Sexual reproduction in mammalsEdexcel A-Level Biology B: Mind map

Exam questions on Sexual reproduction in mammals

1. A fertility clinic is investigating why a couple have been unable to conceive. Analysis of the man's semen sample shows that the sperm swim normally, but in laboratory tests most of them fail to penetrate the layer surrounding an egg.
   Explain why sperm that cannot release the contents of the acrosome are unlikely to fertilise an egg.2 marks
2. Oogenesis begins before a girl is born. By birth her ovaries contain about one million primary oocytes, each surrounded by follicle cells. From puberty, roughly once every 28 days, one follicle matures and an oocyte is released from the ovary.
   Explain why the cell released at ovulation is not yet a mature ovum.2 marks
3. Researchers study fertilisation in the laboratory by adding sperm to secondary oocytes that are surrounded by a layer called the zona pellucida. Many sperm bind to the zona pellucida, but only one sperm nucleus normally enters each egg.
   Describe how a sperm penetrates the layer surrounding the egg and enters it.3 marks