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GCE MAY 2008 : (A2 2) Reproduction, Genetics and Taxonomic Diver

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Centre Number 71 Candidate Number ADVANCED General Certificate of Education 2008 Biology assessing Module 5: Reproduction, Genetics and Taxonomic Diversity A2B21 Assessment Unit A2 2 [A2B21] TUESDAY 20 MAY, AFTERNOON TIME 1 hour 30 minutes. INSTRUCTIONS TO CANDIDATES Write your Centre Number and Candidate Number in the spaces provided at the top of this page. Write your answers in the spaces provided in this question paper. Answer all eight questions. For Examiner s use only Question Number 1 INFORMATION FOR CANDIDATES 2 The total mark for this paper is 75. Section A carries 60 marks. Section B carries 15 marks. You should spend approximately 20 minutes on Section B. You are expected to answer Section B in continuous prose. Quality of written communication will be assessed in Section B. Figures in brackets printed down the right-hand side of pages indicate the marks awarded to each question or part question. 3 4 5 6 7 8 Total Marks A2B21 3670 Marks BLANK PAGE A2B21 3670 2 [Turn over Section A Examiner Only Marks 1 Remark The diagram below shows a longitudinal section through a member of an animal phylum A coelomic spaces gut B C Handbook of Animal Types by Kathleen Cratchley, published by Longman, 1980, page 40 ISBN 0-582-35324-6, reproduced by permission of Pearson Education Ltd (a) Name the tissue layers A to C. A _______________________________________________________ B _______________________________________________________ C _____________________________________________________ [3] (b) Identify the phylum shown in the diagram above. Explain your answer. Phylum __________________________________________________ Reason __________________________________________________ _______________________________________________________ [2] A2B21 3670 3 [Turn over 2 The diagram below shows a human karyotype. A karyotype is constructed by photographing a particular phase in the cell cycle and then arranging the chromosomes in homologous pairs. 1 2 6 7 13 14 19 20 3 8 4 9 10 15 16 21 Remark 5 11 Examiner Only Marks 12 17 22 18 XX Source: Biological Science 1 & 2 (2nd Edition Combined Edition), NPO Green, GW Stout, DJ Taylor (Ed. R Soper), Cambridge, 1984) (a) Identify the phase of a cell cycle in which individual chromosomes would appear as depicted above. _______________________________________________________ [1] (b) Identify the evidence in the karyotype which indicates that the individual suffers from Down s syndrome. _________________________________________________________ _______________________________________________________ [1] A2B21 3670 4 [Turn over (c) Down s syndrome occurs as a result of a faulty meiotic division involving non-disjunction of chromosomes. Examiner Only Marks Remark (i) Explain the term non-disjunction . _____________________________________________________ ___________________________________________________ [1] (ii) Identify the stage of meiosis during which non-disjunction might occur. ___________________________________________________ [1] (d) Down s syndrome is an example of aneuploidy. Explain how aneuploidy differs from polyploidy. _________________________________________________________ _________________________________________________________ _________________________________________________________ _______________________________________________________ [2] A2B21 3670 5 [Turn over 3 The graphs below show the frequency distribution of birth weights of infants born in a London hospital, 1935 1946 (histogram) and the infant death rate in relation to birth weight (broken line). (Weight is shown in Imperial units, pounds.) Examiner Only Marks 50 Percentage mortality 100 10 Percentage of total births 20 Remark 0 0 0 1 2 3 4 5 6 7 8 Birth weight/pounds 9 10 11 12 (a) Describe the trends shown in the graph. _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ ______________________________________________________ [3] A2B21 3670 6 [Turn over (b) The data in the graph is often presented as an example of stabilising selection. Explain what is meant by stabilising selection, and its influence on the birth weight of infants. Examiner Only Marks Remark _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ ______________________________________________________ [4] A2B21 3670 7 [Turn over 4 The standard in-vitro fertilisation technique involves inducing superovulation, removing eggs from the woman s ovaries and letting sperm fertilise them in a fluid medium. Embryos are then transferred to the patient s uterus for implantation and thereby pregnancy. Examiner Only Marks Remark The chance of an individual couple having a baby following IVF treatment depends on two main factors, one of which is the couple s age. The table below shows the pregnancy success rate, following one complete cycle of IVF treatment, in relation to the age of the couple. The table also shows the results achieved by treatment clinics over three successive years. Age of couple 1996 1997 1998 Less than 35 28.4% 30.7% 32.2% 35 37 23.4% 25.4% 26.1% 38 40 16.0% 17.0% 17.9% Over 40 6.4% 7.3% 8.3% (a) The table shows that older couples have a reduced chance of a successful pregnancy following IVF treatment. Suggest one explanation for this. __________________________________________________________ _______________________________________________________ [1] (b) Using the information in the table above, suggest what evidence there is that the second factor determining the success rate of IVF treatment might be the expertise developed by treatment