🌾 Mineral Nutrition – MCQs

Part 1 (Q1–Q25)

Q1. Essential elements are those that

A) Are abundant in soil
B) Increase plant height
C) Are indispensable for life cycle completion ✅
D) Improve taste of fruits

Explanation: An element is essential if its absence prevents completion of life cycle or its role can’t be substituted.

Q2. The technique used to study mineral requirements is

A) Tissue culture
B) Hydroponics ✅
C) Grafting
D) Marcotting

Explanation: Hydroponics grows plants in nutrient solutions, isolating mineral requirements.

Q3. Macronutrients are required in

A) mg kg⁻¹ range
B) g kg⁻¹ (or >10⁻³ of dry matter) ✅
C) ng g⁻¹ range
D) Not required

Explanation: Macronutrients (N, P, K, Ca, Mg, S) are needed in large amounts.

Q4. Which is a micronutrient?

A) Potassium
B) Calcium
C) Iron
D) Zinc ✅

Explanation: Micronutrients: Fe, Mn, Zn, Cu, B, Mo, Cl, Ni—needed in trace amounts.

Q5. Nitrogen is absorbed mainly as

A) NO₂⁻
B) NO₃⁻ ✅
C) NH₄⁺
D) N₂

Explanation: Plants prefer NO₃⁻, though NH₄⁺ can also be absorbed.

Q6. Phosphorus is absorbed as

A) HPO₄²⁻ / H₂PO₄⁻ ✅
B) PO₃³⁻
C) P⁵⁺
D) PH₃

Explanation: Orthophosphate ions are the available forms for uptake.

Q7. Potassium is absorbed as

A) K⁺ ✅
B) KOH
C) KCl
D) KNO₃

Explanation: K⁺ is taken up and functions in stomatal regulation and enzyme activation.

Q8. Sulphur is mainly absorbed as

A) H₂S
B) SO₂
C) SO₄²⁻ ✅
D) S⁰

Explanation: Plants take sulphate (SO₄²⁻) and reduce it to form S-containing amino acids.

Q9. Magnesium is a structural part of

A) ATP
B) Chlorophyll ✅
C) DNA
D) Cutin

Explanation: Mg²⁺ sits at the center of the chlorophyll porphyrin ring and activates many enzymes.

Q10. Iron is essential for

A) Stomatal opening
B) Nitrate reduction & electron transport ✅
C) Cuticle synthesis
D) Lignification

Explanation: Fe is part of cytochromes/ferredoxin and nitrate reductase activity.

Q11. Manganese deficiency primarily affects

A) Transpiration
B) Hill reaction (photolysis of water) ✅
C) Phloem loading
D) Cell division

Explanation: Mn is crucial for the oxygen-evolving complex in PSII.

Q12. Boron is required for

A) Protein synthesis
B) Cell wall formation & pollen tube growth ✅
C) Chlorophyll synthesis
D) Nitrogen fixation directly

Explanation: Boron aids cell wall integrity, membrane function, and reproductive growth.

Q13. Copper is a component of

A) Nitrate reductase
B) Plastocyanin ✅
C) RuBisCO
D) Pyruvate dehydrogenase

Explanation: Cu is in plastocyanin, an electron carrier in the photosynthetic ETC.

Q14. Molybdenum is essential for

A) Photosystem I
B) Nitrogenase & nitrate reductase ✅
C) ATP synthase
D) Cellulose synthase

Explanation: Mo is a cofactor in nitrogen fixation and nitrate reduction enzymes.

Q15. Chlorosis (yellowing of leaves) is commonly due to deficiency of

A) Fe, Mg, N ✅
B) B, Mo, Cl
C) Ca, S, K
D) Na, Si, Al

Explanation: N, Mg, Fe are vital for chlorophyll or its formation → deficiency causes chlorosis.

Q16. Interveinal chlorosis of young leaves typically indicates deficiency of

A) Nitrogen
B) Magnesium
C) Iron ✅
D) Potassium

Explanation: Fe is immobile; deficiency appears first in young leaves as interveinal chlorosis.

