Part 2 — Light Reactions, Photophosphorylation, Z-scheme, Splitting of Water (Q26–50)

Part 2 — Light Reactions, Photophosphorylation, Z-scheme, Splitting of Water (Q26–50)

Q26.

The light-dependent reactions of photosynthesis occur in:
A. Stroma
B. Thylakoid membranes ✅
C. Cytoplasm
D. Mitochondria

Explanation:

• A. Stroma = Calvin cycle.
• B. (Correct) Light reactions (PSI, PSII, electron carriers, ATP synthase) occur in thylakoid membranes.
• C/D. Not involved.

Q27.

The primary electron donor in photosystem II is:
A. Chlorophyll b
B. P680 (chlorophyll a) ✅
C. P700
D. Carotenoid

Explanation:

• A/C/D. Accessory pigments or PSI.
• B. (Correct) P680 (Chl a) in PSII is the reaction center that loses an electron when excited.

Q28.

The splitting of water during photosynthesis occurs in:
A. Photosystem I
B. Photosystem II ✅
C. Stroma
D. Cytochrome complex

Explanation:

• A. PSI does not split water.
• B. (Correct) Water-splitting complex (oxygen-evolving complex, Mn cluster) is associated with PSII.
• C/D. Not sites of photolysis.

Q29.

Which metal is crucial for photolysis of water?
A. Copper
B. Manganese ✅
C. Iron
D. Zinc

Explanation:

• A/C/D. Required in other enzymes.
• B. (Correct) Mn cluster (OEC) catalyzes splitting of H₂O → O₂, protons, electrons.

Q30.

Which products are formed in non-cyclic photophosphorylation?
A. ATP only
B. ATP + NADPH + O₂ ✅
C. NADPH only
D. ATP + CO₂

Explanation:

• A/C/D. Incomplete.
• B. (Correct) Non-cyclic pathway forms ATP, NADPH, and O₂ from water splitting.

Q31.

In cyclic photophosphorylation, electrons:
A. Move from PSI to NADP⁺
B. Cycle back to PSI reaction center ✅
C. Move from PSII to PSI
D. Move from stroma to lumen

Explanation:

• A. Non-cyclic feature.
• B. (Correct) In cyclic, electrons excited in PSI return to PSI via electron carriers → only ATP formed.
• C. Non-cyclic.
• D. Not true.

Q32.

Which statement about cyclic photophosphorylation is correct?
A. O₂ is released
B. NADPH is formed
C. Only ATP is produced ✅
D. Both PSI and PSII are active

Explanation:

• A. No water splitting, no O₂.
• B. NADPH not formed.
• C. (Correct) Only ATP generated.
• D. Only PSI is active.

Q33.

The electron acceptor in PSII after P680 excitation is:
A. Ferredoxin
B. Plastoquinone ✅
C. NADP⁺
D. Cytochrome b6f

Explanation:

• A/C/D. Acceptors downstream.
• B. (Correct) Primary acceptor of PSII is plastoquinone (PQ).

Q34.

The Z-scheme of electron transport represents:
A. Movement of protons across thylakoid
B. Flow of electrons from water to NADP⁺ ✅
C. Calvin cycle
D. CO₂ fixation

Explanation:

• A/C/D. Not Z-scheme.
• B. (Correct) Z-scheme shows electron flow: H₂O → PSII → PQ → Cyt b6f → PC → PSI → Fd → NADP⁺.

Q35.

Which carrier transfers electrons between PSI and PSII?
A. Plastocyanin ✅
B. Ferredoxin
C. NADP⁺
D. Cytochrome oxidase

Explanation:

• A. (Correct) Plastocyanin (PC) transfers e⁻ from Cyt b6f to PSI.
• B/C/D. Not this role.

Q36.

Which enzyme catalyzes ATP formation in chloroplast?
A. Rubisco
B. ATP synthase (CF₀–CF₁ complex) ✅
C. Nitrate reductase
D. Ferredoxin–NADP reductase

Explanation:

• A. CO₂ fixation enzyme.
• B. (Correct) CF₀–CF₁ ATP synthase in thylakoid membranes synthesizes ATP.
• C/D. Other roles.

Q37.

Where is the proton gradient built during light reaction?
A. Between cytoplasm and plasma membrane
B. Across thylakoid membrane (lumen vs stroma) ✅
C. Inside mitochondria
D. Nucleus

Explanation:

• A/C/D. Wrong organelles.
• B. (Correct) Protons accumulate in thylakoid lumen → gradient drives ATP synthase.

Q38.

