Life Sciences Grade 12 Study Guide PDF

c i e n c e s Grade L i fe Study S G u i d e 12  © Department of Basic Education 2014 S c i e n c e s Grade Li fe Study Guid e 12 © Department of Basic Education 2014 This content may not be s...

c i e n c e s Grade L i fe Study S G u i d e 12  © Department of Basic Education 2014 S c i e n c e s Grade Li fe Study Guid e 12 © Department of Basic Education 2014 This content may not be sold or used for commercial purposes. Curriculum and Assessment Policy Statement (CAPS) Mind the Gap Grade 12 Study Guide Life Sciences ISBN 978-1-4315-1947-7 This publication has a Creative Commons Attribution NonCommercial Sharealike license. You can use, modify, upload, download, and share content, but you must acknowledge the Department of Basic Education, the authors and contributors. If you make any changes to the content you must send the changes to the Department of Basic Education. This content may not be sold or used for commercial purposes. For more information about the terms of the license please see: http://creativecommons.org/licenses/by-nc-sa/3.0/. Copyright © Department of Basic Education 2014 222 Struben Street, Pretoria, South Africa Contact person: Dr Patricia Watson Email: [email protected] Tel: (012) 357 4502 http://www.education.gov.za Call Centre: 0800202933 The first edition published in 2012 Revised National Curriculum Statement (RNCS) Mind the Gap Grade 12 Study Guide Life Sciences: ISBN 978-0-621-40906-2 Second edition published in 2014 Curriculum and Assessment Policy Statement (CAPS) Mind the Gap Grade 12 Study Guide Life Sciences : ISBN 978-1-4315-1947-7 Mind the Gap team Series managing editor: Dr Patricia Watson Production co-ordinators for CAPS edition: Lisa Treffry-Goatley and Radha Pillay Authors: Alfie Bouwer, Sivalingam Chetty, Marlena Ford, Jean Goliath, Gayle Lombard, Nontobeko Mjali, Gonasagaren Pillay, Ronel Pretorius, Susan Wiese Expert readers: Esther Makhanywa, Kanthan Naidoo, Christina Nono Editors: Julia Grey, Herbert Opland Proofreader: Jenny de Wet Designers: Alicia Arntzen, Philisiwe Nkosi, Michele Dean, Nomalizo Ngwenya Study skills: Margarita Karnasopoulos Illustrators: Michele Dean, Kenneth Kunene, Vusi Malindi, Bié Venter Cover illustration: Alastair Findlay Onsite writers’workshop support: Wayne Cussons  © Department of Basic Education 2014 Ministerial foreword The Department of Basic Education has pleasure in releasing the second edition of Mind the Gap study guides for Grade 12 learners. These study guides continue the innovative and committed attempt by the Department of Basic Education to improve the academic performance of Grade 12 candidates in the National Senior Certificate (NSC) examination. The study guides have been written by subject expert teams comprised of teachers, examiners, moderators, subject advisors and subject co-ordinators. Research started in 2012 shows that the Mind the Gap series has, without doubt, had a positive impact in improving grades. It is my fervent wish that the Mind the Gap study guides take us all closer towards ensuring that no learner is left behind, especially as we move forward in our celebration of 20 years of democracy. Matsie Angelina Motshekga, MP The second edition of Mind the Gap is aligned to the 2014 Curriculum and Minister of Basic Education Assessment Policy Statement (CAPS). This means that the writers have considered the National Policy pertaining to the programme, promotion requirements and protocol for assessment of the National Curriculum Statement for Grade 12 in 2014. The Mind the Gap CAPS study guides take their brief in part from the 2013 National Diagnostic report on learner performance and draws on the 2014 Grade 12 Examination Guidelines. Each of the Mind the Gap study guides provides explanations of key terminology, simple explanations and examples of the types of questions that learners can expect to be asked in an exam. M a r k i n g m e m o r a n d a are included to assist learners in building their understanding. Learners are also referred to specific questions in past national exam papers and examination memos that are available on the Department’s website – www.education.gov.za. The CAPS edition include Accounting, Economics, Geography, Life Sciences, Mathematics, Mathematical Literacy and Physical Sciences. The series is produced in both English and Afrikaans. There are also nine English First Additional Language study guides. They include EFAL Paper 1 (Language); EFAL Paper 3 (Writing); and a study guide for each of the Grade 12 prescribed literature set works. The study guides have been designed to assist those learners who have been underperforming due to a lack of exposure to the content requirements of the curriculum and aims to mind-the-gap between failing and passing, by bridging the gap in learners’ understanding of commonly tested concepts so candidates can pass. All that is now required is for our Grade 12 learners to put in the hours preparing for the examinations. Learners make us proud – study hard. We wish each and every one of you good luck for your Grade 12 examinations. _________________________________ Matsie Angelina Motshekga, MP Minister of Basic Education May 2014 © Department of Basic Education 2014  © Department of Basic Education 2014 Table of contents Dear Grade 12 learner....................................................................................................... vii How to use this study guide.............................................................................................. viii Top 10 study tips.................................................................................................................. ix Study skills to boost your learning.......................................................................................x On the day of the exam …................................................................................................. xiii Question words to help you answer questions................................................................xiv Learner’s checklist...............................................................................................................xv Chapter 1: Nucleic acids.................................................................................... 