What is true for cyanobacteria?

Options

A. Oxygenic with nitrogenase
B. Oxygenic without nitrogenase
C. Non oxygenic with nitrogenase
D. Non oxygenic without nitrogenase

Answer

### Step-by-Step Solution:

1. **Identify Cyanobacteria**:
- Cyanobacteria, also known as blue-green algae, are prokaryotic organisms classified under the kingdom Monera.

2. **Photosynthetic Nature**:
- Cyanobacteria are photosynthetic organisms. They contain photosynthetic pigments that allow them to perform photosynthesis.

3. **Photosystem II**:
- These organisms possess Photosystem II, which is crucial for the process of photosynthesis. This system is involved in the splitting of water molecules, which releases oxygen (O2) as a byproduct.

4. **Heterocysts**:
- Some cells in cyanobacteria, known as heterocysts, are non-photosynthetic. These cells do not contain Photosystem II and thus do not participate in oxygen production.

5. **Function of Heterocysts**:
- Heterocysts are important for nitrogen fixation. They contain a gene known as NIF, which encodes for the enzyme nitrogenase. This enzyme converts atmospheric nitrogen into ammonia, which is beneficial for soil fertility.

6. **Conclusion**:
- Based on the characteristics of cyanobacteria, the true statement is that they are oxygenic photosynthetic organisms that also perform nitrogen fixation due to the presence of nitrogenase in heterocysts.

### Final Answer:
Cyanobacteria are oxygenic photosynthetic organisms that perform nitrogen fixation.

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