NEET 2020 Botany Question 13 Solution

Biological nitrogen fixation is carried out exclusively by prokaryotes containing the oxygen-sensitive enzyme complex nitrogenase (consisting of an Fe protein dinitrogenase reductase and a Mo-Fe protein dinitrogenase): - The reduction of one mole of dinitrogen ($N_2$) to two moles of ammonia ($\text{NH}_3$) is an energetically demanding, multi-step electron transfer process requiring 8 electrons and 8 protons. - Obligatory Proton Reduction: During the catalytic cycle, two electrons are obligatorily consumed to reduce two protons into molecular hydrogen gas ($\text{H}_2$). - Balanced Chemical Equation: $$\text{N}_2 + 8e^- + 8\text{H}^+ + 16\text{ATP} \xrightarrow{\text{Nitrogenase}} 2\text{NH}_3 + \text{H}_2 + 16\text{ADP} + 16\text{P}_i$$ - Thus, the definitive chemical products of the reaction are Ammonia and Hydrogen.

Nitrogenase is highly susceptible to irreversible oxidative denaturation by molecular oxygen. In legume root nodules, the oxygen-scavenging hemoprotein leghemoglobin maintains an anaerobic microenvironment. Therefore, oxygen can never be a product of this reaction.