Part 3 — Mineral Nutrition and Transport (Q51–75)

Q51.

Which form of nitrogen is primarily absorbed by plants from soil?
A. N₂ gas
B. Nitrate (NO₃⁻) ✅
C. Nitric oxide (NO)
D. Urea

Explanation:

A. N₂ gas is inert, unavailable directly (except by nitrogen-fixing bacteria).
B. (Correct) Plants absorb most nitrogen as NO₃⁻ and NH₄⁺ ions.
C. NO is a signaling molecule, not absorbed nutrient.
D. Urea can be converted to NH₄⁺ but is not directly taken up in large amounts.

Q52.

Which element is a component of chlorophyll?
A. Iron
B. Magnesium ✅
C. Calcium
D. Potassium

Explanation:

A. Iron is required for electron transport, but not part of chlorophyll structure.
B. (Correct) Magnesium is the central atom in chlorophyll porphyrin ring.
C. Calcium strengthens cell wall.
D. Potassium regulates stomata.

Q53.

Which mineral is essential for nitrogen fixation in legumes?
A. Potassium
B. Iron
C. Molybdenum ✅
D. Sulphur

Explanation:

A. Potassium is for enzyme activation, not fixation.
B. Iron is involved but not unique.
C. (Correct) Molybdenum is a cofactor of nitrogenase enzyme.
D. Sulphur is for proteins, not N fixation.

Q54.

Deficiency of potassium in plants leads to:
A. Chlorosis in young leaves
B. Necrosis at leaf margins ✅
C. Purple coloration of leaves
D. Delayed flowering

Explanation:

A. Chlorosis in young leaves = iron deficiency.
B. (Correct) Potassium deficiency causes necrotic edges, weak stems.
C. Phosphorus deficiency.
D. Nitrogen deficiency.

Q55.

Which of the following is an immobile element in plants?
A. Potassium
B. Calcium ✅
C. Nitrogen
D. Magnesium

Explanation:

A/C/D. K, N, Mg are mobile, so deficiency first in older leaves.
B. (Correct) Calcium is immobile → deficiency in young tissues.

Q56.

Which mineral is essential for ATP synthesis?
A. Zinc
B. Phosphorus ✅
C. Sulphur
D. Chlorine

Explanation:

A. Zinc: enzyme activator.
B. (Correct) ATP = adenosine triphosphate, needs phosphorus.
C. Sulphur = proteins/vitamins.
D. Chlorine = osmotic balance.

Q57.

Which nutrient deficiency causes interveinal chlorosis in leaves?
A. Iron ✅
B. Nitrogen
C. Calcium
D. Potassium

Explanation:

A. (Correct) Iron deficiency → chlorosis between veins, veins remain green.
B. Nitrogen deficiency → overall chlorosis.
C. Calcium deficiency → necrosis in young tissues.
D. Potassium → necrotic leaf margins.

Q58.

Which is the main form of phosphorus absorbed by plants?
A. P₂O₅
B. H₂PO₄⁻ ✅
C. PO₄³⁻ only
D. ATP

Explanation:

A. P₂O₅ is a fertilizer form, not absorbed directly.
B. (Correct) Plants absorb phosphorus as H₂PO₄⁻ and HPO₄²⁻ ions.
C. PO₄³⁻ is rare at soil pH.
D. ATP is organic, not absorbed.

Q59.

Which element is part of both ferredoxin and cytochromes?
A. Zinc
B. Iron ✅
C. Manganese
D. Copper

Explanation:

A. Zinc = enzyme activator.
B. (Correct) Iron is part of Fe-S proteins (ferredoxin) and cytochromes.
C. Manganese = photosystem II enzyme cofactor.
D. Copper = plastocyanin.

Q60.

Sulphur is present in which amino acid?
A. Valine
B. Methionine ✅
C. Glycine
D. Proline

Explanation:

A/C/D. These lack sulphur.
B. (Correct) Methionine and cysteine contain sulphur.

Q61.

Which transport mechanism is mainly responsible for mineral ion uptake into roots?
A. Passive diffusion
B. Facilitated diffusion
C. Active transport using carrier proteins ✅
D. Osmosis

Explanation:

A/B. Small contribution, but not main uptake.
C. (Correct) Minerals are absorbed against gradient using ATP-driven carriers.
D. Osmosis = water movement.

Q62.

Which element is essential for splitting of water during photosynthesis?
A. Magnesium
B. Manganese ✅
C. Copper
D. Boron

Explanation:

A. Mg = chlorophyll.
B. (Correct) Mn cluster in PSII splits water (Hill reaction).
C. Cu = electron carrier.
D. Boron = cell wall, pollen.

