Which of the following is an incorrect match ?

Options

A. Free living nitrogen fixing bacteria - Azotobacter
B. Symbiotic nitrogen fixing cyanobacteria - Anabaena
C. Symbiotic nitrogen fixing cyanobacteria - Frankia
D. Symbiotic nitrogen fixing bacteria - Xanthomonas

Answer

To solve the question "Which of the following is an incorrect match?" regarding nitrogen fixation, we will analyze the options provided and determine which one does not correctly represent the association between organisms and their nitrogen-fixing capabilities.

### Step-by-Step Solution:

1. **Understand Nitrogen Fixation**:
- Nitrogen fixation is the process of converting atmospheric nitrogen (N2) into a form that plants can absorb, such as nitrites or nitrates. This can occur through symbiotic relationships or free-living organisms.

**Hint**: Remember that nitrogen fixation can occur through both symbiotic and free-living organisms.

2. **Identify Symbiotic Nitrogen Fixers**:
- Symbiotic nitrogen-fixing bacteria include:
- **Rhizobium**: Forms symbiotic relationships with legumes.
- **Frankia**: Forms symbiotic relationships with non-leguminous plants.
- Symbiotic cyanobacteria include:
- **Anabaena**: Associated with certain plants.

**Hint**: Look for the key examples of symbiotic bacteria and cyanobacteria that fix nitrogen.

3. **Identify Free-Living Nitrogen Fixers**:
- Free-living nitrogen-fixing bacteria include:
- **Azotobacter**: A free-living bacterium that fixes nitrogen.
- Free-living cyanobacteria include:
- **Nostoc**: A free-living cyanobacterium that can fix nitrogen.

**Hint**: Recall that free-living organisms do not form symbiotic relationships but can still fix nitrogen.

4. **Analyze the Options**:
- Check each option against the known classifications:
- **Free-living nitrogen-fixing bacteria is Acetobacter**: This is incorrect; Acetobacter is not primarily known for nitrogen fixation.
- **Anabaena is a symbiotic nitrogen-fixing cyanobacteria**: This is correct.
- **Frankia is a symbiotic nitrogen-fixing cyanobacteria**: This is incorrect; Frankia is a bacterium, not a cyanobacterium.
- **Xanthomonas is a symbiotic nitrogen-fixing bacteria**: This is incorrect; Xanthomonas is primarily a plant pathogen and not known for nitrogen fixation.

5. **Identify the Incorrect Match**:
- The option that states "Frankia is a symbiotic nitrogen-fixing cyanobacteria" is incorrect because Frankia is a bacterium, not a cyanobacterium.

**Hint**: Focus on the classification of organisms to determine if they are correctly categorized as bacteria or cyanobacteria.

### Conclusion:
The incorrect match in the options provided is **"Frankia is a symbiotic nitrogen-fixing cyanobacteria."**