Question

Receptors for sperm binding in mammals are present on:

• A. Vitelline membrane
• B. Corona radiata
• C. Zona pellucida
• D. Perivitelline space

Answer 1

The correct option is C Zona pellucida

Once a sperm enters the female reproductive tract, it swims towards the secondary oocyte and reaches the zona pellucida layer by making its way through the cells of corona radiata. It binds to the receptors on the zona pellucida (ZP3 molecules) to bring about acrosomal reactions.

The hydrolytic enzymes/digestive enzymes present in the acrosome of the sperm help in the degradation of the zona pellucida layer. This enables the sperm to penetrate the zona pellucida layer, perivitelline space (the space between the zona pellucida layer and the plasma membrane) and plasma membrane of the oocyte.

Fig: Secondary oocyte