1 1.1 The structure of DNA and RNA...............................................................................1 1.2 Differences between DNA and RNA.......................................................................2 1.3 DNA replication and its significance......................................................................3 1.4 DNA profiling............................................................................................................3 1.5 Protein synthesis.....................................................................................................5 Chapter 2: Meiosis............................................................................................. 9 2.1 What is meiosis?.....................................................................................................9 2.2 The process of meiosis in animal cells..................................................................9 2.2.1 First meiotic division.............................................................................. 10 2.2.2 Second meiotic division......................................................................... 11 2.3 The significance of meiosis................................................................................. 12 2.4 Abnormal meiosis................................................................................................. 12 2.5 Differences between meiosis I and meiosis II.................................................... 13 Chapter 3: Reproduction in vertebrates......................................................... 17 Chapter 4: Reproduction................................................................................. 19 4.1 Male reproductive system.................................................................................... 19 4.2 Female reproductive system............................................................................... 21 4.3 Puberty.................................................................................................................. 21 4.4 Menstrual cycle.................................................................................................... 22 4.5 Hormonal control of the menstrual cycle........................................................... 23 4.6 Development of the foetus.................................................................................. 25 Chapter 5: Genetics........................................................................................ 27 5.1 Key concepts........................................................................................................ 27 5.2 Genetic crosses.................................................................................................... 29 5.2.1 Complete dominance............................................................................. 30 5.2.2 Incomplete dominance.......................................................................... 31 5.2.3 Co-dominance........................................................................................ 31 5.2.4 Inheritance of sex.................................................................................. 32 5.2.5 Inheritance of sex-linked characteristics.............................................. 32 5.2.6 Dihybrid cross......................................................................................... 35 5.3 Mutations.............................................................................................................. 37 5.4 Pedigree diagrams............................................................................................... 38 5.5 Genetic engineering............................................................................................. 40 5.6 Genetic counselling.............................................................................................. 40 Chapter 6: Responding to the environment – humans................................. 41 6.1 The brain............................................................................................................... 41 6.1.1 Structure and functions of the brain.................................................... 41 6.2 Neurons................................................................................................................. 42 6.3 Reflex arc.............................................................................................................. 44 6.4 The human eye..................................................................................................... 46 6.4.1 Accommodation..................................................................................... 47 6.4.2 Pupillary mechanism............................................................................ 47 6.4.3 Visual defects......................................................................................... 48 6.5 The human ear..................................................................................................... 49 6.5.1 Structure of the ear................................................................................ 49 6.5.2 Hearing................................................................................................... 50 6.5.3 Balance................................................................................................... 51 6.5.4 Hearing defects...................................................................................... 51 © Department of Basic Education 2014 Mind the Gap CAPS Grade 12 Life Sciences contents v  © Department of Basic Education 2014 Chapter 7: Endocrine system.......................................................................... 53 7.1 The human endocrine system............................................................................. 53 7.2 Negative feedback............................................................................................... 54 7.2.1 General sequence of events in a negative feedback mechanism...... 54 7.2.2 Example of a negative feedback mechanism...................................... 54 Chapter 8: Homeostasis in humans................................................................ 56 8.1 Introduction.......................................................................................................... 56 8.2 Negative feedback mechanisms......................................................................... 56 8.2.1 The regulation of glucose levels in the internal environment............. 