 293Index 290
  5. 5. How to use this book Welcome to Twenty First Century Science. This book has been specially written by a partnership between OCR, The University of York Science Education Group, The Nuffield Foundation, and Oxford University Press. On these two pages you can see the types of page you will find in this book, and the features on them. Everything in the book is designed to provide you with the support you need to help you prepare for your examinations and achieve your best.Module Openers Why study?: This The Science: This explains how what box summarises the you’re about to science behind the learn is relevant to module you’re about everyday life. to study. What you already Find out about: know: This list is a Every module starts summary of the things with a short list of you’ve already learnt the things you’ll be that will come up covering. again in this module. Check through them Ideas about Science: in advance and see if Here you can read there is anything that about the key ideas you need to recap on about science covered before you get started. in this module. Find out about: Questions: Use theseMain Pages For every part of the questions to see if book you can see a you’ve understood list of the key points the topic. explored in that section. Summary box: This box sums up the main ideas covered on these Worked examples: pages. These help you understand how to use an equation or to work through a calculation. You can check back whenever you use the calculation in your work to make sure you understand. 4
  6. 6. Science ExplanationsYou should Visual summary:know: This is a Another way to startsummary of the revision is to usemain ideas in the a visual summary,unit. You can use linking ideasit as a starting together in groupspoint for revision, so that you canto check that you see how one topicknow about the relates to another.big ideas covered. You can use this page as a starting point for your own summary. Review Questions Ideas about Science andIdeas about ReviewScience: For Questions:every module this You can beginpage summarises to prepare forthe ideas about your examsscience that by using theseyou need to questions tounderstand. test how well you know the topics in this module. 5
  7. 7. Structure of assessment Matching your course What’s in each module? As you go through the book you should use the module opener pages to understand what you will be learning and why it is important. The table below gives an overview of the main topics each module includes. B1 C1 P1 •  hat are genes and how do they affect the W •  hich chemicals make up air, and which W •  hat do we know about the place of the W way that organisms develop? ones are pollutants? How do I make sense Earth in the Universe? •  hy can people look like their parents, brothers W of data about air pollution? •  What do we know about the the Earth and and sisters, but not be identical to them? •  hat chemical reactions produce air W how it is changing? •  ow can and should genetic information H pollutants? What happens to these be used? How can we use our knowledge of pollutants in the atmosphere? genes to prevent disease? •  hat choices can we make personally, locally, W •  ow is a clone made? H nationally or globally to improve air quality? B2 C2 P2 •  ow do our bodies resist infection? H •  ow do we measure the properties of H •  hat types of electromagnetic radiation W •  hat are vaccines and antibiotics and how W materials and why are the results useful? are there? do they work? •  hy is crude oil important as a source of W •  hich types of electromagnetic radiation W •  hat factors increase the risk of heart W new materials such as plastics and fibres? harm living tissue and why? disease? •  hy does it help to know about the W •  hat is the evidence for global warming, why W •  ow do our bodies keep a healthy water H molecular structure of materials such as might it be occuring? How serious a threat is it? balance? plastics and fibres? •  ow are electromagnetic waves used in H •  hat is nanotechnology and why is it important? W communications? B3 C3 P3 •  ystems in balance – how do different S •  hat were the origins of minerals in Britain W •  ow much energy do we use? H species depend on each other? that contribute to our economic wealth? •  ow can electricity be generated? H •  ow has life on Earth evolved? H •  here does salt come from; why is it important? W •  hich energy sources should we choose? W •  hat is the importance of biodiversity? W •  hy do we need chemicals such as alkalis W and chlorine and how do we make them? •  hat can we do to make our use of W chemicals safe and sustainable? How do the modules fit together? The modules in this book have been GCSE Biology GCSE Chemistry GCSE Physics written to match the specification for GCSE Science. In the diagram to the right B1 C1 P1 GCSE Science you can see that the modules can also be used to study parts of GCSE Biology, GCSE B2 C2 P2 Chemistry, and GCSE Physics courses. B3 C3 P3 GCSE Additional B4 C4 P4 Science B5 C5 P5 B6 C6 P6 B7 C7 P76
  8. 8. GCSE Science assessmentThe content in the modules of this book matches the modules of thespecification.Twenty First Century Science offers two routes to the GCSE Sciencequalification, which includes different exam papers depending on theroute you take.The diagrams below show you which modules are included in each exampaper. They also show you how much of your final mark you will beworking towards in each paper. Marks Unit Modules Tested Percentage Type Time Available A161 B1 B2 B3 25% Written Exam 1h 60 Route 1 A171 C1 C2 C3 25% Written Exam 1h 60 A181 P1 P2 P3 25% Written Exam 1h 60 A144 Controlled Assessment 25% 9h 64 A141 B1 C1 P1 25% Written Exam 1h 60 Route 2 A142 B2 C2 P2 25% Written Exam 1h 60 A143 B3 C3 P3 25% Written Exam 1h 60 A144 Controlled Assessment 25% 9h 64 7
