Question

Which of the following are non-symbiotic, anaerobic, non-photosynthetic, nitrogen-fixing bacteria?
A. Clostridium
B. Nostoc
C. Anabaena
D. Azotobacter

Answer 1

Nitrogen fixation is the process of fixing atmospheric nitrogen in the plants or own body called nitrogen fixation, this process is carried out by several bacteria that are present in the soil that is called nitrogen-fixing bacteria, these nitrogen-fixing bacteria is good for increase the fertility of the soil in term of nitrogen.

Complete answer:
Nitrogen fixation is mediated by oxygen-sensitive enzyme nitrogenase that requires energy, bacteria convert atmospheric nitrogen into ammonia or nitrite and nitrate which is utilized by a plant in the formation of the protein molecule. Nitrogen fixers are present along with plants or fungi in their root nodules and also present in free form.
A. Clostridium is the anaerobic, free-living nitrogen-fixing bacteria and acts as non- non-photosynthetic that is found in soil which converts free atmospheric nitrogen into soluble nitrogen compounds that are further absorbed by plants.
B. Nostoc is the genus of cyanobacteria that are present in various varied environments such as aquatic or terrestrial, which form macro or microscopic filamentous colonies. It fixes the free nitrogen from the environment into the plants or soil, it shows a symbiotic relationship with liverworts, fern, and angiosperm plants.
C. Anabaena is also a genus of cyanobacteria which is filamentous which exists with planktons and also shows symbiotic association with a certain group of the plant such as mosquito fern.
D. Azotobacter:- it is a genus of diazotrophic bacteria which is free-living and often found in alkaline soil or the aquatic environment. It converts the free atmospheric nitrogen into ammonia, and then converts into nitrite and nitrate form to the plant.
Hence, the correct option is A.

Note: Plant does not utilize nitrogen in ammonia form because it acts as a poison for the plant, it first converts into nitrite and then nitrate form, which is utilized by the plants, except paddy plant such as rice plant which is capable to utilize ammonia to fulfill the requirement of nitrogen.