Which molecule donates electrons to P680⁺ after excitation?
A. NADPH
B. Water ✅
C. Ferredoxin
D. Oxygen

Explanation:

• A/C/D. Not correct.
• B. (Correct) Water donates e⁻, split by OEC → replenishes electrons lost by P680.

Q39.

The number of ATP molecules generated per pair of electrons in non-cyclic photophosphorylation is approximately:
A. 1
B. 2 ✅
C. 3
D. 4

Explanation:

• A/C/D. Not correct.
• B. (Correct) About 2 ATP + 1 NADPH produced per electron pair transported.

Q40.

Which statement about PSI is true?
A. Its reaction center is P700 ✅
B. It splits water
C. It reduces plastoquinone
D. It produces O₂

Explanation:

• A. (Correct) PSI has Chl a P700 as reaction center.
• B-D. Functions of PSII.

Q41.

Ferredoxin transfers electrons to:
A. Cytochrome b6f
B. NADP⁺ reductase ✅
C. Plastocyanin
D. Plastoquinone

Explanation:

• A/C/D. Carriers upstream.
• B. (Correct) Ferredoxin passes e⁻ to Fd–NADP⁺ reductase, reducing NADP⁺ → NADPH.

Q42.

What is the role of plastoquinone (PQ) in electron transport?
A. Transfers e⁻ from PSI to NADP⁺
B. Transfers e⁻ from PSII to cytochrome b6f ✅
C. Splits water
D. Generates ATP directly

Explanation:

• A. Ferredoxin does this.
• B. (Correct) PQ transfers e⁻ from PSII to Cyt b6f.
• C/D. Not its function.

Q43.

Which photosystem operates only in cyclic photophosphorylation?
A. PSI ✅
B. PSII
C. Both PSI & PSII
D. Neither

Explanation:

• A. (Correct) Only PSI cycles electrons back to itself.
• B/C/D. Incorrect.

Q44.

What is produced when water splits in photosynthesis?
A. Electrons, O₂, protons ✅
B. ATP and NADPH
C. CO₂ and glucose
D. Only oxygen

Explanation:

• A. (Correct) Water splitting → O₂ + 2H⁺ + 2e⁻.
• B. ATP/NADPH produced later.
• C/D. Wrong.

Q45.

The oxygen released during photosynthesis comes from:
A. CO₂
B. H₂O ✅
C. Glucose
D. Chlorophyll

Explanation:

• A. Old belief disproved.
• B. (Correct) Proven by isotopic labeling (O¹⁸ tracer).
• C/D. Not true.

Q46.

Which statement about non-cyclic photophosphorylation is false?
A. Involves both PSI and PSII
B. Produces ATP and NADPH
C. Produces O₂
D. Produces only ATP ✅

Explanation:

• A–C. True.
• D. (Correct) Non-cyclic produces ATP, NADPH, O₂ (not only ATP).

Q47.

Which complex pumps protons into the thylakoid lumen?
A. Plastoquinone
B. Cytochrome b6f ✅
C. Ferredoxin
D. Plastocyanin

Explanation:

• A/C/D. Electron carriers, not pumps.
• B. (Correct) Cyt b6f complex pumps protons to generate gradient.

Q48.

Which event does NOT occur in cyclic photophosphorylation?
A. ATP formation
B. Water splitting ✅
C. PSI excitation
D. Electron cycling

Explanation:

• A/C/D. Occur.
• B. (Correct) Water not split, no O₂ formed in cyclic.

Q49.

The CF₀ part of ATP synthase functions as:
A. Proton channel ✅
B. ATP binding site
C. Light receptor
D. NADPH generator

Explanation:

• A. (Correct) CF₀ forms H⁺ channel across membrane.
• B. CF₁ has catalytic site.
• C/D. Not roles.

Q50.

The minimum number of photons required to release one O₂ molecule in photosynthesis is:
A. 4 ✅
B. 2
C. 6
D. 8

Explanation:

• A. (Correct) Splitting of 2 H₂O → 1 O₂ requires 4 electrons → 4 photons (minimum).
• B/C/D. Not correct counts.

Photosynthesis Class 11, Photosynthesis NEET MCQs, Light reaction Z scheme, Calvin cycle C3 pathway, C4 pathway Kranz anatomy, Photorespiration C2 cycle, Factors affecting photosynthesis, Class 11 Biology MCQs, photosynthesis in higher plants class 11 mcqs, light reaction and z scheme neet questions, calvin cycle c3 pathway notes ncert, c4 pathway and kranz anatomy neet, photorespiration c2 cycle class 11 biology, factors affecting photosynthesis neet questions, photosynthesis experiments class 11 solved mcqs, class 11 biology photosynthesis online learning for neet