Given below are two statements:
Statement I: Diazotrophs possess Nitrogenase enzyme that helps in biological nitrogen fixation.
Statement II: Both Rhizobium and Azotobacter are symbiotic nitrogen fixers.
In light of the above statements, choose the correct answer from the options given below:
Statement I: Diazotrophs possess Nitrogenase enzyme that helps in biological nitrogen fixation.
Statement II: Both Rhizobium and Azotobacter are symbiotic nitrogen fixers.
In light of the above statements, choose the correct answer from the options given below:
Show Hint
- Symbiotic: Rhizobium, Frankia.
- Free-living (Nonsymbiotic): Azotobacter (aerobic), Clostridium (anaerobic).
- Associative: Azospirillum.
- Both Statement I and Statement II are true
- Both Statement I and Statement II are false
- Statement I is true but Statement II is false
- Statement I is false but Statement II is true
The Correct Option is C
Solution and Explanation
Biological Nitrogen Fixation (BNF) is the process by which atmospheric nitrogen gas ($N_2$) is reduced to ammonia ($NH_3$).
This conversion is carried out by specialized prokaryotic microorganisms known as diazotrophs.
Detailed Explanation:
Let us evaluate both statements:
Statement I:
Diazotrophs are characterized by the presence of the nitrogenase enzyme complex.
This enzyme contains iron and molybdenum-iron proteins and catalyzes the break of the triple bond in $N_2$ to form ammonia:
\[ N_2 + 8H^+ + 8e^- + 16\text{ATP} \rightarrow 2NH_3 + H_2 + 16\text{ADP} + 16P_i \]
This reaction is highly sensitive to oxygen and requires anaerobic or microaerobic conditions inside the cell.
Thus, Statement I is true.
Statement II:
Diazotrophs are classified into symbiotic and free-living nitrogen fixers.
- Rhizobium is a symbiotic nitrogen fixer that forms nodules on the roots of leguminous plants.
- Azotobacter, however, is a free-living, aerobic, non-symbiotic diazotroph that fixes nitrogen in the rhizosphere soil.
Therefore, Statement II is false because Azotobacter is not a symbiotic nitrogen fixer.
Step 2: Final Answer:
Statement I is true, and Statement II is false.
This corresponds to Option (C).
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