  9. 9. Controlled words Command assessment The list below explains some of the common words you will see used in exam questions. Calculate Justify Work out a number. You can use your calculator Give some evidence or write down an explanation to to help you. You may need to use an equation. tell the examiner why you gave an answer. The question will say if your working must be shown. (Hint: don’t confuse with ‘Estimate’ or Outline ‘Predict’.) Give only the key facts of the topic. You may need to set out the steps of a procedure or process – make Compare sure you write down the steps in the correct order. Write about the similarities and differences between two things. Predict Look at some data and suggest a realistic value or Describe outcome. You may use a calculation to help. Dont Write a detailed answer that covers what guess – look at trends in the data and use your happens, when it happens, and where it happens. knowledge of science. (Hint: don’t confuse with Talk about facts and characteristics. (Hint: dont ‘Calculate’ or ‘Estimate’.) confuse with ‘Explain’.) Show Discuss Write down the details, steps, or calculations needed Write about the issues related to a topic. You may to prove an answer that you have given. need to talk about the opposing sides of a debate, and you may need to show the difference between Suggest ideas, opinions, and facts. Think about what you’ve learnt and apply it to a new situation or context. Use what you have learnt to Estimate suggest sensible answers to the question. Suggest an approximate (rough) value, without performing a full calculation or an accurate Write down measurement. Dont just guess – use your Give a short answer, without a supporting argument. knowledge of science to suggest a realistic value. (Hint: don’t confuse with ‘Calculate’ and ‘Predict’.) Top Tips Explain Always read exam questions carefully, even if you Write a detailed answer that covers how and why recognise the word used. Look at the information in the a thing happens. Talk about mechanisms and question and the number of answer lines to see how reasons. (Hint: dont confuse with ‘Describe’.) much detail the examiner is looking for. You can use bullet points or a diagram if it helps your Evaluate answer. You will be given some facts, data, or other kind If a number needs units you should include them, of information. Write about the data or facts and unless the units are already given on the answer line. provide your own conclusion or opinion on them.8
  10. 10. Controlled assessment Making sense of graphsScientists use graphs and charts to present data clearly and to look forpatterns in the data. You will need to plot graphs or draw charts topresent data and then describe and explain what the data is showing.Examination questions may also give you a graph and ask you todescribe and explain what a graph is telling you.Reading the axesLook at these two charts, which both provide data about daily energyuse in several countries. United StatesUnited Kingdom Switzerland Kenya India France China 0 10 000 20 000 30 000 40 000 50 000 60 000 70 000 80 000 national daily energy use 2007 (GWh/day) United StatesUnited Kingdom Switzerland Kenya India France China 0 50 100 150 200 250 300 daily energy use per person (kWh per person/day) Graphs to show energy use in a range of countries, total and per capita.Why are the charts so different if they both represent information aboutenergy use?Look at the labels on the axes.One shows the energy use per person per day, the other shows theenergy use per day by the whole country.For example, the first graph shows that China uses a similar amount ofenergy to the US. But the population of China is much greater – so theenergy use per person is much less.First rule of reading graphs: read the axes and check the units. 9
  11. 11. Describing the relationship between variables The pattern of points plotted on a graph shows whether two factors are related. Look at this scatter graph. 500 400 300 boiling point (ЊC) 200 100 0 0 5 10 15 20 25 30 35 Ϫ100 Ϫ200 number of carbon atoms in hydrocarbon Graph to show the relationship between the number of carbon atoms in a hydrocarbon and the boiling point. There is a pattern in the data; as the number of carbon atoms increases, the boiling point increases. But it is not a straight line, it is quite a smooth curve, so we can say more than that. When the number of carbon atoms is small the boiling point increases quickly with each extra carbon atom. As the number of carbon atoms gets bigger, the boiling point still increases, but less number of salmonella bacteria in patient’s stomach (millions) quickly. Another way of describing this is to say that the slope of the 5 graph – the gradient – gets less as the number of carbon atoms 4 increases. 3 Look at the graph on the right, which shows how the number of bacteria 2 infecting a patient changes over time. 1 How many different gradients can you see? 0 0 1 2 3 4 5 6 7 There are three phases to the graph, each with a different gradient. So time (days) you should describe each phase, including data if possible: Graph of bacteria population against time. • The number of bacteria increases rapidly for the first day until there are about 4.5 million bacteria. • For about the next three days the number remains steady at about 4.5 million. • After the fourth day the number of bacteria declines to less than a million over the following two to three days. Second rule of reading graphs: describe each phase of the graph, and include ideas about the gradient and data, including units.10
