Which one of the following statements about nitrogenase is correct?

Options

A. It is sensitive to `CO_2` and therefore present in isolated nodules.
B. It requires `O_2` and therefore functional during the day
C. It is sensitive to `O_2` and therefore is functional in anaerobic environments
D. It is sensitive to light and therefore functions only in dark.

Answer

To solve the question regarding nitrogenase and identify the correct statement about it, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Function of Nitrogenase**:
- Nitrogenase is an enzyme that catalyzes the conversion of atmospheric nitrogen (N₂) into ammonia (NH₃). This process is known as nitrogen fixation.

2. **Evaluate Each Option**:
- **Option A**: "It is sensitive to CO₂ and therefore present in isolated nodule."
- This statement is incorrect because nitrogenase is sensitive to oxygen, not carbon dioxide (CO₂).

- **Option B**: "It requires oxygen and therefore functional during the day."
- This statement is also incorrect. Nitrogenase is inhibited by oxygen and does not require it to function. In fact, it operates in anaerobic conditions.

- **Option C**: "It is sensitive to oxygen and therefore is functional in an anaerobic environment."
- This statement is correct. Nitrogenase is indeed sensitive to oxygen, and it functions best in an anaerobic environment, which is provided by the presence of leghemoglobin in the root nodules of leguminous plants.

- **Option D**: "It is sensitive to light and therefore functions only in dark."
- This statement is incorrect. Nitrogenase is not sensitive to light; its activity is more related to oxygen levels than to light conditions.

3. **Conclusion**:
- Based on the evaluation of the options, the correct statement about nitrogenase is **Option C**: "It is sensitive to oxygen and therefore is functional in an anaerobic environment."