ETS & Oxidative Phosphorylation — NEET Biology MCQs with Solutions
Free NEET Biology ETS & Oxidative Phosphorylation MCQs with step-by-step solutions (60 questions). Part of Respiration in Plants. Practise online on Prepizo — no login needed.
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Questions with solutions
Q1 — ETS & Oxidative Phosphorylation · easy · theory
The electron transport system (ETS) is located in the:
A. Cytoplasm
B. Matrix
C. Outer membrane
D. Inner mitochondrial membrane ✓ Correct
Solution: The ETS complexes and ATP synthase are embedded in the inner mitochondrial membrane (cristae).
Q2 — ETS & Oxidative Phosphorylation · easy · theory
The final electron acceptor of the ETS in aerobic respiration is:
A. Carbon dioxide
B. Oxygen ✓ Correct
C. FAD
D. NAD⁺
Solution: O₂ accepts electrons and combines with protons to form water — the terminal acceptor.
Q3 — ETS & Oxidative Phosphorylation · medium · theory
The oxidation of one NADH via the ETS yields approximately ______ ATP, and one FADH₂ yields ______ ATP:
A. 3 ATP; 2 ATP ✓ Correct
B. 1 ATP; 1 ATP
C. 4 ATP; 3 ATP
D. 2 ATP; 3 ATP
Solution: Each NADH gives ~3 ATP and each FADH₂ ~2 ATP (FADH₂ enters at complex II, bypassing complex I).
Q4 — ETS & Oxidative Phosphorylation · medium · theory
ATP synthesis in the ETS is coupled to a proton gradient across the inner membrane, a mechanism called:
A. Fermentation
B. Oxidative phosphorylation (chemiosmosis) ✓ Correct
C. Photophosphorylation
D. Substrate-level phosphorylation
Solution: Electron flow pumps protons to the intermembrane space; their return through ATP synthase (F0–F1) drives ATP synthesis.
Q5 — ETS & Oxidative Phosphorylation · hard · theory
The theoretical net ATP yield from the complete aerobic oxidation of one glucose molecule is:
A. 2 ATP
B. 4 ATP
C. 38 ATP ✓ Correct
D. 12 ATP
Solution: Glycolysis (2) + Krebs GTP (2) + 10 NADH (30) + 2 FADH₂ (4) = 38 ATP (idealised; actual ~30–32).
Q6 — ETS & Oxidative Phosphorylation · hard · theory
Cytochrome c oxidase (Complex IV) transfers electrons to O₂. If this complex is blocked (e.g. by cyanide), the immediate effect is:
A. Krebs cycle speeds up
B. More ATP is made
C. Glycolysis stops
D. ETS halts, proton gradient collapses and ATP synthesis stops ✓ Correct
Solution: Blocking the terminal oxidase stops electron flow to O₂, collapsing the gradient and halting oxidative phosphorylation.
Q7 — ETS & Oxidative Phosphorylation · easy · numerical
In the electron transport system, electrons from FADH₂ enter at a different point from those of NADH. Where does FADH₂ feed its electrons?
A. At Complex I (NADH dehydrogenase), the same as NADH
B. Directly at Complex IV (cytochrome c oxidase)
C. At ATP synthase, skipping the cytochromes
D. At Complex II (succinate dehydrogenase), bypassing Complex I ✓ Correct
Solution: FADH₂ transfers electrons at Complex II, downstream of Complex I. Because it pumps fewer protons than the NADH route, each FADH₂ yields less ATP than each NADH.
Q8 — ETS & Oxidative Phosphorylation · easy · numerical
Which mobile carrier shuttles electrons from Complex III to Complex IV of the electron transport chain?
A. Ubiquinone (coenzyme Q)
B. NAD⁺
C. Plastocyanin
D. Cytochrome c ✓ Correct
Solution: Cytochrome c is a small mobile protein that carries electrons from Complex III to Complex IV. (Ubiquinone shuttles between Complexes I/II and III; plastocyanin belongs to photosynthesis.)
Q9 — ETS & Oxidative Phosphorylation · easy · numerical
Oxidative phosphorylation is so named because it couples:
A. The phosphorylation of glucose to its subsequent oxidation
B. The oxidation of reduced coenzymes (via the ETS) to the phosphorylation of ADP to ATP ✓ Correct
C. The oxidation of glucose to the reduction of NAD⁺
D. The direct transfer of a phosphate from a substrate to ADP
Solution: In oxidative phosphorylation the energy released as NADH and FADH₂ are oxidised through the ETS drives ATP synthase to phosphorylate ADP — distinct from substrate-level phosphorylation.
Q10 — ETS & Oxidative Phosphorylation · easy · numerical
The role of oxygen as the terminal acceptor of the electron transport system is described as vital and indispensable because it:
A. Splits glucose into two pyruvate molecules
B. Directly phosphorylates ADP to ATP
C. Removes hydrogen (as water) and keeps electrons flowing, allowing the coenzymes to be reoxidised ✓ Correct
D. Provides the protons that are pumped across the membrane
Solution: O₂ accepts the spent electrons and combines with protons to form water. This continual removal keeps the chain flowing and regenerates NAD⁺/FAD; without it the whole chain and Krebs cycle back up.