  12. 12. Is there a correlation? 0.6 global temperature anomaly (°C) annual mean 0.4 5-year running mean Sometimes we are interested in whether one thing changes when another does. If a change in one factor 0.2 goes together with a change in something else, we 0 say that the two things are correlated. Ϫ0.2 The two graphs on the right show how global Ϫ0.4 temperatures have changed over time and how levels 1880 1900 1920 1940 1960 1980 2000 of carbon dioxide in the atmosphere have changed year over time. 400 (parts per million) atmospheric samples (Mauna Loa) carbon dioxide Is there a correlation between the two sets of data? ice core (Law Dome) 350 Look at the graphs – why is it difficult to decide if 300 there is a correlation? 0 The two sets of data are over different periods of 1750 1800 1850 1900 1950 2000 time, so although both graphs show a rise with time, year Graphs to show increasing global temperatures and carbon it is difficult to see if there is a correlation. dioxide levels. Source: NASA. It would be easier to identify a correlation if both sets of data were plotted for the same time period and placed one above the other, or on the same axes, like this: carbon dioxide (parts per million) 0.6global temperature anomaly (°C) 400 annual mean temperature 0.4 5-year running mean temperature CO2 level 350 0.2 0 300 Ϫ0.2 Ϫ0.4 0 1880 1900 1920 1940 1960 1980 2000 year Graph to show the same data as the above two graphs, plotted on one set of axes. When there are two sets of data on the same axes take care to look at which axis relates to which line. Third rule for reading graphs: when looking for a correlation between two sets of data, read the axes carefully. Explaining graphs When a graph shows that there is a correlation between two sets of data, scientists try to find out if a change in one factor causes a change in the other. They use science ideas to look for an underlying mechanism to explain why two factors are related. 11
  13. 13. Controlled assessment In GCSE Science the controlled assessment counts for 25% of your total grade. Marks are given for a Tip case study and a practical data analysis task. The best advice is plan ahead. Give your work the time it needs and work steadily and evenly Your school or college may give you the mark over the time you are given. Your deadlines will schemes for this. come all too quickly, especially if you have This will help you understand how to get the most coursework to do in other subjects. credit for your work. Case study (12.5%) Selecting information Everyday life has many questions science can help • Collect information from different places – to answer. You may meet these in media reports, books, the Internet, newspapers. for example, on television, radio, in newspapers, • Say where your information has come from. and in magazines. A case study is a report that • Choose only information that is relevant to the weighs up evidence about a scientific question. question you are studying. • Decide how reliable each source of OCR will provide a news sheet with a variety of information is. articles about some of the science topics you have studied in this course. Understanding the question You will choose an issue from the news sheet as the • Use scientific knowledge and understanding to basis for your case study, and identify a question explain the topic you are studying. that you can go on to answer. Your question will • When you report what other people have said, probably fit into one of these categories: say what scientific evidence they used (from • a question where the scientific knowledge is not experiments, surveys, etc.). certain, for example, Does using mobile phones Reaching your own conclusion cause brain damage? • Compare different evidence and points of view. • a question about decision making using • Consider the benefits and risks of different scientific information, for example, Should cars courses of action. be banned from a shopping street to reduce air • Say what you think should be done, and link pollution? or Should the government stop this to the evidence you have reported. research into human cloning? • a question about a personal issue involving Presenting your study science, for example, Should my child have the • Make sure your report is laid out clearly in a MMR vaccine? sensible order – use a table of contents to help organise your ideas. You should find out what different people have said • You may use different presentation styles, for about the issue. Then evaluate this information and example, a written report, newspaper article, reach your own conclusion. PowerPoint presentation, poster or booklet, or You will be awarded marks for: web page. • Use pictures, tables, charts, graphs, and so on to present information. • Take care with your spelling, grammar, and punctuation, and use scientific terms where they are appropriate.12
