Life Sciences Grade 12 Textbook PDF

LIFE SCIENCES Grade 12 Textbook  Contributors Dr Arnold Johannes, Mr Peter Weisswange (editors), Ms Angie Weisswange (illustrator), Ms Tiffany Bell, Ms Margaret Elferink, Mr Jason Field, Ms Michelle Tracy Hagemann, Ms Kathryn Lamarque, Ms Jessica M...

LIFE SCIENCES Grade 12 Textbook  Contributors Dr Arnold Johannes, Mr Peter Weisswange (editors), Ms Angie Weisswange (illustrator), Ms Tiffany Bell, Ms Margaret Elferink, Mr Jason Field, Ms Michelle Tracy Hagemann, Ms Kathryn Lamarque, Ms Jessica Marais, Ms Alydia Monteith, Ms Danielle Stander, Mr Peter Weisswange (all authors), Ms Helena Oosthuizen, Ms Delia Stander, Ms Kerstin Stoltsz.. Quality Assurance by Life Sciences Subject Advisors, under the direction of Mr Kanthan Naidoo (CES): Ms Phumzile Dlamini (EC), Mr Gonasagaren Pillay (KZN), Ms Zimasa Sanda (EC), Ms Jennifer Titus (NC) Produced for the National Department of Basic Education © DBE TABLE OF CONTENTS Introducing Life Sciences 1 Strand: Life at molecular, cellular and tissue level 1. DNA: The Code of Life 6 2. Meiosis 33 Strand: Life processes in plants and animals 3. Reproductive Strategies in Vertebrates 61 4. Human Reproduction 70 Strand: Diversity, change and continuity 5. Genetics and Inheritance 102 Strand: Life processes in plants and animals 6. Human Responses to the Environment 151 7. The Human Endocrine System and Homeostasis 198 8. Plant Responses to the Environment 236 Strand: Diversity, change and continuity 9. Evolution by Natural Selection 258 10. Human Evolution 289 Appendices A Final Word: Assessments 332 Answers to Activities 335 Image Attribution 366 INTRODUCING LIFE SCIENCES The aim of this textbook is to allow you, the learner, to be an active partner in your learning experience. The text has been designed to cover all the content you need for Grade 12, and to provide it in a readable manner that communicates all concepts simply, clearly and in the necessary amount of detail. The next few pages will provide you with a broad overview of Life Sciences and hopefully show you its value as a choice for a school subject. Studying Life Sciences also offers you broader benefits: it will encourage your ability to think critically, to solve problems and seek to understand the world around you. What are the Life Sciences? The term ‘Life Sciences’ indicates clearly the two ideas held together in this subject:  Life refers to all living things – from the most basic of molecules through to the interactions of organisms with one another and their environments.  Science indicates it is necessary to use certain methods in our study of the subject. The two broad aims of any science are to increase existing knowledge and discover new things. We approach this using careful methods that can be copied by others. These include:  proposing hypotheses (the predicted outcome of an investigation) and  carrying out investigations and experiments to test these hypotheses. Scientific knowledge changes over time as more is discovered and understood about our world; as such, Life Sciences is a constantly growing subject. Why choose Life Sciences as a subject?  First, to give you knowledge and skills that are helpful in everyday life, even if you do not pursue Life Sciences after school.  Secondly, to expose you to the wide variety of sub-fields within the subject that could encourage or interest you to pursue a career in the sciences. If you choose to study Life Sciences at school you will be able to study any Life Science specialisations after school - such as microbiology, genetics, environmental studies or biotechnology. 1 What skills will Life Sciences equip you with? This subject will teach you important biological concepts, processes, systems and theories, and provide you with the skills to think, read and write about them. Life Sciences will:  give you the ability to evaluate and discuss scientific issues and processes  provide an awareness of the ways biotechnology and a knowledge of Life Sciences have benefited humankind  show you the ways in which humans have impacted negatively on the environment and organisms within it, and show you how to be a responsible citizen in terms of the environment and conservation  build an appreciation of the unique contribution of South Africa to Life Sciences - both the diversity of the unique biomes within Southern Africa and the contributions of South Africans to the scientific landscape. Life Sciences Strands for Grade 12 Everything you study this year will fit into one of these three broad strands. These knowledge pathways grow over your three years of FET. Within each knowledge strand, ideas should not be studied separately; rather seek to discover the links between related topics so that you grow in your understanding of the inter-connectedness of life. As you study each section or chapter, look for the broad strokes that place it under one of these strands:  Knowledge Strand 1: Life at a Molecular, Cellular and Tissue Level  Knowledge Strand 2: Life Processes in Plants and Animals  Knowledge Strand 3: Diversity, Change and Continuity The Purpose of studying Life Sciences There are three broad purposes, which will expand as we continue:  Aim 1 - knowing the content (theory);  Aim 2 - doing practical work and investigations;  Aim 3 - understanding the applications of Life Sciences in society - both present society (indigenous and western) and within the context of history. Aim 1: Knowing the content of Life Sciences Learning content involves understanding and making meaning of scientific ideas, and then connecting these ideas. Theory is not just recalling facts; it is being able to select important ideas, use different sources to learn, and describe concepts, 2 processes and theories important to Life Sciences. Within this you will learn to write summaries, develop your own diagrams and reorganise data you are given into something meaningful. Additionally, you will learn to interpret the data you are working with and link it to theory you have studied. Aim 2: Doing practical work and investigations Life Science is a fascinating subject and one of the best ways to understand it is for you to see it in action. Therefore, it is important for you to know how to do practical investigations. Within this, you will learn many useful skills like how to follow instructions in a safe manner and how to name, recognise and handle laboratory equipment. During a practical investigation it is important for you to be able to make observations. There are many ways this can be done - by making drawings, describing what you see, taking measurements, and comparing materials before and after a certain treatment. After making these observations it is important for you to be able to measure and record them in a useful way. From here you will interpret your data - you will look for the value in what you gathered and discuss the changes, trends, and applications of what you have shown. Finally, you will learn how to design your own investigations and experiments. An investigation is more straightforward; for example, it could involve observing soil profiles or counting animal populations. Planning an experiment would begin with identifying a problem, and then hypothesising a solution. In planning, you would identify variables and consider ways to control them, select apparatus and materials to assist you, and then plan an experiment that could be repeated by someone else. It is also important to consider ways of capturing and interpreting your data. Aim 3: Understanding the history, importance and modern applications of Life sciences The third aim of Life Sciences is to show you that school science can be relevant to your life and that studying provides enrichment to you, even if you do not pursue it past school level. As you study you will be exposed to the history of science and indigenous knowledge systems from other times and other cultures. As you learn a certain section of work, you will be introduced to how that knowledge was developed by various scientists across the ages as they pursued a deeper understanding of the world around them. Our search of knowledge is shaped by our world view. Therefore, an important concept to be aware of is that modern science (and technology) and traditional, indigenous knowledge systems will sometimes differ in their approach to science. 