Nitrogenase enzyme occurs in

Options

A. cortical cells
B. Xylem of root nodules
C. Bacteroids
D. Peribacteroidal membrane

Answer

**Step-by-Step Solution:**

1. **Understanding Nitrogenase Enzyme**:
- The nitrogenase enzyme is crucial for the process of nitrogen fixation, which converts atmospheric nitrogen (N₂) into ammonia (NH₃), a form that plants can utilize.

2. **Location of Nitrogenase**:
- Nitrogenase is primarily found in prokaryotic organisms, specifically in certain bacteria that are capable of fixing nitrogen. This enzyme is not found in eukaryotic cells.

3. **Types of Nitrogen-Fixing Bacteria**:
- There are two main types of nitrogen-fixing bacteria:
- **Symbiotic Nitrogen-Fixing Bacteria**: These bacteria, such as Rhizobium, form a symbiotic relationship with leguminous plants. They reside in root nodules of these plants.
- **Free-Living Nitrogen-Fixing Bacteria**: These bacteria exist independently in the soil and do not form symbiotic relationships with plants.

4. **Symbiotic Relationship**:
- In the case of symbiotic bacteria like Rhizobium, they infect the root hairs of leguminous plants, leading to the formation of root nodules where nitrogen fixation occurs.

5. **Presence of Nitrogenase**:
- Within these root nodules, the nitrogenase enzyme is present in the modified bacteria known as bacteroids. These bacteroids are formed when Rhizobium bacteria undergo changes after infecting the root hairs.

6. **Protection from Oxygen**:
- The nitrogenase enzyme is sensitive to oxygen, which can inhibit its activity. To protect nitrogenase, leghemoglobin is produced in the root nodules, which helps to maintain a low oxygen environment.

7. **Conclusion**:
- Therefore, the correct answer to the question "Nitrogenase enzyme occurs in" is that it occurs in **reduced bacteroids** within the root nodules of leguminous plants.

**Final Answer**: Nitrogenase enzyme occurs in reduced bacteroids.

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