NEET Topic-wise & A
Topic 1: EXPERIMENTS RELATED WITH PHOTOSYNTHESIS
NEET: Previous Years Questions
01: Oxygen is not produced during photosynthesis by
(1) Green-sulphur bacteria
(2) Nostoc
(3) Cycas
(4) Chara (NEET 2018)
✅ (1) Green-sulphur bacteria
Model Questions
02: Photosynthesis is
(1) A chemical process by which green plants use light energy to synthesise organic compounds.
(2) A physico-chemical process by which green plants use light energy to synthesise organic compounds.
(3) A chemical process by which green plants use light energy to synthesise inorganic compounds.
(4) A physico-chemical process by which green plants use light energy to synthesise inorganic compounds.
✅ (2) A physico-chemical process by which green plants use light energy to synthesise organic compounds.
03: Variegated leaf experiment using starch shows that
(1) Photosynthesis occurs only in green parts of the leaves in presence of light.
(2) CO₂ is required for photosynthesis.
(3) Glucose is produced when plants grow and it is usually stored as starch.
(4) Glucose is made in the green parts of plants.
✅ (1) Photosynthesis occurs only in green parts of the leaves in presence of light.
04: CO₂ is required for photosynthesis. The chemical used to remove CO₂ from entering a control apparatus is
(1) Calcium oxide
(2) Distilled water
(3) KOH solution
(4) Na₂CO₃
✅ (3) KOH solution
05: Which of the following with respect to early experiments of photosynthesis is wrongly matched?
(1) Priestley – Showed that plants release oxygen.
(2) Jan Ingenhousz – Showed that sunlight is essential for photosynthesis.
(3) Julius von Sachs – Proved that plants produce glucose when they grow.
(4) T.W. Engelmann – Showed that the green substance is located within special bodies in plants.
(5) Cornelius van Niel – Showed that hydrogen reduces CO₂ to carbohydrates.
✅ (4) T.W. Engelmann – Showed that the green substance is located within special bodies in plants.
06: In an experiment demonstrating the evolution of oxygen in Hydrilla, sodium bicarbonate is added to the water in the experimental setup. What would happen if all other conditions are favourable?
(1) Amount of oxygen evolved decreases as the availability of CO₂ increases.
(2) Amount of oxygen evolved increases as CO₂ in water is absorbed by sodium bicarbonate.
(3) Amount of oxygen evolved decreases as CO₂ in water is absorbed by sodium bicarbonate.
(4) Amount of oxygen evolved increases as the availability of CO₂ increases.
✅ (4) Amount of oxygen evolved increases as the availability of CO₂ increases.
07: In Purple & green sulphur bacteria, oxygen is not evolved during photosynthesis because hydrogen donor is
(1) H₂O
(2) H₂S
(3) NH₃
(4) CH₄
✅ (2) H₂S
Topic 2: PHOTOSYNTHESIS: SITE AND PIGMENTS
NEET: Previous Years Questions
08: The reaction centre PS II has an absorption maxima at
(1) 700 nm
(2) 660 nm
(3) 780 nm
(4) 680 nm (NEET 2023)
✅ (4) 680 nm
09: Emerson’s enhancement effect and Red drop have been instrumental in the discovery of
(1) photophosphorylation and cyclic electron transport
(2) oxidative phosphorylation
(3) photophosphorylation and non-cyclic electron transport
(4) two photosystems operating simultaneously. (NEET-I 2016)
✅ (1) photophosphorylation and cyclic electron transport
Model Questions
10: Assertion: Chloroplasts are present in the walls of mesophyll cells of leaves.
Reason: It helps to get optimum quantity of incident light.
Reason: It helps to get optimum quantity of incident light.
(1) Both assertion and reason are true and reason is the correct explanation of assertion.
(2) Both assertion and reason are true but reason is not the correct explanation of assertion.
(3) Assertion is true but reason is false.
(4) Both assertion and reason are false.
✅ (1) Both assertion and reason are true and reason is the correct explanation of assertion.
11: In the given figure of chloroplast, what do A, B, C & D represent?
