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Respiration in Plants — NEET Biology MCQs with Solutions
Free NEET Biology Respiration in Plants MCQs with step-by-step solutions covering Cellular Respiration & Glycolysis, Fermentation (Anaerobic), Aerobic Respiration & Krebs Cycle, ETS & Oxidative Phosphorylation, Respiratory Balance Sheet & RQ. Practise online on Prepizo — no login needed.
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Sample questions with solutions
Q1 — Cellular Respiration & Glycolysis · easy · theory
Glycolysis (the EMP pathway) occurs in the ______ of the cell:
A. Mitochondrial matrix
B. Cytoplasm ✓ Correct
C. Inner mitochondrial membrane
D. Nucleus
Solution: Glycolysis takes place in the cytoplasm and is common to both aerobic and anaerobic respiration.
Q2 — Cellular Respiration & Glycolysis · easy · theory
The end product of glycolysis is:
A. Pyruvic acid (pyruvate) ✓ Correct
B. Acetyl CoA
C. Lactic acid
D. Ethanol
Solution: One glucose (6-C) is split into two molecules of pyruvate (3-C) during glycolysis.
Q3 — Fermentation (Anaerobic) · easy · theory
In yeast, anaerobic respiration (fermentation) converts pyruvate to:
A. Water
B. Ethanol and CO₂ ✓ Correct
C. Lactic acid
D. Acetyl CoA
Solution: Yeast performs alcoholic fermentation: pyruvate → acetaldehyde → ethanol + CO₂.
Q4 — Fermentation (Anaerobic) · easy · theory
In our muscle cells during vigorous exercise, pyruvate is converted to ______ under low oxygen:
A. CO₂ and water
B. Glucose
C. Ethanol
D. Lactic acid ✓ Correct
Solution: Lack of O₂ forces lactic acid fermentation in muscles, regenerating NAD⁺ for glycolysis.
Q5 — Aerobic Respiration & Krebs Cycle · easy · theory
The Krebs cycle (citric acid cycle / TCA cycle) takes place in the:
A. Cytoplasm
B. Ribosome
C. Mitochondrial matrix ✓ Correct
D. Outer mitochondrial membrane
Solution: The TCA cycle operates in the mitochondrial matrix; the ETS is on the inner membrane.
Q6 — Aerobic Respiration & Krebs Cycle · easy · theory
Before entering the Krebs cycle, pyruvate is converted to ______ by oxidative decarboxylation:
A. Lactate
B. Oxaloacetate
C. Citrate
D. Acetyl CoA ✓ Correct
Solution: Pyruvate dehydrogenase converts pyruvate to acetyl CoA, releasing CO₂ and forming NADH.
Q7 — 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).
Q8 — 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.
Q9 — Respiratory Balance Sheet & RQ · easy · theory
The ratio of the volume of CO₂ evolved to O₂ consumed in respiration is called the:
A. Compensation point
B. Metabolic rate
C. Photosynthetic quotient
D. Respiratory Quotient (RQ) ✓ Correct
Solution: RQ = volume of CO₂ released / volume of O₂ used, and depends on the respiratory substrate.
Q10 — Respiratory Balance Sheet & RQ · easy · theory
When carbohydrates are the respiratory substrate, the RQ is:
A. 0.7
B. 1.0 ✓ Correct
C. Infinity
D. 0.9
Solution: For carbohydrates (e.g. glucose), CO₂ produced = O₂ consumed, so RQ = 1.
Q11 — Cellular Respiration & Glycolysis · hard · theory
Substrate-level phosphorylation in glycolysis refers to:
A. Direct transfer of a phosphate from a substrate to ADP forming ATP ✓ Correct
B. ATP made via the ETS
C. Phosphorylation using light
D. Chemiosmotic ATP synthesis
Solution: In glycolysis, ATP is produced directly from high-energy intermediates (e.g. 1,3-BPG, PEP), not via the ETS.
Q12 — Cellular Respiration & Glycolysis · hard · theory
In glycolysis, the oxidation of glyceraldehyde-3-phosphate reduces:
A. NADP⁺ to NADPH
B. O₂ to water
C. FAD to FADH₂
D. NAD⁺ to NADH ✓ Correct
Solution: The dehydrogenation of G3P (to 1,3-BPG) reduces NAD⁺ to NADH + H⁺.
Q13 — Fermentation (Anaerobic) · hard · theory
Both alcoholic and lactic acid fermentation are hazardous because:
A. They produce too much ATP
B. Less than 7% of the energy in glucose is released and not all of it is trapped as ATP ✓ Correct
C. They consume oxygen
D. They release only water
Solution: Fermentation is energetically inefficient (only ~2 ATP) and yields incompletely oxidised, sometimes toxic, products.
Q14 — Fermentation (Anaerobic) · hard · theory
The enzyme pyruvic acid decarboxylase and alcohol dehydrogenase are required in ______ fermentation:
A. Alcoholic (yeast) ✓ Correct
B. Photorespiratory
C. Lactic acid
D. Aerobic
Solution: Alcoholic fermentation needs pyruvate decarboxylase (→ acetaldehyde) and alcohol dehydrogenase (→ ethanol).
