Which one is a nonsymbiotic nitrogen fixer

Options

A. Rhizobium
B. Oscillatoria
C. Nostoc
D. Lactobacillus

Answer

To determine which organism is a non-symbiotic nitrogen fixer from the given options (Rhizobium, Oscillatoria, Nostoc, and Lactobacillus), we can follow these steps:

### Step-by-Step Solution:

1. **Understand Nitrogen Fixation**:
- Nitrogen fixation is the process of converting atmospheric nitrogen (N₂) into ammonia (NH₃), which can be utilized by plants.

2. **Identify Types of Nitrogen Fixation**:
- There are two types of nitrogen fixation:
- **Symbiotic Nitrogen Fixation**: This involves a mutual association between plants and nitrogen-fixing bacteria.
- **Non-Symbiotic Nitrogen Fixation**: This involves free-living bacteria that fix nitrogen without any association with plants.

3. **Analyze the Options**:
- **Rhizobium**: This is a symbiotic nitrogen fixer found in the root nodules of leguminous plants. It forms a mutualistic relationship with the plant.
- **Oscillatoria**: This is a type of cyanobacteria that can fix nitrogen but is not typically associated with plants. It reproduces by fragmentation.
- **Nostoc**: This is also a cyanobacteria that can fix nitrogen and is known to be free-living, making it a non-symbiotic nitrogen fixer.
- **Lactobacillus**: This is a bacterium that is involved in fermentation processes, such as curd formation, and is not known for nitrogen fixation.

4. **Conclusion**:
- Based on the analysis, **Nostoc** is the correct answer as it is a non-symbiotic nitrogen fixer.

### Final Answer:
**Nostoc** is the non-symbiotic nitrogen fixer.

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