  14. 14. When will I do my controlledCreating a case study assessment? Your case study will be written in class time over aWhere do I start? series of lessons.Read the news sheet • local public library You may also do some research out of are given and think • your science textbookof a question you want Your practical data analysis task will be done in and notesto find the answer to. class time over a series of lessons. • TVSources of information • radio Your school or college will decide when you docould include: • newspapers and your controlled assessment. If you do more than• Internet magazines one case study or practical data analysis, they will• school library • museums and exhibitions. choose the one with the best marks. Practical data analysis (12.5%) them? Would you get the same results if  you  Scientists collect data from experiments and studies. repeated the experiment? They use this data to explain how something happens. • Comment on the repeatability of your data, You need to be able to assess the methods and data account for any outliers in the data, or explain from scientific experiments. This will help you decide why there are no outliers. how reliable a scientific claim is. • Suggest some improvements or extra data you could collect to be more confident in your conclusions. A practical data analysis task is based on a practical experiment that you carry out. The experiment will be Reviewing the hypothesis designed to test a hypothesis suggested by your • Use your scientific knowledge to decide whether teacher. You may do the experiment alone or work in the hypothesis is supported by your data. groups and pool all your data. Then you interpret and • Suggest what extra data could be collected to evaluate the data. increase confidence in the hypothesis. You will be awarded marks for: Presenting your report • Make sure your report is laid out clearly in a Choosing how to collect the data sensible order. • Carry out the experiment in ways that will give you • Use diagrams, tables, charts, and graphs to high-quality data. present information. • Explain why you chose this method. • Take care with your spelling, grammar, and • Explain how you worked safely. punctuation, and use scientific terms where they Interpreting data are appropriate. • Present your data in tables, charts, or graphs. • Say what conclusions you can reach from your data. • Explain your conclusions using your scientific knowledge and understanding. Evaluating the method and quality of data • Look back at your experiment and say how you could improve the method. • Explain how confident you are in your evidence. Have you got enough results? Do they show a clear  pattern? Have you repeated measurements to check  13
  15. 15. B1 You and your genes14
  16. 16. B1: You and your genesWhy study genes? What makes me the way that I am? How are features passed on from parents to children? Your ancestors probably asked the same questions. You may look like your relatives, but you are unique. Only in the last few generations has science been able to answer questions like these.What you already know The Science• In sexual reproduction fertilisation happens Your environment has when a male and female sex cell join together. a huge effect on you, for example, on your Information from two parents is mixed to appearance, your body, make a new plan for the offspring. The and your health. But offspring will be similar but not identical to these features are also their parents. affected by your genes. In• There are variations between members of the this Module you’ll find out same species that are due to environmental as how. You’ll discover the well as inherited causes. story of inheritance.• Clones are individuals with identical genetic information.• The science of cloning raises ethical issues. Ideas about ScienceFind out about In the future, science could help you to change• how genes and your environment make your baby’s genes before it is born. Cloned you unique embryos could provide• how and why people find out about their genes cells to cure diseases.• how we can use our knowledge of genes But, as new technologies are developed, we must• whether we should allow this. decide how they should be used. These can be questions of ethics – decisions about what is right and wrong. 15
  17. 17. A Same and different Children look like their parents. They inherit information Find out about from them. This information is in genes. Genes control how D what makes us all new organisms develop and function. different All people are very similar. Look at the people around D what genes are and you – the differences between us are very small. But they what genes do are interesting because they make us unique. Both the information you inherit and your environment affect most of your features. Summary box D You inherit genes These sisters have some features in common. from your parents. D Your genes and your Environment makes a difference environment make you unique. The information you inherited from your parents affects D The nuclei of your almost all of your features. For example, your blood group cells contain depends on this information. Some features are the result of chromosomes. only your environment, such as scars and tattoos. Chromosomes are made of DNA. But most of your features are affected by both your genes and D A gene is a section your environment. For example, your weight depends on of DNA. inherited information. But if you eat too much, you will D Genes have the become heavier. information to make proteins. D Structural proteins Questions make up the fabric of your body. 1 Choose two of the students in the photograph on D Enzymes are the left. Write down five ways they look different. proteins; they 2 What two things can affect how you develop? control chemical reactions in the body. 3 explain what is meant by inherited information. 16