3 These seemingly opposite views can be held together as both bring a certain dynamic; they should not be seen as opposing forces. Finally, there are many possible career fields branching out of Life Sciences and, as you learn, some of these will be shown through examples. Different sections would open up different careers choices- in the past (for example palaeontology), the present (like horticulture, game ranch management and preservation) and the future (such as biotechnology and genetic engineering). A final word on using this textbook The best way to use this textbook to increase your understanding and thereby results would be as follows:  Remember, good learning begins in the classroom so always pay careful attention as your teacher works through it with you  Take note of sections you do not understand and revisit them  Ask questions to make sure you understand  Consider the end-of-chapter summaries and build on them to create your own point-form summary note  Practice re-sketching the given diagrams  Work through all the given questions and answers at the end of the chapter 4  Strand life at molecular, cellular and tissue level 5  1: DNA – the code of life Introduction Activity 2: DNA Revision of cellular structure replication The structure of nucleic acids DNA profiling DNA – deoxyribonucleic acid Activity 3: DNA profiling A brief history of the discovery of Protein synthesis DNA Protein synthesis occurs in two The location of DNA stages The structure of DNA Stage 1: Transcription The role of DNA Stage 2: Translation Activity 1: DNA The effect of mutation on protein structure (DNA sequence) RNA – ribonucleic acid Activity 4: Protein The location of RNA synthesis The structure of RNA Activity 5: Codons and amino acids The role of RNA Comparison between DNA and RNA DNA replication End of topic exercises Errors that occur during DNA replication 6 CHAPTER 1: DNA – THE CODE OF LIFE Introduction  All living organisms contain both DNA (deoxyribonucleic acid) and RNA (ribonucleic acid) – we focus on their location, structure and function.  We explore the discovery of DNA, its role in the human body and how it replicates.  Protein synthesis is vital for life – we examine how proteins are formed by both DNA and RNA. Revision of cellular structure It is important to know the location and functions of certain organelles, illustrated in Figure 1 below. cytoplasm polysomes ribosomes nucleus Figure 1: Structure of a cell Cytoplasm is the base substance in which the organelles of the cell are suspended. It is a watery substance and allows for metabolic reactions to take place. Ribosomes are small, round organelles which are mainly found attached to the endoplasmic reticulum or are free-floating in the cytoplasm. Ribosomes can also be found inside other organelles such as the chloroplast and mitochondria but in smaller numbers. They are the site of protein synthesis and consist of RNA and protein. 7 The nucleus controls all of the cell’s activities. nuclear membrane nucleoplasm nucleolus nuclear pore Figure 2: Parts of the nucleus A nucleus has four main parts:  the double nuclear membrane – it encloses the nucleus and contains small pores to allow for the passage of substances in and out of the nucleus  the nucleoplasm – this is a jelly-like fluid within the nucleus  the nucleolus – a dark body suspended in the nucleoplasm which contains free nucleotide bases and produces ribosomes  the chromatin network – found in the nucleoplasm: contains the DNA which forms the chromosomes containing the genetic code of a person / organism The structure of nucleic acids Key terminology nucleic acid a type of organic compound monomer a building block nucleotide the monomer which forms DNA and RNA There are two types of nucleic acids in the human body – DNA (deoxyribonucleic acid) and RNA (ribonucleic acid). Together these form the basis of all life of earth. They consist of monomers (building blocks) called nucleotides. 8 The basic structure of a nucleotide is illustrated in Figure 3 below. Each nucleic acid is composed of a phosphate (P), a sugar molecule (S) and a nitrogenous base (NB). P – phosphate group S – sugar molecule NB – nitrogenous base Figure 3: A nucleotide DNA – deoxyribonucleic acid Key terminology  deoxyribonucleic acid is made up of nucleotides  nitrogenous bases adenine, thymine, guanine and DNA cytosine  carries the genetic code for protein synthesis nuclear DNA DNA found in the nucleus DNA found outside of the nucleus: mitochondrial and extra- nuclear DNA chloroplastic DNA. the shape of DNA consists of two strands joined together double helix and twisted spirally hereditary genetic information passed on from parent to offspring A brief history of the discovery of DNA  1952 – Rosalind Franklin and her assistant Maurice Wilkins researched the structure of DNA using X-ray diffraction images.  Watson and Crick did independent research on DNA. Upon seeing Franklin’s images, they proposed a 3-D double helix model for DNA in 1953.  1962 – Watson and Crick received the Nobel Prize for the discovery of the structure of DNA, and Wilkins received an award for his X-ray photography. Franklin had died of cancer. Rosalind Franklin – background: https://www.youtube.com/watch?v=BIP0lYrdirI 9 The location of DNA DNA is found in two locations in a cell:  Mostly in the nucleus of a cell – this is referred to as nuclear DNA  a small amount is found outside the nucleus – it is referred to as extra- nuclear DNA. There are two types of extra-nuclear DNA: o chloroplastic DNA – found in the chloroplasts of plant cells o mitochondrial DNA – found in the mitochondria (useful for tracing ancestry) The structure of DNA phosphate group nitrogenous base deoxyribose sugar weak hydrogen bonds Figure 4A: DNA double helix Figure 4B: DNA – simplified structure DNA has a double helix structure (Figure 4A), consisting of monomers called nucleotides which link to form long chains, called polymers. The sugar in DNA is deoxyribose sugar and is attached to a nitrogenous base. The phosphate and sugar molecules are attached to one another by strong bonds alternately to form the long chains (Figure 4B). There are four types of nitrogenous bases in DNA: adenine (A) cytosine (C) thymine (T) guanine (G) 10 Nitrogenous bases are complementary, and always join together in a specific order:  adenine always links to thymine (Figure 5A)  guanine always links with cytosine (Figure 5B) A adenine G guanine T thymine C cytosine Figure 5A: adenine with thymine Figure 5B: guanine with cytosine This pairing of bases means that two strands of DNA are joined together, forming a long ladder-like structure. The nitrogenous bases are held together by weak hydrogen bonds. The ladder-like structure becomes coiled and is known as a double helix structure. The DNA strands wind around proteins which are known as histones. The role of DNA DNA carries hereditary information in the form of genes. Genes are short sections of DNA which code for a specific trait, and determine the physical characteristics (e.g. blood grouping, a gene linked to breast cancer) and behaviour of an organism (e.g. whether an organism can be tamed and domesticated). Most of the DNA strands do not code for anything and are known as non-coding DNA. Scientists are still researching the importance of the non-coding DNA. The main functions of DNA include:  Controls the functioning of cells  Regulate the functioning of genes  Passes on hereditary characteristics The structure of DNA: https://www.youtube.com/watch?v=C1CRrtkWwu0 11 Activity 1: DNA The diagram on the next page shows part of a DNA molecule. 