15 Turn over 6 Male fertility can be determined by a number of different factors. (a) Describe the process of spermatogenesis. 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(b) The mean volume of the semen produced by a male ejaculation is 3.4 cm3. This contains a mean concentration of 17 000 sperm mm–3. Calculate the mean total number of sperm in a single ejaculation. Give your answer in standard form. (2) Answer .............................................................. 16 (c) The distance from the point of ejaculation in the vagina to the upper end of the fallopian tube (where fertilisation takes place) is 19 cm. Some sperm travel this distance in three hours. Calculate the mean speed of these sperm in cm min–1. (1) Answer .............................................................. (d) Male fertility can be estimated using scales that take into account the number of sperm, their mobility and the percentage with a normal ‘head’. To calculate male fertility using these scales:  draw a straight line between the observed number of sperm (scale A) and the percentage of sperm motile after 2 hours (scale C)  from the intersection of this line with scale B, draw another straight line to scale E (the percentage of normal-headed sperm)  the point where this second line crosses scale D (the fertility index), provides a relative assessment of fertility. }         A over 80 over 88 over 55 80 65 84 50 50 55 80 35 10 45 78 30 5 34 25 1 25 20 0.5 15 15 0.1 B C D E under 10 under 70 under 10 fertile fertility index observed number of sperm / millions cm–3 motile sperm after 2 hours / % normal-headed sperm / % 45 25 76 possibly fertile infertile 17 Turn over (i) Estimate the fertility of a man who produces a semen sample with:  25 million sperm per cm3  35% of which are motile after 2 hours and  84% of which have normal heads. (2) Answer .............................................................. (ii) Deduce why fertilisation is unlikely to occur if there are 5 million spermatozoa per cm3. 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(Total for Question 6 = 10 marks)