Question

Select the correct match.
a. Nitrosomonas - Conversion of nitrite to nitrate
b. Thiobacillus - Denitrification
c. Nostoc - Free-living nitrogen-fixer
d. Azotobacter - Anaerobic nitrogen-fixer

• A. a and b only
• B. c and d only
• C. b and c only
• D. b and d only
• E. a and c only

Answer 1

The correct option is C b and c only

Under anaerobic conditions some microorganisms use nitrate and other oxidised forms and convert them into free gaseous nitrogen. This process is called as denitrification.

Some of the organisms, which carry out denitrification are Pseudomonas denitrification, Thiobacillus denitrificans and Micrococcus denitrificans.

Cyanobacteria are an important group of free living nitrogen fixers, e.g., Anabaena, Nostoc, Aulosira etc.

Azotobacter is a free living aerobic nitrogen fixer.
Nitrosomonas and Nitrosococcus convert ammonia into nitrite, which is further converted into nitrates by Nitrobacter.