Cyanobacterial cells which are specialised for nitrogen fixation are

Options

A. Phycobilisomes
B. Heterocysts
C. Hormogonia
D. Trichomes.

Answer

**Step-by-Step Solution:**

1. **Understanding the Question:**
The question asks about the specialized cells in cyanobacteria that are responsible for nitrogen fixation.

2. **Identifying the Options:**
The options provided are:
- Phycobilisomes
- Heterocyst
- Hormogonia
- Trichomes

3. **Analyzing Each Option:**
- **Phycobilisomes:** These are light-harvesting complexes found in cyanobacteria but are not involved in nitrogen fixation.
- **Heterocyst:** These are specialized cells in certain cyanobacteria (like Anabaena) that are specifically adapted for nitrogen fixation.
- **Hormogonia:** These are filamentous structures that can help in reproduction and movement but are not directly involved in nitrogen fixation.
- **Trichomes:** These are the filaments of cyanobacteria but do not specifically refer to nitrogen-fixing cells.

4. **Identifying the Correct Answer:**
Based on the analysis, the correct answer is **Heterocyst**. These cells contain the enzyme nitrogenase, which is crucial for converting atmospheric nitrogen into ammonia, a form usable by plants.

5. **Conclusion:**
Therefore, the specialized cyanobacterial cells responsible for nitrogen fixation are **Heterocyst**.

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