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Difficulty: MediumNutrient and Biogeochemical Cycles

Match each nitrogen cycle process listed on the left with its correct biological transformation on the right.

  • NitrificationOxidation of ammonium ions (NH4+NH_4^+) to nitrites (NO2−NO_2^-) and subsequently to nitrates (NO3−NO_3^-)
  • DenitrificationReduction of soil nitrates (NO3−NO_3^-) to gaseous dinitrogen (N2N_2) under anaerobic conditions
  • AmmonificationBreakdown of organic nitrogenous waste and dead organic matter into ammonia (NH3NH_3)
  • Nitrogen fixationConversion of atmospheric dinitrogen (N2N_2) into ammonia (NH3NH_3) or ammonium ions (NH4+NH_4^+)

Answer

Nitrification corresponds to the oxidation of ammonium ions to nitrites and nitrates; Denitrification corresponds to the reduction of soil nitrates to gaseous dinitrogen; Ammonification corresponds to the breakdown of organic nitrogenous waste into ammonia; Nitrogen fixation corresponds to the conversion of atmospheric dinitrogen into ammonia or ammonium ions.
Each process in the nitrogen cycle represents a distinct chemical transformation: Nitrification oxidizes ammonium to nitrite and nitrate; Denitrification reduces soil nitrate to nitrogen gas; Ammonification releases ammonia from decomposing organic nitrogen; Nitrogen fixation reduces atmospheric dinitrogen into ammonia.

Step-by-Step Solution

1
Determine the transformation involved in Nitrification.
Nitrification converts ammonium ions (NH4+NH_4^+) into nitrites (NO2−NO_2^-) and then nitrates (NO3−NO_3^-).
Nitrifying microorganisms derive energy by oxidizing nitrogen in aerobic soil environments.
2
Determine the transformation involved in Denitrification.
Denitrification reduces soil nitrates (NO3−NO_3^-) back into nitrogen gas (N2N_2).
Denitrifying microbes use nitrate as an electron acceptor under anaerobic conditions, replenishing atmospheric nitrogen.
3
Determine the transformation involved in Ammonification.
Ammonification breaks down nitrogenous organic wastes into ammonia (NH3NH_3).
Decomposers hydrolyze organic polymers, releasing inorganic ammonia into the soil.
4
Determine the transformation involved in Nitrogen fixation.
Nitrogen fixation converts gaseous dinitrogen (N2N_2) into usable ammonia (NH3NH_3) or ammonium (NH4+NH_4^+).
Nitrogen-fixing bacteria possess the nitrogenase enzyme complex required to break the triple bond of N2N_2.

Key Concept

Nitrogen Cycle Transformations and Microbial Mechanisms
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Topics

Nutrient and Biogeochemical Cycles

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