56 8.2.2 The regulation of carbon dioxide levels in the internal environment. 57 8.2.3 The regulation of water balance in the internal environment (osmo- regulation).............................................................................................. 58 8.2.4 The regulation of salt balance in the internal environment................ 59 8.3 The process of temperature regulation.............................................................. 60 Chapter 9: Responding to the environment - plants..................................... 62 9.1 Growth and development in plants..................................................................... 62 9.2 Role of auxins in phototropism and geotropism................................................ 63 9.3 Plant defence mechanisms................................................................................. 64 Chapter 10: Evolution....................................................................................... 65 10.1 Evidence for evolution.......................................................................................... 65 10.2 Sources of variation............................................................................................. 65 10.3 Theories of Lamarck and Darwin........................................................................ 66 10.4 Applying the theories of Lamarck and Darwin................................................... 67 10.5 Differences between natural selection and artificial selection......................... 69 10.6 Punctuated equilibrium........................................................................................ 69 10.7 Speciation............................................................................................................. 70 10.7.1 Speciation............................................................................................... 70 10.7.2 Mechanism for reproductive isolation.................................................. 70 10.8 Human evolution.................................................................................................. 72 10.8.1 Similarities between humans (Homo sapiens) and African apes 72 10.8.2 Differences between humans (Homo sapiens) and African apes...... 73 10.8.3 Major phases in hominid evolution....................................................... 76 10.8.4 Out of Africa hypothesis......................................................................... 78 10.8.5 Phylogenetic trees.................................................................................. 78 Chapter 11: Human impact on the environment........................................... 83 11.1 Atmosphere and climate change........................................................................ 83 11.2 Water quality and water availability.................................................................... 87 11.2.1 Availability of water................................................................................ 87 11.2.2 Quality of water...................................................................................... 89 11.3 Food security........................................................................................................ 93 11.4 Loss of biodiversity............................................................................................... 97 11.4.1 Factors that reduce our biodiversity..................................................... 97 11.4.2 Ways in which our biodiversity can be maintained.............................. 98 11.5 Solid waste disposal........................................................................................... 101 Chapter 12: Skills............................................................................................ 105 12.1 Drawing graphs................................................................................................... 105 12.1.1 How to draw a line graph..................................................................... 105 12.1.2 How to draw a bar graph..................................................................... 107 12.1.3 How to draw a histogram..................................................................... 108 12.1.4 How to draw a pie chart....................................................................... 109 12.2 Answering essay questions................................................................................ 110 12.3 Line drawings......................................................................................................113 Appendix 1: Blank drawings.......................................................................... 114 Appendix 2: Exemplar exam paper............................................................... 133 © Department of Basic Education 2014 vi conte nts  Mind the Gap CAPS Grade 12 Life Sciences   © Department of Basic Education 2014 We are Dear Grade 12 learner confident that this Mind the Gap study This Mind the Gap study guide helps you to prepare for the end-of-year guide can help you to prepare well so that you CAPS Life Sciences Grade 12 exam. pass the end-of-year The study guide does NOT cover the entire CAPS curriculum, but it does exams. focus on core content of each knowledge area and points out where you can earn easy marks. You must work your way through this study guide to improve your understanding, identify your areas of weakness and correct your own mistakes. To ensure a good pass, you should also cover the remaining sections of the curriculum using other textbooks and your class notes. Overview of the exam for CAPS Life Sciences Grade 12 The following topics make up each of the TWO Life Sciences exam papers that you write at the end of the year: PAPER 1 WEIGHTING PAPER 2 WEIGHTING Topic % MARKS Topic % MARKS Term 1 Term 1 Meiosis 7 11 DNA: Code of Life 19 27 Reproduction in Vertebrates 4 6 Meiosis 7 12 Human Reproduction 21 31 Term 2 Term 2 Genetics and Inheritance 30 45 Responding to the Environment Terms 3/4 (Humans) 27 40 Evolution 44 66 Term 3 Human Endocrine System 10 15 Homeostasis in Humans 7 11 Responding to the Environment 7 11 (Plants) Term 4 Human Impact (Grade 11) 17 25 100 150 100 150 Both Paper 1 and Paper 2 will include the following types of questions: Section Type of question Marks A Short answer, objective questions such as multiple-choice