Question

Which one of the following fixes nitrogen?

• A. Yeast
• B. TMV
• C. Nostoc
• D. Denitrifying bacteria

Answer 1

Answer: (C)

Certain bacteria are capable of fixing nitrogen. In this process, nitrogen gas is converted to ammonium, a form of nitrogen that is biologically available to plants. The reaction is catalyzed by the enzyme nitrogenase. Because nitrogenase is inactivated by oxygen, the reaction must occur in a low oxygen environment.
Bacterial nitrogen fixation is carried out by both free-living and symbiotic bacteria, e.g., Cyanobacteria (Anabaena, Nostoc), Azotobacter and Clostridium.

TMV is tobacco mosaic virus, which infects plants.
Denitrifying bacteria, microorganisms whose action results in the conversion of nitrates in soil to free atmospheric nitrogen, thus depleting soil fertility and reducing agricultural productivity.