Chapter 13: Photosynthesis in Higher Plants – MCQs
☀️ Photosynthesis in Higher Plants – MCQs
Part 1 (Q1–Q25)
Q1. Photosynthesis is essentially a process of
A) Energy release
B) Energy conversion ✅
C) Energy storage only
D) Energy destruction
Explanation: Light energy is converted into chemical energy (ATP, NADPH; stored in sugars).
Q2. The site of light reactions is the
A) Stroma
B) Thylakoid membranes (grana) ✅
C) Cytosol
D) Matrix
Explanation: Photosystems, ETC, ATP synthase are embedded in thylakoid membranes.
Q3. The site of dark reactions (Calvin cycle) is
A) Grana
B) Stroma ✅
C) Thylakoid lumen
D) Outer membrane
Explanation: Calvin cycle enzymes (Rubisco, etc.) are located in the stroma.
Q4. The primary CO₂ acceptor in C₃ plants is
A) PEP
B) RuBP (ribulose-1,5-bisphosphate) ✅
C) PGA
D) OAA
Explanation: Rubisco carboxylates RuBP to form 2 PGA in C₃ cycle.
Q5. The primary CO₂ acceptor in C₄ plants is
A) RuBP
B) PEP (phosphoenolpyruvate) ✅
C) OAA
D) Malate
Explanation: PEP carboxylase fixes CO₂ (as HCO₃⁻) to PEP → OAA.
Q6. The main product of the Calvin cycle that exits the cycle is
A) RuBP
B) PGA
C) Triose phosphate (G3P) ✅
D) Glucose
Explanation: G3P is exported to cytosol for sucrose or retained for starch.
Q7. The enzyme that fixes CO₂ in C₃ plants is
A) PEP carboxylase
B) Rubisco ✅
C) Malate dehydrogenase
D) Carbonic anhydrase
Explanation: Rubisco catalyzes carboxylation of RuBP in the Calvin cycle.
Q8. The pigment that initiates the light reaction is
A) Xanthophyll
B) β-carotene
C) Chlorophyll a ✅
D) Chlorophyll b
Explanation: Chlorophyll a is the reaction center pigment in both photosystems.
Q9. PS II reaction center absorbs maximally at
A) 700 nm
B) 680 nm (P680) ✅
C) 650 nm
D) 720 nm
Explanation: PS II reaction center is P680; PS I is P700.
Q10. Splitting of water (photolysis) occurs in
A) PS I
B) PS II ✅
C) Stroma
D) Cytosol
Explanation: OEC (Mn complex) of PS II splits water → O₂, e⁻, H⁺.
Q11. The immediate electron donor to P700⁺ is
A) Plastocyanin ✅
B) Ferredoxin
C) Cytochrome b₆f
D) Plastoquinone
Explanation: In the Z-scheme, plastocyanin reduces P700⁺ of PS I.
Q12. Non-cyclic photophosphorylation produces
A) ATP only
B) NADPH only
C) ATP + NADPH + O₂ ✅
D) O₂ only
Explanation: Linear electron flow (PS II → PS I) yields ATP, NADPH, and O₂.
Q13. Cyclic photophosphorylation involves
A) PS I only ✅
B) PS II only
C) Both PS I & II
D) No photosystem
Explanation: Electrons cycle around PS I → ATP only; no NADPH/O₂.
Q14. The “Z-scheme” represents
A) Calvin cycle steps
B) Electron transport in light reactions ✅
C) Photorespiration
D) CAM pathway
Explanation: Z-scheme shows flow of electrons from water (PS II) → NADP⁺ via PS I.
Q15. The first stable product of C₃ cycle is
A) OAA
B) PGA (3-phosphoglycerate) ✅
C) Malate
D) G3P
Explanation: Carboxylation of RuBP gives two PGA (C₃) molecules.
Q16. The first stable product of C₄ cycle is
A) PGA
B) OAA (C₄) ✅
C) G3P
D) RuBP
Explanation: PEP carboxylase forms OAA (C₄) which is converted to malate/aspartate.