1. Label parts 1, 2 and 3 (3) 2. Give the number of nucleotides shown in the diagram (1) 3. Name two places in an animal cell where this nucleic acid may be found. (2) 4. What is the natural shape of this molecule? (1) 5. Draw a nucleotide with the nitrogenous base adenine. (4) (11) RNA – ribonucleic acid Key terminology RNA consists of nucleotides. Nitrogenous bases found in RNA RNA are adenine, uracil, guanine and cytosine mRNA carries the code for protein synthesis from DNA to the messenger RNA ribosome ribosomal RNA rRNA forms ribosomes which are the site of protein synthesis transfer RNA tRNA brings amino acids to the ribosome to form the protein There are three types of RNA (ribonucleic acid), all formed in the nucleus by DNA. They perform different functions in different places in a cell. The types are:  messenger RNA (mRNA)  ribosomal RNA (rRNA)  transfer RNA (tRNA) 12 The location of RNA  Messenger RNA (mRNA) is formed in the nucleus but then enters the cytoplasm where it attaches to ribosomes.  Ribosomal RNA (rRNA) is found in the ribosomes in the cytoplasm of the cell.  Transfer RNA (tRNA) is found freely in the cytoplasm of the cell. The structure of RNA Like DNA, RNA also consists of monomers (nucleotides) which link to form longer chains (polymers). However, RNA is a single-stranded structure which is not coiled. The sugar in RNA is ribose and is attached to a nitrogenous base. The phosphate and sugar molecules are attached to one another alternately to form the chains. The structure of RNA is illustrated in Figure 6 below. phosphate group ribose sugar nitrogenous base Figure 6: RNA – note the chain formed by the phosphate and sugar molecules on the left, and the nitrogenous bases on the right. There are four types of nitrogenous bases in RNA: 13  cytosine (C) adenine (A) uracil (U) – not thymine as in DNA guanine (G) The role of RNA The three types of RNA are very important to the process of protein synthesis, with each type playing a unique role. Comparison between DNA and RNA DNA and RNA are similar in some respects. They both …  contain sugar alternating with phosphate  contain the nitrogenous bases adenine, guanine and cytosine  play a role in protein synthesis DNA and RNA also have significant differences, tabulated in Table 1 below. Table 1: The main differences between DNA and RNA. DNA RNA contains deoxyribose sugar contains ribose sugar double helix and coiled single stranded contains the nitrogenous base thymine contains the nitrogenous base uracil found in the nucleus, ribosomes and found in the nucleus only cytoplasm of cells A comparison DNA and RNA. It is very important to know the differences. https://www.youtube.com/watch?v=0Elo-zX1k8M DNA replication DNA replication is the process through which DNA makes an identical copy of itself. This occurs during interphase of the cell cycle in the nucleus. In Figures 7A to 7E, a small portion of DNA is shown undergoing replication. 14 1. The DNA double helix unwinds 2. The weak hydrogen bonds between the (Figure 7A) nitrogenous bases are broken. The DNA strands separate (they unzip)(Figure 7B) Figure 7A Figure 7B 3. Each original DNA strand 4. Free nucleotides build a DNA strand onto serves as a template on which its each of the original DNA strands, attaching complement is built (Figure 7C) their complementary nitrogenous bases (A to T and C to G) (Figure 7D) Figure 7D Figure 7C 15  5. This results in two identical DNA molecules. Each molecule consists of one original strand and one new strand (Figure 7E). Figure 7E Figure 7A – 7E: The process of DNA replication DNA replication is important for cell division, particularly mitosis. It allows each chromosome to be copied so that each new identical daughter cell produced contains the same number and type of chromosomes. Errors that occur during DNA replication  Errors that occur during DNA replication may sometimes lead to mutations (a change in the nitrogenous base sequence)  If the incorrect nitrogen base attaches to the original strand and a nitrogen base is added or deleted … o the sequence or order of the bases changes on the new DNA molecule … o resulting in a change in the gene structure DNA replication: Understand the process. https://www.youtube.com/watch?v=Qqe4thU-os8 Activity 2: DNA replication Study the diagram below and answer the questions that follow. 16  4 A 1 G 2 3 1. Name the process illustrated in the diagram above. (1) 2. State the significance of the process mentioned in question 1. (1) 3. Identify the parts labelled as 1, 2, 3 and 4. (4) 4. Describe how this process takes place. (6) 5. Give one location of extra-nuclear DNA. (1) (13) DNA profiling A DNA profile is a pattern produced on X-ray film. This pattern consists of lines which are of different lengths and thicknesses and in different positions, as shown in Figure 8. All individuals, except identical twins, have a unique DNA profile. Figure 8: DNA profiles for three different individuals. 17 DNA profiles are used to:  identify crime suspects in forensic investigations  prove paternity (father) and maternity (mother) (biological parents)  determine the probability or causes of genetic defects  establish the compatibility of tissue types for organ transplants  identify relatives DNA profiling is generally accepted as being extremely reliable. The interpretation and comparison of profiles should however be approached with caution, for the following reasons:  Humans interpret the results which means mistakes could be made  The method of profiling may be different in different laboratories producing inconsistencies  Only a small piece of DNA is used in profiling, so the profile might not be 100% unique to a particular individual  DNA profiling is expensive and therefore not readily accessible to those who cannot afford it, particularly in criminal cases  DNA profiles may reveal information about a person which could be used against them in a prejudicial way. For example: being HIV positive or having genetic abnormalities may lead to insurance companies not covering a person or prejudice in the court room Activity 3: DNA profiling DNA profiles from a crime scene. Victim CSS Suspect 1 Suspect 2 Suspect 3 Suspect 4 18 In a fight involving a number of people, one person was seriously injured. Police took blood samples from the victim, the crime scene (CSS – crime scene sample) and four suspects. The DNA was then extracted from each sample. The results of these tests are shown in the diagram above. 1. Which suspect probably injured the victim? (1) 2. Give a reason for your answer to the previous question. (1) 3. List one application of DNA profiling other than for solving crime. (1) 4. Give two reasons why DNA profiling may sometimes be challenged. (2) (5) Protein synthesis Key terminology amino acids monomers of proteins base triplet three nitrogenous bases one after the other on DNA 1st stage of protein synthesis – mRNA formed from DNA transcription carrying code for the protein to be made 2nd stage of protein synthesis – amino acids combine to form translation a protein three nitrogenous bases one after the other on mRNA – codon these are complementary to the triplet on DNA three nitrogenous bases one after the other on tRNA – these anti-codon are complementary to the codon on mRNA The process in which proteins are made is called protein synthesis. Proteins are made by linking various amino acids that are present in the cytoplasm of cells. There are 20 different amino acids, and they combine in a large variety of combinations. The number of amino acids and the sequence of the amino acids determine the type of protein that is formed. Figure 9 illustrates a protein with different amino acids represented by the different shapes and colour. The bond between the amino acids is known as a peptide bond. peptide bond Figure 9: Amino acids linked by peptide bonds The genes found in DNA contain the code which determines which type of protein that will be formed. 