Step 1: Concept Overview:
The nitrogen cycle is a biogeochemical process where nitrogen transforms into various chemical forms, circulating through the atmosphere, land, and marine environments. This question requires sequencing the key processes in their correct order.
Step 2: Process Breakdown:
Let's follow nitrogen's journey through the ecosystem:
A. Nitrogen Fixation: The cycle initiates as atmospheric nitrogen (\(N_2\)), unusable for most organisms, enters the ecosystem. Nitrogen-fixing bacteria convert \(N_2\) into ammonia (\(NH_3\)) or ammonium (\(NH_4^+\)).
B. Nitrification: Soil-based nitrifying bacteria transform ammonium (\(NH_4^+\)) into nitrites (\(NO_2^-\)), and then into nitrates (\(NO_3^-\)).
D. Assimilation: Plants absorb ammonium or nitrates from the soil via their roots, incorporating them into biological molecules (proteins, nucleic acids). Animals acquire nitrogen by consuming plants.
E. Ammonification: Upon the death of plants and animals, decomposers (bacteria, fungi) break down organic nitrogen compounds, releasing ammonium (\(NH_4^+\)) back into the soil.
C. Denitrification: Denitrifying bacteria convert nitrates (\(NO_3^-\)) back into atmospheric nitrogen gas (\(N_2\)), which is released back into the atmosphere, completing the cycle.
This sequence is represented as A \(\rightarrow\) B \(\rightarrow\) D \(\rightarrow\) E \(\rightarrow\) C.
Step 3: Conclusion:
The correct order of processes in the nitrogen cycle is: Nitrogen fixation, Nitrification, Assimilation, Ammonification, and Denitrification.