Q17. Kranz anatomy is characteristic of
A) C₃ plants
B) C₄ plants ✅
C) CAM plants
D) Aquatic plants
Explanation: C₄ leaves show Kranz (wreath) anatomy with bundle sheath chloroplasts.
Q18. Photorespiration is high when
A) CO₂ is high
B) O₂ is high and temperature is high ✅
C) Light is low
D) Water is abundant
Explanation: Rubisco oxygenase activity rises with high O₂/low CO₂, high temperature.
Q19. Photorespiration involves these organelles
A) Chloroplast–Mitochondria–Peroxisome ✅
B) Chloroplast–Vacuole–ER
C) Mitochondria–Golgi–ER
D) Peroxisome–Lysosome–Golgi
Explanation: The glycolate pathway spans chloroplasts, peroxisomes, mitochondria.
Q20. The Hill reaction demonstrates
A) CO₂ fixation
B) O₂ evolution from water ✅
C) Starch formation
D) Photorespiration
Explanation: Hill showed that isolated chloroplasts evolve O₂ in light without CO₂.
Q21. The “red drop” (decrease in quantum yield >680 nm) and its enhancement effect were shown by
A) Blackman
B) Calvin
C) Emerson ✅
D) Hill
Explanation: Emerson discovered red drop and enhancement effect, implying two photosystems.
Q22. The law of limiting factors in photosynthesis was proposed by
A) Sachs
B) Blackman ✅
C) Liebig
D) van Niel
Explanation: Blackman’s law: the slowest (limiting) factor controls the rate.
Q23. The Calvin cycle is also known as
A) Hatch–Slack pathway
B) Reductive pentose phosphate pathway ✅
C) C₂ cycle
D) Glyoxylate cycle
Explanation: Calvin–Benson cycle reduces CO₂ via the reductive pentose phosphate route.
Q24. The key carboxylating enzyme in C₄ mesophyll cells is
A) Rubisco
B) PEP carboxylase ✅
C) Carbonic anhydrase
D) Malic enzyme
Explanation: PEPC fixes HCO₃⁻ to PEP producing OAA (C₄ acid).
Q25. C₄ plants show high photosynthetic efficiency primarily due to
A) More chlorophyll a
B) CO₂ concentrating mechanism ✅
C) Larger leaves
D) More stomata
Explanation: Bundle sheath decarboxylation elevates CO₂ near Rubisco, suppressing photorespiration.
☀️ Photosynthesis in Higher Plants
Part 2 (Q26–Q50)
Q26. The Hatch–Slack pathway operates in
A) C₃ plants
B) C₄ plants ✅
C) CAM plants
D) Algae
Explanation: The C₄ pathway was described by Hatch & Slack in sugarcane, maize, etc.
Q27. CAM plants open stomata
A) During day
B) During night ✅
C) Both day and night
D) Never
Explanation: CAM plants (cacti, pineapple) open stomata at night to minimize water loss.
Q28. The first stable product in CAM pathway is
A) PGA
B) OAA ✅
C) G3P
D) RuBP
Explanation: Like C₄ plants, CAM plants first form OAA at night.
Q29. The C₂ cycle is another name for
A) Calvin cycle
B) Photorespiration ✅
C) CAM pathway
D) Glyoxylate cycle
Explanation: Photorespiration is also called the C₂ cycle, producing 2-carbon glycolate.
Q30. The oxygenase activity of Rubisco leads to
A) CO₂ fixation
B) Photorespiration ✅
C) CAM pathway
D) Dark respiration
Explanation: Rubisco has dual function—carboxylase (CO₂ fixation) and oxygenase (photorespiration).
Q31. Which plant shows highest photosynthetic efficiency?
A) Rice
B) Wheat
C) Sugarcane ✅
D) Cotton
Explanation: Sugarcane (C₄ plant) has high efficiency due to no photorespiration.
Q32. Which light is least effective in photosynthesis?
A) Red
B) Blue
C) Green ✅
D) Violet
Explanation: Green light is reflected, not absorbed → least effective.
Q33. Chlorophyll a absorbs maximally at
A) 680 nm and 700 nm ✅
B) 400 nm and 500 nm
C) 650 nm and 720 nm
D) 600 nm only
Explanation: Chlorophyll a peaks at blue (~430 nm) and red (~680–700 nm).
