Gametes and fertilisation in mammalsEdexcel A-Level Biology A: Mind map

Exam questions on Gametes and fertilisation in mammals

1. A biologist examines human gametes using an electron microscope. The sperm cells have a head, a mid-piece and a tail. The egg is a large cell surrounded by a jelly-like layer called the zona pellucida, with small vesicles lying just beneath its cell surface membrane.
   Describe two ways in which the egg is specialised for its function.2 marks
2. In a fertility laboratory, sperm are added to a dish containing a human egg. The scientists watch as sperm reach the zona pellucida, and they study the events that follow the contact between one sperm and the egg.
   Explain why it would be harmful if more than one sperm fused with the egg.2 marks
3. A fertility clinic investigates two men whose sperm fail to fertilise eggs. In man 1 the sperm have normal tails and mitochondria but have no acrosome. In man 2 the sperm have a normal acrosome but have very few mitochondria in the mid-piece, and their tails barely move.
   Explain why the sperm from man 1 are unable to fertilise an egg.3 marks