Question:
A non-symbiotic heterotrophic aerobic nitrogen fixing microorganism is...
A non-symbiotic heterotrophic aerobic nitrogen fixing microorganism is...
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Azotobacter is widely used as a biofertilizer because it fixes nitrogen aerobically without symbiosis.
Updated On: Sep 29, 2025
- Blue Green Algae
- Nostoc
- Clostridium
- Azotobacter
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The Correct Option is D
Solution and Explanation
Step 1: Nitrogen fixation overview.
Nitrogen fixation can be symbiotic (e.g., Rhizobium in legumes) or non-symbiotic (free-living organisms).
It can also be autotrophic (algae, cyanobacteria) or heterotrophic (bacteria like Azotobacter).
Step 2: Aerobic vs anaerobic fixers.
- Aerobic non-symbiotic fixers: Azotobacter.
- Anaerobic non-symbiotic fixers: Clostridium.
- Autotrophic fixers: Blue Green Algae, Nostoc.
Step 3: Analysis of options.
- (A) Blue Green Algae: Autotrophic nitrogen fixers, not heterotrophic.
- (B) Nostoc: Symbiotic cyanobacterium, autotrophic.
- (C) Clostridium: Heterotrophic but anaerobic, not aerobic.
- (D) Azotobacter: Correct, heterotrophic, aerobic, free-living nitrogen fixer.
Step 4: Conclusion.
Thus, Azotobacter is the correct answer.
Nitrogen fixation can be symbiotic (e.g., Rhizobium in legumes) or non-symbiotic (free-living organisms).
It can also be autotrophic (algae, cyanobacteria) or heterotrophic (bacteria like Azotobacter).
Step 2: Aerobic vs anaerobic fixers.
- Aerobic non-symbiotic fixers: Azotobacter.
- Anaerobic non-symbiotic fixers: Clostridium.
- Autotrophic fixers: Blue Green Algae, Nostoc.
Step 3: Analysis of options.
- (A) Blue Green Algae: Autotrophic nitrogen fixers, not heterotrophic.
- (B) Nostoc: Symbiotic cyanobacterium, autotrophic.
- (C) Clostridium: Heterotrophic but anaerobic, not aerobic.
- (D) Azotobacter: Correct, heterotrophic, aerobic, free-living nitrogen fixer.
Step 4: Conclusion.
Thus, Azotobacter is the correct answer.
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