After a sperm has penetrated in ovum during fertilisation, the entry of further sperms is prevented by

Options

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

Answer

**Step-by-Step Solution:**

1. **Understanding Fertilization**: Fertilization occurs when a sperm successfully penetrates an ovum (egg). The ovum is larger than the sperm and is the female gamete.

2. **Role of the Zona Pellucida**: The outer layer of the ovum is known as the zona pellucida. This is a glycoprotein-rich membrane that surrounds the egg.

3. **Chemical Changes Upon Sperm Entry**: When the first sperm penetrates the ovum, it triggers chemical changes in the zona pellucida. These changes are crucial for the next step.

4. **Prevention of Polyspermy**: The chemical changes in the zona pellucida create a barrier that prevents additional sperm from entering the ovum. This process is essential to ensure that only one sperm fertilizes the egg, preventing a condition known as polyspermy.

5. **Formation of the Fertilization Membrane**: The changes in the zona pellucida lead to the formation of a fertilization membrane, which acts as a protective barrier against other sperm.

6. **Conclusion**: The entry of further sperm is prevented by the formation of the fertilization membrane, which is a result of the changes in the zona pellucida after the first sperm penetrates the ovum.

**Final Answer**: The entry of further sperms is prevented by the formation of the fertilization membrane, which is caused by chemical changes in the zona pellucida after the first sperm penetrates the ovum.

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