(1) A- Stromal lamella, B- Stroma, C- Grana, D- Ribosomes
(2) A- Grana, B- Stromal lamella, C- Stroma, D- Ribosomes
(3) A- Stromal lamella, B- Grana, C- Stroma, D- Ribosomes
(4) A- Stroma, B- Grana, C- Stromal lamella, D- Ribosomes
✅ (3) A- Stromal lamella, B- Grana, C- Stroma, D- Ribosomes
12: Chlorophyll molecules are located in the
(1) Thylakoid lumen
(2) Thylakoid membrane
(3) Stroma
(4) Inner chloroplast membrane
✅ (2) Thylakoid membrane
13: Match the following:
(1) A- (ii), B- (iv), C- (i), D- (iii)
(2) A- (iii), B- (iv), C- (ii), D- (i)
(3) A- (iv), B- (iii), C- (ii), D- (i)
(4) A- (iv), B- (ii), C- (i), D- (iii)
✅ (1) A- (ii), B- (iv), C- (i), D- (iii)
14: The absorption spectrum & action spectrum coincide closely showing that photosynthesis is maximum at
(1) Blue & green regions of the spectrum.
(2) Green & red regions of the spectrum.
(3) Blue & red regions of the spectrum.
(4) Blue & violet regions of the spectrum.
✅ (3) Blue & red regions of the spectrum.
15: The chief pigment associated with photosynthesis is
(1) Chlorophyll a
(2) Chlorophyll b
(3) Xanthophyll
(4) Carotenoids
✅ (1) Chlorophyll a
16: Regarding photosystems, pick out the wrong statement.
(1) Each photosystem has a chlorophyll a and accessory pigments bound by proteins.
(2) All pigments, except one molecule of chlorophyll a, form a light harvesting complex.
(3) Single chlorophyll a acts as reaction centre.
(4) In PS I, the reaction centre absorbs light at 680 nm, and so called P680.
✅ (4) In PS I, the reaction centre absorbs light at 680 nm, and so called P680.
Topic 3: LIGHT REACTION (PHOTOCHEMICAL PHASE)
NEET: Previous Years Questions
17: Which of the following combinations is required for chemiosmosis?
(1) Membrane, proton pump, proton gradient, NADP synthase
(2) Proton pump, electron gradient, ATP synthase
(3) Proton pump, electron gradient, NADP synthase
(4) Membrane, proton pump, proton gradient, ATP synthase (NEET 2023)
✅ (4) Membrane, proton pump, proton gradient, ATP synthase
18: Which of the following statements is incorrect?
(1) Both ATP and NADPH + H⁺ are synthesized during noncyclic photophosphorylation.
(2) Stroma lamellae have PS I only and lack NADP reductase.
(3) Grana lamellae have both PS I and PS II.
(4) Cyclic photophosphorylation involves both PS I and PS II. (NEET 2021)
✅ (4) Cyclic photophosphorylation involves both PS I and PS II.
19: In light reaction, plastoquinone facilitates the transfer of electrons from:
(1) PS-I to NADP⁺
(2) PS-I to ATP synthase
(3) PS-II to Cytb6f complex
(4) Cytb6f complex to PS-I (NEET 2020)
✅ (3) PS-II to Cytb6f complex
20: Which of the following is not a product of light reaction in photosynthesis?
(1) ATP
(2) NADH
(3) NADPH
(4) Oxygen (NEET 2018)
✅ (2) NADH
21: In a chloroplast the highest number of protons are found in
(1) intermembrane space
(2) antennae complex
(3) stroma
(4) lumen of thylakoids (NEET-I 2016)
✅ (4) lumen of thylakoids
Model Questions
22: Assertion: In light reaction of photosynthesis, light is required for the functioning of PS I and PS II, and production of NADPH and ATP.
Reason: Dark reaction does not occur in light.
Reason: Dark reaction does not occur in light.
(1) Both assertion and reason are true and reason is the correct explanation of assertion.
(2) Both assertion and reason are true but reason is not the correct explanation of assertion.
(3) Assertion is true but reason is false.
(4) Both assertion and reason are false.
