Photosynthesis – Light Reaction: NEET MCQs with Answers

15 free questions on Photosynthesis – Light Reaction for NEET (UG), starting with previous-year NEET and AIPMT questions. Try each one, then tap Show answer for the answer and a short explanation.

Syllabus covered: Light Reaction: Photochemical and biosynthetic phases of photosynthesis, Cyclic and non cyclic and photophosphorylation, Chemiosmotic hypothesis

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Question 1

Previous-year question
Which one of the following products diffuses out of the chloroplast during photosynthesis? [Re-NEET 2024]
  1. ADP
  2. NADPH
  3. O₂
  4. ATP
Show answer
Answer: (C) O₂
Explanation: O₂ released by photolysis of water diffuses out of the chloroplast (and the leaf). ATP and NADPH formed in the light reaction are used within the stroma for the Calvin cycle, and ADP is recycled inside the chloroplast.

Question 2

Previous-year question
Which of the following are needed for the light reaction of photosynthesis? [Re-NEET 2024]
A. CO₂
B. O₂
C. H₂O
D. Chlorophyll
E. Light
Choose the correct answer from the options given below:
  1. A, C, D and E only
  2. C, D and E only
  3. A and B only
  4. A, C and E only
Show answer
Answer: (B) C, D and E only
Explanation: The light reaction needs light, chlorophyll (to trap light) and water (as the electron source). CO₂ is used in the dark reaction and O₂ is a product, not a requirement. Hence C, D and E only.

Question 3

Previous-year question
The photochemical phase of photosynthesis includes: [NEET 2024]
A. Oxygen release
B. Formation of NADPH
C. Use of ATP
D. Water splitting
E. Carboxylation
Choose the correct answer from the options given below:
  1. A, B and D only
  2. B, C and E only
  3. A, B, C and D only
  4. C and E only
Show answer
Answer: (A) A, B and D only
Explanation: The photochemical (light) phase includes light absorption, water splitting, oxygen release and formation of ATP and NADPH. Use of ATP and carboxylation belong to the biosynthetic (dark) phase, so A, B and D only.

Question 4

Previous-year question
The synthesis of ATP coupled with the development of a proton gradient across a membrane is explained by the: [NEET 2024]
  1. Wobble hypothesis
  2. Chemiosmotic hypothesis
  3. Rivet Popper hypothesis
  4. Mass flow hypothesis
Show answer
Answer: (B) Chemiosmotic hypothesis
Explanation: Mitchell's chemiosmotic hypothesis explains ATP synthesis as linked to a proton gradient across the thylakoid (or inner mitochondrial) membrane. The wobble hypothesis concerns codon–anticodon pairing, the rivet popper hypothesis concerns biodiversity loss, and mass flow concerns phloem translocation.

Question 5

Previous-year question
Which one of the following statements is incorrect? [NEET 2023 (Manipur)]
  1. Grana lamellae have both PS I and PS II
  2. Cyclic photophosphorylation involves both PS I and PS II
  3. Both ATP and NADPH + H⁺ are synthesised during non-cyclic photophosphorylation
  4. Stroma lamellae lack PS II and NADP reductase
Show answer
Answer: (B) Cyclic photophosphorylation involves both PS I and PS II
Explanation: Cyclic photophosphorylation involves only PS I and occurs in the stroma lamellae, so the statement that it involves both PS I and PS II is incorrect. Grana lamellae contain both photosystems, non-cyclic flow forms ATP and NADPH + H⁺, and stroma lamellae lack PS II and NADP reductase.

Question 6

Previous-year question
Identify the correct statements about the chemiosmotic hypothesis. [Re-NEET 2022]
(a) Splitting of the water molecule takes place on the inner side of the membrane.
(b) Protons accumulate within the lumen of the thylakoids.
(c) The primary acceptor of electrons transfers the electrons to an electron carrier.
(d) The NADP reductase enzyme is located on the stroma side of the membrane.
(e) Protons increase in number in the stroma.
Choose the correct answer from the options given below:
  1. (a), (b) and (e)
  2. (a), (b) and (d)
  3. (b), (c) and (d)
  4. (b), (c) and (e)
Show answer
Answer: (B) (a), (b) and (d)
Explanation: Water is split on the inner (lumen) side of the thylakoid membrane, protons accumulate in the lumen, and NADP reductase lies on the stromal side, so (a), (b) and (d) are correct. The primary electron acceptor passes electrons to a proton carrier (not an electron carrier), and the number of protons in the stroma decreases, so (c) and (e) are wrong.