Q34. Accessory pigments (chlorophyll b, carotenoids, xanthophylls) mainly function to
A) Fix CO₂
B) Transfer energy to chlorophyll a ✅
C) Absorb green light
D) Produce ATP
Explanation: They broaden absorption spectrum and transfer energy to Chl a.
Q35. The end products of light reaction are
A) ATP + NADPH + O₂ ✅
B) ATP + CO₂
C) NADH + H₂O
D) Glucose + O₂
Explanation: Light reaction yields ATP, NADPH, and O₂.
Q36. Which one is a C₄ plant?
A) Wheat
B) Rice
C) Maize ✅
D) Pea
Explanation: Maize is a typical C₄ plant with Kranz anatomy.
Q37. Blackman’s law states
A) Light is not necessary
B) Photosynthesis is controlled by the slowest factor ✅
C) Only CO₂ affects rate
D) Only temperature affects rate
Explanation: Blackman (1905): rate is determined by the limiting factor.
Q38. The assimilatory power for Calvin cycle is
A) ATP + NADPH ✅
B) ATP + NADH
C) FADH₂ + NADPH
D) Glucose + ATP
Explanation: Dark reactions require ATP + NADPH from light reaction.
Q39. The Calvin cycle was discovered using
A) Oxygen isotopes
B) Carbon-14 tracer ✅
C) Hydrogen isotopes
D) Nitrogen isotopes
Explanation: Calvin & Benson used ¹⁴C labeling to trace CO₂ fixation.
Q40. In photosynthesis, the hydrogen donor is
A) CO₂
B) H₂O ✅
C) NADPH
D) Glucose
Explanation: Water donates electrons/H⁺ in light reactions, releasing O₂.
Q41. Photorespiration is considered a wasteful process because
A) It fixes CO₂
B) It releases CO₂ without ATP gain ✅
C) It uses NADPH efficiently
D) It increases sugar production
Explanation: Photorespiration releases CO₂ and consumes ATP/NADPH, reducing efficiency.
Q42. The main sugar transported in plants after photosynthesis is
A) Glucose
B) Sucrose ✅
C) Maltose
D) Fructose
Explanation: Sucrose is the chief transport form in phloem.
Q43. C₄ plants are more efficient because
A) They have more Rubisco
B) They concentrate CO₂ at Rubisco site ✅
C) They need less light
D) They avoid Calvin cycle
Explanation: Bundle sheath decarboxylation increases CO₂ near Rubisco → suppresses oxygenase activity.
Q44. CAM plants are common in
A) Tropical rain forests
B) Deserts ✅
C) Temperate forests
D) Marshy areas
Explanation: CAM plants (cacti, pineapple) are desert plants with water-saving metabolism.
Q45. Which factor is NOT a raw material for photosynthesis?
A) Water
B) CO₂
C) Sunlight
D) Oxygen ✅
Explanation: O₂ is a by-product, not a raw material.
Q46. During photophosphorylation, protons accumulate in
A) Stroma
B) Thylakoid lumen ✅
C) Cytosol
D) Outer membrane
Explanation: H⁺ ions accumulate in thylakoid lumen, driving ATP synthesis.
Q47. The proton gradient in light reaction is used for
A) Oxygen release
B) NADPH synthesis
C) ATP synthesis ✅
D) CO₂ fixation
Explanation: Chemiosmosis uses proton gradient across thylakoid to make ATP.
Q48. Which factor increases photosynthetic rate up to a certain limit?
A) Light intensity ✅
B) O₂ concentration
C) Waterlogging
D) Salt stress
Explanation: Higher light intensity boosts photosynthesis until saturation.
Q49. Which factor causes photorespiration to increase?
A) High CO₂
B) High O₂ ✅
C) Low temperature
D) Low O₂
Explanation: High O₂/CO₂ ratio enhances oxygenase activity of Rubisco.
Q50. The number of ATP required for fixation of one CO₂ in Calvin cycle is
A) 2
B) 3 ✅
C) 4
D) 5
Explanation: 3 ATP + 2 NADPH are needed to fix 1 CO₂ into carbohydrate.
