Question

Free-living nitrogen-fixing aerobic bacterium is :

• A. Rhodospirillum
• B. Anabaena
• C. Nostoc
• D. Beijerinckia
• E. Rhizobium

Answer 1

The correct option is D

Beijerinckia

The correct option is D.

Explanation of the correct option:

1. Nitrogen fixation is the conversion of molecular nitrogen (N₂) in the atmosphere into nitrogen-containing molecules such as ammonia (NH₃).
2. Ammonia can be used by plants to synthesize important nitrogenous biomolecules.
3. Beijerinckia is a free-residing bacterium that can fix nitrogen in the soil aerobically.
4. Another example of a free-living aerobic nitrogen-fixing bacteria is Azotobacter, etc.

Explanations of the incorrect options:

Option A:

1. Rhodospirillum is a gram-negative, free-living anaerobic nitrogen-fixing bacterium.
2. It is a facultative anaerobe, i.e., it can synthesize ATP anaerobically as well as aerobically, hence it can survive in the absence or the presence of oxygen.

Option B:

1. Anabaena is a nitrogen-fixing cyanobacterium.
2. It is discovered with filamentous associations.
3. It is also symbiotic.
4. Cyanobacteria can photosynthetic organisms that live in water and can synthesize their food.
5. They can exist as plankton.

Option C:

1. Nostoc is a filamentous symbiotic nitrogen-fixing bacterium.
2. They can form macroscopic or microscopic colonies.
3. They are found in both terrestrial and aquatic conditions.

Option E:

1. Rhizobium is anaerobic symbiotic nitrogen-fixing bacteria.
2. They are found in close association with root nodules of leguminous plants.

Final answer: Free-living nitrogen-fixing aerobic bacterium is Beijerinckia.