Question

Which of following organisms cannot fix nitrogen?

1. Azotobacter
2. Oscillatoria
3. Anabaena
4. Volvoх
5. Nostoc

Choose the correct answer from the options given below:

Options

• A only

• D only

• B only

• E only

Answer 1

D only

Explanation:

Nitrogen fixation is possible for Azotobacter, Anabaena, Nostoc, and Oscillatoria. Azotobacter is a free-living bacterium that fixes nitrogen. Nostoc and Anabaena are cyanobacteria that use heterocysts to fix nitrogen. Certain species of the filamentous cyanobacterium Oscillatoria are capable of fixing nitrogen. As a colonial green alga, Volvox does not fix nitrogen.