☀️ Photosynthesis in Higher Plants
Part 3 (Q51–Q75)
Q51. The energy currency produced in light reaction is
A) NADPH
B) ATP ✅
C) G3P
D) Sucrose
Explanation: ATP formed in light reactions drives the Calvin cycle and other processes.
Q52. Which is called the universal electron donor in photosynthesis?
A) NADPH ✅
B) ATP
C) G3P
D) RuBP
Explanation: NADPH provides reducing power for CO₂ fixation.
Q53. How many CO₂ molecules are required to form one glucose in the Calvin cycle?
A) 3
B) 6 ✅
C) 4
D) 12
Explanation: 6 CO₂ molecules are fixed → one glucose equivalent.
Q54. How many turns of Calvin cycle are needed to synthesize one G3P molecule?
A) 1
B) 2 ✅
C) 3
D) 6
Explanation: Two turns of the Calvin cycle (2 CO₂) yield one G3P exported.
Q55. How many ATP are required to fix 6 CO₂ molecules into glucose?
A) 12
B) 18 ✅
C) 24
D) 30
Explanation: For 1 CO₂ → 3 ATP; thus 6 CO₂ → 18 ATP.
Q56. How many NADPH are required for fixation of 6 CO₂ molecules?
A) 6
B) 12 ✅
C) 18
D) 24
Explanation: For 1 CO₂ → 2 NADPH; thus 6 CO₂ → 12 NADPH.
Q57. Which of the following is a photoautotroph?
A) Fungi
B) Green plants ✅
C) Animals
D) Amoeba
Explanation: Green plants synthesize food using light + CO₂ → photoautotrophs.
Q58. The action spectrum of photosynthesis was demonstrated by
A) Sachs
B) Engelmann ✅
C) Hill
D) Calvin
Explanation: Engelmann’s experiment (1882) showed maximum photosynthesis in red & blue light using oxygen-seeking bacteria.
Q59. The absorption spectrum of chlorophyll a shows peaks in
A) Red and blue regions ✅
B) Green and yellow
C) Infrared only
D) Orange and violet only
Explanation: Chl a absorbs maximally in blue (~430 nm) and red (~680 nm).
Q60. Which light wavelength is least effective in photosynthesis?
A) 400–500 nm
B) 500–600 nm (green) ✅
C) 600–700 nm
D) 700–720 nm
Explanation: Green light is reflected, thus least effective.
Q61. In C₄ plants, Calvin cycle occurs in
A) Mesophyll cells
B) Bundle sheath cells ✅
C) Guard cells
D) Root cells
Explanation: In C₄ plants, Calvin cycle is confined to bundle sheath chloroplasts.
Q62. In C₄ plants, initial CO₂ fixation occurs in
A) Bundle sheath
B) Mesophyll cells ✅
C) Guard cells
D) Phloem
Explanation: Mesophyll cells fix CO₂ by PEP carboxylase → OAA.
Q63. Kranz anatomy refers to
A) Concentric arrangement of bundle sheath cells ✅
B) Stomatal distribution
C) Root anatomy
D) Epidermal tissue
Explanation: Kranz anatomy = wreath-like arrangement of bundle sheath around vascular bundles in C₄ plants.
Q64. Which of the following is a CAM plant?
A) Wheat
B) Rice
C) Pineapple ✅
D) Sugarcane
Explanation: Pineapple uses CAM pathway to minimize water loss.
Q65. In CAM plants, CO₂ is fixed at night into
A) PGA
B) OAA ✅
C) G3P
D) RuBP
Explanation: CO₂ is fixed into OAA at night (via PEP carboxylase).
Q66. In photorespiration, the substrate for Rubisco is
A) CO₂
B) O₂ ✅
C) RuBP
D) Malate
Explanation: Under high O₂/low CO₂, Rubisco oxygenase fixes O₂, initiating photorespiration.
Q67. The toxic compound formed during photorespiration is
A) Glycolate ✅
B) Malate
C) OAA
D) Acetyl-CoA
Explanation: Rubisco oxygenase forms glycolate (2C) which is metabolized via C₂ cycle.
