Heterocystous cyanobacteria-

Options

A. Only Nostoc
B. Only Anabaena
C. Both Nostoc and Anabaena
D. Vibrio

Answer

**Step-by-Step Solution:**

1. **Understanding Heterocystous Cyanobacteria**:
Heterocystous cyanobacteria are a type of cyanobacteria that have specialized cells called heterocysts. These cells are capable of fixing atmospheric nitrogen into a form that can be utilized by the organism.

2. **Identifying the Options**:
The options provided are:
- A) Nostoc
- B) Anabena
- C) Both A and B
- D) Vibrio

3. **Evaluating the Options**:
- **Nostoc**: This genus is known for its ability to form heterocysts and fix nitrogen, especially during periods of nitrogen starvation.
- **Anabena**: Similar to Nostoc, Anabena also forms heterocysts and is capable of nitrogen fixation.
- **Vibrio**: This genus does not belong to the cyanobacteria group and does not form heterocysts.

4. **Conclusion**:
Since both Nostoc and Anabena are known to be heterocystous cyanobacteria, the correct answer is option C, which states that both A (Nostoc) and B (Anabena) are heterocystous cyanobacteria.

5. **Final Answer**:
The correct answer is C) Both A and B (Nostoc and Anabena).

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