Question:
Some cyanobacteria in aquatic and terrestrial environment that enrich the soil by fixing nitrogen are :
Some cyanobacteria in aquatic and terrestrial environment that enrich the soil by fixing nitrogen are :
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Anabaena and Nostoc are nitrogen-fixing cyanobacteria; the others are bacteria or a fungus.
Updated On: Oct 22, 2026
- Rhizobium and Azotobacter
- Azospirillum and Glomus
- Anabaena and Nostoc
- Azospirillum and Azotobacter
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The Correct Option is C
Solution and Explanation
Step 1: Recall nitrogen-fixing microbes:
Biofertilisers include bacteria, fungi and cyanobacteria. Cyanobacteria are photosynthetic and many of them fix nitrogen.
Examples are Anabaena, Nostoc, Oscillatoria and Aulosira. They fix nitrogen in water and on soil, for example in paddy fields.
Step 2: Check the options:
(A) Rhizobium is a symbiotic bacterium of legume roots and Azotobacter is a free-living bacterium. Neither is a cyanobacterium.
(B) Azospirillum is a bacterium and Glomus is a mycorrhizal fungus. Neither is a cyanobacterium.
(C) Anabaena and Nostoc are both cyanobacteria that fix nitrogen. This is right.
(D) Both are bacteria, so it is wrong.
Final Answer:
The nitrogen-fixing cyanobacteria are Anabaena and Nostoc, option (C).
Biofertilisers include bacteria, fungi and cyanobacteria. Cyanobacteria are photosynthetic and many of them fix nitrogen.
Examples are Anabaena, Nostoc, Oscillatoria and Aulosira. They fix nitrogen in water and on soil, for example in paddy fields.
Step 2: Check the options:
(A) Rhizobium is a symbiotic bacterium of legume roots and Azotobacter is a free-living bacterium. Neither is a cyanobacterium.
(B) Azospirillum is a bacterium and Glomus is a mycorrhizal fungus. Neither is a cyanobacterium.
(C) Anabaena and Nostoc are both cyanobacteria that fix nitrogen. This is right.
(D) Both are bacteria, so it is wrong.
Final Answer:
The nitrogen-fixing cyanobacteria are Anabaena and Nostoc, option (C).
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