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Zona pellucida disintegrates just:...

Zona pellucida disintegrates just:

A

Before fertilization

B

After fertilization

C

Midway during cleavage

D

After completion of cleavage.

Text Solution

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The correct Answer is:
### Step-by-Step Solution: 1. **Understanding the Zona Pellucida**: The zona pellucida is a glycoprotein layer surrounding the plasma membrane of an oocyte (egg). It plays a crucial role in fertilization by facilitating sperm binding and preventing polyspermy. 2. **Fertilization Process**: During fertilization, sperm must penetrate the zona pellucida to reach the oocyte. The sperm releases enzymes from its acrosome, such as acrosin, which help dissolve the zona pellucida. 3. **Timing of Disintegration**: The question asks when the zona pellucida disintegrates. While some dissolution occurs during fertilization to allow sperm entry, the complete disintegration of the zona pellucida does not happen immediately. 4. **Cleavage Stage**: After fertilization, the zygote undergoes cleavage, which is a series of rapid cell divisions. The zona pellucida remains intact during the initial stages of cleavage. 5. **Completion of Cleavage**: The zona pellucida disintegrates completely after the cleavage process is finished. This allows the developing embryo to expand and implant into the uterine wall. 6. **Conclusion**: Based on the above understanding, the correct answer to the question is that the zona pellucida disintegrates after the completion of cleavage. ### Final Answer: **D) After completion of cleavage.** ---
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