Question

Arrange the following steps in the process of nitrogen cycle in correct sequence:
A. Nitrogen fixation
B. Nitrification
C. Denitrification
D. Assimilation
E. Ammonification
Choose the correct answer from the options given below :

• A. A, B, C, D, E
• B. C, D, E, A, B
• C. A, B, D, E, C
• D. C, A, B, D, E

Hint:

Visualize the nitrogen cycle as follows: {Fixation} (into the system), {Nitrification} (conversion in soil), {Assimilation} (uptake by life), {Ammonification} (decomposition/recycling), and {Denitrification} (exit from the system).

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
The nitrogen cycle is the biogeochemical cycle by which nitrogen is converted into multiple chemical forms as it circulates among the atmosphere, terrestrial, and marine ecosystems. The question requires arranging the key processes in a logical sequence.
Step 2: Detailed Explanation:
Let's trace the path of nitrogen through the ecosystem:
A. Nitrogen fixation: The cycle begins with bringing atmospheric nitrogen (\(N_2\)), which is unusable by most organisms, into the ecosystem. Nitrogen-fixing bacteria convert \(N_2\) into ammonia (\(NH_3\)) or ammonium (\(NH_4^+\)).
B. Nitrification: Nitrifying bacteria in the soil convert ammonium (\(NH_4^+\)) first into nitrites (\(NO_2^-\)) and then into nitrates (\(NO_3^-\)).
D. Assimilation: Plants absorb the usable forms of nitrogen (ammonium or nitrates) from the soil through their roots and incorporate them into biological molecules like proteins and nucleic acids. Animals then get nitrogen by eating plants.
E. Ammonification: When plants and animals die, decomposers (bacteria and fungi) break down their organic nitrogen compounds and release ammonium (\(NH_4^+\)) back into the soil.
C. Denitrification: Denitrifying bacteria convert nitrates (\(NO_3^-\)) back into atmospheric nitrogen gas (\(N_2\)), which returns to the atmosphere, thus completing the cycle.
This logical flow corresponds to the sequence A \(\rightarrow\) B \(\rightarrow\) D \(\rightarrow\) E \(\rightarrow\) C.
Step 3: Final Answer:
The correct sequence of steps in the nitrogen cycle is Nitrogen fixation, Nitrification, Assimilation, Ammonification, and Denitrification.