Part 8 — Analytical, Case-based NEET-style Revision (Q176–200)
Part 8 (Q176–200) of Chapter 12 – Mineral Nutrition.
This section contains Analytical, Case-based, Higher-order NEET-style Revision Questions, integrating all subtopics: absorption, transport, soil-plant relations, deficiencies, toxicity, and nitrogen metabolism.
Part 8 — Mineral Nutrition – Analytical, Case-based NEET-style Revision (Q176–200)
Q176.
A farmer observes leaf tip necrosis and poor seed setting. Which nutrient is deficient?
A. Iron
B. Boron ✅
C. Nitrogen
D. Magnesium
Explanation:
- A. Causes interveinal chlorosis in young leaves.
- B. (Correct) Boron deficiency → tip necrosis, poor seed/fruit set due to pollen germination defects.
- C. General chlorosis in old leaves.
- D. Interveinal chlorosis in older leaves.
Q177.
In hydroponics, omission of Mg leads to:
A. Failure of root cap formation
B. Loss of chlorophyll, interveinal chlorosis ✅
C. Purple coloration of leaves
D. Tip necrosis
Explanation:
- A. Ca deficiency affects root tips.
- B. (Correct) Mg deficiency → interveinal chlorosis in old leaves (mobile nutrient).
- C. P deficiency.
- D. Boron deficiency.
Q178.
A plant grown in alkaline soil shows Fe deficiency despite Fe fertilizer application. Why?
A. Fe is leached easily
B. Fe is present as insoluble ferric hydroxide ✅
C. Plant roots cannot absorb Fe³⁺
D. Soil bacteria consume Fe
Explanation:
- A/D. Not the main reason.
- B. (Correct) At high pH, Fe precipitates → unavailable.
- C. Plants absorb Fe²⁺ mainly; high pH prevents reduction.
Q179.
During nitrogen fixation, leghemoglobin maintains:
A. High oxygen concentration
B. Low but steady oxygen concentration ✅
C. Zero oxygen concentration
D. Conversion of nitrate to nitrite
Explanation:
- A. High O₂ would inactivate nitrogenase.
- B. (Correct) Leghemoglobin buffers O₂: enough for respiration but low enough to protect nitrogenase.
- C. Zero O₂ would stop respiration.
- D. Not its function.
Q180.
In a soil rich in nitrifying bacteria but poor in denitrifiers, which compound accumulates?
A. N₂ gas
B. Nitrate (NO₃⁻) ✅
C. Ammonia
D. Amino acids
Explanation:
- A. Produced by denitrification.
- B. (Correct) Nitrification (NH₃ → NO₂⁻ → NO₃⁻) dominates.
- C/D. Not main products here.
Q181.
Which combination of deficiencies would cause both defective cell walls and reduced pollen tube growth?
A. Calcium and Boron ✅
B. Nitrogen and Iron
C. Potassium and Magnesium
D. Phosphorus and Sulphur
Explanation:
- A. (Correct) Ca stabilizes cell walls; B required for pollen tube elongation.
- B-D. Affect other processes.
Q182.
Why do plants grown in sandy soil require frequent fertilization?
A. Sandy soil has low cation exchange capacity ✅
B. Sandy soil retains all nutrients
C. Sandy soil is rich in humus
D. Sandy soil prevents leaching
Explanation:
- A. (Correct) Nutrients leach quickly due to poor retention.
- B-D. Opposite to reality.
Q183.
A legume plant with nodules shows nitrate accumulation in leaves. Which nutrient is most likely deficient?
A. Mo ✅
B. K
C. Mg
D. Zn
Explanation:
- A. (Correct) Mo is required for nitrate reductase; deficiency → nitrate builds up.
- B/C/D. Don’t directly cause nitrate accumulation.
Q184.
If transpiration is blocked but roots remain active, minerals may still reach leaves due to:
A. Diffusion
B. Root pressure ✅
C. Apoplast flow
D. Phloem loading
Explanation:
- A/C. Insufficient for long-distance.
- B. (Correct) Root pressure pushes xylem sap upward at night or low transpiration.
- D. Phloem moves organic solutes.
Q185.
In nitrogen assimilation, the first amino acid formed is:
A. Glycine
B. Glutamate ✅
C. Alanine
D. Proline
Explanation:
- A/C/D. Not the first.
- B. (Correct) Glutamate is primary amino acid formed by incorporation of NH₄⁺.
Q186.
Which symptom distinguishes sulphur deficiency from nitrogen deficiency?
A. Necrosis in root tips
B. Chlorosis in young leaves ✅
C. Interveinal chlorosis
D. Purple coloration
Explanation:
- A. Ca deficiency.
- B. (Correct) S is immobile → chlorosis in young leaves. N deficiency starts in older leaves.
- C. Fe/Mg deficiency.
- D. P deficiency.
Q187.
A farmer notices crinkled leaves and brown spots after applying too much Mn. Which secondary deficiency is expected?
