Gametes and fertilisationEdexcel International A Level Biology: Mind map

Exam questions on Gametes and fertilisation

1. A fertility clinic scientist is examining a sample of human sperm under the electron microscope. Each sperm cell has a head containing the nucleus and a membrane-bound vesicle at its tip, a midpiece packed with mitochondria, and a long tail (flagellum).
   The sperm midpiece contains many mitochondria. Explain how this adaptation helps the sperm to reach and fertilise an oocyte.2 marks
2. In humans, once a sperm cell has made contact with a secondary oocyte, a series of reactions follows. The sperm releases enzymes, and the oocyte then releases the contents of vesicles lying just beneath its plasma membrane. A laboratory study uses mouse gametes. Mouse body cells contain 40 chromosomes.
   Explain why it is important that only one sperm nucleus fuses with the oocyte nucleus.2 marks
3. A plant breeder studies a diploid flowering plant with 14 chromosomes in each body cell. Pollen grains land on the stigma of a flower. Each pollen grain contains a tube nucleus and a generative nucleus, and the generative nucleus divides to give two male nuclei. The ovule contains an embryo sac with an egg cell and a central cell that has two polar nuclei.
   Describe how the male nuclei reach the embryo sac after a pollen grain lands on the stigma.3 marks