Question

By which of the following process do bacteria convert nitrites into nitrates?

• A. Denitrification
• B. Ammonification
• C. Decomposition
• D. Nitrogen fixation
• E. Nitrification

Answer 1

The correct option is E Nitrification

A. Nitrate present in soil is reduced to nitrogen by the process of denitrification. This process is carried out by the bacteria Pseudomonas and Thiobacillus.

B. Proteins and nucleic acids of the dead remains of plants, animals and excretory products of animals are degraded by microorganisms with the liberation of ammonia and this process is called ammonification.

C. Decomposition is the breakdown of complex organic material into simpler ones by the action of detritivores.

D. Nitrogen fixation is the conversion of atmospheric molecular nitrogen into usable forms of nitrogen like nitrate, ammonia, amino acids etc. Nitrogen is present in atmosphere as dinitrogen (N${}_2$) which cannot be utilized directly by plants. So, it is converted or fixed into compounds prior to utilisation by the action of microbes.

E. The conversion of ammonia to nitrate by certain microorganisms is called nitrification. It is performed in two steps, nitrite formation and nitrate formation. In the first step, ammonium ions are oxidised to nitrites by bacteria like Nitrosomonas and in the second step, nitrite is oxidised to nitrate by bacteria like Nitrobacter.

So, the correct answer is 'Nitrification'.