Penetration of sperm into the oocyte is facilitated by

Options

A. Zona reaction
B. Acrosomal reaction
C. Cortical reaction
D. All the above

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks about the process that facilitates the penetration of sperm into the oocyte (egg).

2. **Identifying Key Terms**: The terms mentioned in the options are:
- Zona reaction
- Acrosomal reaction
- Particle reaction
- All of the above

3. **Defining the Acrosomal Reaction**: The acrosomal reaction is a crucial process that occurs when the sperm approaches the oocyte. The acrosome is a cap-like structure located at the head of the sperm, which contains enzymes.

4. **Role of Proteolytic Enzymes**: During the acrosomal reaction, these proteolytic enzymes are released. They play a vital role in breaking down the outer layers of the oocyte, particularly the zona pellucida, which is a protective glycoprotein layer surrounding the egg.

5. **Mechanism of Penetration**: The release of these enzymes helps in hydrolyzing the zona pellucida, allowing the sperm to penetrate the oocyte. This process is essential for fertilization to occur.

6. **Conclusion**: Based on the information, the correct answer to the question is that the penetration of sperm into the oocyte is primarily facilitated by the acrosomal reaction.

**Final Answer**: Acrosomal reaction facilitates the penetration of sperm into the oocyte.

---