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Human Reproduction — BIOLOGY STD 12 Science — Question

Rajasthan BoardEnglish MediumSTD 12 ScienceBIOLOGYHuman Reproduction1 Mark
Question
For two statements are given-one labelled Assertion and the other labelled Reason. Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below.
  1. Both assertion and reason are true, and reason is the correct explanation of assertion.
  2. Both assertion and reason are true, but reason is not the correct explanation of assertion.
  3. Assertion is true, but reason is false.
  4. Both assertion and reason are false.
Assertion: If several spermatozoa hit the egg at the same time, all can enter the egg.
Reason: The above process is called amphimixis which can be prevented by fertilisation membrane.
✓

Answer

  1. Both assertion and reason are false.

​​​​​​​​​​​​​​​​​​​​​​​​​​​​Explanation:

If several spermatozoa hit the egg at the same time, even then only one can get entry into the egg because after the entry of one sperm cell, the egg cell becomes impervious (not able to be penetrated) to other sperm cells. This can be done by fertilizin-antifertilizin compatibility reaction. Fertilizin of egg interacts with antifertilizin of a sperm of the same species. This interaction makes the sperms stick to the egg surface. The process of penetrating the ovum by many sperms is called polyspermy. Once the sperm cell has penetrated the corona radiata and zona pellucida, its unit membrane fuses with the unit membrane surrounding the egg cytoplasm. Just after the entry of sperm in the egg, a fertilisation membrane is fanned (by zona pellucida) in the egg. This membrane prevents polyspermic fertilisation. Amphimixis is the mixing up the chromosomes of a sperm and an ovum.

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