Gamete
specialized cell involved in sexual reproduction (e.g egg/sperm)
Explain the process of fertilisation
- Sperm arrives at egg
- Chemicals from cells surrounding the egg trigger the acrosome reaction.
- The acrosome (sperm lysosome) swells and fuses with the cell surface membrane of the egg.
- Digestive enzymes in the acrosome (sperm lysosome) are released by exocytosis.
- These enzymes digest through the follicle cells, then zona pellucida.
- The sperm fuses through the egg membrane.
- Sperm haploid nucleus enters the egg, leaving the flagellum behind.
- Cortical reaction; enzymes are released from cortical granules (egg lysosomes) by exocytosis causing the zona pellucida to harden to prevent any other sperm from entering.
- Haploid nucleus of egg and haploid nucleus of sperm fuse together to produce a zygote (fertilised egg).
Accrosome reaction
When digestive enzymes in the acrosome (sperm lysosome) are released by exocytosis to digest through follicle cells/zona pellucida.
Cortical reaction
enzymes are released from cortical granules to harden the zona pellucida and prevent any other sperm entering the egg.
Compare and contrast the cortical and acrosome reactions
- Both the cortical and acrosome reaction use lysosomes
- both release chemicals by exocytosis.
- The acrosome reaction involves the digestion of the zona pellucida, whereas the cortical reaction involves the thickening/hardening of the zona pellucida.
Adaptations of sperm cells
Acrosome - contains digestive enzymes to hydrolyse the zona pellucida
Flagellum - propels the sperm forwards (motility)
Large amounts of mitochondria - provide ATP for respiration, energy for swimming
What are the adaptations of an egg cell?
Zona pellucida hardens after fertilisation to prevent polyspermy
Follicle cells provide protective coating
Cytoplasm contains nutrients for the embryo
