State the role of the zona pellucida after a sperm has fused with the ovum.
Answer
It undergoes hardening (zona reaction) to prevent entry of additional sperms, thereby preventing polyspermy.
The correct answer is It undergoes hardening (zona reaction) to prevent entry of additional sperms, thereby preventing polyspermy. — Thus, the zona pellucida’s role after fertilization is to ensure monospermy by preventing polyspermy.
Step-by-step solution
- Recall that after the first sperm fuses with the ovum, cortical granules release their contents into the perivitelline space.
- These enzymes modify the glycoprotein matrix of the zona pellucida, a process called the cortical (zona) reaction.
- The modification causes the zona pellucida to harden, forming a barrier that blocks any additional sperm from penetrating.
- Thus, the zona pellucida’s role after fertilization is to ensure monospermy by preventing polyspermy.
Common mistake: Mentioning only sperm binding and forgetting the cortical reaction that hardens the zona.
Concept tested: Zona pellucida post‑fertilization block
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