24 8 In mammals, gametes are produced by spermatogenesis and oogenesis. (a) The diagram shows some of the stages in spermatogenesis. Stage 1 Stage 2 Stage 3 Stage 4 Spermatogonium Spermatid Development Spermatozoa Meiosis I Primary spermatocyte Mitosis Secondary spermatocyte Meiosis II 2n 2n n n 2n n n n n (i) Explain the significance of mitosis in stage 1 of spermatogenesis. 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Turn over 25 (ii) Explain the events that take place in stage 2, that result in genetic variation. 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(iii) Compare and contrast the products of stage 2 and stage 3 in spermatogenesis with the products from these stages in oogenesis. 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(2) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... 27 (b) The effect of storage time on sperm was investigated. The table shows some results of this investigation. Storage time / hours Percentage of sperm with structural defects (%) Percentage of sperm that could swim (%) 0 8.2 ± 3.9 85.0 ±   5.7 6 9.5 ± 3.1 67.5 ± 11.0 12 18.0 ± 3.9 66.3 ±   7.5 18 21.3 ± 6.1 67.5 ±   2.8 24 19.5 ± 3.1 58.8 ±   8.5 30 26.5 ± 3.1 41.3 ±   7.5 Analyse the data to comment on conclusions that can be made from this investigation. 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(Total for Question 8 = 15 marks) TOTAL FOR PAPER = 80 MARKS 28 BLANK PAGE