NEET Mineral Nutrition Previous Year Questions with Solutions

Photolysis occurs on the inner (lumenal) face of the thylakoid membrane associated with PS II, requiring manganese ($Mn^{2+}$), calcium ($Ca^{2+}$), and chloride ($Cl^-$) ions:

Under Manganese ($Mn$), NCERT explicitly declares: "The best defined function of manganese is in the splitting of water to liberate oxygen during photosynthesis."

The question specifically stipulates "micronutrient". While magnesium ($Mg$) is essential for photosynthesis as the central porphyrin ring coordinator of chlorophyll, magnesium is a macronutrient, whereas manganese is a micronutrient.

Analyzing the specific biochemical roles assigned to each trace element in NCERT:

A maps to III (immediately eliminates Options 1 and 3). B maps to I (confirms Option 4, while Option 2 incorrectly pairs B with II).

Nitrate reductase requires a molybdenum cofactor (MoCo). Auxin synthesis from tryptophan requires $Zn^{2+}$-dependent enzymes. Catalase is a heme-iron enzyme containing ferric iron.

The biological transformation of nitrogen involves distinct specialized bacterial taxa:

The correspondence yields (a)-(ii), (b)-(iv), (c)-(i), (d)-(iii), which is uniquely found in Option (1).

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.

- (a) Iron ($Fe^{3+}$ / $Fe^{2+}$): Constituent of cytochromes and ferredoxin in electron transport; reversibly oxidized during redox reactions. Although not a structural constituent of the chlorophyll porphyrin ring (which contains $Mg^{2+}$), iron is an indispensable cofactor required for chlorophyll biosynthesis. - (b) Zinc ($Zn^{2+}$): Activates diverse dehydrogenases and carbonic anhydrase; plays an obligatory catalytic role in the enzymatic biosynthesis of auxin (indole-3-acetic acid, IAA) from its amino acid precursor tryptophan. - (c) Boron ($BO_3^{3-}$ / $B_4O_7^{2-}$): Essential for $Ca^{2+}$ uptake and utilization, membrane functioning, cell elongation, carbohydrate translocation via phloem, and pollen germination. - (d) Manganese ($Mn^{2+}$): Best known for its role in the photolysis of water (splitting of water) to evolve molecular oxygen ($O_2$) during light reactions of photosynthesis in Photosystem II.

Matching sequence is: (a)-(iii), (b)-(iv), (c)-(ii), (d)-(i). This corresponds perfectly to Option (3).