✅ (3) Assertion is true but reason is false.
23: Light reactions do not include
(1) Water splitting
(2) Use of NADPH to synthesise food
(3) Oxygen release
(4) Formation of ATP & NADPH
✅ (2) Use of NADPH to synthesise food
24: Transfer of electrons from PS II to PS I and finally downhill to NADP⁺ is called
(1) Z scheme
(2) C₄ pathway
(3) C₃ pathway
(4) Photorespiration
✅ (1) Z scheme
25: Which of the following is correctly labelled for the given figure?
(1) A- LHC, B- Ä“ acceptor, C- PS I, D- PS II
(2) A- PS II, B- PS I, C- Ä“ acceptor, D- LHC
(3) A- PS I, B- PS II, C- Ä“ acceptor, D- LHC
(4) A- Ä“ acceptor, B- LHC, C- PS II, D- PS I
✅ (2) A- PS II, B- PS I, C- Ä“ acceptor, D- LHC
26: Pick out the wrong statement.
(1) The water splitting complex in PS II is located on the inner side of the thylakoid membrane.
(2) The protons formed by water splitting are needed to replace the protons that are moved from PS II.
(3) The protons (H⁺) are used to reduce NADP to NADPH.
(4) The PS II provides electrons needed to replace those removed from PS I.
✅ (2) The protons formed by water splitting are needed to replace the protons that are moved from PS II.
27: Which of the following is an essential factor for photophosphorylation?
(1) Sunlight
(2) Carbohydrate
(3) Oxygen
(4) Water
✅ (1) Sunlight
28: Non-cyclic photo-phosphorylation results in the production of
(1) ATP
(2) ADP & NADPH + H⁺
(3) ATP & NADPH + H⁺
(4) NADPH
✅ (3) ATP & NADPH + H⁺
29: Incorrect statement regarding Cyclic photo-phosphorylation is
(1) It occurs in stroma lamellae when only PS I is functional.
(2) Here, ATP and NADPH + H⁺ is synthesised.
(3) The stroma lamellae membranes lack PS II and NADP reductase.
(4) The electron does not pass on to NADP⁺ but is cycled back to PS I complex through electron transport chain.
✅ (2) Here, ATP and NADPH + H⁺ is synthesised.
30: In chloroplast, highest number of protons are found in
(1) Intermembrane space
(2) Antenna complex
(3) Stroma
(4) Lumen of thylakoids
✅ (4) Lumen of thylakoids
31: According to the chemiosmotic hypothesis, ATP production is the result of
(1) Proton gradient developed across the membrane of thylakoids.
(2) Electron gradient developed across the membrane of thylakoids.
(3) Proton gradient developed in stroma.
(4) Electron gradient developed in stroma.
✅ (1) Proton gradient developed across the membrane of thylakoids.
32: Splitting of water occurs on the
(1) Outer side of the thylakoid membrane
(2) Inner side of the thylakoid membrane
(3) Stroma of the chloroplast
(4) Cytoplasm
✅ (2) Inner side of the thylakoid membrane
33: Which of the following is not required for chemiosmosis?
(1) A membrane
(2) A proton pump & A proton gradient
(3) Bundle sheath cells
(4) ATP synthase
✅ (3) Bundle sheath cells
34: During the light-dependent reactions of photosynthesis, the primary electron acceptor associated with photosystem II (PSII) transfers electrons to an H carrier. This process directly results in:
(1) Release of protons into the stroma.
(2) Uptake of protons from the lumen.
(3) Removal of protons from the stroma and release of protons into the lumen.
(4) Movement of electrons directly to NADP⁺.
✅ (3) Removal of protons from the stroma and release of protons into the lumen.
35: The proton gradient across the thylakoid membrane is crucial for ATP synthesis. Which of the following statements accurately describes the establishment and utilization of this gradient?
(1) Protons accumulate in the stroma, leading to a decrease in stromal pH and driving ATP synthesis through F1.
(2) The breakdown of the proton gradient involves the movement of protons from the stroma to the lumen through ATP synthase.
