Which of the following organisms cannot fix nitrogen? Choose the correct answer from the options given below:
- B only
- E only
- A only
- D only
Answer
(4) D only
Solution
A: Azotobacter is a free-living soil bacterium that fixes atmospheric nitrogen.
B, C, E: Oscillatoria, Anabaena and Nostoc are cyanobacteria that fix atmospheric nitrogen and are used as biofertilisers.
D: Volvox is a colonial green alga (Chlorophyceae); it cannot fix nitrogen.
Answer: (4)