Q63.

Zinc deficiency causes:
A. Interveinal chlorosis
B. Shortened internodes and little leaf disease ✅
C. Necrosis of root tips
D. Purple coloration

Explanation:

A. Iron deficiency.
B. (Correct) Zinc deficiency → stunted growth, small leaves.
C. Calcium deficiency.
D. Phosphorus deficiency.

Q64.

Which element is NOT a macronutrient?
A. Nitrogen
B. Potassium
C. Boron ✅
D. Calcium

Explanation:

A/B/D. Macronutrients required in large amounts.
C. (Correct) Boron is a micronutrient.

Q65.

Boron is mainly required in plants for:
A. Photosystem II
B. Cell wall formation and pollen germination ✅
C. ATP synthesis
D. Stomatal opening

Explanation:

A. PSII requires Mn.
B. (Correct) Boron functions in cell wall and pollen tube growth.
C. ATP requires P.
D. Stomatal movement requires K⁺.

Q66.

Which element is an essential component of proteins and coenzymes?
A. Sulphur ✅
B. Chlorine
C. Molybdenum
D. Calcium

Explanation:

A. (Correct) Sulphur occurs in amino acids (cysteine, methionine), vitamins, coenzymes.
B. Cl maintains ionic balance.
C. Mo = nitrogenase cofactor.
D. Ca = structural.

Q67.

Which deficiency symptom is first visible in older leaves?
A. Calcium deficiency
B. Potassium deficiency ✅
C. Boron deficiency
D. Sulphur deficiency

Explanation:

A/C/D. These are immobile → symptoms in young tissues.
B. (Correct) Potassium is mobile, so deficiency appears in older leaves.

Q68.

Nitrogen deficiency in plants leads to:
A. Accumulation of anthocyanin and yellowing of older leaves ✅
B. Curling of leaf margins
C. Little leaf disease
D. Death of meristems

Explanation:

A. (Correct) Nitrogen deficiency causes chlorosis (older leaves first), stunted growth.
B. Curling margins = K deficiency.
C. Little leaf = Zn deficiency.
D. Death of meristems = Ca deficiency.

Q69.

Iron is essential for:
A. Nitrate reduction and chlorophyll synthesis ✅
B. Cell wall formation
C. Translocation of sugars
D. Turgor maintenance

Explanation:

A. (Correct) Iron required for ferredoxin, cytochromes, enzymes, and chlorophyll synthesis.
B. Boron aids cell wall.
C. Phloem activity needs P.
D. Turgor by K⁺.

Q70.

Which element deficiency causes “brown heart” disease in sugar beet?
A. Boron ✅
B. Copper
C. Manganese
D. Zinc

Explanation:

A. (Correct) Boron deficiency → internal necrosis, brown heart.
B/C/D. Not this disorder.

Q71.

Chlorosis is caused by deficiency of all EXCEPT:
A. Nitrogen
B. Magnesium
C. Iron
D. Sodium ✅

Explanation:

A/B/C. N, Mg, Fe are chlorosis-causing nutrients.
D. (Correct) Sodium is not essential in most plants.

Q72.

Which element regulates osmotic balance and stomatal movement?
A. Calcium
B. Potassium ✅
C. Nitrogen
D. Phosphorus

Explanation:

A. Ca is structural.
B. (Correct) K⁺ accumulation/depletion regulates guard cell turgor.
C. N = proteins.
D. P = ATP.

Q73.

The element essential for activation of RuBisCO is:
A. Iron
B. Magnesium ✅
C. Copper
D. Sulphur

Explanation:

A. Not for RuBisCO.
B. (Correct) Mg²⁺ activates RuBisCO enzyme.
C. Cu = plastocyanin.
D. Sulphur = amino acids.

Q74.

Which transport protein is directly involved in uptake of mineral ions in roots?
A. Aquaporins
B. Ion channels and carrier proteins ✅
C. Plasmodesmata
D. Xylem vessels

Explanation:

A. Aquaporins transport water.
B. (Correct) Carrier proteins + ion channels in membranes uptake ions.
C. Plasmodesmata = cytoplasmic connections.
D. Xylem transports long-distance, not uptake.

Q75.

Which element is involved in photolysis of water?
A. Copper
B. Manganese ✅
C. Phosphorus
D. Sulphur

Explanation:

A. Copper = electron transfer.
B. (Correct) Mn is required in the water-splitting complex of PSII.
C/D. Not directly.

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Part 3 — Mineral Nutrition and Transport (Q51–75)