19   The smallest protein contains 50 amino acids linked together  Proteins generally contain 300 or more amino acids. Three consecutive nitrogenous bases on the DNA strand are called the base triplet. The base triplets determine which amino acid will be placed into the protein as well as the sequence in which the amino acids will be joined. Protein synthesis occurs in two stages Stage 1: Transcription Stage 2: Translation Stage 1: Transcription The first stage of protein synthesis, called transcription, occurs in the nucleus (see Figure 10 below). Stage 1 DNA nucleus cytoplasm mRNA transcription mRNA transport to cytoplasm for next phase of protein synthesis – translation Figure 10: Transcription 20  1. A section of the DNA double helix unwinds. As a result,  the weak hydrogen bonds between the nitrogenous bases of DNA break  the DNA unzips (in this particular section of the DNA) 2. One strand acts as a template 3. This DNA template is used to form a complementary strand of messenger RNA (mRNA)  This is done using free RNA nucleotides in the nucleoplasm  The mRNA now contains the code for the protein which will be formed  Three adjacent nitrogenous bases on the mRNA are known as codons. These code for a particular amino acid. 4. mRNA moves out of the nucleus through a nuclear pore into the cytoplasm, where it attaches onto a ribosome Stage 2: Translation The second stage of protein synthesis, called translation (Figure 11) , occurs in the cytoplasm. Stage 2 amino acid protein forming tRNA with amino acid cytoplasm mRNA Figure 11: Translation 21  5. Transfer RNA (tRNA) in the cytoplasm has three adjacent nitrogenous bases known as the anti-codon  mRNA’s codon will be complementary to a tRNA’s anti-codon  Each tRNA will carry a specific amino acid  According to the codons on the mRNA, the tRNA will bring the required amino acid to the ribosome 6. The amino acids are linked by a peptide bond to form the required protein. Figure 12 below shows the full process of protein synthesis DNA nucleus mRNA transcription mRNA cytoplasm transport to cytoplasm for the next phase of protein tRNA synthesis – translation mRNA cell membrane Figure 12: Protein synthesis 22 Note: it is important to know the difference between base triplets (DNA), codons (mRNA) and anti-codons (tRNA). The effect of mutation on protein structure (DNA sequence)  A mutation is a change in the nitrogenous base sequence of a DNA molecule (or a gene)  since mRNA is copied from the DNA molecule during transcription.  This will result in a change in the codons.  As a result, different tRNA molecules carrying different amino acids will be required.  The sequence of amino acids changes, resulting in the formation of a different protein.  If the same amino acid is coded for, there will be no change in the protein structure. Protein synthesis: https://www.youtube.com/watch?v=oefAI2x2CQM&t=43s Activity 4: Protein synthesis The diagram below represents a process that occurs during protein synthesis. B A C D E 1. Identify the process above. (1) 23  2. Name … a) organelle A (1) b) molecule B (1) c) the bond at E (1) 3. Provide the letter and name of the molecule that … a) carries the amino acid (1) b) is the monomer of a protein (1) 4. Name and describe the process occurring in the nucleus which results in the formation of the mRNA molecule. (6) (12) Activity 5: Codons and amino acids The sequence of amino acids in a protein molecule is coded for by DNA and RNA. The table below shows some mRNA codons and the corresponding amino acids. mRNA codons amino acid AGC serine GAU aspartate CUA leucine UAU tyrosine UUC phenylalanine AGU serine GAC aspartate UUU phenylalanine CUC leucine GAG glutamic acid 1. According to the table, how many codons code for phenylalanine? (1) 2. What is the anti-codon for glutamic acid? (1) 3. A section of mRNA has the following base sequence and is read from left to right: GAU CUC GAC AGC AUG ACC Give the … a) DNA base triplet for the last codon on this section of mRNA (1) b) 1st amino acid coded for by this section of mRNA (1) (4) 24 DNA – The code of life: End of topic exercises Section A Question 1 1.1 Various options are provided as possible answers to the following questions. Choose the correct answer and write only the letter (A- D) next to the question number (1.1.1 – 1.1.5) on your answer sheet, for example 1.1.6 D 1.1.1 A molecule of RNA is copied from DNA by the process of A transcription. B mitosis. C mutation. D translation. 1.1.2 In a DNA molecule A guanine pairs with adenine. B adenine pairs with thymine. C cytosine pairs with adenine. D Guanine pairs with thymine. 1.1.3 A codon is a sequence of three nucleotides on a molecule of A rRNA. B mRNA. C tRNA. D DNA. 1.1.4 DNA was analysed and found to contain 14% T (thymine). What percentage of the molecule is cytosine? A 14% B 28% C 36% D 72% 1.1.5 A gene in a bacterium codes for a protein that has 120 amino acids. How many mRNA nucleotides code for this protein? A 30 B 40 C 360 D 480 (5 × 2 = 10) 25 1.2 Give the correct biological term for each of the following descriptions. Write only the term next to the question number. 1.2.1 Proteins that form part of the chromosomes. 1.2.2 Which type of RNA travels from the nucleoplasm to the cytoplasm. 1.2.3 The nitrogenous base found in RNA but not in DNA. 1.2.4 A sugar that is a component of DNA. 1.2.5 A sudden change in the sequence / order of the nitrogenous bases of a nucleic acid. 1.2.6 The name of the bond that forms between amino acids in a protein molecule. 1.2.7 The type of nucleic acid that carries a specific amino acid. 1.2.8 A segment of DNA coding for a particular characteristic. 1.2.9 The bonds that form between nitrogenous bases in a DNA, 1.2.10 The organelle in the cytoplasm on which protein synthesis occurs. (10 x 1) = (10) 1.3 Indicate whether each of the descriptions in Column I applies to A ONLY, B ONLY, BOTH A AND B or NONE of the items in Column II. Write A only, B only, both A and B or none next to the question number. Column I Column II A: DNA 1.3.1 Contains ribose sugar B: RNA A: Mendel 1.3.2 Discovery of DNA B: Darwin A: nucleus 1.3.3 Location of DNA. B: mitochondria 1.3.4 The process where one DNA A: replication molecule produces two B: reproduction identical DNA molecules. A: DNA 1.3.5 Pairing of nitrogenous bases B: RNA (5 x 2) = (10) 26 1.4 The diagram below represents a portion of a nucleic acid. 1 2 C 3 4 5 1.4.1 Name the nucleic acid. (1) 1.4.2 Name two places in animal cells where this nucleic acid may be found. (2) 1.4.3 Identify a) portion 1 (1) b) nitrogenous base 3 (1) c) molecule 5 (1) d) bond 2 (1) 1.4.4 What is the natural shape of this molecule? (2) 1.4.5 Name the process in which this molecules make a copy of itself? (1) (10) 1.5 The diagram below represents DNA replication. 27  1.5.1 Identify the following: a) molecules W and U (2) b) parts of molecule W labelled X and Y (2) c) bond Z (1) d) nitrogenous base V (1) 1.5.2 Where in the cell does this process take place? (1) 1.5.3 Name the phase of the cell cycle where replication takes place. (1) 1.5.4 What is the purpose of DNA replication? (2) (10) Section A: Section B Question 2 2.1 The following sequence represents a part of the nitrogenous base sequence on a DNA molecule. TAC TCT CCA Triplet 1 Triplet 2 Triplet 3 2.1.1. Write down the base sequence of the anticodon of triplet 1 shown above. (1) 2.1.2. The table below shows the amino acids that correspond with different mRNA codons. mRNA codon Amino Acid AGA arginine AUG methionine GGU glycine AUC isoleucine a) Give the correct sequence of amino acids for DNA triplets 1 to 3. (2) b) During DNA replication a mutation occurred on triplet 1 resulting in C being replaced by G. Describe how this mutation will affect the structure of the protein formed. (3) 28  2.1.3. Name and describe the process occurring in the nucleus which results in the formation of an mRNA molecule. (6) 2.1.4. Draw a RNA nucleotide with a complementary base to adenine. (2) (14) 2.2 The diagrams below represent the process of protein synthesis. Study them and answer the questions that follow. Nucleus X 1 W Amino acid Amino acid 2 3 Z 2.2.1 Identify the structures labelled 1,2 and 3. (3) 2.2.2 Name and describe the stage of protein synthesis taking place at Z (5) 2.2.3 Using the table below, work out the names of the amino acids labelled W and X. (4) 29  Base Triplet on mRNA coding Amino acid coded for for the amino acid GAG glutamate CAG histidine AGG arginine CUG leucine UCC proline GUG valine (12) Question 3 3.1 The diagram below represents two stages of protein synthesis. 