  18. 18. B1: You and Your genesWhere is all the information kept?Living organisms are made up of cells. Most cells contain nuclei. Inside each nucleus are long threads called chromosomes. Each chromosome has thousands of genes. Genes control how you develop. nucleus genes genetic material (chromosomes) cell chromosome 0.25 mm nucleus The nucleus of a cell has all the information to make a whole human being. The nucleus is just 0.006 mm across!What are chromosomes made of?Chromosomes are made of very long molecules of DNA. DNA scientists have stained these plant cells to show up their nuclei. oneis short for deoxyribonucleic acid. A gene is a section of a cell is dividing. The separatingDNA molecule. chromosomes can be seen.How do genes control your development? enzymes speed upGenes are instructions for making proteins. Each gene is the move chemical muscles reactions in‘recipe’ for making a different protein. build the body cellsWhat’s so important about proteins?There are many different proteins in the body, and each one has an important job. They may be: • structural proteins – to build the body, eg collagen (the protein found in tendons) fight send chemical• functional proteins – to take part in the chemical reactions bacteria carry messages and viruses oxygen of the body, eg enzymes such as amylase in the round the blood bodyGenes control which proteins a cell makes. This is how they There are about 50 000 typesdirect what the cell does and how an organism develops. of proteins in the human body. Questions 4 Write these cell parts in order starting 6 a List two kinds of job that proteins do in with the smallest: the human body. chromosome, gene, cell, nucleus b name two proteins in the human body 5 explain how genes control what a cell does. and say what they do. A: saMe and dIFFerenT 17
  19. 19. B Same but different Genes decide a lot about how a baby will grow and develop. Find out about A few characteristics, like dangly earlobes or dimples, are D why identical twins decided by one pair of genes only. Mostly several different look like each other genes work together. In this way they decide characteristics D why identical twins such as your height, your weight, and your eye colour. But do not stay identical your genes don’t tell the whole story. D what a clone is Twins and the environment Summary box D Identical twins have the same genetic information. D There may be differences in some characteristics because of the environment. D A clone is a living organism with the same genetic information as Identical twins have the same genes but they don‘t look exactly the same. another living organism. Sometimes a fertilised egg starts to divide and splits to form two babies instead of one. These are identical twins. Each baby has the same genes. Any differences between them must be because of the environment. Most identical twins grow up in the same family. Their Questions environment is very similar. But sometimes twins are 1 how are dimples, separated after birth and adopted by different parents. Then green eyes, and being scientists can find out what difference the environment makes 2 m tall inherited to the twins’ characteristics. differently? Often the separated twins are still very alike. Genes have a 2 Why do scientists find very strong influence. But some things, like weight, are more studying identical different in twins who grow up apart than twins who live in the twins so useful? same environment. 18
  20. 20. B1: You and Your genesCloningWe call any genetically identical organisms clones. So identical twins are human clones! Scientists can use clones to find out the effect of the environment on growth and development. But it would be wrong for scientists to separate babies. For this reason scientists often study plants.Plant clones are quite common. For example, strawberry plants and spider plants make plant clones at the end of runners. Bulbs, like daffodils, also produce clones.Cloning plantsIt is easy for people to clone plants artificially. A piece of the adult plant is cut off. It soon forms new roots and stems to become a small plant. The new plant is a clone. It has the same each of these baby spider plants isgenes as the parent plant and is identical. a clone of its parent plant and of all the other baby plants.You can also place tiny pieces of a plant on special jelly, called agar. They grow into plants, which are all clones. In this way, you can make hundreds of clones from a single plant.Cloned plants are usefulYou can use clones to look at how the environment affects them. If the parent plant grew very tall, that will be partly down to its genes. But what happens if it doesn’t get enough nutrients or water? Will it still grow tall? We can look at the effects of different factors on the characteristics of cloned plants. This helps us to understand how genes and the environment interact. Questions 3 What is a clone? 4 Why are cloned plants so useful to scientists? 5 The environment affects the appearance of plants. describe how you could use cloned plants to show this. You may make cauliflower clones like these. B: saMe BuT dIFFerenT 19