Q11 — ETS & Oxidative Phosphorylation · medium · numerical
According to the chemiosmotic hypothesis, ATP synthesis by ATP synthase requires two structural conditions. Which pair is correct?
A. A gradient of electrons and a membrane freely permeable to ATP
B. A high concentration of ATP and a permeable inner membrane
C. A proton gradient across a membrane and a membrane that is otherwise impermeable to protons except through the F₀ channel ✓ Correct
D. Free diffusion of protons across the whole membrane and the absence of any gradient
Solution: Chemiosmosis needs a proton gradient (built by the ETS) and a membrane through which protons return only via the F₀ channel of ATP synthase (F₁), whose F₁ head catalyses ATP formation.
Q12 — ETS & Oxidative Phosphorylation · medium · numerical
Assertion (A): The number of ATP molecules synthesised depends on the nature of the electron donor. Reason (R): Oxidation of one NADH gives about 3 ATP whereas oxidation of one FADH₂ gives about 2 ATP.
A. Both A and R are true but R is not the correct explanation of A
B. Both A and R are true and R is the correct explanation of A ✓ Correct
C. A is true but R is false
D. A is false but R is true
Solution: FADH₂ enters at Complex II and pumps fewer protons than NADH (which enters at Complex I), so FADH₂ yields ~2 ATP versus ~3 ATP for NADH — hence yield depends on the donor.
Q13 — ETS & Oxidative Phosphorylation · medium · numerical
A researcher applies cyanide, which blocks cytochrome c oxidase (Complex IV). Besides ATP synthesis stopping, what happens to NADH and the Krebs cycle?
A. FADH₂ takes over the role of oxygen and ATP synthesis continues
B. NADH is rapidly oxidised, speeding up the Krebs cycle
C. The Krebs cycle continues unaffected because it does not depend on the ETS
D. NADH cannot be reoxidised, so it accumulates and the Krebs cycle halts ✓ Correct
Solution: Blocking Complex IV stops electron flow, so NADH (and FADH₂) cannot be reoxidised to NAD⁺/FAD. Lacking oxidised coenzymes, the Krebs cycle and link reaction grind to a halt.
Q14 — ETS & Oxidative Phosphorylation · medium · numerical
What is the immediate energetic role of the electrons as they pass, step by step, down the electron transport chain?
A. Each transfer directly attaches a phosphate to ADP
B. Each transfer synthesises one molecule of NADH
C. Each transfer fixes one molecule of CO₂
D. The energy released at each transfer is used to pump protons across the inner mitochondrial membrane ✓ Correct
Solution: As electrons move to carriers of successively higher affinity, the released energy pumps protons, creating the electrochemical gradient that ATP synthase later uses — energy is not spent directly on making ATP at each carrier.
Q15 — ETS & Oxidative Phosphorylation · medium · numerical
The electron transport chain and ATP synthase are embedded in a specific membrane of the mitochondrion. Which membrane, and why is its large surface area important?
A. The outer membrane; its cristae hold the Krebs-cycle enzymes
B. The outer mitochondrial membrane; its smoothness allows faster proton diffusion
C. The inner membrane; its impermeability to O₂ concentrates oxygen
D. The inner mitochondrial membrane; its folding into cristae increases area for more ETS/ATP synthase complexes ✓ Correct
Solution: The ETS and ATP synthase reside in the inner mitochondrial membrane, whose infoldings (cristae) greatly enlarge the surface, accommodating more respiratory complexes and boosting ATP output.
Q16 — ETS & Oxidative Phosphorylation · medium · numerical
A single molecule of glucose is fully oxidised aerobically. Considering only the ETS/oxidative phosphorylation step and using the conventional values (NADH ≈ 3 ATP, FADH₂ ≈ 2 ATP), how many ATP arise from the 10 NADH and 2 FADH₂ delivered to the chain?
A. Thirty-four ATP ✓ Correct
B. Thirty-eight ATP
C. Thirty ATP
D. Thirty-six ATP
Solution: 10 NADH × 3 = 30 and 2 FADH₂ × 2 = 4, giving 34 ATP from oxidative phosphorylation. Adding the 4 substrate-level ATP (2 glycolysis + 2 Krebs) makes the classic total of 38.
Q17 — ETS & Oxidative Phosphorylation · medium · theory
What is the role of O2 in the respiration process? i. Acts in hydrogen removal from the system. ii. Acts as the final hydrogen acceptor. iii. It bonds with C atom and releases CO2.
A. iii only
B. All of the above
C. Both i and ii ✓ Correct
D. ii and iii
Solution: O2 is the final/terminal hydrogen (electron) acceptor and its removal of hydrogen keeps ETS running; CO2 is released by decarboxylation, not by O2, so iii is wrong.
