Photosynthesis Top 100 MCQs With Answer and Explanation

1. Photosynthesis mainly occurs in _____________.
A) Roots
B) Stems
C) Leaves
D) Flowers

2. Photosynthesis takes place in which cell organelle?
A) Mitochondria
B) Chloroplast
C) Golgi body
D) Ribosome

3. Which pigment is essential for photosynthesis?
A) Carotene
B) Xanthophyll
C) Chlorophyll
D) Anthocyanin

4. The general equation for photosynthesis is _____________.
A) CO₂ + H₂O + Light → Glucose + O₂
B) O₂ + H₂O → Glucose + CO₂
C) Glucose + O₂ → Energy + CO₂
D) CO₂ + Glucose → O₂ + H₂O

5. Photosynthesis is an example of _____________.
A) Catabolism
B) Anabolism
C) Respiration
D) Fermentation

6. Who discovered that plants release oxygen during photosynthesis?
A) Robert Hooke
B) Joseph Priestley
C) Ingenhousz
D) Blackman

7. Who demonstrated that sunlight is essential for photosynthesis?
A) Priestley
B) Ingenhousz
C) Von Sachs
D) Blackman

8. The law of limiting factors in photosynthesis was given by _____________.
A) Calvin
B) Blackman
C) Hill
D) Ruben

9. Chlorophyll absorbs mainly _____________.
A) Red and blue light
B) Green light
C) Yellow light
D) White light

10. Which pigment gives green color to leaves?
A) Xanthophyll
B) Chlorophyll
C) Carotene
D) Anthocyanin

11. Chlorophyll is located in _____________.
A) Matrix of mitochondria
B) Thylakoid membrane of chloroplast
C) Cytoplasm
D) Cell wall

12. Which pigment is called the “primary photosynthetic pigment”?
A) Chlorophyll a
B) Chlorophyll b
C) Xanthophyll
D) Carotene

13. Which pigments are accessory pigments in photosynthesis?
A) Chlorophyll a
B) Chlorophyll b, carotenoids, xanthophylls
C) Anthocyanins
D) Hemoglobin

14. Hill reaction demonstrates _____________.
A) Release of O₂ from water
B) Fixation of CO₂
C) ATP synthesis
D) Glucose formation

15. The splitting of water during photosynthesis is called _____________.
A) Hydrolysis
B) Photolysis
C) Fermentation
D) Respiration

16. Who discovered photophosphorylation?
A) Hill
B) Arnon
C) Calvin
D) Blackman

17. The oxygen released in photosynthesis comes from _____________.
A) Carbon dioxide
B) Water
C) Glucose
D) Chlorophyll

18. Photosynthetically active radiation (PAR) has wavelength range _____________.
A) 100–400 nm
B) 400–700 nm
C) 700–1000 nm
D) 1000–1500 nm

19. Chloroplasts are generally abundant in _____________.
A) Root cortex
B) Leaf mesophyll cells
C) Stem epidermis
D) Xylem

20. The site of light reaction is _____________.
A) Stroma
B) Thylakoid membrane
C) Cytoplasm
D) Outer membrane of chloroplast

21. The site of dark reaction is _____________.
A) Thylakoid
B) Stroma of chloroplast
C) Mitochondria
D) Cytoplasm

22. Which is the first stable product of Calvin cycle?
A) Glucose
B) PGA (3-phosphoglyceric acid)
C) RuBP
D) NADPH

23. The first CO₂ acceptor in Calvin cycle is _____________.
A) PEP
B) RuBP
C) PGA
D) Malate

24. Which enzyme fixes CO₂ in Calvin cycle?
A) PEP carboxylase
B) RuBisCO
C) ATP synthase
D) NADP reductase

25. The strongest biological oxidizing agent in photosynthesis is _____________.
A) NADP⁺
B) Water
C) Mn²⁺
D) P680⁺

26. Light reaction of photosynthesis occurs in _____________.
A) Stroma
B) Thylakoid membrane
C) Cytoplasm
D) Matrix of mitochondria