(3) The proton gradient is established by the pumping of protons into the lumen, leading to a decrease in lumen pH, and its breakdown powers ATP synthesis via proton movement through F0 of ATP synthase to the stroma.
(4) The primary electron acceptor pumps protons directly into the stroma, creating the gradient used by ATP synthase.
✅ (3) The proton gradient is established by the pumping of protons into the lumen, leading to a decrease in lumen pH, and its breakdown powers ATP synthesis via proton movement through F0 of ATP synthase to the stroma.
36: Which of the following correctly describes the roles of the F₀ and F₁ parts of ATP synthase during oxidative phosphorylation or photosynthesis?
(1) F₀ – ATP synthesis; F₁ – Proton channel
(2) F₀ – Conformational change to release ATP; F₁ – Proton gradient breakdown
(3) F₀ – Facilitated diffusion of protons; F₁ – ATP synthesis
(4) F₀ – Binds ADP and inorganic phosphate; F₁ – Proton pumping.
✅ (3) F₀ – Facilitated diffusion of protons; F₁ – ATP synthesis
Topic 4: DARK REACTION (BIOSYNTHETIC PHASE) - USE OF ATP & NADPH
NEET: Previous Years Questions
37: Which of the following are required for the dark reaction of photosynthesis? (NEET 2024)
A. Light
B. Chlorophyll
C. CO₂
D. ATP
E. NADPHChoose the correct answer from the options given below:
(1) A, B and C only
(2) B, C and D only
(3) C, D and E only
(4) D and E only
✅ (3) C, D and E only
38: How many molecules of ATP and NADPH are required for every molecule of CO₂ fixed in the Calvin cycle?
(1) 2 molecules of ATP and 3 molecules of NADPH
(2) 2 molecules of ATP and 2 molecules of NADPH
(3) 3 molecules of ATP and 3 molecules of NADPH
(4) 3 molecules of ATP and 2 molecules of NADPH (NEET 2024)
✅ (4) 3 molecules of ATP and 2 molecules of NADPH
39: Given below are two statements: (NEET 2024)
Statement I: In C₃ plants, some O₂ binds to RuBisCO, hence CO₂ fixation is decreased.
Statement II: In C₄ plants, mesophyll cells show very little photorespiration while bundle sheath cells do not show photorespiration.
In the light of the above statements, choose the correct answer from the options given below:
(1) Both Statement I and Statement II are true
(2) Both Statement I and Statement II are false
(3) Statement I is true but Statement II is false
(4) Statement I is false but Statement II is true
✅ (3) Statement I is true but Statement II is false
40: How many ATP and NADPH₂ are required for the synthesis of one molecule of Glucose during Calvin cycle?
(1) 18 ATP and 12 NADPH₂
(2) 12 ATP and 16 NADPH₂
(3) 18 ATP and 16 NADPH₂
(4) 12 ATP and 12 NADPH₂ (NEET 2023)
✅ (1) 18 ATP and 12 NADPH₂
41: The first stable product of CO₂ fixation in sorghum is:
(1) Pyruvic acid
(2) Oxaloacetic acid
(3) Succinic acid
(4) Phosphoglyceric acid (NEET 2021)
✅ (2) Oxaloacetic acid
42: The oxygenation activity of RuBisCO enzyme in photorespiration leads to the formation of:
(1) 1 molecule of 6-C compound
(2) 1 molecule of 4-C compound and 1 molecule of 2-C compound
(3) 2 molecules of 3-C compound
(4) 1 molecule of 3-C compound (NEET 2020)
✅ (4) 1 molecule of 3-C compound
43: Phosphoenol pyruvate (PEP) is the primary CO₂ acceptor in (NEET 2017)
(1) C₄ plants
(2) C2 plants
(3) C₃ and C₄ plants
(4) C₃ plants
✅ (1) C₄ plants
44: The process which makes major difference between C₃ and C₄ plants is (NEET-II 2016)
(1) glycolysis
(2) Calvin cycle
(3) photorespiration
(4) respiration
✅ (3) photorespiration
45: A plant in your garden avoids photorespiratory losses, has improved water use efficiency, shows high rates of photosynthesis at high temperatures and has improved efficiency of nitrogen utilisation. In which of the following physiological groups would you assign this plant?
