Question:
Which one of the following organisms is NOT free living?
Which one of the following organisms is NOT free living?
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Nitrogen-fixing organisms:
- Free-living: Azotobacter, Cyanobacteria, Rhodospirillum.
- Symbiotic: Rhizobium (legumes), Frankia (actinorhizal plants).
- Free-living: Azotobacter, Cyanobacteria, Rhodospirillum.
- Symbiotic: Rhizobium (legumes), Frankia (actinorhizal plants).
Updated On: Aug 27, 2026
- Azotobacter
- Cyanobacteria
- Rhodospirillum
- Frankia
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Verified By Collegedunia
The Correct Option is D
Solution and Explanation
Step 1: Understanding the Question:
This question tests knowledge of free-living and symbiotic nitrogen-fixing organisms.
Step 2: Detailed Explanation:
Frankia (D) is NOT free-living.
It is a symbiotic nitrogen-fixing bacterium that forms root nodules on actinorhizal plants (e.g., Alnus, Casuarina).
Other organisms:
- Azotobacter (A): Free-living, aerobic nitrogen-fixer.
- Cyanobacteria (B): Free-living, photosynthetic nitrogen-fixer (e.g., Anabaena).
- Rhodospirillum (C): Free-living, anaerobic nitrogen-fixer.
Thus, Frankia is not free-living.
Step 3: Final Answer:
Thus, Frankia is NOT free-living, which corresponds to option (D).
[0.5cm]
This question tests knowledge of free-living and symbiotic nitrogen-fixing organisms.
Step 2: Detailed Explanation:
Frankia (D) is NOT free-living.
It is a symbiotic nitrogen-fixing bacterium that forms root nodules on actinorhizal plants (e.g., Alnus, Casuarina).
Other organisms:
- Azotobacter (A): Free-living, aerobic nitrogen-fixer.
- Cyanobacteria (B): Free-living, photosynthetic nitrogen-fixer (e.g., Anabaena).
- Rhodospirillum (C): Free-living, anaerobic nitrogen-fixer.
Thus, Frankia is not free-living.
Step 3: Final Answer:
Thus, Frankia is NOT free-living, which corresponds to option (D).
[0.5cm]
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