clinics. __________________________________________________________ _______________________________________________________ [1] A2B21 3670 8 [Turn over Initially, IVF was developed to overcome infertility due to problems of the fallopian tube. However, it was found to be successful in overcoming other causes of infertility when used in conjunction with other recently developed techniques. Some of these include Intracytoplasmic sperm injection (ICSI) a sperm nucleus is directly injected into the egg using micromanipulation Surrogacy the embryonic stage is implanted into the receptive uterus of a woman who had not provided the eggs Remark Cryopreservation (freezing) of eggs allows a future pregnancy in women who are likely to lose their ovarian egg reserve due to ongoing chemotherapy Examiner Only Marks Preimplantation genetic diagnosis (PGD) the embryo is tested for genetic disorders before it is implanted in the uterus. (c) Apart from fallopian tube problems, the major causes for infertility are sperm defects, failure of ovulation and endometriosis (uterus fails to become receptive). Using the information above and/or your own understanding, suggest an appropriate treatment for each of these causes. In each case explain your reasoning. Sperm defects _________________________________________ _____________________________________________________ _____________________________________________________ Failure of ovulation _____________________________________ _____________________________________________________ _____________________________________________________ Endometriosis _________________________________________ _____________________________________________________ __________________________________________________ [5] (d) Suggest why preimplantation genetic diagnosis (PGD) would be advised for some couples. _________________________________________________________ ______________________________________________________ [1] A2B21 3670 9 [Turn over (e) Suggest two ethical issues that have been raised about IVF and associated developments. Examiner Only Marks Remark 1. _______________________________________________________ _________________________________________________________ 2. _______________________________________________________ _______________________________________________________ [2] A2B21 3670 10 [Turn over 5 (a) The diagram below shows a carpel (stigma, style and ovary) of a flowering plant. Pollen grains in different stages of pollen tube growth are also shown. Examiner Only Marks Remark generative nucleus polar nuclei X egg cell male gametes (i) Explain how a pollen grain represents the male gametophyte of the flowering plant. _____________________________________________________ _____________________________________________________ _____________________________________________________ __________________________________________________ [2] (ii) Name the structure labelled X. __________________________________________________ [1] (iii) Describe what happens to the male gametes following the arrival of the pollen tube at the structure labelled X. _____________________________________________________ _____________________________________________________ _____________________________________________________ __________________________________________________ [2] A2B21 3670 11 [Turn over (b) In the primrose (Primula vulgaris) there are two forms of plant: pineyed and thrum-eyed. In pin-eyed plants the stigmas are higher than the anthers in the flower, while in thrum-eyed plants the reverse situation occurs, as shown in the diagram below. Pin-eyed flower Examiner Only Marks Remark Thrum-eyed flower stigma anther anther stigma style ovary Source: Ecological Genetics, EB Ford, Methuen (London), 1965 It has been suggested that the position of the stigma and anthers in the two forms promotes cross pollination an insect visiting a flower will collect pollen on a part of its body which corresponds to the position of the stigma on the other form. (i) The stigmas of both pin-eyed and thrum-eyed plants have been analysed for the presence of the different types of pollen (designated pin pollen and thrum pollen). The results are shown in the table below. Frequency of Pin pollen Thrum pollen Stigma of pin-eyed flower 183 267 Stigma of thrum-eyed flower 305 145 Explain how the data in the table above provides evidence for the promotion of cross pollination. ______________________________________________________ ______________________________________________________ ______________________________________________________ ___________________________________________________ [2] A2B21 3670 12 [Turn over (ii) Even if pollen is transferred to a stigma of the same plant type, fertilisation is not ensured, a situation known as self-incompatibility. The table below shows the responses of pollen after arrival on the stigma of the same plant type. Pin pollen on pin stigma Good Poor Percentage germination of pollen grains 30% 70% Successful growth of pollen tube down the style Poor Remark Thrum pollen on thrum stigma Pollen adhesion to stigma Examiner Only Marks None From the data above, which plant type exhibits the most complete example of self-incompatibility? Explain your answer. ______________________________________________________ ______________________________________________________ ______________________________________________________ ___________________________________________________ [2] (c) Explain the advantages of cross pollination in plants such as the primrose. __________________________________________________________ __________________________________________________________ __________________________________________________________ _______________________________________________________ [2] A2B21 3670 13 [Turn over 6 (a) Discuss the events in meiosis that explain Mendel s laws of inheritance. Examiner Only Marks Remark (i) Mendel s first law the law of segregation. _____________________________________________________ _____________________________________________________ _____________________________________________________ __________________________________________________ [2] (ii) Mendel s second law the law of independent assortment. _____________________________________________________ _____________________________________________________ _____________________________________________________ __________________________________________________ [2] (b) The inheritance of fruit shape in the summer squash (Cucurbita pepo) is controlled by the interaction of two independently inherited genes, A/a and B/b. Three fruit shapes may be produced a dominant allele at both loci results in disc-shaped fruit a dominant allele at either locus results in sphere-shaped fruit in the absence of dominant alleles, the fruit is long. (i) A plant of genotype AABB is crossed with a plant of genotype aabb. Determine the genotype and phenotype of the offspring produced as a result of this cross. Genotype _____________________ Phenotype _____________________ A2B21 3670 14 [2] [Turn over (ii) The plants of the offspring produced in the cross opposite are allowed to self-fertilise. Determine the possible genotypes produced as a result of this cross and the expected phenotypic (fruit shape) proportions. Show your working in a genetic diagram in the following space. Examiner Only Marks Remark [5] A2B21 3670 15 [Turn over 7 In the banded snail (Cepaea nemoralis) the colour of the shell is either yellow (appearing green with the live snail inside) or pink. In a sample of 300 snails from a population in an area of sand dune near Magilligan strand, 192 had yellow shells. The colour of the shell is genetically determined and pink is the expression of the dominant allele. Examiner Only Marks Remark (a) (i) Calculate the proportion of the population that have yellow shells. __________________________________________________ [1] (ii) Assuming the population to be in Hardy Weinberg equilibrium for shell colour, calculate the relative frequencies of the yellow and pink alleles, and the number in the sample of 300 that might be expected to be heterozygous. (Show your working in the space below.) Relative frequency of the yellow allele ______________ Relative frequency of the pink allele ______________ Number of heterozygous snails in the sample ______________ [3] A2B21 3670 16 [Turn over (b) These snails are predated by song thrushes. The thrush, having captured a snail, breaks open the shell by hammering it against a stone, so that examination of the shells found at these anvil sites reveals the frequencies of the forms predated. Of 35 shells found at such sites, 28 were yellow. Examiner Only Marks Remark (i) Calculate the proportion of the predated snails that have yellow shells. __________________________________________________ [1] (ii) Given this information about predation, can it be assumed that the population is in Hardy Weinberg equilibrium with respect to the shell colour? Explain your answer. _____________________________________________________ _____________________________________________________ _____________________________________________________ __________________________________________________ [2] (iii) Other studies have suggested that predators tend to take proportionally more of the more common form when faced with the choice of prey. Suggest how such predation would maintain both forms (for example yellow and pink snails) in a polymorphic population. _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ __________________________________________________ [3] A2B21 3670 17 [Turn over Section B Examiner Only Marks Remark In this section you are expected to answer in continuous prose, supported, where appropriate, by diagrams. You are reminded that up to two marks in this question are awarded for the quality of written communication. [2] 8 Give an account of the methods by which the members of the different kingdoms obtain food. [13] ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ A2B21 3670 18 [Turn over ____________________________________________________________ Examiner Only Marks Remark ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ A2B21 3670 19 [Turn over Examiner Only ____________________________________________________________ Marks Remark ____________________________________________________________ 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____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ A2B21 3670 20 [Turn over ____________________________________________________________ Examiner Only Marks Remark ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ A2B21 3670 21 [Turn over Examiner Only ____________________________________________________________ Marks Remark ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ A2B21 3670 22 [Turn over THIS IS THE END OF THE QUESTION PAPER A2B21 3670 23 Permission to reproduce all copyright material has been applied for. In some cases, efforts to contact copyright holders may have been unsuccessful and CCEA will be happy to rectify any omissions of acknowledgement in future if noti ed. 3670 529-022-1 A2B21 3670 24 [Turn over

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Additional Info : Gce Biology May 2008 Assessment Unit A2 2 - Module 5: Reproduction, Genetics and Taxonomic Diversity
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