A. Fe ✅
B. Ca
C. B
D. P
Explanation:
- A. (Correct) Excess Mn inhibits Fe uptake, showing chlorosis.
- B-D. Not strongly linked.
Q188.
If nodules are ineffective (white, not pink), the plant will:
A. Assimilate nitrates from soil ✅
B. Continue fixing N₂
C. Produce excess leghemoglobin
D. Survive without nitrogen
Explanation:
- A. (Correct) If nodules fail, plant depends on soil nitrate.
- B/C/D. Not possible without functional symbiosis.
Q189.
A soil test shows abundant nitrate but stunted plant growth. Likely reason?
A. Mo deficiency blocking nitrate reductase ✅
B. Excess calcium
C. Root hairs absent
D. Too much phosphorus
Explanation:
- A. (Correct) Nitrate present but cannot be reduced to NH₄⁺ without Mo.
- B-D. Not the main explanation.
Q190.
Which condition enhances denitrification in soil?
A. Aerobic respiration in roots
B. Anaerobic waterlogging ✅
C. High humus with good aeration
D. Sandy dry soil
Explanation:
- A/C/D. Not favorable.
- B. (Correct) Denitrifiers thrive in anaerobic conditions.
Q191.
A maize plant shows poor photosynthesis and stunted growth despite adequate light. Soil test reveals low nitrogen. Which remedy?
A. Add urea ✅
B. Add lime
C. Spray boron
D. Reduce watering
Explanation:
- A. (Correct) Urea supplies nitrogen → improved growth.
- B/C/D. Don’t correct N deficiency.
Q192.
Nitrate assimilation in leaves depends directly on:
A. Glycolysis
B. Light and ferredoxin ✅
C. Root pressure
D. Phloem transport
Explanation:
- A. Indirect.
- B. (Correct) Light-driven ferredoxin reduces nitrite → NH₄⁺.
- C/D. Not primary factors.
Q193.
Why do legumes enrich soil nitrogen content?
A. They absorb more nitrate
B. Rhizobium fixes atmospheric N₂ into usable forms ✅
C. Their roots excrete nitrate
D. They prevent denitrification
Explanation:
- A/C/D. Not correct.
- B. (Correct) Symbiotic fixation enriches soil with nitrogen compounds.
Q194.
In case of excess nitrate in diet, human infants suffer methemoglobinemia (“blue baby syndrome”). This is because:
A. NO₃⁻ converts hemoglobin to methemoglobin ✅
B. NO₃⁻ enhances ATP breakdown
C. NO₃⁻ lowers RBC count
D. NO₃⁻ kills WBCs
Explanation:
- A. (Correct) Nitrate → nitrite, oxidizes Hb to metHb, reducing O₂ carrying.
- B-D. Not causes.
Q195.
A hydroponic solution lacks K⁺. Plant shows:
A. Root tip necrosis
B. Chlorosis in young leaves
C. Marginal necrosis in leaves ✅
D. Purple pigmentation
Explanation:
- A. Ca deficiency.
- B. Fe/S deficiency.
- C. (Correct) K deficiency → scorching, marginal necrosis.
- D. P deficiency.
Q196.
Which deficiency directly reduces chlorophyll formation without being a part of the molecule?
A. Fe ✅
B. Mg
C. N
D. S
Explanation:
- A. (Correct) Fe is not in chlorophyll structure but needed for its biosynthesis.
- B. Central atom of chlorophyll.
- C/D. Needed indirectly.
Q197.
Why is ammonium not a preferred nitrogen source in fertilizers?
A. It leaches rapidly
B. It volatilizes easily and is toxic ✅
C. It cannot be assimilated
D. It is immobile in soil
Explanation:
- A. Nitrate leaches faster than NH₄⁺.
- B. (Correct) NH₄⁺ is volatile (NH₃ gas) and toxic to plants if not quickly assimilated.
- C. Assimilable but dangerous.
- D. NH₄⁺ is relatively immobile.
Q198.
In the nitrogen cycle, which process directly depends on decomposers?
A. Nitrification
B. Ammonification ✅
C. Nitrogen fixation
D. Denitrification
Explanation:
- A/C/D. Bacteria involved but not decomposers per se.
- B. (Correct) Decomposers convert organic N → NH₄⁺ (ammonification).
Q199.
Why does potassium deficiency reduce stomatal opening?
A. K⁺ controls guard cell turgor ✅
B. Ca²⁺ binds stomata
C. Mg²⁺ activates RuBisCO
D. Fe regulates ATP
Explanation:
- A. (Correct) K⁺ influx/efflux regulates guard cell osmotic pressure → stomatal movement.
- B-D. Not correct.
Q200.
A plant grown without Mo and Fe will fail to:
A. Carry out photolysis
B. Assimilate nitrate into amino acids ✅
C. Absorb calcium
D. Translocate sugars
Explanation:
- A. Mn is essential for photolysis.
- B. (Correct) Mo and Fe are cofactors of nitrate/nitrite reductases → without them, nitrate assimilation fails.
- C/D. Not directly affected.
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