(1) CAM
(2) Nitrogen fixer
(3) C₃
(4) C₄ (NEET-I 2016)
✅ (4) C₄
Model Questions
46: Which of the following is not a product of light reaction?
(1) ATP
(2) NADPH
(3) O₂
(4) CO₂
✅ (4) CO₂
47: Select the wrong statement regarding dark reaction.
(1) It is the use of ATP and NADPH to drive the processes for the synthesis of food.
(2) This phase directly depends on the light.
(3) It is dependent on the products of the light reaction.
(4) It is also known as Biosynthetic phase.
✅ (2) This phase directly depends on the light.
48: Two types of CO₂ assimilation during photosynthesis are
(1) C₃ pathway and C₄ pathway
(2) Light reaction and dark reaction
(3) Anabolic pathway and catabolic pathway
(4) Cyclic and Non-cyclic phosphorylation
✅ (1) C₃ pathway and C₄ pathway
49: First stable product of CO₂ fixation in C₃ pathway is
(1) 3-phosphoglyceric acid (PGA)
(2) Oxaloacetic acid (OAA)
(3) Phosphoenol pyruvate (PEP)
(4) Ribulose-1,5-bisphosphate (RuBP)
✅ (1) 3-phosphoglyceric acid (PGA)
50: C₃ pathway was discovered by
(1) Louis Pasteur
(2) Melvin Calvin
(3) Hatch and Slack
(4) Robert Hill
✅ (2) Melvin Calvin
51: First stable product in C₄ pathway is
(1) Ribulose-1,5-bisphosphate (RuBP)
(2) Phosphoenol pyruvate (PEP)
(3) 3-phosphoglyceric acid (PGA)
(4) Oxaloacetic acid (OAA)
✅ (4) Oxaloacetic acid (OAA)
52: Pick out the false statement about C₃ pathway.
(1) It occurs only in C₃ plants.
(2) It includes 3 stages such as carboxylation, reduction & regeneration.
(3) It does not have Kranz anatomy.
(4) In this, RuBP is the primary CO₂ acceptor.
✅ (1) It occurs only in C₃ plants.
53: Most crucial step of C₃ pathway is
(1) Carboxylation of RuBP
(2) Reduction
(3) Regeneration of RuBP
(4) Photorespiration
✅ (1) Carboxylation of RuBP
54: The enzyme RuBP carboxylase is also termed "RuBisCO" because it:
(1) Catalyzes only the carboxylation of ribulose-1,5-bisphosphate (RuBP) in the Calvin cycle.
(2) Exhibits dual activity, functioning as both a carboxylase and an oxygenase.
(3) Is involved in the regeneration of RuBP during the Calvin cycle.
(4) Facilitates CO₂ fixation exclusively in C₄ plants.
✅ (2) Exhibits dual activity, functioning as both a carboxylase and an oxygenase.
55: During the reduction phase of the Calvin cycle, how many ATP and NADPH molecules are required to synthesize one glucose molecule?
(1) 12 ATP and 12 NADPH
(2) 18 ATP and 12 NADPH
(3) 12 ATP and 18 NADPH
(4) 6 ATP and 6 NADPH
✅ (2) 18 ATP and 12 NADPH
56: In the Calvin cycle, the regeneration of ribulose-1,5-bisphosphate (RuBP) requires ATP. This difference in the stoichiometry of ATP and NADPH consumption during the dark reaction is compensated by which of the following processes?
(1) Non-cyclic photophosphorylation
(2) Photorespiration
(3) Cyclic photophosphorylation
(4) Oxidative phosphorylation
✅ (3) Cyclic photophosphorylation
57: To make 1 glucose molecule, how many turns of the Calvin cycle are needed?
(1) 1
(2) 2
(4) 4
(4) 6
✅ (4) 6
58: In the Calvin cycle, which of the following correctly represents the inputs and outputs for the synthesis of one molecule of glucose?
