Part 7 — Critical & Complex NEET-style Integrative MCQs (Q151–175)

Part 7 (Q151–175) of Chapter 12 – Mineral Nutrition, focusing on Critical & Complex NEET-style Integrative Questions. These link deficiency, absorption, translocation, nitrogen metabolism, and soil-plant interactions.

Part 7 — Critical & Complex NEET-style Integrative MCQs (Q151–175)

Q151.

A farmer notices older leaves turning yellow while younger ones remain green. Which deficiency is most likely?
A. Iron
B. Nitrogen ✅
C. Calcium
D. Boron

Explanation:

• A. Fe is immobile → young leaves affected first.
• B. (Correct) N is mobile → older leaves show chlorosis first as N is moved to new growth.
• C/D. Immobile elements → symptoms in young tissues.

Q152.

If Casparian strip in roots is absent, what would happen?
A. Mineral uptake would be more selective
B. Apoplastic movement into xylem would be uncontrolled ✅
C. Phloem loading would stop
D. Nitrogen fixation would increase

Explanation:

• A. Selectivity decreases, not increases.
• B. (Correct) Casparian strip forces solutes into symplast → selective control. Without it, uncontrolled apoplastic entry occurs.
• C/D. Unrelated.

Q153.

Which combination deficiency will reduce both chlorophyll synthesis and nitrogen fixation?
A. N and Ca
B. Mg and Mo ✅
C. P and K
D. Fe and B

Explanation:

• A. Ca is structural, not fixation-related.
• B. (Correct) Mg (central atom of chlorophyll) + Mo (cofactor for nitrogenase) → both functions impaired.
• C/D. Affect other processes.

Q154.

A legume plant with pink nodules is healthy. If nodules turn white/green, what is impaired?
A. Nitrogenase production
B. Leghemoglobin function ✅
C. Photosynthesis
D. Nitrate assimilation

Explanation:

• A. Nitrogenase may still be present.
• B. (Correct) Leghemoglobin loss → O₂ not regulated → nitrogenase inactivated.
• C/D. Not directly tied to nodule color.

Q155.

A hydroponic experiment omits molybdenum. Which result is expected?
A. Decreased ATP synthesis
B. Accumulation of nitrate in tissues ✅
C. Reduced lignification
D. Increased sugar transport

Explanation:

• A. Not directly Mo-related.
• B. (Correct) Mo is a cofactor for nitrate reductase; without it, nitrate cannot be reduced → accumulates.
• C. Cu deficiency symptom.
• D. Boron deficiency symptom.

Q156.

Which condition will maximize passive absorption of ions?
A. High soil ion concentration and transpiration ✅
B. Low soil ion concentration, low transpiration
C. Anaerobic root environment
D. ATP inhibitor applied

Explanation:

• A. (Correct) Passive uptake increases with high gradient + water movement (transpiration).
• B/C/D. Reduce uptake.

Q157.

Zinc deficiency impairs auxin synthesis because it is required for:
A. Ferredoxin
B. Tryptophan metabolism ✅
C. Nitrate assimilation
D. Ammonia detoxification

Explanation:

• A/C/D. Not correct.
• B. (Correct) Zn is cofactor for enzymes in tryptophan → IAA pathway.

Q158.

Which element is directly linked with oxygen-evolving complex in photosynthesis and nitrogen metabolism enzymes?
A. Iron
B. Manganese ✅
C. Boron
D. Calcium

Explanation:

• A. Fe is electron carrier.
• B. (Correct) Mn is crucial for water-splitting in PSII, also functions in enzyme systems.
• C/D. Roles elsewhere.

Q159.

Why is ammonium toxic if not quickly assimilated?
A. It alkalizes cytoplasm
B. It uncouples proton gradients ✅
C. It oxidizes chlorophyll
D. It inhibits ATP synthesis directly

Explanation:

• A. Not the main reason.
• B. (Correct) Excess NH₄⁺ disrupts proton gradients, toxic → must be assimilated via GS-GOGAT.
• C/D. Not direct roles.

Q160.

Which deficiency would directly lower RuBisCO activity?
A. Phosphorus
B. Magnesium ✅
C. Potassium
D. Molybdenum

Explanation:

• A. P is for ATP.
• B. (Correct) Mg²⁺ is cofactor for RuBisCO.
• C. Osmotic role.
• D. Nitrate reductase, not RuBisCO.

Q161.

Which nitrogen cycle process decreases soil fertility?
A. Nitrification
B. Nitrogen fixation
C. Denitrification ✅
D. Ammonification

Explanation:

• A/B/D. Retain/replenish nitrogen in soil.
• C. (Correct) Denitrification releases N₂ gas → loss of usable nitrogen.

Q162.

Why are young leaves unaffected in nitrogen deficiency?
A. They synthesize N themselves
B. Nitrogen is mobile and moves from older leaves ✅
C. They are insensitive to N deficiency
D. They store extra nitrate

Explanation:

• A/C/D. Incorrect.
• B. (Correct) N is mobile → remobilized to growing young tissues.