27. The light reaction produces _____________.
A) Glucose and CO₂
B) ATP, NADPH, O₂
C) RuBP and glucose
D) Pyruvate and NADH

28. The two photosystems involved in light reactions are _____________.
A) PSI and PSII
B) PSII and PEP
C) RuBP and PGA
D) ATP and NADPH

29. The reaction center of Photosystem II has _____________.
A) P700
B) P680
C) P600
D) P500

30. The reaction center of Photosystem I has _____________.
A) P680
B) P700
C) P600
D) P720

31. Photolysis of water takes place in _____________.
A) Photosystem I
B) Photosystem II
C) Stroma
D) Cytoplasm

32. The oxygen released in photosynthesis comes from _____________.
A) Carbon dioxide
B) Water
C) Chlorophyll
D) Glucose

33. The process of ATP synthesis during photosynthesis is called _____________.
A) Oxidative phosphorylation
B) Photophosphorylation
C) Substrate-level phosphorylation
D) Chemiosmosis only

34. Non-cyclic photophosphorylation involves _____________.
A) Only PSI
B) Only PSII
C) Both PSI and PSII
D) No photosystem

35. Cyclic photophosphorylation involves _____________.
A) Only PSI
B) Only PSII
C) Both PSI and PSII
D) RuBisCO

36. Which of the following is not produced in cyclic photophosphorylation?
A) ATP
B) NADPH
C) Proton gradient
D) Electron flow

37. The electron acceptor in Photosystem II is _____________.
A) Plastoquinone
B) NADP⁺
C) Ferredoxin
D) Plastocyanin

38. The electron acceptor in Photosystem I is _____________.
A) Plastoquinone
B) Ferredoxin
C) NADPH
D) ATP

39. NADPH is finally formed by the action of _____________.
A) ATP synthase
B) NADP reductase
C) Ferredoxin
D) Plastoquinone

40. Proton gradient in photosynthesis is generated in _____________.
A) Cytoplasm
B) Thylakoid lumen
C) Stroma
D) Nucleus

41. The enzyme that synthesizes ATP in photosynthesis is _____________.
A) ATP synthase
B) RuBisCO
C) NADP reductase
D) Kinase

42. The process of ATP synthesis by proton gradient across thylakoid membrane is called _____________.
A) Oxidation
B) Photolysis
C) Chemiosmosis
D) Fermentation

43. The immediate source of energy for ATP synthesis in chloroplast is _____________.
A) Sunlight directly
B) Proton gradient
C) Water splitting
D) CO₂ fixation

44. In non-cyclic photophosphorylation, the flow of electrons is _____________.
A) PSI → PSII
B) PSII → PSI → NADP⁺
C) PSI → Ferredoxin → PSII
D) PSII → Ferredoxin only

45. The main function of cyclic photophosphorylation is to _____________.
A) Produce NADPH
B) Produce ATP
C) Produce O₂
D) Fix CO₂

46. In non-cyclic photophosphorylation, electrons lost by PSII are replaced by _____________.
A) Electrons from PSI
B) Water (photolysis)
C) NADPH
D) RuBP

47. In cyclic photophosphorylation, the final electron acceptor is _____________.
A) NADP⁺
B) Ferredoxin
C) P700 (PSI reaction center)
D) O₂

48. ATP and NADPH formed in light reaction are used in _____________.
A) Photorespiration
B) Calvin cycle (dark reaction)
C) Glycolysis
D) Krebs cycle

49. The “Z-scheme” of photosynthesis refers to _____________.
A) Calvin cycle
B) Electron transport chain in light reaction
C) Photorespiration pathway
D) Cyclic phosphorylation

50. In photophosphorylation, the final hydrogen acceptor is _____________.
A) Water
B) Oxygen
C) NADP⁺
D) ATP

51. Dark reaction of photosynthesis takes place in _____________.
A) Thylakoid lumen
B) Cytoplasm
C) Stroma of chloroplast
D) Outer membrane