3.1.1 Provide labels for: a) molecule 1 (1) b) organelle 6 (1) 3.1.2 Give only the number of the part which represents a: a) DNA template strand (1) b) monomer of proteins (1) c) codon (1) 3.1.3 Describe translation as it occurs in organelle 6. (4) 3.1.4 Provide the: a) DNA sequence that codes for glycine (2) 30  b) codon for proline (2) 3.1.5 State two differences between a DNA nucleotide and an RNA nucleotide. (4) (17) 3.2 The first 7 triplets of nitrogenous bases that form part of the gene coding for one chain of the haemoglobin protein that makes up red blood corpuscles in humans is shown below. Study the table and answer the questions that follow. DNA CAC GTG GAC TGA GGA CTC CTC Template Base triplet 1 2 3 4 5 6 7 number 3.2.1 How many of the following are coded for in the DNA template sequence above? a) Nitrogenous bases (1) b) Different types of tRNA molecules that are required to form the polypeptide from this piece of DNA. (1) 3.2.2 Write down the mRNA sequence for the triplets numbered 4 and 6 in the above table. (2) 3.2.3 Using the table below, determine the amino acid sequence coded for by triplet numbers 4 and 6. (2) Anticodons on tRNA coding for the amino Amino acid coded for acid CUC glutamate GUC histidine GGA proline GAC leucine UGA threonine CAC valine 31 3.2.4. If the T in the 6th base triplet changed to A in the DNA template above, write down the new amino acid (using the table above) that this 6th triplet now codes for. (1) (7) Section B: Total Marks: 32  2: Meiosis Introduction Prophase II Significance of DNA replication for meiosis Metaphase II The karyotype Anaphase II Meiosis – the process Telophase II Introduction Comparing mitosis and meiosis The process of meiosis Activity 1: Meiosis I and Meiosis II First meiotic division Abnormal meiosis (chromosome mutation) Prophase I Chromosome mutations Metaphase I Enrichment Anaphase I Telophase I End of topic exercises Second meiotic division 33 CHAPTER 2: MEIOSIS Introduction In Grade 10 you learnt that when a cell divides by mitosis, two exact copies of the mother cell are produced. Cells divide by mitosis for the purpose of growth and repair. Worn out or damaged cells are replaced by the mitotic division of somatic cells (body cells) and some organisms are able to reproduce asexually by mitosis. Meiosis is a special type of cell division that halves the number of chromosomes. Four genetically different haploid daughter cells are formed from one diploid cell. Meiosis is important because  haploid gametes are produced  the doubling effect of fertilization on chromosome number of future generations is overcome  genetic variation occurs Key terminology a threadlike structure made up of DNA and protein found in chromosome the nucleus of most living cells, chromosome carrying genetic information in the form of genes chromatid one of the two identical strands centromere chromatid of a replicated chromosome region where the two centromere chromatids of a chromosome are held together homologous chromosomes – one from the mother and a pair of chromosomes of the one from the father same shape, size and having homologous similar genes for each chromosomes characteristic occupying the same position a pair of homologous chromosomes which lie next to each other and are physically bivalent in contact with each other at a point where crossing over will occur 34  an unreplicated "chromosome" unreplicated unreplicated chromosome has a single double-stranded chromosomes DNA molecule DNA replication a replicated "chromosome" has replicated replicated two identical double-stranded chromosomes chromosome DNA molecules the phase in the cell cycle interphase when DNA replication occurs diploid (2n) haploid (n) two complete set of diploid (2n) chromosomes in a cell one complete sets of haploid (n) chromosomes in a cell a segment of DNA in a chromosome that contains the gene gene code for a particular characteristic DNA organelle (containing two spindle fibres centrosome centrioles) found only in animal cells centriole structures formed when the centrosome divides into two; centriole they move to opposite ends of the cell during cell division chromosome Overlapping of homologous chromosomes resulting in the crossing over exchange of genetic material during Prophase I point where two chromatids crossing over chiasma chiasma overlap during crossing over 35  a representation of the number, shape and karyotype arrangement of a full set of chromosomes in the nucleus of a somatic cell the first 22 pairs of chromosomes which control autosome the appearance, structure and functioning of the body gonosomes the pair of chromosomes (XX (sex chromo- or XY) responsible for sex somes) determination Any cells in an organism excluding male and female somatic cells gametes – they are diploid (body cells) (have 2 sets of chromosomes) and are produced through mitosis somatic cell – chromosomes are in homologous pairs specialized cells called gametes (sperm cell and egg sex cells cell). They have a haploid (gametes) number of chromosomes and are produced through meiosis gamete single unpaired chromosomes normal meiosis when homologous non- chromosome pairs disjunction fail to separate in meiosis non- normal disjunction meiosis 36  Karyo means “nucleus” and kinesis means “synthesis or division.” karyokinesis Karyokinesis is the process of division karyokinesis of the nucleus of a cell Cyto means “cytoplasm,” and kinesis mean “synthesis or division.” cytokinesis cytokinesis Cytokinesis is the process of division during which the cytoplasm of a single cell divides into two daughter cells. Significance of DNA replication for meiosis Each species of living organism has a characteristic number of chromosomes found floating in the nucleoplasm of the nucleus.  When the cell is not dividing, the genetic material forms a tangled chromatin network.  During interphase, DNA replication takes place.  Single-stranded chromosomes become double-stranded.  Each chromosome will now consist of two chromatids joined by a centromere.  This ensures the sharing of the hereditary material by all the daughter cells that will be formed. 37 Meiosis – the process Introduction If meiosis does not occur, gametes will not be formed and sexual reproduction would not be able to take place.  During meiosis haploid gametes are formed, these gametes have half the number of chromosomes.  This is important so that the chromosome number is not doubled when fertilisation occurs. Instead, when two haploid gametes fuse, the diploid number is restored.  Meiosis thus ensures that the same number of chromosomes within a species remains constant from generation to generation. In animals, meiosis occurs in the sex organs (ovaries and testes) to produce gametes (gametogenesis). In plants meiosis produces spores which are used for reproduction in mosses and ferns. In flowering plants (angiosperms) meiosis takes place in the anther and in the ovule. The process of meiosis NOTE that a human cell has 46 chromosomes arranged in 23 pairs of homologous chromosomes. Explaining meiosis using a human cell is very complex. The same principle, however, applies to all somatic cells so for the sake of simplicity, meiosis will be explained using a cell with only 4 chromosomes. In meiosis, the cell undergoes two divisions which are referred to as Meiosis I and Meiosis II.  