Q163.

If a root hair cell has higher solute concentration than soil, water enters by:
A. Active transport
B. Osmosis ✅
C. Exocytosis
D. Facilitated diffusion of ions

Explanation:

• A. No ATP needed for water.
• B. (Correct) Water moves down potential gradient by osmosis.
• C/D. Not relevant.

Q164.

If Nitrosomonas is inhibited, which compound accumulates?
A. Nitrate
B. Ammonia ✅
C. Nitrite
D. Amino acids

Explanation:

• A. Produced later.
• B. (Correct) Nitrosomonas oxidizes NH₃ → NO₂⁻. Inhibition → NH₃ builds up.
• C/D. Not primary accumulation.

Q165.

Deficiency of which two nutrients can cause similar chlorosis, but differ in tissue location?
A. N (older leaves) and Fe (younger leaves) ✅
B. Ca (older leaves) and B (older leaves)
C. K (young leaves) and Mg (young leaves)
D. P (young leaves) and Zn (older leaves)

Explanation:

• A. (Correct) Both cause chlorosis: N (mobile → older leaves first), Fe (immobile → young leaves).
• B/C/D. Not correct pairings.

Q166.

A farmer applies too much Mn fertilizer. Which secondary deficiencies appear?
A. Mo and P
B. Fe and Mg ✅
C. K and Ca
D. B and Zn

Explanation:

• A/C/D. Not main interactions.
• B. (Correct) Excess Mn competes with Fe and Mg → their deficiencies show.

Q167.

Why does leghemoglobin enhance nitrogen fixation?
A. It activates nitrogenase directly
B. Buffers O₂ concentration for nitrogenase ✅
C. Reduces ATP requirement
D. Converts nitrate to ammonia

Explanation:

• A/C/D. Incorrect roles.
• B. (Correct) Leghemoglobin binds O₂, keeping nitrogenase safe but allowing respiration.

Q168.

Which two processes together ensure continuous nitrate supply in soil?
A. Nitrification and denitrification
B. Nitrogen fixation and nitrification ✅
C. Ammonification and denitrification
D. Phloem loading and xylem flow

Explanation:

• A/C. Denitrification removes nitrate.
• B. (Correct) Fixation adds NH₃ → nitrification oxidizes to NO₃⁻.
• D. Transport processes, not soil cycle.

Q169.

In hydroponics, a plant shows purple coloration of leaves. Likely deficiency?
A. Phosphorus ✅
B. Potassium
C. Iron
D. Molybdenum

Explanation:

• A. (Correct) P deficiency causes anthocyanin accumulation → purpling.
• B. Necrosis at margins.
• C. Chlorosis in young leaves.
• D. Whiptail in cauliflower.

Q170.

Which step in nitrogen cycle requires the most ATP?
A. Ammonification
B. Nitrogen fixation ✅
C. Nitrification
D. Denitrification

Explanation:

• A/C/D. Energy neutral or low.
• B. (Correct) N₂ reduction by nitrogenase requires ~16 ATP per N₂.

Q171.

Which soil condition leads to loss of nitrogen as gas?
A. Aerated sandy soil
B. Waterlogged soil with denitrifiers ✅
C. Neutral loam
D. Soil with high Ca²⁺

Explanation:

• A/C/D. Not primary loss conditions.
• B. (Correct) Denitrifiers thrive in anaerobic waterlogged soils → N₂/N₂O gases lost.

Q172.

Why is Ca deficiency irreversible in plants?
A. Ca is immobile and cannot be remobilized to new tissues ✅
B. Ca is highly mobile and lost quickly
C. Ca is stored in xylem sap only
D. Ca is replaced by Mg easily

Explanation:

• A. (Correct) Ca is immobile → deficiency in growing tissues cannot be corrected by remobilization.
• B-D. Not true.

Q173.

In nitrate assimilation, why must NO₂⁻ be quickly reduced in chloroplast?
A. It inhibits electron transport ✅
B. It increases ATP
C. It activates RuBisCO
D. It is a stable molecule

Explanation:

• A. (Correct) NO₂⁻ is toxic and interferes with photosynthesis.
• B/C/D. Not correct.

Q174.

Which set of nutrients directly affect flowering and fruit setting?
A. P, B, Ca ✅
B. N, Fe, Zn
C. K, Mn, Mo
D. S, Mg, Cu

Explanation:

• A. (Correct) P (energy, flowering), B (pollen germination), Ca (cell wall, seed development).
• B-D. Other roles.

Q175.

A plant shows interveinal chlorosis in young leaves, but hydroponics solution contains sufficient Fe. Which is the likely cause?
A. pH too alkaline, Fe unavailable ✅
B. Excess Ca in medium
C. N deficiency
D. B deficiency

Explanation:

• A. (Correct) Fe is insoluble at alkaline pH → deficiency despite presence.
• B. Excess Ca can worsen, but pH is key.
• C/D. Cause different symptoms.

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