Chemiosmosis — NEET Biology MCQs with Solutions
Free NEET Biology Chemiosmosis MCQs with step-by-step solutions (38 questions). Part of Photosynthesis in Higher Plants. Practise online on Prepizo — no login needed.
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Questions with solutions
Q1 — Chemiosmosis · easy · theory
ATP synthesis in the chloroplast is driven by a proton gradient across the ______ membrane:
A. Nuclear
B. Mitochondrial inner
C. Thylakoid ✓ Correct
D. Outer chloroplast
Solution: Protons accumulate in the thylakoid lumen; their flow back through ATP synthase makes ATP — chemiosmosis.
Q2 — Chemiosmosis · easy · theory
During the light reaction, protons accumulate in the ______ of the thylakoid:
A. Lumen (inner space) ✓ Correct
B. Cytosol
C. Intermembrane space of mitochondria
D. Stroma
Solution: Water splitting (in the lumen) and electron transport pump protons into the lumen, creating a gradient.
Q3 — Chemiosmosis · medium · theory
The enzyme that uses the proton-motive force to phosphorylate ADP is:
A. NADP reductase
B. RuBisCO
C. Cytochrome oxidase
D. ATP synthase (CF0–CF1) ✓ Correct
Solution: ATP synthase has a channel (CF0) letting protons cross and a catalytic head (CF1) that makes ATP.
Q4 — Chemiosmosis · medium · theory
Protons move from the thylakoid lumen back to the stroma through ATP synthase because:
A. They are pumped uphill
B. Of active transport
C. The stroma is more acidic
D. They flow down their electrochemical (concentration) gradient ✓ Correct
Solution: The high-H⁺ lumen releases protons to the low-H⁺ stroma; this diffusion powers ATP synthesis.
Q5 — Chemiosmosis · hard · theory
In the chloroplast, NADPH and ATP are released into the ______, where the Calvin cycle occurs:
A. Stroma ✓ Correct
B. Cytosol
C. Thylakoid lumen
D. Intermembrane space
Solution: ATP synthase's catalytic site faces the stroma, so ATP (and NADPH) are made available in the stroma for carbon fixation.
Q6 — Chemiosmosis · hard · theory
Three factors set up the transmembrane proton gradient in the thylakoid: water splitting in the lumen, proton transport across the membrane by the electron carriers, and:
A. Uptake of CO₂
B. Removal of protons from the stroma by NADP⁺ reduction ✓ Correct
C. Photolysis in the stroma
D. Glucose oxidation
Solution: NADP⁺ reductase on the stromal side takes up stromal protons to make NADPH, deepening the gradient.
Q7 — Chemiosmosis · medium · numerical
According to the chemiosmotic hypothesis, ATP synthesis in the chloroplast requires a proton gradient that is built up such that protons accumulate:
A. inside the thylakoid lumen, making it more acidic than the stroma ✓ Correct
B. in the intermembrane space between the two chloroplast envelopes
C. inside the stroma, making it more acidic than the lumen
D. evenly on both sides of the thylakoid membrane
Solution: Water splitting and electron-carrier pumping deposit protons in the lumen; the resulting high H⁺ concentration (low pH) inside the thylakoid drives ATP synthesis as protons exit to the stroma.
Q8 — Chemiosmosis · medium · numerical
Three processes together establish the trans-thylakoid proton gradient. Which of the following is NOT one of them?
A. Release of protons into the lumen when water is split at PS II
B. Active pumping of protons out of the lumen into the stroma by ATP synthase ✓ Correct
C. Transport of protons across the membrane as plastoquinone carries electrons
D. Removal of protons from the stroma when NADP⁺ is reduced to NADPH
Solution: The gradient is built by water-splitting (adds H⁺ to lumen), plastoquinone shuttling H⁺ into the lumen, and NADP⁺ reduction removing H⁺ from the stroma; ATP synthase lets protons flow the other way, it does not build the gradient.
Q9 — Chemiosmosis · medium · numerical
The chloroplast enzyme that couples the return flow of protons from lumen to stroma with the phosphorylation of ADP has two parts, CF0 and CF1. The role of the CF0 part is to:
A. catalyse the actual joining of ADP and inorganic phosphate in the stroma
B. form the membrane channel through which protons cross into the stroma ✓ Correct
C. reduce NADP⁺ using the electrons delivered by ferredoxin
D. split water molecules to release the protons into the lumen
Solution: CF0 is the membrane-embedded channel that conducts protons across the thylakoid membrane; the protruding CF1 head uses that flux to synthesise ATP.