  21. 21. C What makes you the way you are? People in a family look like each other. You may have inherited Find out about a feature you don’t like, such as your dad’s big ears. But family D how you inherit likenesses can be very serious. genes D Huntington’s disease Robert’s story (an inherited illness) I’m so frustrated. I can’t sit still in a chair. I’m more and more forgetful and I fall over. The doctor has said it might be Huntington’s disease. She said I can have a blood test to find out. Huntington’s disease You can’t catch Huntington’s disease. It’s an inherited disorder. Parents pass the disease on to their children. The symptoms of Huntington’s disease don’t happen until middle age. They are: • difficulty controlling muscles, which shows up as twitching • becoming forgetful • difficulty understanding things and concentrating • mood changes. After a few years, sufferers can’t control their movements. Sadly, the condition is fatal. Robert, 56 Eileen, 58 Ive been Robert’s mum forgetting was just the things and same. David stumbling. looks just like his father. robert and his grandson Craig. Sarah, 32 David, 35 Clare, 33 Im definitely Im not having a Davids got the right having the test test. It wont idea, just getting on if Dads got it. change what with his life. Mind Questions I need to know so I can plan happens to me. you, Im really worried about him now – and my life. Craig and Hannah. 1 List the symptoms of huntington’s disease. Craig, 16 Hannah, 14 Its not fair. I want No-one seems 2 explain why to find out but they wont let me. They to want to tell me anything huntington’s disease is think Im too young about it at all. to understand. called an inherited disorder. Craig’s family. 20
  22. 22. B1: You and your genesHow do you inherit your genes? QuestionsIn some families brothers and sisters look like each other. Inothers they look very different. They may also look different 3 a Draw a diagram tofrom their parents. This is because of genes. show a sperm cell, an egg cell, and theParents pass on genes in their sex cells. In animals these are fertilised egg cellsperm and egg cells. Sex cells have copies of half the parent’s they make.chromosomes. When a sperm cell fertilises an egg cell, the b Explain why thefertilised egg cell gets a full set of chromosomes. It is called fertilised egg cell hasan embryo. pairs of chromosomes. 4 Explain why childrenThe number of chromosomes in each cell may look a bit likeChromosomes come in pairs. Every human body cell has each of their parents.23 pairs of chromosomes. The chromosomes in most pairs arethe same size and shape. They carry the same genes in the same genesame place. So your genes also come in pairs.Sex cells have single chromosomesSex cells are made with copies of half the parent’schromosomes. This makes sure that the fertilised egg cell hasthe right number of chromosomes – 23 pairs. One chromosome chromosome chromosome from father from mothercame from the egg cell. The other came from the sperm cell.Each chromosome carries thousands of genes. Each chromosome pairchromosome in a pair carries the same genes along its length. These chromosomes are a pair.So the fertilised egg cell has a mixture of the parents’ genes.Half of the new baby’s genes are from the mother. Half are from Summary boxthe father. This is why children resemble both their parents. DDYour sex cells only have one of each 46 chromosomes 23 chromosomes chromosome pair. DDAn egg cell and a 46 chromosomes sperm cell join to male body cell sperm cell form an embryo. fertilisation DDYou inherit half of your genes from 46 chromosomes your mother and half fertilised egg cell from your father. egg cell DDHuntington’s disease 23 chromosomes is caused by a faultyfemale body cell gene. It is passed on The cells in this diagram are not drawn to scale. A human egg cell is or inherited from one 0.1 mm across. This is 20 times larger than a human sperm cell. of your parents. C: What makes you the way you are? 21
  23. 23. D Male or female? What decides an embryo’s sex? Find out about A fertilised human egg cell has 23 pairs of chromosomes. D what decides if you Males have an X chromosome and a Y chromosome – XY. are male or female Females have two X chromosomes – XX. D how a Y chromosome makes a baby male Question 1 What sex chromosome(s) would be in the nucleus of: a a man’s body cell? b an egg cell? c a woman’s body cell? X Y d a sperm cell? Women have two X chromosomes. These chromosomes are from the Men have an X and a Y. nucleus of a woman’s body cell. They are lined up in pairs. What’s the chance of being male or female? A parent’s chromosomes are in pairs. When sex cells are made they only get one chromosome from each pair. So half a man’s sperm cells get an X chromosome and half get a Summary box Y chromosome. A woman’s egg cells all get an X chromosome. D Males have XY When a sperm cell fertilises an egg cell the chances are 50% that chromosomes. it will be an X sperm and 50% that it will be a Y sperm. This D Females have XX chromosomes. means that there is a 50% chance that the baby will be a boy and 50% chance a girl. X male body cell female body ALL cell egg cells XY OR XX X Y 22
  24. 24. A unique mix of genes EWill this baby be tall and have red hair? Will she be good at music or sport? Both her environment and her genes will affect Find out aboutthese features. A few features are controlled by just one gene. D how pairs of genesWe can understand these more easily. control some features D cystic fibrosis (an inherited illness) D testing a baby’s genes before they are born This baby has inherited a unique mix of genetic information.Genes come in different versionsBoth chromosomes in a pair carry genes that control the same features. Each pair of genes controlling a feature is in the same place on the chromosomes.But genes in a pair can be slightly different versions. You can think about it like football strips. A team’s home and away strips are both based on the same pattern, but they’re not the same. Different versions of the same genes are called alleles. do you have dimples whenThe gene that controls dimples has two alleles. The D allele you smile?gives you dimples. The d allele won’t cause dimples. This diagram shows one Question pair of chromosomes. The gene controlling dimples 1 Write down what is meant by the word allele. is coloured in. E: a unIQue MIX oF genes 23
