Which process in the nitrogen cycle converts atmospheric N2 to ammonia or related forms?

Which process in the nitrogen cycle converts atmospheric N2 to ammonia or related forms?

• A. Nitrogen fixation
• B. Nitrification
• C. Denitrification
• D. Assimilation

Answer: (A)

Converting atmospheric nitrogen into a usable form like ammonia is nitrogen fixation. Certain bacteria and cyanobacteria carry nitrogenase, an enzyme that breaks the strong N≡N triple bond and reduces N2 to ammonia, which can then become ammonium in the soil. This step provides the essential nitrogen that plants and other organisms need to build amino acids and nucleotides. Other steps in the cycle move nitrogen between different inorganic forms or incorporate it into organic molecules after fixation—nitrification turns ammonia into nitrite and nitrate, denitrification reduces nitrate back to N2, and assimilation is the uptake of available inorganic nitrogen by plants into organic compounds. So the process that directly converts atmospheric N2 to ammonia is nitrogen fixation.

Converting atmospheric nitrogen into a usable form like ammonia is nitrogen fixation. Certain bacteria and cyanobacteria carry nitrogenase, an enzyme that breaks the strong N≡N triple bond and reduces N2 to ammonia, which can then become ammonium in the soil. This step provides the essential nitrogen that plants and other organisms need to build amino acids and nucleotides. Other steps in the cycle move nitrogen between different inorganic forms or incorporate it into organic molecules after fixation—nitrification turns ammonia into nitrite and nitrate, denitrification reduces nitrate back to N2, and assimilation is the uptake of available inorganic nitrogen by plants into organic compounds. So the process that directly converts atmospheric N2 to ammonia is nitrogen fixation.