Question 7

Previous-year question
What are the products of the light reaction of photosynthesis? [NEET 2022 (Overseas)]
  1. ATP, NADPH, O₂ and H₂O
  2. ATP, NADPH and H₂O
  3. ATP, NADPH and CO₂
  4. ATP, NADPH and O₂
Show answer
Answer: (D) ATP, NADPH and O₂
Explanation: The light reaction produces ATP and NADPH (assimilatory power) along with O₂, which is released as a by-product of photolysis of water. Water is consumed, not produced, and CO₂ is used in the dark reaction.
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Question 8

Previous-year question
Non-cyclic photophosphorylation leads to the formation of: [NEET 2021 (Paper-2)]
  1. ATP and NADH + H⁺
  2. ATP only
  3. ATP and NADPH + H⁺
  4. ATP, ADP and NADH + H⁺
Show answer
Answer: (C) ATP and NADPH + H⁺
Explanation: In non-cyclic photophosphorylation both PS II and PS I work in series; ATP is synthesised and electrons finally reduce NADP⁺ to NADPH + H⁺. Cyclic photophosphorylation gives ATP only, and NADH is not formed in photosynthesis.

Question 9

Previous-year question
Which one of the following statements is incorrect? [NEET 2021]
  1. Both ATP and NADPH + H⁺ are synthesised during non-cyclic 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.
Show answer
Answer: (D) Cyclic photophosphorylation involves both PS I and PS II.
Explanation: Cyclic photophosphorylation involves only PS I; electrons cycle back to PS I and only ATP is formed, so the statement that it involves both PS I and PS II is incorrect. The other statements are correct: non-cyclic flow forms ATP and NADPH + H⁺, stroma lamellae have only PS I and lack PS II and NADP reductase, and grana lamellae have both photosystems.

Question 10

Previous-year question
In the light reaction, plastoquinone facilitates the transfer of electrons from [NEET 2020]
  1. Cyt b₆f complex to PS-I
  2. PS-I to NADP⁺
  3. PS-I to ATP synthase
  4. PS-II to Cyt b₆f complex
Show answer
Answer: (D) PS-II to Cyt b₆f complex
Explanation: Plastoquinone is the mobile lipid-soluble carrier that shuttles electrons from the primary acceptor of PS II to the cytochrome b₆f complex, and in doing so it carries protons from the stroma into the lumen, contributing to the proton gradient.

Question 11

Previous-year question
Which of the following is NOT a product of the light reaction of photosynthesis? [NEET 2018]
  1. ATP
  2. NADH
  3. Oxygen
  4. NADPH
Show answer
Answer: (B) NADH
Explanation: The light reaction yields ATP, NADPH + H⁺ and oxygen. NADH is the reduced coenzyme of respiration, produced in glycolysis and the Krebs cycle; in photosynthesis it is NADP⁺ and not NAD⁺ that is reduced.

Question 12

Previous-year question
In a chloroplast, the highest number of protons are found in the [NEET 2016]
  1. stroma
  2. lumen of the thylakoids
  3. inter-membrane space
  4. antennae complex
Show answer
Answer: (B) lumen of the thylakoids
Explanation: Splitting of water inside the lumen, transfer of protons across the membrane by the carriers, and removal of protons from the stroma during NADP⁺ reduction all combine to accumulate protons in the thylakoid lumen and to lower the pH there.

Question 13

Previous-year question
Emerson’s enhancement effect and the red drop have been instrumental in the discovery of [NEET 2016]
  1. photophosphorylation and non-cyclic electron transport
  2. two photosystems operating simultaneously
  3. photophosphorylation and cyclic electron transport
  4. oxidative phosphorylation
Show answer
Answer: (B) two photosystems operating simultaneously
Explanation: Emerson observed that the yield of photosynthesis falls sharply beyond 680 nm (the red drop) but is greatly enhanced if shorter-wavelength light is supplied at the same time. This could only be explained by the existence of two distinct photosystems working in series.

Question 14

Previous-year question
The oxygen evolved during photosynthesis comes from water molecules. Which one of the following pairs of elements is involved in this reaction? [AIPMT 2015]
  1. Manganese and potassium
  2. Magnesium and molybdenum
  3. Magnesium and chlorine
  4. Manganese and chlorine
Show answer
Answer: (D) Manganese and chlorine
Explanation: The oxygen evolving complex associated with PS II requires manganese, along with chloride and calcium ions, to split water. Manganese carries out the actual water-splitting reaction while chloride is essential for the photochemical step.

Question 15

Previous-year question
NADP⁺ is reduced to NADPH during [AIPMT 1988]
  1. PS-I
  2. PS-II
  3. the Calvin cycle
  4. non-cyclic photophosphorylation
Show answer
Answer: (D) non-cyclic photophosphorylation
Explanation: In non-cyclic photophosphorylation both PS-I and PS-II operate. Electrons released by the photolysis of water are transferred to PS-II and then via a series of carriers to PS-I; P₇₀₀ then releases an electron that reaches NADP⁺ through Fe-S protein and ferredoxin. NADP⁺ + 2e⁻ + H⁺ → NADPH (catalysed by NADP reductase).

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