Which of the following gene clusters in bacteria is responsible for nitrogen fixation ?

Options

A. (a) Nod, Nif, Fix
B. (b) Nod, Ndf, Nfx
C. (c) nod, Nix, Nfx
D. (d) Ndx, Nif, Fix

Answer

**Step-by-Step Solution:**

1. **Understanding Nitrogen Fixation**: Nitrogen fixation is the process by which nitrogen in the atmosphere is converted into ammonia or related nitrogenous compounds in soil. This is crucial for plants as they cannot directly use atmospheric nitrogen.

2. **Role of Nitrogen-Fixing Bacteria**: Certain bacteria, such as Rhizobium, play a significant role in nitrogen fixation. They form a symbiotic relationship with legume plants, where they fix atmospheric nitrogen into a usable form (nitrate) for the plants.

3. **Identifying Gene Clusters**: In Rhizobium, there are specific gene clusters responsible for nitrogen fixation. The main gene clusters involved are:
- **Nod**: Responsible for nodule formation in the roots of legume plants.
- **NIF**: Involved in the production of nitrogenase, the enzyme that facilitates the conversion of nitrogen gas to ammonia.
- **FIX**: Also contributes to the nitrogen fixation process.

4. **Analyzing the Options**: The question provides multiple options regarding gene clusters:
- Option A: NOD, NIF, and FIX
- Option B: NOD, NADF, and NFX
- Option C: NOD, NIF, and NFX
- Option D: NADX, NIF, and FIX

5. **Evaluating the Correct Answer**:
- Option A includes all three correct gene clusters (NOD, NIF, FIX).
- Options B, C, and D include incorrect gene clusters (NADF, NFX, NADX), which are not associated with nitrogen fixation.

6. **Conclusion**: Therefore, the correct answer is Option A: NOD, NIF, and FIX.

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