questions, terminology, 50 columns/statement and items B A variety of question types. There will be two questions of 40 marks each. Both of these questions will be divided 2 × 40 into two to four subsections. C Essay 20 © Department of Basic Education 2014 Mind the Gap CAPS Grade 12 Life Sciences introduction vii  © Department of Basic Education 2014 Look out for these icons in the How to use this study guide study guide. This study guide covers selected parts of the different topics of the CAPS Grade 12 Life Sciences curriculum in the order they are usually taught during the year. The selected parts of each topic arePAYpresentedSPECIAL ATTENTION in the following way: NB PAY SPECIAL ATTENTION NB NB NB An explanation of terms and concepts; Worked examples to explain and demonstrate; Activities NB with questions for you to answer; PAY SPECIAL ATTENTION HINT! NB and HINT! Answershint for you to use to check your hint own work. Hints to help you remember a concept NB PAY SPECIAL ATTENTION Pay special attention NBe.g. hint HINT! EG - worked examples or guide you in e.g. EG - worked examples Worked examples solving problems exams exams Activities with Step-by-step Refers you to exam HINT! e.g. EG - worked examples questions for you hint instructions questions to answer exams from the exam guidelines for Life Sciences has been A checklist e.g. EG - worked examples provided on page xvii for you to keep track of your activity progress. Once you activity have mastered the core concepts ACTIVITIES boy and have confidence in your answers ACTIVITIES boy and girl-left and exams to the questions provided, right tick the last column of the checklist. right of page and girl-left and of page The activities are based on exam-type questions. activity Cover the answers activity activity provided and do each activity on your own. Then check your answers. ACTIVITIES boy Reward yourself for the things you get right. If you get any incorrect and girl-left and right of page answers, make sure you understand where you went wrong before activity comment Step by step comment comment activity moving on to the next section. Step by step comment boy In Chapter 12, you will find a section on graphing skills which you ACTIVITIES and girl-left and right of page must master when preparing for both Paper 1 and Paper 2. This chapter also provides comment oncomment Step by step guidelines how to answer essay-type activity questions in the exam. You will be asked to draw a labelled diagram in the exam. On page 115 to 132 are a set of blank diagrams that you can use to practise comment Step by step comment your drawing and labelling skills. Filling in these blank diagrams is a good way to test yourself and work out what you know well and what Use this study guide as a workbook. you still need more practice in. Make notes, draw pictures Exemplar Exam papers are included in the study guide for you to and highlight important do. Check your answers by looking back at your notes and the exam concepts. memoranda. Past exam papers go a long way in preparing you for what to expect and help reduce exam anxiety. Go to www.education.gov.za to download past exam papers. © Department of Basic Education 2014 viii introduction  Mind the Gap CAPS Grade 12 Life Sciences  © Department of Basic Education 2014 Top 10 study tips Try these study tips to 1. Have all your materials ready before you begin studying – pencils, pens, highlighters, paper, etc. make learning easier. 2. Be positive. Make sure your brain holds on to the information you are learning by reminding yourself how important it is to remember the work and get the marks. 3. Take a walk outside. A change of scenery will stimulate your learning. You’ll be surprised at how much more you take in after being outside in the fresh air. 4. Break up your learning sections into manageable parts. Trying to learn too much at one time will only result in a tired, unfocused and anxious brain. 5. Keep your study sessions short but effective and reward yourself with short, constructive breaks. 6. Teach your concepts to anyone who will listen. It might feel strange at first, but it is definitely worth reading your revision notes aloud. 7. Your brain learns well with colours and pictures. Try to use them whenever you can. 8. Be confident with the learning areas you know well and focus your brain energy on the sections that you find more difficult to take in. 9. Repetition is the key to retaining information you have to learn. Keep going – don’t give up! 10. Sleeping at least 8 hours every night, eating properly and drinking plenty of water are all important things you need to do for your brain. Studying for exams is like strenuous exercise, so you must be physically prepared. If you can’t explain it simply, you don’t understand it well enough. Albert Einstein © Department of Basic Education 2014 Mind the Gap CAPS Grade 12 Life Sciences introduction ix © Department of Basic Education 2014 Study skills to boost your learning This guide includes 3 study techniques you can use to help you learn the material: 1. Mobile notes 2. Mnemonics 3. Mind maps Mobile notes These Mobile notes are excellent techniques will tools for learning all the key help you to study concepts in the study guide. smarter! Mobile notes are easy to make and you can take them with you wherever you go: 1. Fold a blank piece of paper in half. Fold it in half again. Fold it again. 2. Open the paper. It will now be divided into 8 parts. 3. Cut or tear neatly along 1. Fold an A4 paper into the folded lines. 8 squares. Cut or tear 4. On one side of each of neatly along the folded these 8 bits of paper, lines. write the basic concept. 5. On the other side, write the meaning or the Gene explanation of the basic concept. 6. Use different colours and add pictures to help you remember. 