What is true for cyano bacteria : -

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. **Understanding Cyanobacteria**:
- Cyanobacteria, also known as blue-green algae, are photosynthetic bacteria found in various environments, including freshwater and marine ecosystems. They are among the oldest living organisms on Earth.

2. **Photosynthesis Type**:
- Cyanobacteria perform oxygenic photosynthesis, which means they produce oxygen as a byproduct of their photosynthetic process. This distinguishes them from non-oxygenic photosynthetic organisms.

3. **Nitrogen Fixation**:
- Cyanobacteria have the capability to fix atmospheric nitrogen. They possess specialized cells known as heterocysts that allow them to convert atmospheric nitrogen (N2) into ammonia (NH3) or nitrates (NO3-), which can be utilized for growth.

4. **Presence of Nitrogenase**:
- The enzyme nitrogenase is crucial for the nitrogen fixation process in cyanobacteria. This enzyme facilitates the conversion of nitrogen gas into ammonia, confirming that cyanobacteria indeed possess nitrogenase.

5. **Conclusion**:
- Based on the characteristics of cyanobacteria, they are classified as oxygenic (due to their photosynthetic process that produces oxygen) and they possess nitrogenase (due to their ability to fix nitrogen). Therefore, the correct statement regarding cyanobacteria is: **"Oxygenic with nitrogenase."**

### Final Answer:
- The correct option is **Option 1: Oxygenic with nitrogenase.**