Reproduction T3

Question 1

Compare and contrast the acrosome reaction and the cortical reaction.
(3)

Answer 1

• Both involve vesicles.
• Both involve release of chemicals/enzymes by exocytosis.
• Acrosome reaction causes digestion of zona pellucida, cortical reaction causes thickening of zona pellucida.

Question 2

Describe the events of fertilisation that occur after the acrosome reaction.
(3)

Answer 2

• Sperm cell membrane and ovum cell membrane fuse.
• Cortical granules release contents into zona pellucida.
• Zona pellucida hardens.
• Fusion of ovum and sperm haploid nuclei.

Question 3

Describe and explain how events following the acrosome reaction prevent more then one sperm from fertilising the egg.
(4)

Answer 3

• Sperm cell fuses with ovum membrane.
• Cortical granules fuse with ovum cell membrane.
• Contents of cortical granules released into zona pellucida/ cortical reaction.
• Zona pellucida hardens.
• Change in charge across egg cell membrane.