Which characteristic is shared by Azospirillum, Anabaena, Nostoc, and Oscillatoria?

Both (a) and (b)

a-Nitrogen-fixing microbes

b-Prokaryotic organisms

The correct answer is (c) Both (a) and (b).

d-Eukaryotic organisms

Azospirillum, Anabaena, Nostoc, and Oscillatoria share two characteristics:

(a) Nitrogen-fixing microbes: All of these organisms have the ability to fix atmospheric nitrogen into a form that plants can utilize. Azospirillum is nitrogen-fixing rhizosphere bacteria that are Gram-negative and free-living. The bacteria in the genus Azospirillum are extremely mobile.

Anabaena, Nostoc, and Oscillatoria are all examples of cyanobacteria, which are photosynthetic bacteria that can fix atmospheric nitrogen through specialized cells called heterocysts. This nitrogen fixation process is essential for enriching the soil with available nitrogen, benefiting the surrounding plants and ecosystems.

(b) Prokaryotic organisms: Azospirillum, Anabaena, Nostoc, and Oscillatoria are all prokaryotes, which means they lack a membrane-bound nucleus and other membrane-bound organelles found in eukaryotic organisms. They are single-celled organisms with a simple cellular structure.

Therefore, the correct answer is (c) Both (a) and (b). These organisms are nitrogen-fixing microbes and belong to the group of prokaryotic organisms.