Nitrogen fixation by organism requires conditions that are

Options

A. (a) highly alkaline
B. (b) anaerobic
C. (c) saturated with sunlight
D. (d) free of water

Answer

To answer the question regarding the conditions required for nitrogen fixation by organisms, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Nitrogen Fixation**:
- Nitrogen fixation is the process by which certain organisms convert atmospheric nitrogen (N₂) into a more usable form, such as nitrates (NO₃⁻), which plants can absorb and utilize for growth.

2. **Identifying the Organisms Involved**:
- This process is primarily carried out by certain microorganisms, including bacteria (e.g., Rhizobium) that form symbiotic relationships with the roots of leguminous plants.

3. **Role of Nitrogenase Enzyme**:
- The key enzyme involved in nitrogen fixation is called nitrogenase. This enzyme is responsible for the conversion of atmospheric nitrogen to ammonia (NH₃), which can then be further converted to nitrates.

4. **Sensitivity to Oxygen**:
- Nitrogenase is highly sensitive to molecular oxygen (O₂). The presence of oxygen can inhibit its activity, leading to decreased nitrogen fixation.

5. **Anaerobic Conditions**:
- To facilitate nitrogen fixation, anaerobic conditions (absence of oxygen) are required. Some microorganisms have adaptations to create such environments, such as the presence of leghemoglobin in the root nodules of legumes, which helps to maintain low oxygen levels while still supplying some oxygen to the bacteria.

6. **Evaluating the Options**:
- Now, let's evaluate the options given in the question:
- a) Highly alkaline: Not a requirement for nitrogen fixation.
- b) Anaerobic: Correct, as nitrogen fixation requires low oxygen levels.
- c) Saturated with sunlight: Not a requirement for nitrogen fixation.
- d) Free of water: Not a requirement; in fact, water is essential for plant growth.

7. **Conclusion**:
- Based on the analysis, the correct answer is **b) anaerobic**.