Which among the following is an autotrophic microbe that can fix atmospheric nitrogen?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → All of these
Biofertilisers are organisms that add nutrients to the soil. Cyanobacteria (blue-green algae) are autotrophic, which means they make their own food by photosynthesis. Many of them can also fix atmospheric nitrogen. In paddy fields they are an important biofertiliser.
Option (1) Anabaena — Correct statement, but it is only one of the correct points, so on its own it is not the answer. Anabaena is a cyanobacterium that makes its own food and fixes nitrogen.
Option (2) Nostoc — Correct statement, but it is only one of the correct points, so on its own it is not the answer. Nostoc is also a nitrogen-fixing cyanobacterium named in the book.
Option (3) Oscillatoria — Correct statement, but it is only one of the correct points, so on its own it is not the answer. Oscillatoria is the third nitrogen-fixing cyanobacterium the book names.
NCERT Extract:
Microbes as Biofertilisers – “… Cyanobacteria are autotrophic microbes widely distributed in aquatic and terrestrial environments many of which can fix atmospheric nitrogen, e.g. Anabaena, Nostoc, Oscillatoria, etc. In paddy fields, cyanobacteria serve as an important biofertiliser.”