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Biology · 2026 · 3 marks
CBSE 2026 · Region 4 · Set 3 · Q23
(a) Draw a diagram of human ovum prior to fertilization. Label any four parts. (b) Explain how polyspermy is avoided during fertilization.
(a)
Draw a diagram of human ovum prior to fertilization. Label any four parts.
(b)
Explain how polyspermy is avoided during fertilization.
Marking-scheme solution
(a)
(b)
When a sperm comes in contact with the zona pellucida layer of the ovum it induces changes in the membrane that blocks the entry of additional sperm thus avoiding polyspermy.
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CBSE Class 12 Biology past-paper question from the 2026 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.