(1) Inputs: 6 CO₂, 18 ATP, 12 NADPH;
Outputs: 1 glucose, 18 ADP, 12 NADP⁺
(2) Inputs: 6 CO₂, 12 ATP, 18 NADPH;
Outputs: 1 glucose, 12 ADP, 18 NADP⁺
(3) Inputs: 12 CO₂, 18 ATP, 12 NADPH;
Outputs: 2 glucose, 18 ADP, 12 NADP⁺
(4) Inputs: 3 CO₂, 9 ATP, 6 NADPH;
Outputs: 1 glucose, 9 ADP, 6 NADP⁺
✅ (1) Inputs: 6 CO₂, 18 ATP, 12 NADPH;
Outputs: 1 glucose, 18 ADP, 12 NADP⁺
Outputs: 1 glucose, 18 ADP, 12 NADP⁺
59: Kranz anatomy in C₄ plants is characterized by:
(1) Thin-walled mesophyll cells with abundant chloroplasts
(2) Bundle sheath cells arranged in a ring around vascular tissues
(3) Presence of air spaces in bundle sheath cells for gas exchange
(4) Vascular bundles surrounded by palisade parenchyma
✅ (2) Bundle sheath cells arranged in a ring around vascular tissues
60: In C₄ plants, the main biosynthetic pathway responsible for carbohydrate synthesis is:
(1) C₃ pathway (Calvin cycle)
(2) C₄ pathway (Hatch & Slack pathway)
(3) CAM pathway
(4) Glycolytic pathway
✅ (1) C₃ pathway (Calvin cycle)
61: In the Hatch and Slack (C₄) pathway, the primary CO₂ acceptor and the enzyme responsible for its fixation in mesophyll cells are:
(1) Ribulose-1,5-bisphosphate (RuBP) and RuBisCO
(2) Phosphoenol pyruvate (PEP) and PEP carboxylase
(3) Oxaloacetic acid (OAA) and Malate dehydrogenase
(4) 3-phosphoglyceric acid (PGA) and Pyruvate kinase
✅ (2) Phosphoenol pyruvate (PEP) and PEP carboxylase
62: Why do mesophyll cells in C₄ plants lack the Calvin cycle?
(1) They do not contain the enzyme RuBisCO.
(2) They lack NADPH required for the Calvin cycle.
(3) They are specialized only for ATP synthesis.
(4) They cannot transport malic acid to bundle sheath cells.
✅ (1) They do not contain the enzyme RuBisCO.
63: In C₄ plants, bundle sheath cells play a critical role in photosynthesis. Which of the following statements is correct regarding these cells?
(1) Bundle sheath cells contain PEP carboxylase (PEPcase) and are the primary site for CO₂ fixation into C₄ acids.
(2) Bundle sheath cells lack RuBisCO but use the C₄ pathway to generate glucose directly.
(3) Bundle sheath cells are rich in RuBisCO and facilitate the Calvin cycle, while mesophyll cells regenerate PEP.
(4) Bundle sheath cells transport C₃ acids to mesophyll cells for the synthesis of oxaloacetic acid (OAA).
✅ (3) Bundle sheath cells are rich in RuBisCO and facilitate the Calvin cycle, while mesophyll cells regenerate PEP.
64: Which of the following is a correct feature of C₄ plants?
(1) They exhibit high photorespiration and low temperature tolerance.
(2) They lack Kranz anatomy but have high biomass productivity.
(3) They perform photosynthesis only under low light intensities.
(4) They possess Kranz anatomy and lack photorespiration, leading to higher biomass production.
✅ (4) They possess Kranz anatomy and lack photorespiration, leading to higher biomass production.
65: In Calvin pathway, the reaction catalyzed by Rubisco is correctly represented by
(1) RuBP + CO₂ → 3 x 3PGA
(2) RuBP + O₂ → 2 x 3PGA
(3) RuBP + CO₂ → 2 x 3PGA
(4) RuBP + O₂ → 3 x 3PGA
✅ (3) RuBP + CO₂ → 2 x 3PGA
66: The most abundant enzyme in the world is
(1) RuBisCO
(2) Catalase
(3) PEP Carboxylase
(4) ATP Synthase
✅ (1) RuBisCO
67: Photorespiration occurs when RuBisCO binds to O₂ instead of CO₂. Which factor primarily determines whether RuBisCO acts as a carboxylase or an oxygenase?