Meiosis I is a reduction division which reduces the diploid number of chromosomes to haploid. First meiotic division Although meiosis is a continuous process, the events are placed into phases for convenience. 38 Prophase I chromosome centriole spindle fibres Figure 1: Cell dividing in Prophase I  Nuclear membrane and nucleolus start to disappear.  Centrosome splits and the two centrioles move apart forming spindle fibres.  Chromatin network condenses into individual chromosomes and pairs of homologous chromosomes lie next to each other forming a bivalent.  Inner chromatids from each homologous chromosomes overlap and touch each other at a point called the chiasma (plural: chiasmata) in a process called crossing over (see Figure 2)  Chromatid segments break off and are exchanged, resulting in the exchange of genetic material.  This process is called crossing over and it brings about variation. Figure 2: The process of crossing over Metaphase I Figure 3: Cell undergoing Metaphase I 39   Homologous chromosomes move to the middle of the cell (the equator). The two homologous chromosomes lie on opposite sides of the equator parallel to each other (Figure 3).  Which chromosome lies on which side of the equator is totally up to chance. This is called random arrangement and brings about further variation.  Each chromosome in the pair becomes attached to a spindle thread by the centromere. Anaphase I Figure 4: Cell undergoing Anaphase I  One whole chromosome from each pair is pulled to opposite poles by contraction of the spindle fibres (see Figure 4).  This separates the homologous chromosomes – one to each pole. Telophase I Figure 5: Cell undergoing Telophase I  A new nuclear membrane forms around the group of chromosomes at each pole (Figure 5).  Nucleolus returns.  Cytokinesis (division of cytoplasm) splits the mother cell into two daughter cells. Important: Each daughter cell now has half the number of chromosomes and each has a slightly different genetic make-up due to crossing over. 40 Second meiotic division The second meiotic division takes place in both daughter cells formed during Meiosis I. Prophase II Figure 6: Cells undergoing Prophase II  Nuclear membrane and nucleolus start to disappear.  Centrosome splits into two centrioles and a spindle forms.  Chromosomes are NOT in pairs (Figure 6). Remember: Each chromosome is made of TWO chromatids. Metaphase II Figure 7: Cells undergoing Metaphase II  Single chromosomes arrange themselves randomly along the equator with the centromere in line with the equatorial plane (Figure 7). Which chromatid faces which pole is totally up to chance.  Each chromosome becomes attached to a spindle fibre. 41 Anaphase II Figure 8: Cell undergoing Anaphase II  The centromere splits and the two chromatids are pulled to opposite poles (Figure 8). Telophase II 1 3 Figure 9: Cells at start of Telophase II 2 4  A new nuclear membrane forms around the unreplicated chromosomes at each pole (Figure 9).  Cytokinesis splits the cell into two new cells (Figure 10). 1 2 3 4 Figure 10: Daughter cells at the end of Telophase II 42  Important: As Meiosis II took place in TWO cells, there will now be FOUR daughter cells. These cells will be haploid and genetically different to each other. The four stages of meiosis can be remembered in the following way - PMAT Prophase – chromosome PAIR up (crossing over). Metaphase – chromosomes move to MIDDLE. Anaphase – chromosomes move APART to the poles. Telophase – TERMINAL phase where daughter cells are formed. Why is ‘Crossing over’ important?  Crossing over brings about an exchange of genetic material during the process of gamete formation which results in the formation of new genetic combinations.  This results in formation of gametes that will give rise to individuals that are genetically different from their parents and siblings. Meiosis made SUPER EASY: https://www.google.co.za/search?q=videos+on+meiosis&rlz=1C1AZAA_enZA747ZA 747&oq=videos+on+meiosis&aqs=chrome..69i57j0l4.6731j0j8&sourceid=chrome&ie =UTF-8 Importance of meiosis  Production of gametes (four daughter cells are formed).  Halving of the chromosome number (diploid to haploid) so that the chromosome number remains constant from generation to generation within a species.  Mechanism to introduce genetic variation through:  Crossing over during Prophase I.  The random arrangement of chromosomes at the equator during Metaphase I and II as can be seen in Figure 11 below. 43  or Metaphase 1 or Metaphase 2 or Figure 11: Random arrangement of chromosomes Differences between meiosis I and meiosis II Table 1: The differences between Meiosis I and Meiosis II Meiosis I Meiosis II Chromosomes arrange at the equator of Chromosomes line up at the equator of the cell in homologous pairs the cell individually Whole chromosomes move to opposite Chromatids move to opposite poles of poles of the cell the cell Two cells are formed at the end of this Four cells are formed at the end of this division division The chromosome number is halved The chromosome number remains the during meiosis I (diploid → haploid) same (haploid) during meiosis II Crossing over takes place Crossing over does not take place 44 Comparing mitosis and meiosis Table 2: Showing the differences between mitosis and meiosis Mitosis Meiosis Mitosis occurs in body cells Meiosis occurs in sex organs Both karyokinesis and cytokinesis occurs Both karyokinesis and cytokinesis once occurs twice Two daughter cells are formed Four daughter cells are formed Daughter cells are genetically identical to Daughter cells are genetically different one another and to the parent cell from each other and from the parent cell Chromosome number remains constant Chromosome number is halved Crossing over does not occur Crossing over occurs The differences between mitosis and meiosis as a rap song: https://youtu.be/qH4WUUQ5pOI  The only similarities are between mitosis (Prophase, Metaphase and Anaphase) and meiosis II (Prophase II, Metaphase II and Anaphase II). The differences between mitosis and meiosis are illustrated in the following diagram. 45  Mitosis Meiosis Prophase Metaphase I Chromosomes don’t form pairs Anaphase I Whole Chromosome chromosomes Prophase I pairs line up pulled to poles Homologous on equator chromosomes Metaphase pair up Telophase I Individual Two haploid chromosomes daughter cells arranged on formed equator Meiosis I Prophase II Anaphase Centromeres split and chromatids move to Metaphase II opposite poles Telophase Meiosis II (Mitosis for Two identical daughter cells haploid cells) Anaphase II formed Telophase II Cytokinesis Cytokinesis Two identical cell formed Four haploid non-identical cells formed Figure 12: The difference between MITOSIS and MEIOSIS 46 Activity 1: Meiosis I and Meiosis II 1. Various options are provided as possible answers to the following questions. Choose the correct answer and write only the letter (A – D) next to the question number (1.1.1 – 1.1.5) on your answer sheet, for example 1.1.6 D 1.1 Which one of the following correctly describes the daughter cells produced by meiosis? Cells produced by meiosis Chromosome number Genetic composition A haploid different B diploid identical C diploid different D haploid identical 1.2 If there are 38 chromosomes in the body cell of a donkey. How many of these chromosomes are autosomes? A 38 B 19 C 36 D 44 1.3 Use the sketch below to identify processes 1, 2 and 3. 