  25. 25. dimples Dominant alleles – they’re in charge D D The D allele is dominant. You only need one copy of a dominant allele to have its feature. The d allele is recessive. You must have two copies of a recessive allele to have its feature – in this case no dimples. This person inherited a D allele from both parents. They have dimples. Which alleles can a person inherit? Sex cells get one chromosome from each pair of their parents’ no dimples chromosomes. If a parent has two D or two d alleles, they can only pass on a D or a d allele to their children. d d But a parent could have one D and one d allele. Then half of their sex cells will get the D allele and half will get the d allele. This person inherited a d allele The human lottery from both parents. They don’t We don’t know which egg and sperm cells will meet at have dimples. fertilisation. This genetic diagram is called a Punnett square. It shows all the possibilities for one couple. dimples A father with d d father D d two d alleles (no dimples) One of the alleles goes in each sperm cell This person inherited one D and sex cells d d one d allele. They have dimples. One of the alleles goes in each egg cell mother D D d D d D d d d d d d children There is a A mother with 50% chance of a one D and one child having dimples d allele (dimples) Questions 2 Explain how you inherit two alleles for each gene. 3 Explain the difference between a dominant and a recessive allele.24
  26. 26. B1: You and Your genesWhy don’t brothers and sisters lookthe same? Summary box D There are differentHuman beings have about 23 000 genes. Each gene has versions of genes—different alleles. Both of the alleles you inherit can be the they are calledsame or different. alleles. D If you have oneBrothers and sisters are different because they each get a copy of a dominantdifferent mixture of alleles from their parents. Except for allele, you will haveidentical twins, each one of us has a unique set of genes. that feature. D You have to have two copies of a recessive allele to show that feature. The allele that gives you The allele that gives you hair on straight thumbs is dominant the middle of your fingers is (T). The allele for curved dominant (r). The allele for no thumbs is recessive (t). hair is recessive (r).What about the family?A small number of disorders are caused by faulty alleles of a single gene. Huntington’s disease is caused by a dominant allele. You only need to inherit the allele from one parent to have the condition. Craig and Hannah’s grandfather, Robert, has Huntington’s disorder. So their dad, David, may have inherited this faulty allele. At the moment he has decided I’m not having the test. It won’tnot to have the test to find out. change what happens to me. Questions 4 What are the possible pairs of alleles a 5 use a diagram to explain why a couple person could have for: who have dimples could have a child a dimples? with no dimples. b straight thumbs? 6 use a diagram to work out the chance c no hair on the second part of their that david has inherited the huntington’s ring finger? disease allele. E: a unIQue MIX oF genes 25
  27. 27. Dear Clare, y husband Huw Please help us. M en told that our Cystic fibrosis — in depth and I have just be first child has cy one in our family stic fibrosis. No has ever had Did I do W e’ve had a huge postbag in response to last month’s letter from Emma. So this month we’re looking in depth at cystic fibrosis, a disease that one in 25 of us carries in the UK. this disease before. during my something wrong pregnancy? I’m so worried. What is cystic fibrosis? Y Dear Emma, ou can’t catch cystic fibrosis. It is a genetic disorder. It is passed on from Yours sincerely What a difficult time for parents to their children. Emma you all. First of all, The cells that make mucus in the body are faulty. The mucus is too thick. nothing you did during This causes problems for breathing, digestion, and reproduction. There is your pregnancy could no cure at the moment. But treatments are getting better and life have affected this, so don’t expectancy is increasing. feel guilty. Cystic fibrosis is an inherited disorder … Problem Symptom Treatment Mucus blocks up lungs. • Difficult to breathe. • Physiotherapy. • People with CF get • Use of enzyme spray breathless. thins out mucus in the • Lots of chest pains. lungs. This makes it Emma’s parents Huw’s parents easier to clear mucus. • Antibiotics. Mucus blocks up tubes that • Shortage of enzymes in • Take tablets of missing Emma Huw take enzymes from the the gut. gut enzymes. pancreas to the gut. • Food is not digested properly. • People with CF can be Emma and Huw’s child short of nutrients. with cystic fibrosis Mucus blocks up tubes in Can’t have children. Female with dominant allele F reproductive system. Female with recessive allele f Male with dominant allele F Male with recessive allele f This family tree shows how Emma F f father This diagram shows how and Huws child inherited CF. healthy parents who are both carriers of the faulty cystic fibrosis allele can have a child affected by the disease. The allele is recessive. F f sex cells mother f F f f f F f children There is a 25% chance that a child from the carrier parents will F F F f F have cystic fibrosis.26
