Pollination occurs when a pollen grain

Options

A. releases its sperm nuclei
B. lands on stigma
C. matures and has 3 nuclei
D. releases its sperm nuclei and fertilize the egg and polar nuclei

Answer

**Step-by-Step Solution:**

1. **Understanding Pollination**: Pollination is defined as the transfer of pollen grains from the male part of the flower (anther) to the female part (stigma). This is a crucial step in the reproductive process of flowering plants.

2. **Identifying the Options**:
- **Option 1**: Releases its sperm nuclei.
- **Option 2**: Lands on the stigma.
- **Option 3**: Matures and has three nuclei.
- **Option 4**: Releases its sperm nuclei and fertilizes the egg and the polar nuclei.

3. **Analyzing Each Option**:
- **Option 1**: This refers to the germination of the pollen grain, which occurs after pollination, not during it.
- **Option 2**: This option correctly describes the process of pollination, where the pollen grain lands on the stigma.
- **Option 3**: This relates to the development of the pollen grain (microgametogenesis), which happens after pollination.
- **Option 4**: This describes the process of fertilization, which occurs after pollination has taken place.

4. **Determining the Correct Answer**: Based on the definitions and processes involved, the correct answer to the question "Pollination occurs when a pollen grain" is **Option 2: lands on the stigma**.

5. **Conclusion**: Pollination is specifically the act of pollen grains landing on the stigma, which is essential for the subsequent processes of fertilization and reproduction in flowering plants.

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