Q68. The oxygenase activity of Rubisco occurs in
A) Mesophyll cells
B) Chloroplast stroma ✅
C) Mitochondria
D) Peroxisomes
Explanation: Rubisco is located in the chloroplast stroma.
Q69. Which organelle is NOT involved in photorespiration?
A) Chloroplast
B) Mitochondria
C) Peroxisome
D) Golgi apparatus ✅
Explanation: Golgi is not involved; photorespiration involves chloroplasts, peroxisomes, mitochondria.
Q70. C₄ plants minimize photorespiration because
A) They lack Rubisco
B) They concentrate CO₂ in bundle sheath ✅
C) They have less stomata
D) They absorb more green light
Explanation: C₄ plants elevate CO₂ near Rubisco, preventing oxygenase action.
Q71. The enzyme PEP carboxylase has
A) High affinity for O₂
B) High affinity for CO₂ ✅
C) No affinity for CO₂
D) Dual affinity for O₂ and CO₂
Explanation: PEPC has high CO₂ affinity, no oxygenase activity.
Q72. The productivity of C₄ plants is higher than C₃ plants because
A) They need less light
B) They avoid photorespiration ✅
C) They fix less CO₂
D) They produce less NADPH
Explanation: C₄ plants eliminate photorespiration, thus more productive.
Q73. The wasteful process associated with Rubisco oxygenase activity is
A) CAM cycle
B) Photorespiration ✅
C) Glycolysis
D) Fermentation
Explanation: Rubisco oxygenase activity → photorespiration.
Q74. The function of carotenoids is
A) Absorb green light
B) Photoprotection and accessory pigments ✅
C) Fix CO₂
D) Oxygen release
Explanation: Carotenoids protect from photooxidation and extend absorption spectrum.
Q75. The Calvin cycle was discovered by
A) Blackman
B) Hill
C) Calvin and Benson ✅
D) Emerson
Explanation: Melvin Calvin and Andrew Benson elucidated the Calvin cycle using ¹⁴C tracers.
Great 🌱 Let’s wrap it up with Part 4 (Q76–Q100) of the 100 MCQs on “Plant Physiology – Photosynthesis in Higher Plants.”
Each question has options (A–D), the correct answer marked, and a short NEET + CBSE explanation.
☀️ Photosynthesis in Higher Plants
Part 4 (Q76–Q100)
Q76. Which statement about Rubisco is correct?
A) It is the most abundant protein on earth ✅
B) It fixes nitrogen
C) It is a pigment protein
D) It splits water
Explanation: Rubisco is the most abundant enzyme, catalyzing CO₂ fixation.
Q77. Which event does not occur during cyclic photophosphorylation?
A) ATP formation
B) NADPH formation ✅
C) Electron cycling through PS I
D) Proton gradient formation
Explanation: Cyclic photophosphorylation makes ATP only, no NADPH or O₂.
Q78. Which pigment absorbs maximum blue light?
A) Chlorophyll a
B) Chlorophyll b ✅
C) Carotenoids
D) Xanthophyll
Explanation: Chlorophyll b absorbs strongly in the blue region (450–500 nm).
Q79. In the Z-scheme, the electron ultimately reduces
A) O₂
B) NADP⁺ ✅
C) Water
D) ATP
Explanation: Electrons from water → PS II → PS I → reduce NADP⁺ → NADPH.
Q80. Oxygen in photosynthesis is released from
A) CO₂
B) H₂O ✅
C) NADPH
D) ATP
Explanation: Photolysis of water releases O₂ as a by-product.
Q81. The plant that shows CAM pathway is
A) Maize
B) Wheat
C) Opuntia ✅
D) Rice
Explanation: Opuntia (cactus) is a CAM plant, fixing CO₂ at night.
Q82. The wasteful cycle that decreases photosynthetic yield is
A) Calvin cycle
B) Photorespiration ✅
C) Glycolysis
D) CAM cycle
Explanation: Photorespiration consumes ATP/NADPH and releases CO₂ → wasteful.