Q17. Tip-burn and die-back of shoots indicate deficiency of

A) Potassium
B) Calcium ✅
C) Phosphorus
D) Sulphur

Explanation: Ca is immobile, essential for cell wall (middle lamella)—deficiency causes necrosis at tips.

Q18. Old leaf marginal chlorosis & scorching is typical of

A) Potassium deficiency ✅
B) Boron deficiency
C) Iron deficiency
D) Zinc toxicity

Explanation: K is mobile; deficiency symptoms start in older leaves with marginal scorch.

Q19. “Little leaf” and shortened internodes commonly indicate

A) Zinc deficiency ✅
B) Manganese deficiency
C) Iron deficiency
D) Copper toxicity

Explanation: Zn is needed for IAA synthesis; deficiency → little leaf, rosetting.

Q20. “Whip-tail” disease in cauliflower is due to deficiency of

A) Molybdenum ✅
B) Boron
C) Sulphur
D) Iron

Explanation: Mo deficiency impairs nitrate reduction, causing leaf malformations (“whip-tail”).

Q21. Legume nodulation and nitrogen fixation require

A) Rhizobium and nitrogenase ✅
B) Azotobacter and RuBisCO
C) Nitrosomonas and catalase
D) Cyanobacteria only

Explanation: Rhizobium–legume symbiosis uses nitrogenase (Mo–Fe) to fix N₂ in nodules.

Q22. The oxygen-scavenging pigment in legume nodules is

A) Hemoglobin
B) Myoglobin
C) Leghemoglobin ✅
D) Cytochrome c

Explanation: Leghaemoglobin maintains low O₂ to protect nitrogenase yet supply respiration.

Q23. Biological nitrogen fixation converts

A) NO₃⁻ → NH₄⁺
B) N₂ → NH₃ ✅
C) NH₄⁺ → NO₂⁻
D) NO₂⁻ → NO₃⁻

Explanation: Nitrogenase reduces N₂ → NH₃, using ATP and reductant.

Q24. The first stable product of nitrate assimilation in plants is

A) Nitrite (NO₂⁻) in cytosol
B) Ammonia (NH₃) in stroma
C) Glutamine via GS enzyme ✅
D) Urea in peroxisome

Explanation: Nitrate → nitrite (cytosol) → ammonium (plastid), then GS–GOGAT forms glutamine/glutamate.

Q25. A classic complete nutrient solution (Hoagland & Arnon) contains

A) Only macronutrients
B) Only micronutrients
C) Both macro- and micronutrients ✅
D) Only nitrogen and potassium

Explanation: Hoagland solution supplies all essential elements at optimal concentrations.

🌱 Plant Physiology – Mineral Nutrition

Part 2 (Q26–Q50)

Q26. The deficiency symptom “necrosis” (death of tissue) is commonly due to

A) Nitrogen and iron
B) Calcium, magnesium, copper, potassium ✅
C) Boron and molybdenum
D) Sodium and chloride

Explanation: Deficiency of Ca, Mg, Cu, K causes necrotic patches on leaves.

Q27. Chlorosis occurs due to deficiency of

A) N, Mg, Fe, S ✅
B) Cu, B, Zn
C) Na, Mo, Cl
D) Si, Al, Se

Explanation: Chlorosis = yellowing of leaves due to loss of chlorophyll synthesis.

Q28. Phosphorus deficiency symptoms appear first in

A) Young leaves
B) Old leaves ✅
C) Roots
D) Flowers

Explanation: Phosphorus is mobile in phloem, so deficiency shows up in older leaves first.

Q29. Nitrogen deficiency results in

A) Rosette formation
B) Stunted growth & chlorosis ✅
C) Whip-tail
D) Scorched margins

Explanation: N deficiency reduces chlorophyll, causing chlorosis and poor growth.

Q30. Sulphur deficiency causes

A) Little leaf
B) Whip-tail
C) General chlorosis in young leaves ✅
D) Marginal scorch

Explanation: S is immobile, so deficiency appears in young leaves as yellowing.

Q31. Calcium is absorbed by plants as

A) Ca²⁺ ✅
B) CaCl₂
C) CaSO₄
D) CaCO₃

Explanation: Plants absorb calcium in ionic form (Ca²⁺) from soil.

