During the process of fertilisation the pollen tube of the pollen grain usually enters the embryo sac through

Options

A. integument
B. nucellus
C. chalaza
D. micropyle

Explanation

To answer the question, "During the process of fertilization, the pollen tube of the pollen grain usually enters the embryo sac through," we will follow these steps:

### Step-by-Step Solution:

1. **Understanding the Structure of the Ovule**:
- The ovule is a crucial part of the plant's reproductive system. It contains the embryo sac where fertilization occurs.

2. **Identifying Key Parts of the Ovule**:
- The ovule has several important parts, including:
- **Integuments**: These are the protective layers surrounding the ovule.
- **Micropyle**: This is a small opening in the integuments of the ovule.
- **Hilum**: The point of attachment of the ovule to the ovary wall.
- **Funiculus**: The stalk that connects the ovule to the ovary.

3. **Pollen Tube Growth**:
- When pollen grains land on the stigma of a flower, they germinate and form a pollen tube. This tube grows down through the style towards the ovule.

4. **Entry Point of the Pollen Tube**:
- The pollen tube must find a way to enter the embryo sac for fertilization to occur. The entry point is through the **micropyle**.

5. **Conclusion**:
- Therefore, the correct answer to the question is that the pollen tube usually enters the embryo sac through the **micropyle**.

### Final Answer:
The pollen tube of the pollen grain usually enters the embryo sac through the **micropyle**.

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