  28. 28. B1: You and Your genesHow do you get cystic fibrosis? What are the options?M ost people who have CF can’t have children. Babies with CF are usually born to healthy parents. How can this be? I f a couple know there is a risk they could have children with cystic fibrosis, they could have tests. During pregnancy,The CF gene has two versions. One is dominant. It tells cells to doctors can collectmake normal mucus. The other is a faulty recessive gene. There cells from the developing fetus. The couple should beare errors in the DNA. It instructs cells to make thick mucus. aware of theA person with one normal (F) dominant allele and a faulty (f) following about the tests:recessive allele will not have CF But they can pass the faulty . • there is a risk of up to 1% that they could lose thegene on to their children. They are carriers. baby (miscarriage)Half the sex cells of CF carriers contain the normal allele and half • there is a very small risk of infectioncontain the faulty allele. If two faulty alleles meet at • the results are not 100% reliable.fertilisation, the baby will have CF One in 25 people in the UK .carry the CF allele. Amniocentesis test. amniotic fluid withdrawn ultrasound probe syringe needle womb (uterus) placenta fetus amniotic fluid The results of the tests containing some cervix fetal cells D octors examine the genes. If the fetus has two faulty (ff) CF alleles, the child will have cystic fibrosis. Then the parents may choose to end the pregnancy. This is done with a medical operation called a termination (abortion). The fetal cells for the genetic test can be • 1% miscarriage risk • very small risk of infection collected in an amniocentesis test. • results at 15–18 weeks • results not 100% reliableQuestions Summary box D A recessive allele causes 7 The magazine doctor is sure that nothing emma cystic fibrosis. It causes a did during her pregnancy caused her baby to have person to have thick cystic fibrosis. how can she be so sure? mucus. If a person has only 8 People with cystic fibrosis make thick, sticky mucus. one faulty CF allele, they have normal mucus. They describe the health problems that this may cause. are carriers. A genetic test 9 explain what it means when someone is a ‘carrier’ of a fetus may show two of cystic fibrosis. faulty CF alleles. The baby would have cystic fibrosis. A couple could have a termination. E: a unIQue MIX oF genes 27
  29. 29. F Making ethical decisions Elaine’s nephew has cystic fibrosis. When they found out, Find out about Elaine and Peter became worried about any children they D how people make might have. They both had a genetic test. The tests showed ethical decisions that they were both carriers for cystic fibrosis. D how genetic information could be used ‘We had a test for each of my pregnancies,’ says elaine. ‘sadly we felt we had to terminate the first one, because the fetus had CF. We are lucky enough now to have two healthy children – and we know we haven’t got to watch them suffer.’ Elaine and Peter decided to have a prenatal genetic test of the fetus when Elaine was pregnant. The test was positive. Elaine and Peter’s unborn child would have cystic fibrosis. They decided to end the pregnancy. This was a very hard decision. When a person has to make a decision about what is the right or wrong thing to do, they are thinking about ethics. Deciding whether to have a termination is an example of an ethical question. Summary box Ethics – right and wrong D Ethics is about For some ethical questions, the right answer is clear. For deciding whether example, should you feed your pet? But in some situations something is right or wrong there may not be one right answer. People think about ethical questions in different ways. 28
  30. 30. B1: You and Your genesWeighing up the consequencesElaine and Peter had to decide to either continue with the pregnancy or have a termination. They thought about how each choice would affect all the people involved. They judged the problems their unborn child would face. Elaine and Peter also had to think about: • the effects that an ill child would have on their lives and also on the lives of any other children they might have • whether they feel they could cope with caring for a child Jo has a serious genetic disorder. her parents believe that termination with a serious genetic disorder. is wrong. They decided not to have more children, rather than useDifferent choices information from a test.Not everyone weighing up the consequences of each choice would have come to the same decision as this couple did. What are the ethical argumentsSome people feel that any illness would make a person’squality for a decision?of life terrible. But some people lead very happy, full lives with very serious disabilities.When you believe that an action is wrongFor some people having a termination is completely wrong The right decision isin itself. They believe that an unborn child has the right to the one which leads to the best outcome forlife. Other people believe that terminating a pregnancy is the most people.unnatural, and that we should not interfere. These viewpoints could be their own personal beliefs or their religious beliefs. Some actions areElaine and Peter may have felt that termination was wrong. wrong and should never be done.They could have decided not to have children at all. This would mean that they could not pass on the faulty allele. Or they could decide to have children, and to care for any child that did inherit the disease. Questions It’s wrong to have a termination. We’ll look after 1 explain what is meant by ‘an ethical question’. our baby whatever. 2 describe three different points of view that a couple in elaine and Peter’s position might take. Is it fair for us to have a baby knowing it is going to suffer so much? F: MakIng e ThICaL deCIsIons 29