Question

In the given diagram, A and B represent which of the following?

A) A: Mineralisation, B: Demineralisation
B) A: Ammonification, B: Denitrification
C) A: Denitrification, B: Ammonification
D) A: Denitrification, B: Mineralisation

Answer 1

A. This process takes place by the action of heterotrophic bacteria such as Paracoccus denitrificans.
B. This process occurs through the action of nitrogen-fixing bacteria, usually in leguminous plants.

Complete answer: ’A’ represents denitrification: It is defined as the process of reduction of nitrates and nitrites by the action of heterotrophic bacteria which results in the escape of molecular nitrogen into the atmosphere. This process is facilitated by the action of bacteria such as Paracoccus denitrificans , Pseudomonas , Thiobacillus denitrificans , etc. ‘B’ represents ammonification: It is defined as the process by which the amine or amide group molecules are converted into ammonium ion by the action of microorganisms present in the soil and water. Both ammonification and denitrification occur in the process of Nitrogen fixation in plants. It is a process of conversion of molecular nitrogen of the atmosphere into ammonia by the action of nitrogen-fixing bacteria such as Azotobacter and Archaea.
Hence, the correct answer is option C.

Additional information: There are two types of nitrogen fixation:
1. Physical nitrogen fixation; which involves
a) Natural nitrogen fixation
b) Industrial nitrogen fixation, and
2. Biological nitrogen fixation

Note: There are a few prokaryotes like bacteria and Cyanobacteria which are capable of fixing atmospheric nitrogen. These are termed as nitrogen fixers for diazotrophs. Following are the types of Diazotrophs:
i. Free-living nitrogen-fixing bacteria: Azotobacter , Clostridium.
ii. Free-living nitrogen-fixing cyanobacteria: _Anabaena,Nostoc.
iii. Symbiotic nitrogen-fixing cyanobacteria: _Anabaena,Nostoc.
iv. Symbiotic nitrogen-fixing bacteria: Rhizobium.