During fertilization, zona pellucida is dissolved by

Options

A. Hyaluronidase
B. Hyaluronic acid
C. Renin
D. Acrosin

Answer

### Step-by-Step Solution:

1. **Understanding Fertilization**: Fertilization is the process where a sperm cell fuses with an egg cell (ovum) to form a zygote. This process involves several layers surrounding the ovum, including the zona pellucida.

2. **Role of the Zona Pellucida**: The zona pellucida is a glycoprotein layer that surrounds the plasma membrane of the oocyte. It plays a crucial role in fertilization by protecting the egg and facilitating sperm binding.

3. **Acrosomal Reaction**: When a sperm reaches the ovum, it undergoes a process called the acrosomal reaction. This reaction involves the release of enzymes from the acrosome, a cap-like structure on the head of the sperm.

4. **Enzymes Released**: During the acrosomal reaction, the sperm releases several enzymes, including hyaluronidase and acrosin. Hyaluronidase helps to digest the corona radiata, which is the layer of cells surrounding the ovum.

5. **Dissolution of Zona Pellucida**: After the corona radiata is penetrated, the enzyme acrosin plays a key role in dissolving the zona pellucida. Acrosin is a proteolytic enzyme that breaks down the proteins in the zona pellucida, allowing the sperm to reach the egg's plasma membrane.

6. **Fusion of Membranes**: Once the zona pellucida is dissolved, the membranes of the sperm and egg can fuse, leading to the fertilization of the egg and the formation of a zygote.

7. **Final Answer**: Based on the above steps, the enzyme responsible for dissolving the zona pellucida during fertilization is **acrosin**.

### Answer:
**D. Acrosin**

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