What is the correct order of the main steps in the nitrogen cycle?

What is the correct order of the main steps in the nitrogen cycle?

• A. Nitrogen fixation, ammonification, nitrification, assimilation, denitrification
• B. Denitrification, assimilation, nitrification, ammonification, nitrogen fixation
• C. Nitrification, assimilation, am­monification, nitrogen fixation, denitrification
• D. Assimilation, nitrogen fixation, nitrification, denitrification, ammonification

Answer: (A)

Nitrogen moves through ecosystems by converting atmospheric N2 into usable forms, feeding living things, and then returning to the air. The first step is nitrogen fixation, where bacteria convert N2 gas into ammonia or ammonium that organisms can use. Next comes ammonification, as decomposers break down organic nitrogen from dead material and waste, releasing more ammonium into the soil. Then nitrification takes place, turning that ammonium first into nitrite and then into nitrate, which is a form plants can readily take up. Plants obtain nitrogen through assimilation, incorporating nitrate or ammonium into amino acids and other organic molecules. Finally, denitrification occurs under certain conditions, where bacteria convert nitrate back into nitrogen gas, releasing it to the atmosphere and completing the cycle. This order shows how nitrogen becomes available to living things and then returns to the air.

Nitrogen moves through ecosystems by converting atmospheric N2 into usable forms, feeding living things, and then returning to the air. The first step is nitrogen fixation, where bacteria convert N2 gas into ammonia or ammonium that organisms can use. Next comes ammonification, as decomposers break down organic nitrogen from dead material and waste, releasing more ammonium into the soil. Then nitrification takes place, turning that ammonium first into nitrite and then into nitrate, which is a form plants can readily take up. Plants obtain nitrogen through assimilation, incorporating nitrate or ammonium into amino acids and other organic molecules. Finally, denitrification occurs under certain conditions, where bacteria convert nitrate back into nitrogen gas, releasing it to the atmosphere and completing the cycle. This order shows how nitrogen becomes available to living things and then returns to the air.