2. Write the basic concept 7. Take these mobile notes on one side of a bit of with you wherever you paper. go and look at them whenever you can. A small port 8. As you learn, place the DNA co dingion of cards in 3 different piles: particular for a characterist I know this ic information well. I’m getting there. I need more 3. Write the definition of practice. the basic concept on 9. The more you learn the back of the piece of them, the better you paper. will remember them. © Department of Basic Education 2014 x introduction  Mind the Gap CAPS Grade 12 Life Sciences  © Department of Basic Education 2014 Mnemonics A mnemonic code is a useful technique for learning information that is difficult to remember. Below are two examples of mnemonics. Here is a made-up word to help you remember the structure of a sperm cell – each letter of the word stands for a part of the cell: M – Mitochondria A – Acrosome N – Nucleus T – Tail Here is a sentence to help you remember the 4 nitrogenous bases in DNA – each word in the sentence begins with the same letter as one of the nitrogenous bases: There is another example of a mnemonic on page 12. All Teachers Get Chocolate Adenine Thymine Guanine Cytosine Mnemonics code information and make it easier to remember. The more creative you are and the more you link your ‘codes’ to familiar things, the more helpful your mnemonics will be. This guide provides ideas for using mnemonics. Be sure to make up your own. Education helps one cease being intimidated by strange situations. Maya Angelou © Department of Basic Education 2014 Mind the Gap CAPS Grade 12 Life Sciences introduction xi  © Department of Basic Education 2014 Mind maps There are several mind maps included in this guide, summarising some of the sections. Have a look at the following pictures of a brain cell (neuron) and, below it, a mind map: Figure 1: Brain cell or neuron Figure 2: Mind map rules Mind maps work because they show information that we have to learn in the same way that our brains ‘see’ information. As you study the mind maps in the guide, add pictures to each of the branches to help you remember the content. You can make your own mind maps as you finish each section. How to make your own mind maps: Mind 1. Turn your paper sideways so your brain has space to spread out in all mapping your notes makes directions. them more interesting 2. Decide on a name for your mind map that summarises the and easier to information you are going to put on it. remember. 3. Write the name in the middle and draw a circle, bubble or picture around it. 4. Write only key words on your branches, not whole sentences. Keep it short and simple. 5. Each branch should show a different idea. Use a different colour for each idea. Connect the information that belongs together. This will help build your understanding of the learning areas. 6. Have fun adding pictures wherever you can. It does not matter if you can’t draw well. © Department of Basic Education 2014 xii introduction  Mind the Gap CAPS Grade 12 Life Sciences  © Department of Basic Education 2014 On the day of the exam … 1. Make sure you have all the necessary stationery for your exam, i.e. pens, pencils, eraser, protractor, compass, calculator (with new batteries). Make sure you bring your ID document and examination admission letter. 2. Arrive on time, at least one hour before the start of the exam. 3. Go to the toilet before entering the exam room. You don’t want to waste valuable time going to the toilet during the exam. 4. Use the 10 minutes reading time to read the instructions carefully. This helps to ‘open’ the information in your brain. Start with the question you think is the easiest to get the flow going. 5. Break the questions down to make sure you understand what is being asked. If you don’t answer the question properly you won’t get any marks for it. Look for the key words in the question to know how to answer it. A list of these words is on page xiv of this study guide. 6. Try all the questions. Each question has some easy marks in it so make sure that you do all the questions in the exam. 7. Never panic, even if the question seems difficult at first. It will be linked with something you have covered. Find the connection. 8. Manage your time properly. Don’t waste time on questions you are unsure of. Move on and come back if time allows. You have GOOD LUCK! 150 minutes (2½ hours) to answer each of the 150-mark Life Sciences question papers. Spend the following amounts of time on each question: Question 1: 50 marks = 45 minutes Question 2: 40 marks = 35 minutes Question 3: 40 marks = 35 minutes Question 4: 20 marks = 15 minutes The remaining 20 minutes can be used to check your answers and attempt to answer any question that you might have left out. 9. Check weighting – how many marks have been allocated for your answer? Take note of the ticks in this study guide as examples of marks allocated. Do not give more or less information than is required. 10. Write big and bold and clearly. You will get more marks if the marker can read your answer clearly. © Department of Basic Education 2014 Mind the Gap CAPS Grade 12 Life Sciences introduction xiii  © Department of Basic Education 2014 Question words to help you answer questions It is important to look for the question words (the words that tell you what to do) to correctly understand what the examiner is asking. Use the words in the table below as a guide when answering questions. Question word What is required of you Analyse Separate, examine and interpret Calculate This means a numerical answer is required – in general, you should show your working, especially where two or more steps are involved Classify Group things based on common characteristics Compare Point out or show both similarities and differences between things, concepts or phenomena Define Give a clear meaning Describe State in words (using diagrams where appropriate) the main points of a structure/process/phenomenon/investigation Determine To calculate something, or to discover the answer by examining evidence Differentiate Use differences to qualify categories Discuss Consider all information and reach a conclusion Explain Make clear; interpret and spell out Identify Name the essential characteristics PAY SPECIAL ATTENTION LabelNB Identify on a diagram or drawing NB List Write a list of items, with no additional detail Mention Refer to relevant points Name Give the name (proper noun) of something State Write HINT! down information without discussion hint Suggest Offer an explanation or a solution Tabulate Draw a table and indicate the answers as direct pairs e.g. Examples of question words EG - worked examples In every exam Questions exams question, put a CIRCLE 1. Figure 6.12 shows a longitudinal section through the human eye. around the question word and Study the diagram and answer the questions that follow. underline any other important key words. These words tell a) Label parts 2, 3, 4 and 5 respectively. (4) you exactly what is b) Name and describe the process that causes part 1 to dilate being asked. (become wider). (5) 2. Figure 6.13 is a longitudinal section through the human eye. The activity structures which enable the eye to focus on objects are missing in this diagram. Study the diagram ACTIVITIES and boy answer the questions that follow. and girl-left and right of page Draw a longitudinal section through the missing parts of Figure 6.13 toactivity indicate the appearance of these structures when you are... a) reading a book.  (6) b) looking at an object more than 6 metres away. (6) Step by step comment comment © Department of Basic Education 2014 xiv introduction  Mind the Gap CAPS Grade 12 Life Sciences  © Department of Basic Education 2014 Learner’s checklist Use this checklist to monitor your progress when preparing for the examination. The ticks (3) tell you which aspects of the curriculum are covered in this study guide. The stars (*) tell you to go to textbooks and class notes. study guide understand understand Covered in I do not TOPIC ASPECT I DNA: The code of life Discovery of DNA structure * Nucleic acids terminology 3 Structure of DNA and RNA 3 Differences between DNA and RNA 3 DNA replication and the importance thereof 3 DNA profiling 3 Protein synthesis 3 Meiosis The process of meiosis using diagrams 3 Significance of meiosis 3 Abnormal meiosis 3 Differences between meiosis I and meiosis II 3 Reproduction in Diversity in reproductive strategies 3 vertebrates Human reproduction Male reproductive system 3 Female reproductive system 3 Puberty 3 Menstrual cycle 3 Development of the foetus 3 Gestation 3 Role of placenta 3 Genetics and Genetic terminology 3 inheritance Complete dominance 3 Incomplete dominance 3 Co-dominance 3 Inheritance of sex 3 Sex-linked characteristics 3 Dihybrid crossing 3 Mutations 3 Pedigree diagrams 3 Genetic engineering 3 Genetic counselling 3 Paternity testing and DNA fingerprinting 3 Responding to the The brain 3 environment: Humans Neurons, reflex actions and reflex arcs 3 Peripheral nervous system * Autonomic nervous system * Brain disorders and injuries * Effects of drugs on the central nervous system * Structure and functions of parts of the eye 3 © Department of Basic Education 2014 Mind the Gap CAPS Grade 12 Life Sciences introduction xv © Department of Basic Education 2014 Responding to the Accommodation 3 environment: Humans Pupillary mechanism 3 Visual defects 3 Structure and functions of parts of the ear 3 Hearing 3 Balance 3 Hearing defects 3 Human endocrine Glands and the hormones they secrete 3 system Negative feedback – glucose 3 Negative feedback – thyroxin 3 Homeostasis in humans Negative feedback – glucose 3 Negative feedback – carbon dioxide 3 Negative feedback – water 3 Negative feedback – salts 3 The role of the skin on hot and cold days 3 Responding to the Functions of auxins, gibberillins and abscisic acid 3 environment: Plants Role of auxins in phototropism and geotropism 3 Plant defence mechanisms is included 3 Evolution Evidence for evolution 3 Sources of variation 3 Lamarck and Darwin’s theories 3 Natural and artificial selection 3 Punctuated equilibrium 3 Speciation 3 Mechanisms for reproductive isolation 3 Evolution in present times 3 Human evolution: similarities to African apes 3 Human evolution: differences from African apes 3 Major phases in hominid evolution 3 Out of Africa hypothesis 3 Phylogenetic trees 3 Human impact on the Atmosphere and climate change 3 environment Water availability 3 Water quality 3 Food security 3 Loss of biodiversity 3 Waste disposal 3 Skills Draw a line graph 3 Draw a bar graph 3 Draw a histogram 3 Draw a pie chart 3 Answering essay questions 3 © Department of Basic Education 2014 xvi introduction  Mind the Gap CAPS Grade 12 Life Sciences  Chapter 1 Paper 2 Nucleic acids 1.1 The structure of DNA and RNA Two kinds of nucleic acids are found in a cell, namely DNA and RNA. These two nucleic acids are made of building blocks (or monomers) called nucleotides. P Figure 1.1 (right) shows what a nucleotide looks like. N S Table 1.1 (below) shows the nitrogenous bases of DNA and RNA. DNA has four different nitrogenous RNA has four different nitrogenous P – Phosphate group bases – adenine, thymine, guanine bases – adenine, uracil, guanine and S – Deoxyribose or ribose and cytosine. cytosine. sugar N – Nitrogenous base A Adenine A Adenine (adenine, thymine, guanine, cytosine or Uracil uracil) T Thymine U Figure 1.1 A nucleotide Adenine always pairs with thymine. RNA contains uracil instead of thymine. G Guanine G Guanine C Cytosine C Cytosine Guanine always pairs with cytosine. Table 1.1 Nitrogenous bases of DNA and RNA Figure 1.2 below shows the structure of DNA and RNA. Study the diagrams COMPARE & CONTRAST Nucleic acids DNA RNA ALIKE/SIMILAR Nitrogenous bases present: Adenine, cytosine, guanine DIFFERENT Nitrogenous base Nitrogenous base present: Thymine present: Uracil Contains sugar: Contains sugar: Deoxyribose Ribose Double-stranded Single-stranded molecule molecule © Department of Basic Education 2014 Mind the Gap CAPS Grade 12 Life Sciences chapter 1 Nucle ic acids (paper 2) 1 1 Chapter in Figure 1.2, and then read the information in the boxes below the diagrams to find out how to tell a DNA molecule from an RNA molecule. DNA (deoxyribonucleic acid) RNA (ribonucleic acid) Phosphate group Phosphate group A T A Nitrogenous base G C Deoxyribose G Ribose A Nitrogenous base G Weak hydrogen bonds U How to recognise a DNA molecule How to recognise an RNA molecule Double-stranded molecule Single-stranded molecule Contains the nitrogenous base Contains the nitrogenous base thymine (T) instead of uracil (U) uracil (U) instead of thymine (T) A always joins with T G always joins with C Figure 1.2 The structure of DNA and RNA 1.2 Differences between DNA and RNA Table 1.2 below summarises the differences between DNA and RNA molecules. DNA RNA 1. Double-stranded molecule 1. Single-stranded molecule 2. Contains deoxyribose (sugar) 2. Contains ribose (sugar) 3. Contains the nitrogenous base, 3. Contains the nitrogenous base, thymine uracil Table 1.2 The differences between DNA and RNA © Department of Basic Education 2014 2 chapter 1 Nucle ic acids (pape r 2)  Mind the Gap CAPS Grade 12 Life Sciences  Chapter 1 1.3 DNA replication DNA replication takes place at interphase before mitosis or meiosis begins. DNA replication is the process during which a DNA molecule makes an exact copy (replica) of itself. This is shown in Figure 1.3 below. 