Q32. Magnesium is absorbed as

A) MgCO₃
B) Mg²⁺ ✅
C) MgO
D) MgCl₂

Explanation: Plants uptake Mg²⁺, which is mobile and central in chlorophyll.

Q33. The element associated with photolysis of water in photosynthesis is

A) Fe
B) Mn ✅
C) Cu
D) Zn

Explanation: Manganese is essential for oxygen-evolving complex (OEC) in PSII.

Q34. Nitrogenase enzyme is inactivated by

A) O₂ ✅
B) CO₂
C) H₂
D) N₂

Explanation: Nitrogenase is extremely oxygen-sensitive; protected by leghemoglobin.

Q35. Nitrate reductase is located in the

A) Chloroplast
B) Cytosol ✅
C) Mitochondria
D) Vacuole

Explanation: Nitrate → nitrite reduction occurs in cytosol via nitrate reductase.

Q36. Nitrite reductase is located in the

A) Cytosol
B) Chloroplast/plastids ✅
C) Mitochondria
D) Ribosome

Explanation: Nitrite → ammonium reduction occurs in chloroplasts (plastids).

Q37. Which micronutrient is involved in splitting of water during photosynthesis?

A) Zinc
B) Manganese ✅
C) Copper
D) Boron

Explanation: Mn²⁺ ions are essential in the water-splitting complex.

Q38. Which micronutrient deficiency causes “little leaf” disease in plants?

A) Iron
B) Zinc ✅
C) Boron
D) Molybdenum

Explanation: Zn deficiency → shortened internodes & small leaves.

Q39. Which micronutrient deficiency causes “brown heart” in turnip?

A) Molybdenum
B) Boron ✅
C) Zinc
D) Iron

Explanation: Boron deficiency causes brown heart/rot in turnip.

Q40. Which micronutrient deficiency causes “die-back” disease in citrus?

A) Copper ✅
B) Iron
C) Manganese
D) Boron

Explanation: Cu deficiency → death of shoot tips, called die-back.

Q41. Which element is essential for nitrogen fixation?

A) Zn
B) Mo ✅
C) Mg
D) Ca

Explanation: Molybdenum is a cofactor of nitrogenase enzyme.

Q42. The most abundant element in plant tissue is

A) Oxygen ✅
B) Carbon
C) Hydrogen
D) Nitrogen

Explanation: Oxygen (from water) is most abundant (~80% of plant body).

Q43. Which element is not considered essential but is beneficial?

A) Na ✅
B) K
C) P
D) N

Explanation: Sodium is not essential but beneficial in C₄ and CAM plants.

Q44. The total number of essential elements for plants is

A) 10
B) 17 ✅
C) 25
D) 12

Explanation: Plants require 17 essential elements (9 macro + 8 micro).

Q45. A plant nutrient is considered “essential” if

A) It is abundant in soil
B) It promotes faster growth
C) Its absence prevents life cycle completion ✅
D) It is present in all plants

Explanation: Essentiality criteria by Arnon: needed for life cycle completion and irreplaceable.

Q46. Which element is absorbed as NO₃⁻, NO₂⁻, or NH₄⁺?

A) Sulphur
B) Nitrogen ✅
C) Phosphorus
D) Potassium

Explanation: N is absorbed as NO₃⁻ (main), sometimes as NH₄⁺.

Q47. Which element is absorbed as SO₄²⁻?

A) Sulphur ✅
B) Phosphorus
C) Calcium
D) Iron

Explanation: Sulphur is taken as sulphate (SO₄²⁻) and reduced in plastids.

Q48. Which element is absorbed as H₂PO₄⁻ and HPO₄²⁻?

A) Potassium
B) Phosphorus ✅
C) Nitrogen
D) Magnesium

Explanation: Plants absorb orthophosphates (H₂PO₄⁻ / HPO₄²⁻).

Q49. Which element deficiency leads to accumulation of anthocyanin (purple leaves)?

A) Nitrogen ✅
B) Iron
C) Boron
D) Zinc

Explanation: N deficiency → reduced chlorophyll + purple coloration due to anthocyanin.

