Leaving Certificate Biology Practice Test

What is the process of converting ammonia into nitrite and then nitrate called?

Nitrification Denitrification Ammonification Nitrogen fixation

Correct Answer:

Nitrification

Explanation:

Nitrification is the conversion of ammonia into nitrite and then nitrate through two linked oxidation steps carried out by specialized bacteria. In the first step, ammonia-oxidizing bacteria take ammonia (NH3) and oxidize it to nitrite (NO2−), gaining energy in the process. In the second step, nitrite-oxidizing bacteria convert nitrite to nitrate (NO3−), releasing more energy. Both steps require oxygen, so this process happens under aerobic conditions. This distinguishes nitrification from ammonification, which releases ammonia during decomposition; from denitrification, which reduces nitrate to nitrogen gas under low-oxygen conditions; and from nitrogen fixation, which converts atmospheric N2 into ammonia.

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