Q10 — Chemiosmosis · medium · numerical
Assertion (A): A pH gradient alone across the thylakoid membrane is sufficient to power ATP synthesis. Reason (R): The breakdown of this gradient releases energy that ATP synthase uses to phosphorylate ADP.
A. A is true but R is false
B. A is false but R is true
C. Both A and R are true and R is the correct explanation of A ✓ Correct
D. Both A and R are true but R is not the correct explanation of A
Solution: The book states that the gradient (proton-motive force) is important because its breakdown, as protons diffuse through ATP synthase, drives ADP phosphorylation — R correctly explains A.
Q11 — Chemiosmosis · medium · numerical
Compared with the mitochondrion, chemiosmosis in the chloroplast differs in that protons accumulate:
A. in the outer cytoplasm surrounding the whole chloroplast
B. in the intermembrane space, exactly as in the mitochondrion
C. in the thylakoid lumen (an enclosed space inside the organelle) ✓ Correct
D. in the stroma, from where they flow into the lumen
Solution: In chloroplasts protons build up in the thylakoid lumen and flow out to the stroma, whereas mitochondria accumulate protons in the intermembrane space; the direction of the driving flux differs.
Q12 — Chemiosmosis · easy · numerical
The immediate energy currency that the CF1 head of ATP synthase produces as protons flow through it is:
A. NADPH from NADP⁺
B. oxygen from water
C. glucose from CO₂
D. ATP from ADP and inorganic phosphate ✓ Correct
Solution: ATP synthase (CF0–CF1) makes ATP by phosphorylating ADP; NADPH is made separately by ferredoxin/NADP reductase, and glucose is a Calvin-cycle product.
Q13 — Chemiosmosis · easy · numerical
For every ATP synthesised through the chloroplast ATP synthase, what physically moves through the enzyme?
A. Water molecules entering the lumen
B. Electrons transferred from ferredoxin
C. Carbon dioxide molecules bound to RuBP
D. Protons diffusing down their electrochemical gradient ✓ Correct
Solution: It is the transmembrane movement of protons (H⁺) down the gradient, not electrons or CO₂, that drives the conformational changes making ATP.
Q14 — Chemiosmosis · easy · numerical
Both the ATP and the NADPH generated by chemiosmosis and the electron transport chain are released on the side of the thylakoid membrane where they are used, namely the:
A. space between the two chloroplast envelope membranes
B. thylakoid lumen, where carbon fixation takes place
C. cytosol just outside the chloroplast
D. stroma, where the enzymes of the Calvin cycle operate ✓ Correct
Solution: The CF1 head and NADP reductase face the stroma, so ATP and NADPH are released there — exactly where the Calvin-cycle enzymes need them.
Q15 — Chemiosmosis · easy
ATP formation occurs upon-
A. build up of potential gradient
B. None of these
C. break down of potential gradient ✓ Correct
D. Both of these
Solution: ATP is synthesised when the proton (electrochemical) gradient built across the thylakoid membrane breaks down, driving protons through ATP synthase.
Q16 — Chemiosmosis · easy
The transmembrane channel in ATP synthase enzyme is formed by
A. CF0 ✓ Correct
B. CF2
C. CF1
D. Both (1) and (2)
Solution: The CF0 part of ATP synthase is embedded in the membrane and forms the transmembrane channel through which protons cross.
Q17 — Chemiosmosis · medium
The transmembrane channel allows _____ across membrane for ATP synthesis
A. Facilitated diffusion of electron
B. Simple diffusion of proton
C. Osmosis of protons
D. Facilitated diffusion of proton ✓ Correct
Solution: The CF0 channel permits facilitated diffusion of protons down their gradient across the thylakoid membrane, powering ATP synthesis.
Q18 — Chemiosmosis · easy
The ATP synthase has two parts I & II. Identify I and II.
A. None
B. CF ; CF0
C. CF1 ; CF0
D. CF0 ; CF1 ✓ Correct
Solution: ATP synthase consists of CF0 (transmembrane channel) and CF1 (protruding on the stroma side that makes ATP).