52. The dark reaction is also known as _____________.
A) Light reaction
B) Carbon fixation reaction
C) Photolysis
D) Electron transport

53. The enzyme responsible for CO₂ fixation in Calvin cycle is _____________.
A) PEP carboxylase
B) RuBisCO
C) ATP synthase
D) NADP reductase

54. The first CO₂ acceptor in Calvin cycle is _____________.
A) RuBP
B) PGA
C) PEP
D) Malate

55. The first stable product of Calvin cycle is _____________.
A) RuBP
B) 3-PGA (phosphoglyceric acid)
C) Glucose
D) Malate

56. How many molecules of CO₂ are required to synthesize one molecule of glucose in Calvin cycle?
A) 2
B) 4
C) 6
D) 12

57. The Calvin cycle is also called _____________.
A) C₄ pathway
B) C₃ pathway
C) CAM pathway
D) Z-scheme

58. Who discovered the Calvin cycle?
A) Blackman
B) Calvin, Benson, and Bassham
C) Arnon
D) Hill

59. The number of ATP and NADPH required for one glucose in Calvin cycle is _____________.
A) 6 ATP + 6 NADPH
B) 12 ATP + 12 NADPH
C) 18 ATP + 12 NADPH
D) 30 ATP + 20 NADPH

60. The main limitation of RuBisCO enzyme is _____________.
A) Works only in dark
B) Acts as both carboxylase and oxygenase
C) Requires high temperature
D) Requires light directly

61. In photorespiration, the wasteful product is _____________.
A) Oxygen
B) Ammonia
C) CO₂
D) Glucose

62. C₄ plants minimize photorespiration by _____________.
A) Having Kranz anatomy and PEP carboxylase
B) Using only RuBisCO
C) Performing photosynthesis at night only
D) Absorbing less CO₂

63. The first stable product in C₄ pathway is _____________.
A) 3-PGA
B) Malate (or oxaloacetate)
C) Glucose
D) RuBP

64. The primary CO₂ acceptor in C₄ plants is _____________.
A) RuBP
B) PEP (phosphoenol pyruvate)
C) PGA
D) Malate

65. Kranz anatomy is characteristic of _____________.
A) C₃ plants
B) C₄ plants
C) CAM plants
D) Algae

66. In C₄ plants, the Calvin cycle occurs in _____________.
A) Mesophyll cells
B) Bundle sheath cells
C) Guard cells
D) Epidermal cells

67. The advantage of C₄ plants over C₃ plants is _____________.
A) Lower water requirement and reduced photorespiration
B) Faster growth only in shade
C) Less ATP requirement
D) Absence of RuBisCO

68. The first stable product of CAM pathway is _____________.
A) 3-PGA
B) Malate
C) RuBP
D) Fructose

69. In CAM plants, CO₂ fixation occurs _____________.
A) Day only
B) Night only
C) Day and night, but temporally separated
D) In roots only

70. CAM plants are adapted to _____________.
A) Cold regions
B) Deserts and arid conditions
C) Rainforests
D) Aquatic environment

71. Example of C₄ plants is _____________.
A) Wheat and rice
B) Maize and sugarcane
C) Mango and banana
D) Beans and peas

72. Example of CAM plants is _____________.
A) Rice and wheat
B) Maize and sorghum
C) Pineapple and cactus
D) Mustard and pea

73. In C₄ cycle, decarboxylation of malate occurs in _____________.
A) Mesophyll cells
B) Bundle sheath cells
C) Guard cells
D) Epidermal cells

74. Photorespiration is more common in _____________.
A) C₃ plants
B) C₄ plants
C) CAM plants
D) Algae only

75. CAM pathway helps plants by _____________.
A) Fixing CO₂ at night and reducing water loss
B) Increasing photorespiration
C) Avoiding ATP use
D) Producing oxygen at night

76. Which element is essential for the photolysis of water in photosynthesis?
A) Iron
B) Magnesium
C) Manganese
D) Potassium

