Leghemoglobin:

Options

A. Maintains aerobic condition in a root nodule
B. Is found only in legumes
C. Is synthesised by all nitrogen fixed bacteria
D. Is a poor `O_(2)` carrier

Answer

**Step-by-Step Solution:**

1. **Understanding Leghemoglobin**: Leghemoglobin is a protein found in the root nodules of leguminous plants. It is similar to hemoglobin in animals and is involved in the process of nitrogen fixation.

2. **Function of Leghemoglobin**: The primary role of leghemoglobin is to bind oxygen. In root nodules, where nitrogen fixation occurs, it helps maintain a low concentration of oxygen. This is crucial because the nitrogen-fixing enzyme, nitrogenase, functions effectively in anaerobic (low oxygen) conditions.

3. **Analyzing the Options**:
- **Option A**: "Maintain aerobic condition in a root nodule" - This is incorrect. Leghemoglobin creates an anaerobic environment by reducing oxygen levels.
- **Option B**: "Is found only in the legume" - This is correct. Leghemoglobin is specifically associated with leguminous plants and their symbiotic relationship with nitrogen-fixing bacteria (like Rhizobium).
- **Option C**: "Is synthesized by all nitrogen fixation bacteria" - This is incorrect. Not all nitrogen-fixing bacteria produce leghemoglobin; it is specific to those associated with legumes.
- **Option D**: "Is a poor oxygen carrier" - This is also incorrect. Leghemoglobin is an effective oxygen carrier, but it regulates oxygen levels to favor nitrogen fixation.

4. **Conclusion**: The correct answer is that leghemoglobin is found only in legumes. It plays a critical role in creating the right conditions for nitrogen fixation by managing oxygen levels in the root nodules.