Reproduction: block to polyspermy: practice question

A Physiology question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Physiology · Reproduction: block to polyspermy

Sample item

After one sperm penetrates the oocyte, cortical granules release their contents into the perivitelline space. What is the functional result?

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

C. Alteration of the zona pellucida so that no further sperm can bind

The cortical reaction releases enzymes that modify zona pellucida proteins, including the sperm receptor, so other sperm cannot bind or penetrate. This is the block to polyspermy and ensures a diploid zygote.

Option by option

  • A. Initiation of capacitation of nearby sperm

    Capacitation takes place in the female tract before binding and is not triggered by cortical granules.

  • B. Completion of the first meiotic division

    The first meiotic division is completed before ovulation, not by the cortical reaction.

  • C. Alteration of the zona pellucida so that no further sperm can bind (correct)

    Correct. Cortical granule enzymes modify the zona and block the entry of more sperm.

  • D. Triggering of the acrosome reaction in other sperm

    The acrosome reaction occurs when sperm bind the zona and is not induced by cortical granule contents.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

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Questions about this Physiology question

What is the answer to this Physiology question?

The best answer is C, Alteration of the zona pellucida so that no further sperm can bind. The cortical reaction releases enzymes that modify zona pellucida proteins, including the sperm receptor, so other sperm cannot bind or penetrate.

Why is "Initiation of capacitation of nearby sperm" not the answer?

Capacitation takes place in the female tract before binding and is not triggered by cortical granules.

Why is "Completion of the first meiotic division" not the answer?

The first meiotic division is completed before ovulation, not by the cortical reaction.

Why is "Triggering of the acrosome reaction in other sperm" not the answer?

The acrosome reaction occurs when sperm bind the zona and is not induced by cortical granule contents.

What concept does this question test?

It tests Reproduction: block to polyspermy in Physiology. This is the block to polyspermy and ensures a diploid zygote.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Reproduction: block to polyspermy?

For each system, sketch the key graph (pressure–volume loop, oxygen dissociation curve, nephron handling) and explain it aloud. Then use the flashcards and the other Physiology questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.