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Difficulty: MediumNutrient and Biogeochemical Cycles

Arrange the following biological transformations of nitrogen in the correct sequence, starting from organic waste breakdown and ending with the release of free nitrogen gas into the atmosphere.

  1. 1Breakdown of organic proteins and nucleic acids into ammonium ions by saprophytic ammonifying bacteria.
  2. 2Oxidation of ammonium ions into nitrite ions by Nitrosomonas bacteria.
  3. 3Conversion of nitrite ions into nitrate ions by Nitrobacter bacteria.
  4. 4Reduction of nitrate ions into atmospheric nitrogen gas by Pseudomonas bacteria.

Answer

The correct sequence starts with ammonification of organic waste into ammonium ions, followed by Nitrosomonas oxidation to nitrites, Nitrobacter oxidation to nitrates, and finally denitrification to nitrogen gas by Pseudomonas.
The biological nitrogen cycle begins with ammonification (converting organic matter to ammonium), followed by a two-stage nitrification process where Nitrosomonas oxidizes ammonium to nitrite, and Nitrobacter oxidizes nitrite to nitrate. Finally, anaerobic denitrifying bacteria such as Pseudomonas reduce nitrate to atmospheric nitrogen gas.

Step-by-Step Solution

1
Identify the starting compound and initial biochemical step.
Decomposers perform ammonification, breaking organic proteins down into ammonium ions (NH4+NH_4^+).
Organic waste must first be converted into inorganic nitrogenous forms before nitrification can occur.
2
Determine the first oxidation stage of nitrification.
Nitrosomonas converts ammonium ions (NH4+NH_4^+) into nitrite ions (NO2−NO_2^-).
Nitrification proceeds in two distinct bacterial steps, starting with ammonium oxidation.
3
Determine the second oxidation stage of nitrification.
Nitrobacter converts nitrite ions (NO2−NO_2^-) into nitrate ions (NO3−NO_3^-).
Nitrate is the primary oxidized form utilized by plants and susceptible to denitrification.
4
Identify the final step returning nitrogen to the atmosphere.
Denitrifying bacteria like Pseudomonas reduce nitrates (NO3−NO_3^-) back into gaseous nitrogen (N2N_2).
Denitrification completes the biogeochemical cycle by converting fixed nitrogen back into gaseous form.

Key Concept

Nitrogen Cycle Bacterial Transformations
Estimated Time:1m 30s
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Topics

Nutrient and Biogeochemical Cycles

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