Q19 — Chemiosmosis · easy
CF0 is -
A. protruding on outer surface of chloroplast
B. None of these
C. protruding on inner surface of chloroplast membrane
D. Embedded in chloroplast membrane ✓ Correct
Solution: CF0 is embedded in the thylakoid (chloroplast) membrane and forms the proton channel.
Q20 — Chemiosmosis · medium
CF1 is-
A. None of these
B. protruding on inner surface of chloroplast
C. embedded in chloroplast membrane
D. protruding on outer surface of chloroplast membrane ✓ Correct
Solution: CF1 protrudes on the outer (stroma) surface of the thylakoid membrane and catalyses ATP synthesis.
Q21 — Chemiosmosis · medium
Conformational change in ____ makes ATP.
A. CF1 ✓ Correct
B. None
C. CF0
D. Both
Solution: The conformational change in the CF1 particle drives the synthesis of ATP as protons move through CF0.
Q22 — Chemiosmosis · medium
For creating proton gradient across thylakoid membrane ________ .
A. Energy is used ✓ Correct
B. Energy is released
C. None of these
D. No energy is used
Solution: Energy from electron transport is used to pump/accumulate protons and create the gradient across the thylakoid membrane.
Q23 — Chemiosmosis · medium
The end products of light reaction are
A. immediately used up in next round of light reaction
B. None of these
C. stored till dark reaction takes place at night
D. transferred to the stroma from lumen to be used in biosynthetic reaction occurring in stroma ✓ Correct
Solution: ATP and NADPH produced in the light reaction are made available in the stroma, where they drive the biosynthetic (Calvin cycle) reactions.
Q24 — Chemiosmosis · medium
ATP synthesis is linked to ___(i)___ gradient across a membrane in ___(ii)___.
A. Proton ; Photosynthesis and respiration ✓ Correct
B. Electron ; Photosynthesis only
C. Proton ; Photosynthesis but not respiration
D. Electron ; Photosynthesis & respiration
Solution: ATP synthesis is linked to the development of a proton gradient across a membrane in both photosynthesis and respiration.
Q25 — Chemiosmosis · hard
Which of the following statements is true?
A. The protons accumulate towards outer side of membrane in photosynthesis
B. The protons accumulate towards outer side of thylakoid membrane in respiration
C. None of these ✓ Correct
D. The protons accumulate towards inner side (lumen) of thylakoid in respiration.
Solution: In photosynthesis protons accumulate in the thylakoid lumen (inner side), and thylakoids are not involved in respiration, so all listed statements are wrong.
Q26 — Chemiosmosis · medium
The proton gradient may be formed in photosynthesis due to-
A. Both (1) and (2)
B. Splitting of water ✓ Correct
C. None of these
D. Reduction of NAD+
Solution: Splitting of water releases protons into the lumen; NADP+ (not NAD+) reduction removes protons from the stroma, so only splitting of water applies here.
Q27 — Chemiosmosis · hard
Assertion : As electrons move through photosystems, protons are transported across membrane. Reason : Primary acceptor of electrons is an H carrier.
A. Both Assertion & Reason are correct and Reason is explanation of Assertion
B. Assertion & Reason both are incorrect
C. Both Assertion & Reason are correct and Reason is not the explanation for Assertion
D. Assertion is correct but Reason is not correct ✓ Correct
Solution: Electron movement does transport protons, but the H carrier (e.g. plastoquinone) is not the primary electron acceptor, so the Reason is incorrect.
Q28 — Chemiosmosis · medium
Which of these is H carrier?
A. Plastoquinone ✓ Correct
B. PS II
C. Ferredoxin
D. Plastocyanin
Solution: Plastoquinone acts as the hydrogen (H) carrier, moving protons from the stroma into the thylakoid lumen.
Q29 — Chemiosmosis · medium
NADP reductase enzyme is located on ________ of thylakoid membrane.
A. Lumen side (i.e. inner side)
B. Lumen side (i.e. outer side)
C. Stroma side (outer side) ✓ Correct
D. Stroma side (i.e. inner side)
Solution: NADP reductase is located on the stroma (outer) side of the thylakoid membrane, where it reduces NADP+ to NADPH.
Q30 — Chemiosmosis · medium
The proton gradient is also formed due to-
A. reduction of NADP+ ✓ Correct
B. reduction of FAD+
C. reduction of both NAD+ & NADP+
D. reduction of NAD+
Solution: Reduction of NADP+ on the stroma side removes protons from the stroma, contributing to the proton gradient across the thylakoid membrane.