Question

Which of the given prokaryotes fixes nitrogen symbiotically as well as in free living state?

• A. Azotobacter
• B. Anabaena
• C. Rhizobium
• D. Frankia

Answer 1

The correct option is B

Anabaena

The correct option is B.

Explanation of correct option:

1. Anabaena is a nitrogen-fixing blue-green algae genus with beadlike or barrel-like cells with intermittent larger spores (heterocysts) that can be found as plankton in shallow water and on moist soil.
2. Solitary and colonial forms exist, with the latter resembling Nostoc, a closely related genus.

Explanation of incorrect option:

Option A:

1. Azotobacter is a genus of bacteria that are motile, oval, or spherical, and create thick-walled cysts (as well as a hard crust) and vast amounts of capsular slime.

Option C:

1. Rhizobium is a bacterium that lives in a symbiotic relationship with leguminous plants' root nodules.
2. Nitrogen fixation is not possible on its own.
3. Rhizobium requires a plant host for this reason.
4. Rhizobium is an important supplier of nitrogen for agricultural soils, especially in arid areas.

Option D:

1. Frankia is a species of nitrogen-fixing bacteria that live in symbiosis with actinorhizal plants.

Final answer: Anabaena is a prokaryote that fixes nitrogen symbiotically as well as in free living state