Q83. In C₄ cycle, decarboxylation of malate occurs in
A) Mesophyll
B) Bundle sheath ✅
C) Guard cells
D) Phloem
Explanation: C₄ acids (malate/aspartate) release CO₂ in bundle sheath for Calvin cycle.
Q84. The ATP: NADPH ratio in cyclic photophosphorylation is
A) 1:1
B) More ATP, no NADPH ✅
C) More NADPH, no ATP
D) 2:1
Explanation: Cyclic flow yields ATP only, no NADPH.
Q85. The ATP: NADPH ratio in non-cyclic photophosphorylation is
A) 1:1 ✅
B) 2:1
C) 3:1
D) Variable
Explanation: Linear flow produces equal amounts of ATP and NADPH.
Q86. Which scientist discovered that O₂ comes from water, not CO₂?
A) Hill
B) van Niel ✅
C) Calvin
D) Sachs
Explanation: van Niel proposed O₂ evolves from H₂O splitting, later proven.
Q87. Which is the major site of photosynthesis in plants?
A) Stem
B) Leaf ✅
C) Root
D) Flower
Explanation: Leaves with chloroplast-rich mesophyll are main photosynthetic organs.
Q88. Which plant group lacks Kranz anatomy?
A) C₄ plants
B) C₃ plants ✅
C) CAM plants
D) Maize
Explanation: C₃ plants (e.g., rice, wheat) do not have Kranz anatomy.
Q89. The CO₂ compensation point is lowest in
A) C₃ plants
B) C₄ plants ✅
C) CAM plants
D) Algae
Explanation: C₄ plants have nearly zero photorespiration, very low CO₂ compensation point.
Q90. Which light has maximum photosynthetic efficiency?
A) Green
B) Red ✅
C) Blue
D) Yellow
Explanation: Red light (~680 nm) is most efficient for photosynthesis.
Q91. Which cycle fixes atmospheric CO₂ directly into carbohydrate?
A) C₄ cycle
B) Calvin cycle ✅
C) CAM cycle
D) Glycolate cycle
Explanation: Calvin cycle incorporates CO₂ into sugars.
Q92. The end product of photorespiration is
A) PGA
B) CO₂ ✅
C) Glucose
D) Malate
Explanation: Photorespiration ultimately releases CO₂ without ATP gain.
Q93. Which organelle provides reducing power for Calvin cycle?
A) Mitochondria
B) Chloroplast ✅
C) Peroxisome
D) Cytosol
Explanation: Chloroplast light reactions provide ATP + NADPH for Calvin cycle.
Q94. The dark reaction is called so because
A) It occurs at night only
B) It does not need direct light ✅
C) It requires darkness
D) It happens in mitochondria
Explanation: Dark reactions are light-independent, though they occur in day using ATP/NADPH.
Q95. The number of ATP needed to produce one molecule of O₂ in photosynthesis is
A) 2
B) 3
C) 4 ✅
D) 6
Explanation: 4 electrons are needed to evolve 1 O₂ → linked to 4 ATP synthesis.
Q96. Which compound is the immediate hydrogen donor in Calvin cycle?
A) NADPH ✅
B) FADH₂
C) ATP
D) Water
Explanation: NADPH reduces 3-PGA to G3P in Calvin cycle.
Q97. Which pigment protects chlorophyll from photooxidation?
A) Carotenoids ✅
B) Chlorophyll b
C) Anthocyanins
D) Phytochrome
Explanation: Carotenoids quench excess light energy, preventing oxidative damage.
Q98. Which is the direct product of Calvin cycle?
A) Glucose
B) G3P (triose phosphate) ✅
C) Starch
D) Sucrose
Explanation: Calvin cycle yields G3P, used for glucose, starch, sucrose synthesis.
Q99. The number of Calvin cycle turns required to form one glucose molecule is
A) 3
B) 6 ✅
C) 4
D) 12
Explanation: 6 turns (fixing 6 CO₂) are needed to form one glucose equivalent.
Q100. The main significance of photosynthesis is
A) CO₂ release
B) Conversion of light to chemical energy ✅
C) O₂ consumption
D) Glucose oxidation
Explanation: Photosynthesis sustains life by converting light → chemical energy (glucose, ATP) and producing O₂.
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