1 2 3 A meiosis fertilisation mitosis B fertilisation mitosis meiosis C mitosis meiosis fertilisation D fertilisation meiosis mitosis 1.4 Cytokinesis is a term that describes … A nuclear division B cytoplasmic division C reduction of the chromosome number D doubling the chromosome number 47  1.5 The diagrams below represent six different phases of meiosis taking place in a particular cell. 1 2 3 4 5 6 1.5.1 The diploid number of chromosomes in this cell is … A 2 B 4 C 8 D 46 1.5.2 The correct sequence from the start of meiosis till the end is … A 1, 2, 3, 4, 5, 6 B 6, 2, 5, 4, 1, 3 C 3, 5, 4, 2, 6, 1 D 3, 4, 5, 6, 1, 2 1.6 Interphase is the stage during which … A nothing happens in the cell. B a dividing cell forms a spindle. C cytokinesis occurs. D a cell grows and duplicates its DNA. (7 × 2) = (14) 2. Each of the following questions consist of a statement in Column I and two items in Column II. Decide which item(s) relate(s) to the statement. Write A only, B only, Both A and B or None next to the question number. Column I Column II Chromosome number changes from A: Meiosis 2.1 diploid to haploid B: Mitosis A: Mitosis 2.2 Takes place to form sex cells B: Meiosis A: before mitosis 2.3 Replication of DNA takes place B: before meiosis 48  A: Prophase in mitosis 2.4 Crossing over takes place B: Prophase I in meiosis Chromosomes are pulled to opposite A: Anaphase in mitosis 2.5 poles B: Anaphase I in meiosis A: crossing over 2.6 Results in genetic variation B: random arrangement Chromosomes lengthen to form a A: Metaphase 2.7 chromatin network B: Anaphase (7 × 2) = (14) 3. Study the diagram below. 1 2 A B 3 3.1 What type of cell division is occurring? (1) 3.2 What phase is depicted? (1) 3.3 Provide labels for parts labelled 2 and 3. (2) 3.4 What process resulted in the exchange of segments labelled 1? (1) 3.5 Explain why the process mentioned in 3.4 is important. (1) (6) 4. Refer to the diagram below which shows two cells dividing by meiosis. 49  4.1 Which phase of meiosis is depicted? (1) 4.2 Give two visible reasons for your answer to 4.1. (2) 4.3 Why do some of the chromatids have two different colours? (1) 4.4 Do you think that these cells were taken from a human? (1) 4.5 Give a reason for your answer to 4.4. (1) 4.6 If these cells were taken from an angiosperm, name the two parts of the flower where this type of division would occur. (2) (8) 5. Explain why meiosis is important for the survival of a human. (8) (50) Abnormal meiosis (chromosome mutation)  Sometimes mistakes occur during the process of meiosis.  This can happen in Anaphase I where there may be non-disjunction of homologous chromosomes into separate chromosomes (Figure 13).  It can also happen in Anaphase II when there may be non-disjunction of chromosomes into single-stranded daughter chromosomes (chromatids).  If there is non-disjunction of chromosome pair 21 in humans, it leads to the formation of an abnormal gamete with an extra copy of chromosome 21.  If there is fusion between a normal gamete (with 23 chromosomes) and an abnormal gamete (with an extra copy of chromosome 21) it leads to Down Syndrome (47 chromosomes in the zygote). 50  Non-disjunction in Non-disjunction in Anaphase I Anaphase II non-disjunction normal meiosis non- normal meiosis disjunction normal meiosis Figure 13: Non-disjunction of chromosomes resulting in Down Syndrome. C represents a chromosome ENRICHMENT Figure 14: Boy with Down Syndrome Down Syndrome is caused by the non-disjunction of chromosomes which results in the presence of an extra chromosome number 21 (referred to as trisomy). 51  Mother cell 46 meiosis I 24 22 meiosis II 23 24 22 22 22 sperm ovum 47 zygote Figure 15: How a child with Down Syndrome is formed This mutation leads to various malformations in the developing child, such as upwardly slanted eyes, small nose (with flat bridge) and mouth (Figure 14), various degrees of mental retardation, decreased muscle tone, hearing loss and heart defects. The chance of non-disjunction occurring in sex cells increases with the age of a parent, especially the mother, and it is incurable. In the case of older parents, it is advisable to test the foetus while it is still in the uterus. An amniocentesis is the process by which amniotic fluid is removed, so that the karyotype of foetal cells in the amniotic fluid can be analysed. The parents can then decide whether or not to have the baby. 52 Meiosis: End of Topic Exercises Section A Question 1 1.1 Various options are provided as possible answers to the following questions. Choose the correct answer and write only the letter (A – D) next to the question number (1.1.1 – 1.1.5) on your answer sheet, for example 1.1.6 D 1.1.1 During which phase of meiosis do homologous chromosome pairs separate? A Metaphase I B Anaphase I C Anaphase II D Telophase II 1.1.2 Which of the following distinguishes Prophase I of meiosis from Prophase of mitosis? A Homologous chromosomes pair up B Spindle forms C Nuclear membrane breaks down D Chromosome becomes visible 1.1.3 Which one of the following events occurs during Metaphase I of meiosis? A Homologous chromosomes arrange themselves at the equator. B Centrioles move to the opposite poles. C Chromosomes arrange themselves singly at the equator. D The cytoplasm is split. 1.1.4 Which one of the following combinations results in genetic variation in organisms? A Mitosis; sexual reproduction; mutations. B Meiosis; asexual reproduction; mutations. C Mitosis; meiosis; sexual reproduction. D Meiosis; sexual reproduction; mutations. 53  1.1.5 In bees, females are diploid and males are haploid. Females and males produce haploid gametes. This means that A females produce gametes by mitosis. B males produce gametes by meiosis. C males produce gametes by mitosis. D Females have half the number of chromosomes that males have. (5 × 2) = (10) 1.2 Give the correct biological term for each of the following descriptions. Write only the term next to the question number. 1.2.1 The division of the cytoplasm after a cell nucleus has divided. 1.2.2 The point of crossing over between two adjacent chromosomes. 1.2.3 The name of the process when homologous chromosome pairs fail to separate during meiosis. 1.2.4 Region where the two chromatids of a chromosome are held together. 1.2.5 Chromosome condition describing the presence of a single set of chromosomes in a cell. 1.2.6 The structure responsible for pulling chromosomes to the poles of an animal cell during cell division. 1.2.7 The DNA in a nucleus of a non-dividing cell. 1.2.8 The structure that is made up of two chromatids joined at the centromere 1.2.9 A phase in the cell cycle that occurs before cell division. 1.2.10 A source of genetic variation that arises during Metaphase I. (10 × 1) = (10) 1.3 Indicate whether each of the descriptions in Column I applies to A ONLY, B ONLY, BOTH A AND B or NONE of the items in Column II. Write A only, B only, both A and B or none next to the question number. Column I Column II A: Metaphase I 1.3.1 Chromosomes align at equator B: Metaphase II A: division of the cytoplasm 1.3.2 Occurs during Telophase of B: centrioles move to the meiosis I opposite poles 1.3.3 Phase during which chromatids A: Anaphase I are pulled to opposite poles B: Anaphase II 54  1.3.4 Contributes to each gamete A: Prophase I receiving DNA segments from B: Prophase II each parent. 