Nitrogen fixation by organism requires conditions that are

Options

A. highly alkaline
B. anaerobic
C. saturated with sunlight
D. free of water

Answer

### Step-by-Step Solution:

1. **Understanding Nitrogen Fixation**: Nitrogen fixation is the process through which atmospheric nitrogen (N₂) is converted into a form that plants can use, such as nitrates (NO₃⁻) or nitrites (NO₂⁻).

2. **Role of Nitrogenase**: The enzyme responsible for this conversion is called nitrogenase. It plays a crucial role in the nitrogen fixation process.

3. **Sensitivity to Oxygen**: Nitrogenase is highly sensitive to oxygen. High concentrations of oxygen can inhibit its activity, making it less effective in converting nitrogen.

4. **Creating Anaerobic Conditions**: To facilitate nitrogen fixation, it is essential to maintain low oxygen levels. This is achieved through the presence of leghemoglobin, a molecule found in the root nodules of leguminous plants.

5. **Function of Leghemoglobin**: Leghemoglobin acts as an oxygen scavenger, binding to oxygen and thereby reducing its concentration in the root nodules. This creates an anaerobic environment, which is favorable for the activity of nitrogenase.

6. **Conclusion**: Therefore, the condition required for nitrogen fixation by organisms is an anaerobic environment, which is characterized by the absence of oxygen.

### Final Answer:
Nitrogen fixation by organisms requires anaerobic conditions (absence of oxygen).

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