1 The double helix CG unwinds. A–T AT 2 Weak hydrogen bonds between G-C 1. Unwinds nitrogenous bases break and two G–C DNA strands unzip (separate). T–A G–C 3 Each original DNA G– –C 2. Unzips strand serves as a T– –A template on which its G– Template complement is built. T– –C 3. Template A– A –A 4 Free nucleotides T A T – build a DNA strand C–G C–G onto each of T–A T–A the original two A–T A–T DNA strands by attaching to their A–T T–A A–T T–A 4. Complementary strand forms complementary nitrogenous bases A–T A–T (A to T and C to G). T-A T-A 5 This results in C–G C–G two identical DNA G-C G-C molecules. Each molecule consists of one original strand and one new strand. 5. Two identical DNA molecules Figure 1.3 DNA replication Significance of DNA replication DNA replication is important because it: Doubles the genetic material so it can be shared between the resulting daughter cells during cell division. Results in the formation of identical daughter cells during mitosis. 1.4 DNA profiling Every person except identical twins has her/his own unique DNA profile. It can be described as an arrangement of black bars representing DNA fragments of the person. It is used to: Identify criminals Identify dead bodies Identify relatives Identify paternity © Department of Basic Education 2014 Mind the Gap CAPS Grade 12 Life Sciences chapter 1 Nucle ic acids (paper 2) 3 1 Chapter 1 4 2 Activity 1 3 1. A DNA molecule contains 600 nitrogen bases. If 20% of this is adenine, determine the number of each nitrogen base in the DNA molecule. (3) 5 C 2. Figure 1.4 (left) represents part of a nucleic acid molecule. Study the diagram and answer the questions that follow. 6 A 2.1 Identify the nucleic acid shown in Figure 1.4. (1) 2.2 Label the following: KEY a) Part 1 (1) A – Adenine b) Part 2 (1) C – Cytosine c) The nitrogenous bases 4, 5 and 6 (3) Figure 1.4 Part of a nucleic 2.3 What is the collective name for the parts numbered 1, 2 and 3?(1) acid molecule 3. Questions 3.1 and 3.2 are based on Figure 1.5 (left). This is a diagrammatic representation of a part of two different nucleic acid molecules found in the cells of organisms during a stage in the A process of protein synthesis. 3.1 Name the molecules 1 and 2. (2) 3.2 Give a reason for your answer in question 3.1. (2) G 4. The result of profiling various DNA samples in a criminal investigation is shown below U 1 2 3 4 5 Key: 1. blood sample of victim 2. blood sample of suspect X 3. blood sample of suspect Y C 4. first sample of DNA from the crime scene 5. second sample of DNA from crime scene T 4.1 Was suspect X or suspect Y involved in the crime? (1) Molecule 1 Molecule 2 4.2 Does the DNA of the suspect (from answer 4.1) match the Figure 1.5 Two nucleic acid first or second sample? (2) molecules Answers to activity 1 1. 20% adenine = 20% thymine3 30% cytosine3 = 30% guanine3 20 × 600 = 120A = 120T 30 × 600 = 180C = 180G (3) 100 100 2.1 DNA3 (1) 2.2 a) Phosphate3 group (1) b) Deoxyribose3 sugar (1) c) 4 – adenine (A)3 5 – guanine (G)3 6 – thymine3 (3) 2.3 Nucleotide3 (1) 3.1 1 – DNA 2 – mRNA/RNA3 (2) 3.2 DNA contains the nitrogenous base thymine (T).3 RNA contains the nitrogenous base uracil (U).3 (2) 4.1 Suspect X was involved. 3 (1) 4.2 The DNA of suspect X matches with the second sample. 33 (2) © Department of Basic Education 2014 4 chapter 1 Nucle ic acids (pape r 2)  Mind the Gap CAPS Grade 12 Life Sciences  Chapter 1 1.5 Protein synthesis Protein synthesis is the process by which proteins are made in each cell PAY SPECIAL ATTENTION of an organism to form enzymes, hormones and new structures for cells. NB In the nucleus Remember this order: 1. DNA Order DNA Example AGT HINT! 2. mRNAhint UCA (codon) tRNA AGU A. TRANSCRIPTION e.g. EG - worked examples U C A G G C A C A exams In the cytoplasm 3. mRNA Codon (triplet) Codon Ribosome 4. activity B. TRANSLATION Anticodon U C A G G C A C A ACTIVITIE A G U and girl-le right of pa 5. tRNA activity Step by step comm 6. Protein Figure 1.6 The process of protein synthesis There are two main processes involved in protein synthesis, namely transcription and translation. They are labelled as A and B in Figure 1.6 mRNA above. (messenger RNA) – carries the Note that the numbers on the diagram correspond with the description below. message. A Transcription (takes place in the nucleus) 1. DNA unwinds and splits. 2. One DNA strand acts as a template for forming mRNA. 3. Free nucleotides arrange to form mRNA according to the DNA template. This process is called transcription. 4. The mRNA leaves the nucleus through the nuclear pores. Stage B now takes place when mRNA in the cytoplasm attaches to the ribosome. © Department of Basic Education 2014 Mind the Gap CAPS Grade 12 Life Sciences chapter 1 Nucle ic acids (paper 2) 5 1 Chapter B Translation (takes place in the cytoplasm on the ribosome) tRNA (transfer RNA) 5. Each tRNA brings a specific amino acid to the mRNA. – transports the This is called translation. amino acids 6. The amino acids are linked together to form a particular protein. The diagram shown in Figure 1.6 (on page 5) may appear in exam questions in different ways. Do not let the different representations confuse you. Just try to identify the following components by looking for the features listed here: DNA – double-stranded; look for presence of thymine; found in nucleus only. Nuclear membrane – has nuclear pores through which mRNA moves. mRNA – single-stranded; look for presence of uracil; contains a triplet of bases (codon) found in nucleus and cytoplasm. Ribosome – usually mRNA attached to it. tRNA – contains a triplet of bases (anticodon); look for attached amino acid. Activity 2 Question 1 Study Figure 1.7 (below), which shows the process of protein synthesis, and answer the questions. D A F G G U U U G B UG U U CG C A G C For two more problems on G G protein synthesis refer to E G U these National Life Sciences CYS ALA exam papers: Life Sciences Paper 1 Amino acids March 2009 – Question 2.2 on page 9. Figure 1.7 Protein synthesis Life Sciences Paper 1 1.1 Label structures A, B and D.  (3) November 2010 – Question 1.2 State ONE function of molecule D.  (1) 1.5 on page 7. © Department of Basic Education 2014 6 chapter 1 Nucle ic acids (pape r 2)  Mind the Gap CAPS Grade 12 Life Sciences  Chapter 1 1.3 Which stage of protein synthesis takes place at F? (1) 1.4 Identify organelle C.  (1) 1.5 Name and describe the stage of protein synthesis that takes place at organelle C. (7) 1.6 Write down the codon of anticodon E from top to bottom.  (1) 1.7 Name the type of bond (labelled G) between the amino acids. (1) Answers to question 1 1.1 A – Nuclear membrane3 B – mRNA3 D – DNA3 (3) 1.2 Carrying hereditary characteristics from parents to their offspring 3 OR Controls the synthesis (manufacturing) of proteins3 (1) 1.3 Transcription3 (1) 1.4 Ribosome3 (1) 1.5 Translation3 The mRNA strand from the nucleus becomes attached3 to a ribosome with its codons exposed each tRNA molecule carrying a specific amino acid3 according to its anticodon3 matches up with/complements the codon of the mRNA3 You don’t so that the amino acids are placed in the correct sequence3 have to know the adjacent amino acids are linked3 names of the amino acids related to the to form a protein3 (7) base triplets. 1.6 CAC3 (the anticodon is GUG, so the complementary codon is CAC) (1) 1.7 Peptide Bond (1) Question 2 Table 1.3 below shows the DNA base triplets that code for different amino acids. Amino acid Base triplet in DNA template Leu (leucine) GAA His (histidine) GTA Lys (lysine) TTT Pro (proline) GGG Ala (alanine) CGA Trp (tryptophan) ACC Phe (phenylalanine) AAA Gly (glycine) CCT Table 1.3 Different amino acids and their DNA base triplets © Department of Basic Education 2014 Mind the Gap CAPS Grade 12 Life Sciences chapter 1 Nucle ic acids (paper 2) 7  1 Chapter The following is a part of a sequence of amino acids that forms a particular AL ATTENTION protein molecule: NB Ala His Trp Leu Lys Remember this order: Order Example 2.1 Name the process by which mRNA is formed from a DNA DNA CGA template. (1) mRNA (codon) GCU 2.2 How many mRNA codons would be involved in forming the portion tRNA CGA of protein shown above? (1) 2.3 Write down the sequence of the first three mRNA codons ed examples (from left to right) for this portion of the protein. (3) Answers to question 2 2.1 Transcription3 (1) 2.2 53 (1) 2.3 GCU3– CAU3– UGG3  (3) ACTIVITIES boy and girl-left and right of page p comment comment Keep going! © Department of Basic Education 2014 8 chapter 1 Nucle ic acids (pape r 2)  Mind the Gap CAPS Grade 12 Life Sciences  Chapter 2 Pa per 1 and 2 Meiosis 2.1 What is meiosis? Meiosis is a type of cell division whereby a diploid cell (somatic cell) undergoes two cell divisions, and divides to form four dissimilar haploid Chromosome cells (sex cells). Diploid cells have two sets of chromosomes, where each chromosome has a homologous partner. Haploid cells only have one set Chromatid of chromosomes. Chromosomes in haploid cells have no homologous Centromere partners. Before meiosis begins (during interphase), DNA replication takes place. The result is two sets of chromosomes consisting of two identical chromatids Homologous joined together with a centromere. This is shown in Figure 2.1 (right). chromosomes – one from the mother and one 2.2 The process of meiosis from the father Figure 2.1 Homologous in animal cells chromosomes Meiosis is the type of cell division used to Meiosis produce gametes or sex cells (sperm and egg cells). A cell undergoing meiosis will divide twice – the first division is meiosis I and the second is meiosis II. DNA replication and recombination In the first meiotic division, the number of cells is doubled, but the number of chromosomes is Meiosis I not. This results in half as many chromosomes per cell. In the second meiotic division, the number of chromosomes does not get reduced. The diagram alongside shows how meiosis Meiosis II starts with a diploid cell and divides twice (meiosis I and II), resulting in four haploid cells. Now turn the page to find out what happens during each stage of meiosis I and II. © Department of Basic Education 2014 Mind the Gap CAPS Grade 12 Life Sciences chapter 2 meiosis (paper 1 an d 2) 9 2 Chapter 2.2.1 First meiotic division Prophase 1 Chromosomes shorten and become visible as two Spindle fibres chromatids joined by a centromere. Homologous pairs of chromosomes are now visible. The nuclear membrane and nucleolus disappear. The spindle starts to form. Chromatids from each homologous pair touch. Homologous chromosomes The point where they touch is called a chiasma. DNA is crossed over (swopped) at the chiasma. The spindle continues to form. Figure 2.2 Prophase 1 Metaphase 1 The spindle extends across the whole cell. The homologous chromosomes line up along the equator of the spindle in their homologous pairs. One chromosome of each pair lies on either side of the equator. The centromere of each chromosome attaches to the spindle fibres. Figure 2.3 Metaphase 1 Anaphase 1 The spindle fibres shorten and pull each chromosome of each chromosome pair to opposite poles of the cell. Figure 2.4 Anaphase 1 Telophase 1 The chromosomes reach the poles of the cell. Each pole has half the number of chromosomes Constriction present in the original cell. The cell membrane constricts and divides the cytoplasm in half to form two cells. Figure 2.5 Telophase 1 © Department of Basic Education 2014 10 chapte r 2 meio sis (paper 1 and 2)  Mind the Gap CAPS Grade 12 Life Sciences  Chapter 2 2.2.2 Second meiotic division Prophase 2 Each cell formed during meiosis I now divides again. A spindle forms in each of the new cells. Figure 2.6 Prophase 2 Metaphase 2 Individual chromosomes line up at the equator of each cell, with the centromeres attached to the spindle fibres. Figure 2.7 Metaphase 2 Anaphase 2 The spindle fibres start to contract. The centromeres split and daughter chromosomes/ chromatids are pulled to the opposite poles of each cell. Figure 2.8 Anaphase 2 Telophase 2 The daughter chromosomes/chromatids reach the poles and a new nucleus forms. The cell membrane of each cell constricts and the cytoplasm divides into two cells. Four haploid daughter cells are formed. Each daughter cell has half the number of nucleus chromosomes of the original cell. The daughter cells are genetically different from each other. Figure 2.9 Telophase 2 © Department of Basic Education 2014 Mind the Gap CAPS Grade 12 Life Sciences chapter 2 meiosis (paper 1 an d 2) 11 2 Chapter An easy way to remember the events of meiosis is to use the word mnemonic IPMAT.