Problem 48 - Objective Biology for NEET

Question

Reduction of nitrogen to ammonia by living organism is called (a) Nitrification (b) Denitrification (c) Biological nitrogen fixation (d) Ammonification

Step-by-Step Solution

Answer

The reduction of nitrogen to ammonia by living organism is called Biological Nitrogen Fixation.

Step 1: Understanding the Terms

Nitrification: It is the biological oxidation of ammonia into nitrite followed by the oxidation of these nitrites into nitrates. Denitrification: It is the microbially facilitated process where nitrate is reduced and ultimately produces molecular nitrogen (N2) through a series of intermediate gaseous nitrogen oxide products. Biological Nitrogen Fixation: It is the process by which atmospheric nitrogen is converted by either a natural or an industrial means to a form of nitrogen such as ammonia. Ammonification: It is the process by which the organically bound nitrogen of microbial, plant, and animal biomass is recycled after their death.

Step 2: Connecting the terms with the definition in exercise

From the definitions, it can be inferred that the reduction of nitrogen to ammonia by living organism is called Biological Nitrogen Fixation.

Key Concepts

Nitrification

Nitrification is a crucial step in the nitrogen cycle, where ammonia ( \(NH_3\)) is converted into nitrite ( \(NO_2^-\)), and then into nitrate ( \(NO_3^-\)). This process is performed by specialized nitrifying bacteria. Initially, bacteria such as Nitrosomonas oxidize ammonia to nitrite. This reaction can be written as:
\[ NH_3 + O_2 \rightarrow NO_2^- + 3H^+ + 2e^- \]After this step, other bacteria like Nitrobacter convert nitrite to nitrate through the following equation:
\[ NO_2^- + \dfrac{1}{2} O_2 \rightarrow NO_3^- \]This transformation is essential for soil and water systems, aiding in nutrient cycling and availability. Nitrates act as the primary nitrogen source for plants, promoting their growth and development.

Denitrification

Denitrification is a process where nitrates ( \(NO_3^-\)) are converted back to molecular nitrogen ( \(N_2\)) and released into the atmosphere. This is achieved by a series of intermediary stages involving different gaseous nitrogen oxides like nitric oxide ( \(NO\)) and nitrous oxide ( \(N_2O\)). This process is facilitated by denitrifying bacteria, such as those from the genus Pseudomonas, under anaerobic conditions where oxygen is scarce.
The steps in denitrification are typically as follows:

• \(NO_3^-\) to \(NO_2^-\)
• \(NO_2^-\) to \(NO\)
• \(NO\) to \(N_2O\)
• \(N_2O\) to \(N_2\)

Denitrification aids in reducing nitrogen buildup in ecosystems, preventing the toxicity that can be associated with high nitrate levels. It helps maintain ecosystem balance by closing the nitrogen cycle loop, returning nitrogen to the atmosphere.

Ammonification

Ammonification is a vital process by which organic nitrogen is converted into ammonia ( \(NH_3\)) or ammonium ions ( \(NH_4^+\)). This conversion takes place when organisms such as plants, animals, or microbes decompose. Microorganisms, including bacteria and fungi, break down organic matter, releasing nitrogen back into the ecosystem in the form of ammonia.
The steps of ammonification include:

• Decomposition of organic material
• Conversion of nitrogenous compounds into ammonia

Ammonification ensures that nitrogen is made available in a usable form for other organisms. It plays a significant role in maintaining soil fertility, promoting an environment rich in nutrients for plant uptake. Without ammonification, nitrogen would remain locked in organic matter, unavailable for future use by plants.