(1) The pH of the chloroplast stroma
(2) The relative concentrations of CO₂ and O₂
(3) The availability of ATP and NADPH
(4) The enzyme’s higher affinity for O₂
✅ (2) The relative concentrations of CO₂ and O₂
68: In C₃ plants, photorespiration occurs because:
(1) RuBisCO has a higher affinity for O₂ than CO₂
(2) RuBP binds with O₂, forming phosphoglycerate and phosphoglycolate
(3) RuBisCO fixes CO₂ at a higher rate in the presence of O₂
(4) RuBP directly binds to CO₂, reducing O₂ fixation
✅ (2) RuBP binds with O₂, forming phosphoglycerate and phosphoglycolate
69: Photorespiration is a wasteful process because
(1) It synthesizes ATP and NADPH without producing sugars.
(2) It uses ATP and releases CO₂ without synthesizing sugars, ATP, or NADPH.
(3) It prevents CO₂ fixation by inhibiting RuBisCO activity.
(4) It consumes ATP and NADPH to synthesize sugars inefficiently.
✅ (2) It uses ATP and releases CO₂ without synthesizing sugars, ATP, or NADPH.
70: Photorespiration does not occur in C₄ plants because
(1) RuBisCO in C₄ plants lacks oxygenase activity.
(2) CO₂ is directly fixed into sugars in the mesophyll cells.
(3) C₄ plants maintain a high CO₂ concentration at RuBisCO's enzyme site.
(4) Oxygen concentration is reduced in the mesophyll cells.
✅ (3) C₄ plants maintain a high CO₂ concentration at RuBisCO's enzyme site.
71: What advantages do C₄ plants have over C₃ plants?
(1) Higher RuBisCO activity, higher oxygenase activity and better water conservation
(2) Faster growth due to higher oxygenase activity of RuBisCO
(3) Better CO₂ fixation at low temperatures and presence of photorespiration
(4) Increased productivity, tolerance to higher temperatures, and absence of photorespiration
✅ (4) Increased productivity, tolerance to higher temperatures, and absence of photorespiration
72: Which of the following statements correctly distinguishes C₃ plants from C₄ plants?
(1) C₃ plants have dimorphic chloroplasts, while C₄ plants have only granal chloroplasts.
(2) C₄ plants have a higher CO₂ compensation point compared to C₃ plants.
(3) Photosynthesis in C₄ plants occurs in both mesophyll and bundle-sheath cells, while in C₃ plants, it occurs only in mesophyll cells.
(4) C₃ plants are more photosynthetically efficient and have higher productivity than C₄ plants.
✅ (3) Photosynthesis in C₄ plants occurs in both mesophyll and bundle-sheath cells, while in C₃ plants, it occurs only in mesophyll cells.
73: In C₃ plants and C₄ plants, optimum temperature for photosynthesis is
(1) C₃ plants: 30°C - 40°C
C₄ plants: 35°C - 45°C
(2) C₃ plants: 35°C - 45°C
C₄ plants: 30°C - 40°C
(3) C₃ plants: 35°C - 45°C
C₄ plants: 25°C
(4) C₃ plants: 25°C
C₄ plants: 35°C - 45°C
✅ (4) C₃ plants: 25°C
C₄ plants: 35°C - 45°C
C₄ plants: 35°C - 45°C
74: Which of the following sets are completely C₄ plants?
(1) Maize, rice, wheat, sorghum
(2) Maize, sugarcane, amaranth, sorghum
(3) Rice, wheat, bean, potato
(4) Rice, bean, potato, sugarcane
✅ (2) Maize, sugarcane, amaranth, sorghum
Topic 5: FACTORS AFFECTING PHOTOSYNTHESIS
NEET: Previous Years Questions
75: With reference to factors affecting the rate of photosynthesis, which of the following statements is not correct?
