During fertilisation, the entry of additional sperms (polyspermy) is blocked because:
AThe first sperm induces changes in the ovum's zona pellucida that prevent further sperm entry
BThe remaining sperms lose motility immediately
CThe ovum disintegrates
DThe zona pellucida is removed
Answer & Solution
Correct answer: A. The first sperm induces changes in the ovum's zona pellucida that prevent further sperm entry
The first sperm to contact the zona pellucida induces a **block to polyspermy** (changes in the membrane preventing entry of more sperms), so only one sperm fertilises the ovum.
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