Q15 — Aerobic Respiration & Krebs Cycle · hard · theory
Per glucose molecule, complete oxidation via glycolysis + Krebs cycle produces how many NADH in total (before ETS)?
A. 10 NADH ✓ Correct
B. 4 NADH
C. 2 NADH
D. 6 NADH
Solution: Glycolysis (2) + pyruvate→acetyl CoA (2) + Krebs (6) = 10 NADH, plus 2 FADH₂, per glucose.
Q16 — Aerobic Respiration & Krebs Cycle · hard · theory
The only ATP produced directly (substrate-level) within the Krebs cycle is at the step:
A. Malate → OAA
B. Succinyl CoA → Succinate (forming GTP/ATP) ✓ Correct
C. Fumarate → Malate
D. Citrate → Isocitrate
Solution: Succinyl CoA synthetase makes one GTP (≈ATP) by substrate-level phosphorylation.
Q17 — 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).
Q18 — 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.
Q19 — Respiratory Balance Sheet & RQ · hard · theory
An RQ greater than 1 (or approaching infinity) is characteristic of ______ respiration:
A. Protein
B. Fat
C. Anaerobic (fermentation, where CO₂ is released without O₂ uptake) ✓ Correct
D. Aerobic carbohydrate
Solution: In anaerobic respiration CO₂ is released while O₂ is not consumed, so RQ > 1 (or infinite).
Q20 — Respiratory Balance Sheet & RQ · hard · theory
The assumptions in the standard respiratory balance sheet (38 ATP) include all EXCEPT:
A. ATP is used only when required
B. Glycolysis, TCA and ETS pathways operate at different times in a stepwise sequential manner ✓ Correct
C. NADH is oxidised via the ETS
D. A sequential, orderly pathway with one substrate
Solution: In reality the pathways occur simultaneously and are not neatly sequential, so the 38-ATP figure is a theoretical maximum.
Q21 — Cellular Respiration & Glycolysis · medium · theory
The net gain of ATP and NADH per glucose in glycolysis is:
A. 8 ATP and 2 NADH
B. 2 ATP and 4 NADH
C. 4 ATP and 4 NADH
D. 2 ATP and 2 NADH ✓ Correct
Solution: Glycolysis uses 2 ATP and makes 4 (net 2 ATP) plus 2 NADH per glucose molecule.
Q22 — Cellular Respiration & Glycolysis · medium · theory
The enzyme-catalysed first committed step where glucose is phosphorylated uses:
A. ATP (converting glucose to glucose-6-phosphate) ✓ Correct
B. Inorganic phosphate only
C. NADH
D. FADH₂
Solution: Glucose is phosphorylated to glucose-6-phosphate using ATP — one of two priming (investment) steps.
Q23 — Fermentation (Anaerobic) · medium · theory
The purpose of fermentation (reducing pyruvate) is to:
A. Fix carbon dioxide
B. Regenerate NAD⁺ so that glycolysis can continue ✓ Correct
C. Produce large amounts of ATP
D. Synthesise glucose
Solution: Fermentation reoxidises NADH back to NAD⁺, allowing glycolysis to keep making its small ATP yield without O₂.
Q24 — Fermentation (Anaerobic) · medium · theory
The net ATP yield per glucose in fermentation is only ______, because:
A. 4 ATP; ETS runs
B. 38 ATP; O₂ is used
C. 2 ATP; glucose is only partially oxidised ✓ Correct
D. 36 ATP; glucose is fully oxidised
Solution: Without the Krebs cycle and ETS, only the 2 ATP of glycolysis are gained — glucose is not fully broken down.
Q25 — Aerobic Respiration & Krebs Cycle · medium · theory
The compound with which acetyl CoA combines to start the Krebs cycle, forming citrate, is:
A. Succinate
B. Fumarate
C. Oxaloacetic acid (OAA) ✓ Correct
D. Malate
Solution: Acetyl CoA (2-C) condenses with OAA (4-C) to form citric acid (6-C), regenerating CoA.
Q26 — Aerobic Respiration & Krebs Cycle · medium · theory
For each turn of the Krebs cycle, the number of CO₂ molecules released and NADH produced is:
A. 3 CO₂ and 2 NADH
B. 2 CO₂ and 3 NADH ✓ Correct
C. 1 CO₂ and 1 NADH
D. 2 CO₂ and 1 NADH
Solution: One TCA turn releases 2 CO₂ and yields 3 NADH, 1 FADH₂ and 1 GTP (ATP).
Q27 — 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).
Q28 — 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.
Q29 — Respiratory Balance Sheet & RQ · medium · theory
For fats as the respiratory substrate, the RQ is:
A. Less than 1 (about 0.7) ✓ Correct
B. Equal to 1
C. Exactly 0
D. Greater than 1
Solution: Fats need more O₂ (they are less oxidised), giving RQ ≈ 0.7.
Q30 — Respiratory Balance Sheet & RQ · medium · theory
The amphibolic nature of the respiratory pathway means it:
A. Does not involve intermediates
B. Only builds molecules
C. Is only catabolic
D. Serves in both breakdown (catabolism) and synthesis (anabolism) ✓ Correct
Solution: Respiratory intermediates (e.g. acetyl CoA, OAA) are drawn off to synthesise fats, amino acids, etc. — hence amphibolic.