Problem 43 - Objective Biology for NEET

Question

What happens to ammonia formed by ammonification? (a) Some gets volatilized (b) Most of it gets converted into nitrate by soil bacteria (c) Some will undergo biological nitrogen fixation (d) Both (a) and (b)

Step-by-Step Solution

Answer

The ammonia formed by ammonification can get volatilized and most of it gets converted into nitrate by soil bacteria.

Step 1 Identify the processes involving ammonia

Ammonia, usually generated from the decomposition of organic matter, undergoes a couple of key processes in the soil: volatilization, where it escapes into the air, and nitrification, where it's converted into nitrate by soil bacteria. It does not directly undergo the process of biological nitrogen fixation as this change only involves atmospheric nitrogen (N2).

Step 2 Correlate the identified processes with the given options

By correlating the processes identified in step 1 with the given options, it can be seen clearly that options (a) Some gets volatilized and (b) Most of it gets converted into nitrate by soil bacteria are both applicable to ammonia. Option c is not applicable as this process involves atmospheric nitrogen and not ammonia.

Step 3 Determine the final answer

Based on the correlation in step 2, the final answer is (d) Both (a) and (b).

Key Concepts

Ammonification

Ammonification is one of the initial steps in the nitrogen cycle.
It involves the conversion of organic nitrogen from dead plants and animals into ammonia (NH₃) by bacteria and fungi.
This process is critical as it recycles nitrogen back into a form that can be used again by plants and other organisms.

• Ammonification occurs mostly through the action of decomposer microbes in the soil.
• Once ammonia is formed, it can be further transformed into other nitrogen compounds.

The ammonia produced during ammonification can either become available for plants immediately or enter other processes like volatilization and nitrification.
Volatilization allows some ammonia to escape into the atmosphere, while nitrification aids in further conversion.

Nitrification

Nitrification is a subsequent step after ammonification and is vital for turning ammonia into something that plants can easily utilize.
In this process, specific soil bacteria oxidize ammonia into nitrites (NO₂⁻) and then into nitrates (NO₃⁻), which are usable forms of nitrogen for most plants.

• The first phase of nitrification is carried out by bacteria like Nitrosomonas, which convert ammonia into nitrite.
• Then, Nitrobacter and similar bacteria further process nitrite to form nitrate.

This transformation is essential since nitrate is the form of nitrogen readily absorbed by plant roots.
Nitrification not only increases the availability of nitrogen in the soil but also decreases potential nitrogen loss from volatilization or leaching.

Biological Nitrogen Fixation

Biological nitrogen fixation is a major biological process that enables the conversion of atmospheric nitrogen gas (N₂) into ammonia.
This ammonia is then utilized by plants or further processed in soil, but it's different from using ammonia produced by ammonification.

• This process is mainly performed by specific bacteria, including Rhizobium in legume root nodules and free-living soil bacteria.
• These bacteria possess enzymes such as nitrogenase, which facilitate the conversion of N₂ to NH₃.

Biological nitrogen fixation is crucial because atmospheric nitrogen is inert and cannot be used directly by most organisms.
It fills an essential role in the nitrogen cycle, ensuring that nitrogen continues to flow through ecosystems as part of ongoing nutrient cycles.