(1) Increasing atmospheric CO₂ concentration up to 0.05% can enhance CO₂ fixation rate.
(2) C₃ plants respond to higher temperature with enhanced photosynthesis while C₄ plants have much lower temperature optimum.
(3) Tomato is a greenhouse crop which can be grown in CO₂ enriched atmosphere for higher yield.
(4) Light saturation for CO₂ fixation occurs at 10% of full sunlight. (NEET 2017)
✅ (2) C₃ plants respond to higher temperature with enhanced photosynthesis while C₄ plants have much lower temperature optimum.
Model Questions
76: Which of the following combinations correctly categorizes internal (plant) and external factors affecting photosynthesis?
(1) Internal: Number of leaves, chlorophyll amount
External: Temperature, soil pH
(2) Internal: Mesophyll cells, internal CO₂ concentration
External: Sunlight, atmospheric CO₂
(3) Internal: Leaf orientation, water availability
External: Genes, growth rate
(4) Internal: Age of leaves, soil nutrients
External: Light intensity, humidity
✅ (2) Internal: Mesophyll cells, internal CO₂ concentration
External: Sunlight, atmospheric CO₂
External: Sunlight, atmospheric CO₂
77: “If a biochemical process is affected by more than one factor, its rate is determined by the factor nearest to its minimal value: it is the factor which directly affects the process if its quantity is changed.” This is called
(1) Liebig's Law of the Minimum
(2) Blackman’s Law of Limiting Factors
(3) Law of Segregation
(4) Shelford's Law of Tolerance
✅ (2) Blackman’s Law of Limiting Factors
78: Which of the following statements best describes the relationship between light intensity and the rate of CO₂ fixation in photosynthesis?
(1) CO₂ fixation rate increases linearly with light intensity indefinitely, even at very high light levels.
(2) Light saturation occurs at 10% of full sunlight, after which CO₂ fixation plateaus due to limiting factors like temperature or CO₂ availability.
(3) At high light intensities, chlorophyll synthesis increases, leading to a proportional rise in photosynthesis.
(4) Light is the primary limiting factor for photosynthesis in all plants, regardless of their habitat.
✅ (2) Light saturation occurs at 10% of full sunlight, after which CO₂ fixation plateaus due to limiting factors like temperature or CO₂ availability.
79: Regarding carbon dioxide concentration, which statement is wrong?
(1) CO₂ is the major limiting factor for photosynthesis.
(2) Increase in CO₂ concentration in atmosphere beyond 0.05% can become damaging for plants.
(3) At low light, C₃ and C₄ plants respond to high CO₂.
(4) C₃ plants respond to increased CO₂ concentration and saturation is seen only beyond 450 μlL-1.
✅ (3) At low light, C₃ and C₄ plants respond to high CO₂.
80: Why are the dark reactions of photosynthesis more sensitive to temperature changes compared to the light reactions?
(1) Chlorophyll stability decreases at higher temperatures.
(2) Light reactions depend on enzymatic processes.
(3) Electron transport in light reactions is inhibited by heat.
(4) Dark reactions involve temperature-sensitive enzymatic steps.
✅ (4) Dark reactions involve temperature-sensitive enzymatic steps.
81: Which of the following correctly describes the temperature adaptation of C₃ and C₄ plants?
(1) C₃ plants have a higher temperature optimum than C₄ plants.
(2) C₄ plants perform better at lower temperatures due to PEP carboxylase.
(3) C₄ plants thrive at higher temperatures, while C₃ plants have lower optima.
(4) Both C₃ and C₄ plants have the same temperature optimum globally.
✅ (3) C₄ plants thrive at higher temperatures, while C₃ plants have lower optima.
82: Which of the following is the primary reason for reduced photosynthesis during water stress in plants?
(1) Increased stomatal aperture enhances CO₂ loss.
(2) Enhanced chlorophyll synthesis in wilted leaves.
(3) Reduced CO₂ availability and decreased leaf surface area.
(4) Accelerated photorespiration due to high O₂ concentration.
✅ (3) Reduced CO₂ availability and decreased leaf surface area.