During in vitro fertilization (IVF), what causes polyspermy to be blocked after the initial sperm entry?

💡 Explanation

Polyspermy block after fertilization involves the cortical reaction, because cortical granules release enzymes that modify the zona pellucida, causing it to harden and prevent additional sperm from binding. Therefore, the zona hardening prevents further fertilization, rather than oolemma changes or sperm motility effects being primary.

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