After a sperm has penetrated an ovum, entry of further sperm is prevented by

Options

A. condensation of yolk
B. formation of pigment coat
C. development of vitelline membrane
D. development of fertlisation membrane

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks what mechanism prevents the entry of additional sperm into an ovum after the first sperm has successfully penetrated it.

2. **Fertilization Process**: During fertilization, a sperm cell penetrates the plasma membrane of the ovum (egg cell). This is the initial step where the male gamete (sperm) fuses with the female gamete (ovum).

3. **Cortical Granules**: Once the sperm penetrates the ovum, structures called cortical granules within the ovum come into play. These granules are located just beneath the plasma membrane of the ovum.

4. **Fusion of Cortical Granules**: The cortical granules undergo fusion and release their contents into the space surrounding the ovum, known as the perivitaline space. This release is crucial for the next steps.

5. **Formation of the Fertilization Membrane**: The contents released from the cortical granules lead to the hardening of the perivitaline space, resulting in the formation of a structure called the fertilization membrane.

6. **Impenetrability**: The fertilization membrane acts as a barrier, making the ovum impermeable to any additional sperm. This is essential to prevent multiple sperm from fertilizing the same ovum, which could lead to a condition called polyembryony.

7. **Conclusion**: Therefore, the entry of further sperm is prevented by the development of the fertilization membrane after the first sperm has penetrated the ovum.

**Final Answer**: The entry of further sperm is prevented by the development of the fertilization membrane.

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