Given below are two statements, one is labelled as Assertion (A) and other one labelled as Reason (R).
Assertion (A) : Nitrogen fixing bacteria require a rich supply of carbohydrates.
Reason (R) : The process of nitrogen fixation requires 16 ATP molecules for the synthesis every 2 ammonia molecules.
In light of the above statements, choose the correct answer from the options given below.
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To connect Assertion and Reason, insert the word "because" between them: "Nitrogen-fixing bacteria require carbohydrates *because* the process of fixing nitrogen requires 16 ATP for every 2 ammonia molecules." If it reads logically, then R is the correct explanation.
Both Assertion & Reason are true and the reason is the correct explanation of the assertion.
Both Assertion & Reason are true but the reason is not the correct explanation of the assertion.
Assertion is true statement but Reason is false.
Both Assertion and Reason are false statements.
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The Correct Option isA
Solution and Explanation
Step 1: Understanding the Concept:
This problem addresses the energy demands of biological nitrogen fixation and how diazotrophic microorganisms obtain the energy required to drive this endergonic biochemical process. Step 2: Detailed Explanation:
Let us analyze both statements and their relationship:
Assertion (A): Nitrogen-fixing bacteria (whether free-living like Azotobacter or symbiotic like Rhizobium) require a constant and rich supply of carbohydrates.
These carbohydrates undergo glycolysis and the citric acid cycle to generate high-energy electrons (NADH, \(\text{FADH}_2\)) and ATP via oxidative phosphorylation. Thus, Assertion (A) istrue.
Reason (R): The reduction of one mole of dinitrogen gas (\(N_2\)) to two moles of ammonia (\(NH_3\)) is extremely energy-intensive due to the high activation energy of breaking the nitrogen-nitrogen triple bond.
The biological reaction requires at least 16 ATP molecules to reduce one \(N_2\) molecule:
\[ N_2 + 8H^+ + 8e^- + 16\text{ATP} \rightarrow 2NH_3 + H_2 + 16\text{ADP} + 16P_i \]
This means 16 ATP are consumed for every 2 ammonia molecules synthesized. Thus, Reason (R) istrue.
Explanation check: Because the nitrogenase reaction requires 16 ATP molecules for every 2 ammonia molecules produced, the bacteria must maintain a very high rate of cellular respiration.
To sustain this respiration and generate sufficient ATP, they require a constant, rich supply of carbohydrates (which, in symbiotic systems, are directly supplied by the host plant's photosynthate pool).
Therefore, Reason (R) directly explains why Assertion (A) is true. Step 2: Final Answer:
The correct option is (A).
