Question

Non-symbiotic nitrogen fixing prokaryote is
(A) Rhizobium
(B) Nostoc
(C) Frankia
(D) Azotobacter

Answer 1

Symbiosis is a process where two organisms are placed in a symbiotic relationship because they can't live without each other. Facultative symbiosis is a process where the species live together by choice. There are four important types of symbiotic relationships: mutualism, commensalism, parasitism, Predation, and competition. The non-symbiotic bacteria is a free bacteria which does not depend on other organisms to survive.

Complete answer:
(A) Rhizobium is a genus of Gram-negative soil bacteria that fix nitrogen into plant roots and soil. These species have an endo-symbiotic nitrogen-fixing association with roots of legumes and Parasponia. So this is the wrong option.
(B) Nostoc is a genus of cyanobacteria which is found in various environmental conditions. These are present in colonies that are composed of filaments of moniliform cells in a gelatinous sheath.it is a symbiotic bacteria. So this option is the wrong option.
(C) Frankia sp. is a filamentous nitrogen-fixing bacteria that grow by branching and tip extension. They live in the soil and have a symbiotic relationship with certain angiosperms. So this option is wrong.
(D) Azotobacter is a genus of free-living diazotrophic bacteria that has a resting stage as a cyst. It has several metabolic capabilities and one of them is atmospheric nitrogen fixation by conversion to ammonia. since it is a free-living bacteria, then this option is correct.

The correct answer is the option (D) that is Azotobacter.

Note: The above mention all bacteria are nitrogen-fixing bacteria. The nitrogen-fixing bacteria fixed nitrogen into the soil. Azotobacter is generally found in neutral to alkaline like soil conditions, in aquatic environments, and on some plants. Azotobacter is one of the free-living bacteria and it does not depend upon any other organism for its survival.