1.3.5 The structure that moves A: centrosomes chromosomes / chromatids to B: spindle fibres the poles during cell division. (5 × 2) = 10 1.4 The diagrams below represent a chromosome pair in a female human cell. The cells (A, B and C) show different events in a phase of meiosis, which are not necessarily in the correct sequence. Y A B C 1.4.1 How many pairs of chromosomes occur in a normal human cell? (1) 1.4.2 Give labels for: a) region X (1) b) area Y (1) 1.4.3 Name the organ in the human female where meiosis occurs. (1) 1.4.4 Name the a) process occurring in diagram B. (1) b) phase represented by the diagrams above. (1) c) type of cell that would result from meiosis of this cell. (1) 1.4.5 Arrange letters A, B and C to show the correct sequence of the events. (1) 1.4.6 What is the biological importance of meiosis? (2) (10) 55 1.5 The diagrams below show different phases in meiosis. Study the diagrams and answer the questions that follow. A B C D 1.5.1 Label structures W and X. (2) 1.5.2 How many chromosomes are present in each cell: a) phase A (1) b) phase C (1) 1.5.3 Give the letter of the diagram that represents Anaphase II. (1) 1.5.4 State the name and function of region Y and structure Z. (4) 1.5.5 Which phase precedes (occurs before) phase A? (1) (10) Section A: Section B Question 2 2.1 The diagram below represents a phase in meiosis. Cell Y undergoes division to give rise to cells X and Z. Some alleles are indicated by letters. Cell Y Cell X Cell Z 56  2.1.1 Explain why cell Y does not belong to a human. (2) 2.1.2 How many chromosomes would be present in: a) cell X at the end of Telophase I. (1) b) the daughter cells produced by cell Z after meiosis II. (1) 2.1.3 Draw a labelled diagram of a gamete that will result from cell Y. (5) 2.1.4 Describe the events of Anaphase II. (3) (12) 2.2 Study the diagrams below representing two phases of meiosis and answer the questions that follow. B A Diagram 1 Diagram 2 2.2.1 Identify the phase represented by: a) Diagram 1 (1) b) Diagram 2 (1) 2.2.2 Name the part labelled B. (1) 2.2.3 Describe what happens during the phase illustrated in Diagram 1. (2) 2.2.4 In Diagram 2 the part circled, and labelled A is an abnormality during the process of meiosis. a) Name this abnormality. (1) b) What genetic disorder would result in humans if this abnormality occurred in chromosome pair no. 21? (1) c) Give one symptom of the genetic abnormality mentioned in question 2.2.4 (b). (1) (8) 57 2.3 The graph shows information about the movement of chromatids in a cell that has just started Metaphase II. Movement of chromatids in a cell Key distance between chromatids distance between each chromatid and the pole to which it is moving 40 35 30 Distance (μm) 25 X Y 20 15 10 5 0 0 5 10 15 20 25 30 35 Time after start of metaphase (minutes) Start of metaphase 2.3.1 Name one difference between Metaphase I and Metaphase II. (2) 2.3.2 What is the duration of Metaphase II in this cell? (1) 2.3.3 Use line X to calculate the duration of Anaphase II in this cell. (2) (5) QUESTION 3 3.1 Describe the behaviour of the chromosomes during the process of meiosis I by referring to the following phases: 3.1.1 Prophase I (6) 3.1.2 Metaphase I (3) 3.1.3 Anaphase I (2) 58  3.1.4 Telophase I (3) (14) 3.2 The diagram below shows chromosome pair 21 in the nucleus of a cell of the ovary of a woman. The chromosomes are involved in a process that takes place in a phase of meiosis. Diagram X Diagram Y Diagram Z 3.2.1 Give labels for A and B. (2) 3.2.2 Rearrange the letters X, Y and Z to show the correct sequence in which the events take place in this phase. (1) 3.2.3 Explain why chromosomes in Diagram X and Diagram Y are different in appearance. (3) 3.2.4 The diagram below shows the nuclei of the four cells that resulted from meiosis involving chromosomes in Diagram X above. Nuclei of the cells formed at the end of meiosis II Daughter chromosomes a) Explain why nuclei O and P do NOT have chromosomes. (2) b) Name and explain the disorder that will result if Diagram M represents an egg cell that fuses with a normal sperm cell. (3) (11) Section B: Total Marks: 59 60  3: Reproductive strategies in vertebrates Introduction The amniotic egg consists of External and internal fertilisation Activity 2: Amniotic egg External fertilisation Precocial and Altricial Internal fertilisation development Comparison of external Major differences between vs internal fertilisation precocial and altricial Ovipary, ovovivipary and vivipary development Comparison of ovipary, Parental care ovovivipary and vivipary Activity 3: Activity 1: Development and Fertilisation care The amniotic egg 61 CHAPTER 3: REPRODUCTIVE STRATEGIES IN VERTEBRATES Introduction Reproduction ensures the continued existence of a species. Different species display different reproductive strategies to make sure that their offspring survive. Reproductive strategies differ in:  the number of eggs produced by the female  the site of fertilisation, inside or outside the body of the female  the place of development of the embryo and its nourishment  how quickly the young can fend for themselves  the type of parental care given to offspring. Key terminology reproductive structural, functional and behavioural adaptations that improve strategy the chances of fertilisation and the survival of offspring external fertilisation that takes place outside the female’s body, usually in fertilisation water internal fertilisation that occurs inside the female’s body where the male fertilisation has deposited its sperm ovipary eggs are laid; the embryo develops outside the mother’s body young develop from eggs fertilised internally and retained within ovovivipary the mother's body after fertilisation until they hatch the young develop inside the uterus of mother after eggs are vivipary fertilised internally; young are nourished through the placenta the embryo inside the egg is protected by a hard shell; the egg amniotic egg consists of many extra-embryonic membranes that serve different functions extra- membranes that surround the developing embryo inside the embryonic amniotic egg or uterus. membranes produces amniotic fluid which cushions embryo and protects it amnion from mechanical injury, temperature changes, dehydration collects the embryo’s nitrogenous waste and assists in the allantois exchange of gases allows for gaseous exchange in the amniotic egg and forms the chorion placenta in mammals 62  yolk sac contains the food reserves for the developing embryo precocial when hatchlings are well developed as they hatch, able to move development and feed themselves, with eyes open – limited parental care when hatchlings are underdeveloped as they hatch, unable to altricial move or feed or fend for themselves – young require more development parental care includes the building of nests, protection, teaching of young and parental care feeding – the care, or lack thereof, directly influences the survival of the young External and internal fertilisation  Fertilisation occurs when a sperm cell and egg cell fuse to form a zygote.  Fertilisation can either occur outside or inside the female’s body and varies in its water dependency. External fertilisation External fertilisation takes place outside the female’s body. Water is required for fertilisation (Figure 1A and 1B). Figure 1A: Salmon breeding Figure 1B: Fertilised salmon eggs (spawning) in a lake 63 Internal fertilisation Internal fertilisation takes places inside the female’s body. No water is required. See Figures 2 and 3. Figure 2: Internal fertilisation in Figure 3: Internal fertilisation in mammals via a penis birds Comparison of external and internal fertilisation Table 1 compares external with internal fertilisation. Table 1: Comparison – external vs. internal fertilisation External fertilisation Internal fertilisation  Requires water for fertilisation  No water required for fertilisation  Gametes (sperm and egg cells) are  Sperm cells are released into the released into water female’s body  Many gametes released  Fewer gametes released  Lower mortality rates among young  High mortality rates among young – protection provided by the due to lack of protection. Eggs can mother’s body or a hardened easily desiccate or be predated on calcareous / leathery shell.  e.g. fish and amphibia  e.g. reptiles; birds and mammals Ovipary, ovovivipary and vivipary Ovipary, ovovivipary and vivipary are reproductive strategies that differ in respect to:  where the zygote is formed  where development occurs  how the embryo receives its nourishment  the type of egg or its presence or absence 64 Comparison of ovipary, ovovivipary and vivipary Table 2 compares the three reproductive strategies, namely, ovipary, ovovivipary and vivipary. Table 2: Three reproductive strategies Ovipary Ovovivipary Vivipary fertilisation external or internal internal internal development external to the body of inside the body of the inside the of embryo the female female female’s body Yolk is the only form of Young receive