Root nodules on plants of the legume family contain

Options

A. Cyanobacteria
B. Nitrococcus
C. Rhizobium
D. Nitrobacter

Answer

**Step-by-Step Solution:**

1. **Understanding Root Nodules**: Root nodules are specialized structures found on the roots of certain plants, particularly those in the legume family (Fabaceae). These nodules are formed as a result of a symbiotic relationship between the plant and specific bacteria.

2. **Identifying the Bacteria**: The primary bacteria associated with the root nodules of legumes are known as Rhizobium. These bacteria are capable of fixing atmospheric nitrogen, which is crucial for the plant's growth and development.

3. **Function of Rhizobium**: Rhizobium bacteria convert atmospheric nitrogen (N2) into ammonia (NH3) through a process called nitrogen fixation. This process makes nitrogen available to the plant in a form that it can utilize for its metabolic needs.

4. **Evaluating Other Options**:
- Option 1: Cyanobacteria - Incorrect, as these are not typically found in root nodules of legumes.
- Option 2: Nitrococcus - Incorrect, as this genus is not associated with legume root nodules.
- Option 4: Nitrobacter - Incorrect, as this genus is involved in the nitrification process, not nitrogen fixation in legumes.

5. **Conclusion**: The correct answer to the question regarding what is found in the root nodules of the legume family is **Rhizobium**.

**Final Answer**: Option 3, Rhizobium.

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