Q50. Which element deficiency leads to “frost damage susceptibility” in cereals?

A) Boron
B) Potassium ✅
C) Calcium
D) Molybdenum

Explanation: K deficiency → weak cell walls → lodging + frost susceptibility.

🌱 Plant Physiology – Mineral Nutrition

Part 3 (Q51–Q75)

Q51. Which element is a component of coenzyme thiamine pyrophosphate?

A) Sulphur ✅
B) Magnesium
C) Copper
D) Zinc

Explanation: Sulphur is present in vitamins like thiamine (B1) and coenzyme A.

Q52. Which micronutrient is part of the enzyme superoxide dismutase (SOD)?

A) Manganese ✅
B) Sodium
C) Calcium
D) Boron

Explanation: Mn-SOD detoxifies reactive oxygen species in chloroplasts/mitochondria.

Q53. Zinc plays a major role in

A) Auxin synthesis ✅
B) Photolysis of water
C) ATP production
D) Cuticle formation

Explanation: Zn is required for tryptophan → IAA synthesis, regulating growth.

Q54. Which element is a part of ferredoxin?

A) Iron ✅
B) Zinc
C) Calcium
D) Molybdenum

Explanation: Fe is a component of ferredoxin, essential in electron transfer.

Q55. Which micronutrient is essential for pollen germination?

A) Boron ✅
B) Zinc
C) Copper
D) Iron

Explanation: Boron helps in pollen tube elongation and seed set.

Q56. Which element deficiency reduces protein synthesis?

A) Nitrogen ✅
B) Potassium
C) Calcium
D) Manganese

Explanation: Nitrogen is the main constituent of amino acids and proteins.

Q57. “Black necrotic spots” on leaves are due to deficiency of

A) Potassium
B) Manganese ✅
C) Nitrogen
D) Iron

Explanation: Mn deficiency → black necrotic spots + chlorosis.

Q58. “Black heart” of celery is caused by deficiency of

A) Zinc
B) Boron ✅
C) Copper
D) Molybdenum

Explanation: Boron deficiency causes black heart in celery.

Q59. “Hooked tips” of barley leaves occur due to deficiency of

A) Copper ✅
B) Zinc
C) Calcium
D) Magnesium

Explanation: Cu deficiency → curling and hooked tips in barley leaves.

Q60. Nodule formation in legumes is initiated by

A) Bacteria only
B) Plant–bacteria interaction ✅
C) Mycorrhizae
D) Nitrosomonas

Explanation: Legume roots + Rhizobium interaction → nodule formation for N₂ fixation.

Q61. The enzyme RuBisCO requires which ion as activator?

A) Na⁺
B) Mg²⁺ ✅
C) Fe²⁺
D) Ca²⁺

Explanation: RuBisCO, key enzyme of photosynthesis, needs Mg²⁺ for activation.

Q62. Which nutrient controls permeability of cell membranes?

A) Potassium ✅
B) Sulphur
C) Iron
D) Zinc

Explanation: K⁺ maintains osmotic balance and membrane permeability.

Q63. The only nutrient absorbed as a gas by plants is

A) Oxygen
B) Nitrogen
C) Carbon dioxide ✅
D) Sulphur dioxide

Explanation: Plants absorb CO₂ gas for photosynthesis (all others absorbed in ionic form).

Q64. Which element is part of Vitamin B12 (cobalamin)?

A) Iron
B) Cobalt ✅
C) Nickel
D) Magnesium

Explanation: Cobalt forms the central atom of cobalamin (Vit B12).

Q65. Which element activates nitrate reductase?

A) Zinc
B) Molybdenum ✅
C) Copper
D) Iron

Explanation: Mo acts as cofactor for nitrate reductase.

Q66. Which element is required for nitrogenase activity in cyanobacteria?

A) Molybdenum ✅
B) Iron
C) Copper
D) Zinc

Explanation: Mo–Fe protein forms the active site of nitrogenase.

Q67. Which nutrient is called a “second messenger” in plant signalling?

A) Calcium ✅
B) Magnesium
C) Potassium
D) Sodium

Explanation: Ca²⁺ acts as a secondary messenger in signal transduction pathways.

