Cyanobacteria are// Nostoc is

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 the Organism**: The question asks about Cyanobacteria and specifically mentions Nostoc. It is important to recognize that Nostoc is a genus within the Cyanobacteria group.

2. **Understand the Characteristics of Nostoc**: Nostoc is known for its ability to perform photosynthesis. It is classified as an oxygenic photosynthetic organism, meaning it produces oxygen during the process of photosynthesis.

3. **Nitrogen Fixation**: Nostoc has the ability to fix atmospheric nitrogen. This means it can convert nitrogen gas from the atmosphere into ammonia, which is a usable form of nitrogen for plants and other organisms.

4. **Role of Heterocysts**: Within Nostoc, there are specialized cells called heterocysts. These cells are crucial for nitrogen fixation as they create a micro-anaerobic environment that protects the nitrogenase enzyme from being inactivated by oxygen.

5. **Presence of Nitrogenase**: Nitrogenase is the enzyme responsible for the fixation of nitrogen. Since Nostoc has heterocysts that contain nitrogenase, it confirms that Nostoc is capable of nitrogen fixation.

6. **Evaluate the Options**: Now, let's analyze the provided options:
- Option 1: Oxygenic with nitrogenase (correct)
- Option 2: Oxygenic without nitrogenase (incorrect, as it has nitrogenase)
- Option 3: Non-oxygenic with nitrogenase (incorrect, as Nostoc is oxygenic)
- Option 4: Non-oxygenic without nitrogenase (incorrect, as Nostoc is oxygenic and has nitrogenase)

7. **Conclusion**: Based on the analysis, the correct answer is that Cyanobacteria, specifically Nostoc, is "oxygenic with nitrogenase."

**Final Answer**: Cyanobacteria are Nostoc is oxygenic with nitrogenase.

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