77. The Z-scheme in photosynthesis represents _____________.
A) Calvin cycle
B) Cyclic photophosphorylation
C) Electron transport chain in light reaction
D) CAM pathway

78. Which part of the chloroplast contains the enzymes of Calvin cycle?
A) Grana
B) Stroma
C) Thylakoid lumen
D) Cristae

79. The primary function of light reaction is to _____________.
A) Fix carbon dioxide
B) Produce ATP and NADPH
C) Break down glucose
D) Release CO₂

80. Which of the following organisms first released oxygen into Earth’s atmosphere?
A) Algae
B) Cyanobacteria
C) Ferns
D) Fungi

81. What is the full form of RuBisCO?
A) Ribulose-1,5-bisphosphate carboxylase oxygenase
B) Ribose bisphosphate carboxylase oxidase
C) Ribulose-5-phosphate carbon oxidase
D) Ribose-5-carboxylase oxygenase

82. The net gain of glucose from the Calvin cycle requires _____________.
A) 6 CO₂, 12 ATP, 12 NADPH
B) 6 CO₂, 18 ATP, 12 NADPH
C) 12 CO₂, 18 ATP, 6 NADPH
D) 12 CO₂, 12 ATP, 12 NADPH

83. Which scientist used radioactive carbon (¹⁴C) to trace carbon fixation in photosynthesis?
A) Blackman
B) Hill
C) Calvin
D) Arnon

84. In the light reaction, protons accumulate in _____________.
A) Stroma
B) Thylakoid lumen
C) Cytoplasm
D) Nucleus

85. C₄ plants are better adapted to _____________.
A) Cold and shaded conditions
B) High light intensity, high temperature, low CO₂
C) Low light, low temperature, high CO₂
D) Desert night photosynthesis

86. CAM plants open their stomata during _____________.
A) Day only
B) Night only
C) Day and night
D) Never

87. The pigment system of photosynthesis was first demonstrated by _____________.
A) Hill
B) Emerson
C) Calvin
D) Blackman

88. The absorption spectrum of chlorophyll matches closely with _____________.
A) Respiration spectrum
B) Action spectrum of photosynthesis
C) Reflection spectrum
D) Calvin cycle

89. The red drop (Emerson effect) refers to _____________.
A) Drop in photosynthesis beyond 680 nm light
B) Increase in photosynthesis beyond 700 nm
C) Drop in respiration rate
D) Drop in chlorophyll content

90. Which gas is essential for photosynthesis?
A) Oxygen
B) Nitrogen
C) Carbon dioxide
D) Hydrogen

91. The ATP–NADPH ratio from cyclic photophosphorylation is _____________.
A) 1:1
B) 2:1
C) 3:2
D) Only ATP, no NADPH

92. The “quantasome” is _____________.
A) Functional unit of photosynthesis in thylakoid membrane
B) Functional unit of mitochondria
C) Part of Calvin cycle
D) ATP–NADPH pump

93. How many photons of light are required (minimum) to evolve one molecule of O₂ in photosynthesis?
A) 2
B) 4
C) 6
D) 8

94. In C₃ plants, the first stable product of CO₂ fixation is _____________.
A) 3-PGA
B) Oxaloacetate
C) Malate
D) Glucose

95. In C₄ plants, the Calvin cycle takes place in _____________.
A) Mesophyll cells
B) Bundle sheath cells
C) Guard cells
D) Root cells

96. In CAM plants, CO₂ fixation at night occurs by _____________.
A) RuBisCO
B) PEP carboxylase
C) ATP synthase
D) Ferredoxin

97. The first stable product of CAM pathway is _____________.
A) 3-PGA
B) Malate
C) RuBP
D) Sucrose

98. Which of the following is a C₄ plant?
A) Wheat
B) Maize
C) Rice
D) Potato

99. Which of the following is a CAM plant?
A) Sugarcane
B) Wheat
C) Pineapple
D) Barley

100. The overall efficiency of energy conversion in photosynthesis is approximately _____________.
A) 1–2%
B) 5–8%
C) 10–12%
D) 20–25%