Name the microorganism that fixes nitrogen.

Options

A. Diazotrophs
B. Pathogens
C. Pasteurization
D. Preservatives

Explanation

**Step-by-Step Solution:**

1. **Understanding Nitrogen Fixation**: Nitrogen fixation is the process by which certain microorganisms convert atmospheric nitrogen (N2) into a form that plants can use, such as ammonia (NH3) or other nitrogenous compounds.

2. **Identifying Nitrogen-Fixing Microorganisms**: The primary microorganisms known for fixing nitrogen are certain types of bacteria. These bacteria are often found in the soil and in symbiotic relationships with plants.

3. **Recognizing Diazotrophic Bacteria**: The term "diazotrophic" refers to organisms that can fix atmospheric nitrogen. These organisms play a crucial role in the nitrogen cycle.

4. **Specific Example - Rhizobium**: One of the most well-known nitrogen-fixing bacteria is *Rhizobium*. This bacterium forms a symbiotic relationship with the roots of leguminous plants (like peas, beans, and clover), where it converts nitrogen gas from the atmosphere into a form that the plant can absorb and utilize.

5. **Conclusion**: Therefore, the microorganism that fixes nitrogen is *Rhizobium*, which is a type of diazotrophic bacteria.

**Final Answer**: The microorganism that fixes nitrogen is *Rhizobium*.

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