Question

The end product of nitrification is

• A. Ionised ammonia nitrogen
• B. Unionised ammonia nitrogen
• C. Nitrite
• D. Nitrate

Hint:

Nitrification Pathway: Ammonia ($\text{NH}_3$) $\xrightarrow{\textit{Nitrosomonas}}$ Nitrite ($\text{NO}_2^-$) $\xrightarrow{\textit{Nitrobacter}}$ NITRATE ($\text{NO}_3^-$, End Product).

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Biological nitrogen cycle in aquatic ecosystems: two-step obligate aerobic autotrophic bacterial nitrification sequentially oxidizes toxic ammonia to nitrite and terminates in relatively non-toxic nitrate.
Key Formula or Approach:
\[ \underbrace{\text{NH}_4^+ + 1.5\text{O}_2 \xrightarrow{\textit{Nitrosomonas}} \text{NO}_2^- + \text{H}_2\text{O} + 2\text{H}^+}_{\text{Step 1: Ammonia Oxidation}} \quad \longrightarrow \quad \underbrace{\text{NO}_2^- + 0.5\text{O}_2 \xrightarrow{\textit{Nitrobacter}} \mathbf{NO}_3^-}_{\text{ Nitrite Oxidation (End Product)}} \]

Step 2: Detailed Explanation:
In aquatic chemistry, aquaculture water quality, and biofiltration:
- Nitrification is a two-step aerobic chemolithoautotrophic microbiological oxidation process:
1. Step 1 (Ammonia Oxidation): Ammonia-oxidizing bacteria (AOB, e.g., Nitrosomonas, Nitrosococcus) oxidize toxic ammonia ($\text{NH}_3 / \text{NH}_4^+$) to intermediate Nitrite ($\text{NO}_2^-$).
2. Step 2 (Nitrite Oxidation): Nitrite-oxidizing bacteria (NOB, e.g., Nitrobacter, Nitrospira) rapidly oxidize nitrite to Nitrate ($\text{NO}_3^-$).
- Therefore, the stable, oxidized terminal end product of nitrification is Nitrate ($\text{NO}_3^-$).

Step 3: Final Answer:
Therefore, the end product of nitrification is Nitrate, corresponding to option (D).