How many of the following organisms not fix the atmospheric nitrogen in free living condition?
Frankia, Anabaena, Rhodospirillum, Bijrenickia, Rhizobium, Azotobacter, Nostoc.

Options

A. Two
B. Four
C. Five
D. Three

Answer

To determine how many of the listed organisms do not fix atmospheric nitrogen in free-living conditions, we will analyze each organism one by one.

### Step-by-Step Solution:

1. **Identify the Organisms**: The organisms listed are:
- Frankia
- Anabaena
- Rhodospirillum
- Bijernickia
- Rhizobium
- Azotobacter
- Nostoc

2. **Understand Nitrogen Fixation**: Nitrogen fixation is the process by which certain organisms convert atmospheric nitrogen (N₂) into ammonia (NH₃) or related compounds, which are usable by plants. Some organisms do this in a free-living state, while others do it in symbiotic relationships with plants.

3. **Analyze Each Organism**:
- **Frankia**: This organism is known to fix nitrogen but primarily in symbiotic relationships with certain plants (e.g., actinorhizal plants). It does not fix nitrogen in a free-living condition.
- **Anabaena**: This is a cyanobacterium that can fix nitrogen in both free-living conditions and in symbiotic relationships (e.g., with certain ferns).
- **Rhodospirillum**: This is a free-living nitrogen-fixing bacterium.
- **Bijernickia**: This organism is also known to fix nitrogen in free-living conditions.
- **Rhizobium**: This bacterium is primarily known for its symbiotic nitrogen-fixing ability with legumes and does not fix nitrogen in a free-living state.
- **Azotobacter**: This is a free-living nitrogen-fixing bacterium.
- **Nostoc**: Similar to Anabaena, Nostoc can fix nitrogen in both free-living conditions and in symbiotic relationships.

4. **Count the Organisms Not Fixing Nitrogen in Free-Living Conditions**:
- From the analysis:
- Frankia (does not fix in free-living)
- Anabaena (can fix in free-living)
- Rhodospirillum (fixes in free-living)
- Bijernickia (fixes in free-living)
- Rhizobium (does not fix in free-living)
- Azotobacter (fixes in free-living)
- Nostoc (can fix in free-living)

The organisms that do not fix nitrogen in free-living conditions are Frankia and Rhizobium.

5. **Final Count**: Therefore, there are **2 organisms (Frankia and Rhizobium)** that do not fix atmospheric nitrogen in free-living conditions.

### Final Answer:
**2 organisms do not fix atmospheric nitrogen in free-living conditions.**

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