10 5 Reproduction in mammals involves specialised cells called gametes. The production and structure of the gametes can be affected by chemicals in the environment. (a) (i) A sperm cell contains a specialised lysosome called the acrosome. Describe the role of the acrosome in fertilisation. 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(ii) Following fertilisation a zygote is formed. The zygote then divides by (1) A meiosis to produce diploid cells B meiosis to produce haploid cells C mitosis to produce diploid cells D mitosis to produce haploid cells 11 Turn over (b) Human fertility may be affected by chemicals in the environment such as polychlorinated biphenyls (PCBs). It is thought PCBs affect the functioning of the mitochondria. (i) The diagram shows the structure of a sperm cell. P R Q S © QA International / Science Photo Library Which labelled part of the sperm cell contains mitochondria? (1) A P B Q C R D S 12 (ii) The table shows the effect of different concentrations of PCB on the speed of movement of sperm cells. PCB concentration / mg dm–3 Mean speed of sperm / μm s–1 0 37 1 35 5 29 25 28 Calculate the percentage decrease in the mean speed of sperm in 25 mg dm–3 of PCB compared with the control. (2) Answer .............................................................. (iii) Deduce how PCBs could affect the speed of movement of sperm. 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(Total for Question 5 = 9 marks)