Q68. Which ion regulates stomatal movement?

A) K⁺ ✅
B) Na⁺
C) Ca²⁺
D) Mg²⁺

Explanation: K⁺ influx/efflux regulates guard cell turgidity.

Q69. The enzyme urease requires

A) Iron
B) Nickel ✅
C) Zinc
D) Copper

Explanation: Urease enzyme requires Ni²⁺ for activity.

Q70. Which micronutrient is essential for hydrogenase enzyme?

A) Ni ✅
B) Cu
C) Mn
D) Zn

Explanation: Ni is required in hydrogenase, involved in nitrogen metabolism.

Q71. The process of converting nitrate to ammonia is called

A) Ammonification
B) Assimilatory nitrate reduction ✅
C) Nitrogen fixation
D) Denitrification

Explanation: Assimilation: NO₃⁻ → NO₂⁻ → NH₄⁺ inside plant cells.

Q72. Which bacteria convert ammonium compounds into nitrite?

A) Nitrobacter
B) Nitrosomonas ✅
C) Rhizobium
D) Azotobacter

Explanation: Nitrosomonas oxidizes NH₄⁺ → NO₂⁻ (nitrification step 1).

Q73. Which bacteria convert nitrite into nitrate?

A) Nitrosomonas
B) Nitrobacter ✅
C) Pseudomonas
D) Clostridium

Explanation: Nitrobacter oxidizes NO₂⁻ → NO₃⁻ (nitrification step 2).

Q74. Which bacteria convert nitrates back to N₂ (denitrification)?

A) Nitrosomonas
B) Nitrobacter
C) Pseudomonas ✅
D) Azotobacter

Explanation: Pseudomonas/Thiobacillus reduce nitrates → N₂ gas (denitrification).

Q75. Which free-living aerobic bacteria fix nitrogen?

A) Rhizobium
B) Azotobacter ✅
C) Clostridium
D) Frankia

Explanation: Azotobacter is a free-living aerobic nitrogen fixer.

🌱 Plant Physiology – Mineral Nutrition

Part 4 (Q76–Q100)

Q76. Which anaerobic bacteria fix nitrogen?

A) Rhizobium
B) Azotobacter
C) Clostridium ✅
D) Nitrosomonas

Explanation: Clostridium is a free-living anaerobic nitrogen fixer.

Q77. Which symbiotic actinomycete fixes nitrogen in non-leguminous plants like Alnus?

A) Azotobacter
B) Frankia ✅
C) Rhizobium
D) Nostoc

Explanation: Frankia forms nodules with non-legumes (Alnus, Casuarina).

Q78. Which cyanobacterium is a free-living nitrogen fixer?

A) Nostoc ✅
B) Nitrobacter
C) Pseudomonas
D) Clostridium

Explanation: Nostoc and Anabaena are cyanobacteria fixing N₂.

Q79. Which cyanobacterium lives symbiotically in water fern Azolla?

A) Nostoc
B) Anabaena ✅
C) Oscillatoria
D) Rivularia

Explanation: Anabaena–Azolla symbiosis is used as biofertilizer in rice fields.

Q80. Which bacteria form symbiotic association in legume root nodules?

A) Nitrobacter
B) Rhizobium ✅
C) Clostridium
D) Frankia

Explanation: Rhizobium–legume symbiosis fixes atmospheric nitrogen.

Q81. The enzyme complex nitrogenase requires

A) Fe only
B) Mo–Fe ✅
C) Zn–Mg
D) Ni–Fe

Explanation: Nitrogenase = Mo–Fe protein + Fe protein, catalyzing N₂ fixation.

Q82. How many ATP molecules are required to fix one N₂ molecule?

A) 4
B) 8
C) 16 ✅
D) 32

Explanation: Biological nitrogen fixation consumes 16 ATP per N₂.

Q83. Which oxygen-scavenging pigment protects nitrogenase?

A) Chlorophyll
B) Leghemoglobin ✅
C) Phytochrome
D) Myoglobin

Explanation: Leghemoglobin maintains low O₂ for nitrogenase.