Q18 — ETS & Oxidative Phosphorylation · easy · theory
The ATP synthesis in ETS of respiration is called
A. Oxidative photophosphorylation
B. Reductive phosphorylation
C. Substrate-level phosphorylation
D. Oxidative phosphorylation ✓ Correct
Solution: ATP formation coupled to electron transport in ETS is called oxidative phosphorylation.
Q19 — ETS & Oxidative Phosphorylation · medium · theory
Which among the following is wrong about ATP synthase? i. It is also called complex V. ii. It synthesises ATP using energy released during ETS. iii. It works on the basis of a proton gradient. iv. It consists of two major components, F1 and F0.
A. None of the above ✓ Correct
B. Both i and iii
C. Only ii
D. i and iv
Solution: All four statements about ATP synthase (complex V, proton-gradient driven, F1 and F0 parts) are correct, so none is wrong.
Q20 — ETS & Oxidative Phosphorylation · easy · theory
What is F1 in ATP synthase?
A. It contains a site for ATP production from ADP ✓ Correct
B. It contains a site for ADP synthesis from ATP
C. It acts as a channel through which protons cross the inner membrane
D. It contains a site for protein synthesis
Solution: The F1 head bears the catalytic site that synthesises ATP from ADP and inorganic phosphate.
Q21 — ETS & Oxidative Phosphorylation · easy · theory
What is the role of F0 in ATP synthase?
A. It acts as a channel through which electrons cross the inner membrane
B. It acts as a channel through which protons cross the inner membrane ✓ Correct
C. It is the site for ATP synthesis
D. It is a mobile protein carrier of electrons across the inner membrane
Solution: F0 is the membrane-embedded channel through which protons flow across the inner mitochondrial membrane.
Q22 — ETS & Oxidative Phosphorylation · medium · theory
For each ATP produced, ________ passes through F0 from the intermembrane space to the matrix down the electrochemical proton gradient.
A. 4H+
B. 2H+ ✓ Correct
C. 1H+
D. 3H+
Solution: NCERT states two protons pass through F0 for each ATP synthesised.
Q23 — ETS & Oxidative Phosphorylation · easy · theory
ETS occurs at which place?
A. Outer membrane of mitochondria
B. Inner membrane of mitochondria ✓ Correct
C. Matrix of mitochondria
D. Cytoplasm
Solution: The electron transport system is located on the inner mitochondrial membrane.
Q24 — ETS & Oxidative Phosphorylation · easy · theory
Energy stored in NADH + H+ and FADH2 is released in ETS through ________.
A. Phosphorylation of these molecules
B. Hydrolysis of these molecules
C. Reduction of these molecules
D. Oxidation of these molecules ✓ Correct
Solution: NADH and FADH2 are oxidised in the ETS, releasing their stored energy stepwise.
Q25 — ETS & Oxidative Phosphorylation · easy · theory
ETS stands for
A. Energy Transport System
B. Electrical Transport System
C. Electron Transport System ✓ Correct
D. Electron Transmission System
Solution: ETS = Electron Transport System.
Q26 — ETS & Oxidative Phosphorylation · easy · theory
When the electrons are passed on to O2 in ETS, it leads to the formation of
A. H2O ✓ Correct
B. ATP
C. NADH + H+
D. CO2
Solution: O2 accepts electrons and, with protons, is reduced to water.
Q27 — ETS & Oxidative Phosphorylation · easy · theory
Ubiquinone is located at ________.
A. Outer membrane of mitochondria
B. Inner membrane of nucleus
C. Matrix of mitochondria
D. Inner membrane of mitochondria ✓ Correct
Solution: Ubiquinone is a mobile carrier within the inner mitochondrial membrane.
Q28 — ETS & Oxidative Phosphorylation · medium · theory
Ubiquinone receives electrons from which of the following? i. From NADH produced in the mitochondrial matrix during TCA. ii. From FADH2 produced during oxidation of succinate in TCA.
A. Neither i nor ii
B. Only ii
C. Both i and ii ✓ Correct
D. Only i
Solution: Ubiquinone receives electrons from NADH (via complex I) and from FADH2 formed during succinate oxidation (via complex II).
Q29 — ETS & Oxidative Phosphorylation · easy · theory
Electrons from NADH produced during TCA are oxidised by which enzyme?
A. NAD+ hydrogenase
B. NADH dehydrogenase ✓ Correct
C. NAD+ hydroxylase
D. NADH dehydroxylase
Solution: NADH is oxidised by NADH dehydrogenase (complex I).
Q30 — ETS & Oxidative Phosphorylation · medium · theory
The reduced ubiquinone is also called
A. Ubiquinal
B. Ubiquinate
C. Ubiquinase
D. Ubiquinol ✓ Correct
Solution: Reduced ubiquinone is known as ubiquinol.