Q84. Ammonia produced in nitrogen fixation is first assimilated into

A) Glutamate ✅
B) Alanine
C) Glycine
D) Proline

Explanation: GS–GOGAT pathway incorporates NH₃ into glutamine → glutamate.

Q85. Which pathway converts ammonium into amino acids?

A) Calvin cycle
B) GS–GOGAT cycle ✅
C) Glycolysis
D) Krebs cycle

Explanation: GS–GOGAT cycle incorporates NH₄⁺ into amino acids.

Q86. Which amino acid acts as the main donor of amino groups in transamination?

A) Aspartate
B) Glutamate ✅
C) Serine
D) Proline

Explanation: Glutamate donates –NH₂ groups in most transaminase reactions.

Q87. The process of converting organic nitrogen into ammonia is

A) Nitrification
B) Ammonification ✅
C) Denitrification
D) Assimilation

Explanation: Decomposition of organic matter → NH₃ = ammonification.

Q88. The conversion of nitrates into nitrogen gas is

A) Nitrification
B) Denitrification ✅
C) Ammonification
D) Assimilation

Explanation: Pseudomonas converts NO₃⁻ → N₂ in denitrification.

Q89. The conversion of ammonia into nitrite is done by

A) Nitrobacter
B) Nitrosomonas ✅
C) Rhizobium
D) Azotobacter

Explanation: Nitrosomonas oxidizes NH₄⁺ → NO₂⁻ (nitrification step 1).

Q90. The conversion of nitrite into nitrate is done by

A) Nitrosomonas
B) Nitrobacter ✅
C) Pseudomonas
D) Nostoc

Explanation: Nitrobacter oxidizes NO₂⁻ → NO₃⁻ (nitrification step 2).

Q91. Excessive nitrate in soil leads to

A) Chlorosis
B) Lodging and poor growth ✅
C) Stunted root growth
D) Leaf necrosis

Explanation: Excess nitrate causes luxury consumption → weak stems → lodging.

Q92. The first step of nitrogen assimilation in plants is

A) Reduction of NO₃⁻ to NO₂⁻ ✅
B) Reduction of NO₂⁻ to NH₃
C) Formation of amino acids
D) Incorporation into proteins

Explanation: Nitrate reductase (cytosol) reduces NO₃⁻ → NO₂⁻.

Q93. Nitrite reductase is located in

A) Cytosol
B) Plastids ✅
C) Nucleus
D) Vacuole

Explanation: Plastids (chloroplasts) contain nitrite reductase.

Q94. Which enzyme catalyzes transfer of –NH₂ groups between amino acids and keto acids?

A) Reductase
B) Transaminase ✅
C) Dehydrogenase
D) Ligase

Explanation: Transaminases transfer amino groups → keto acids → new amino acids.

Q95. Which amino acid is formed first during nitrogen assimilation?

A) Glycine
B) Glutamine ✅
C) Serine
D) Histidine

Explanation: Glutamine is the first product of ammonia assimilation (via GS enzyme).

Q96. The “Law of Minimum” (plant growth limited by least-available nutrient) was given by

A) Arnon
B) Liebig ✅
C) Blackman
D) Sachs

Explanation: Liebig’s Law → plant growth is limited by the scarcest resource.

Q97. Hydroponics was first demonstrated by

A) Liebig
B) Sachs ✅
C) Arnon
D) Hoagland

Explanation: Julius von Sachs (1860) pioneered hydroponic culture.

Q98. Hoagland solution is used in

A) Tissue culture
B) Hydroponics ✅
C) Grafting
D) Photosynthesis experiments

Explanation: Hoagland–Arnon solution supplies all essential minerals for hydroponic growth.

Q99. Which element is essential for C4 and CAM plants but not for all plants?

A) Sodium ✅
B) Calcium
C) Boron
D) Molybdenum

Explanation: Na⁺ is beneficial/essential for C₄ & CAM metabolism.

Q100. The total number of essential mineral elements required by plants is

A) 12
B) 14
C) 17 ✅
D) 20

Explanation: Plants require 17 essential elements: 9 macronutrients + 8 micronutrients.

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