Respiration in PlantsNEET MCQs with solutions
Respiration in Plants traces glucose through glycolysis, fermentation, the link reaction, the Krebs cycle and the electron transport system. NEET questions test where each step happens, how many NADH, FADH₂, ATP and CO₂ are made, and respiratory quotients of different substrates.
- Class
- 11 Biology
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- 24 questions
- In the RankUp app
- 441 questions
- ELITE questions
- 31
- NCERT topics
- 9
Practise 24 questions
Tap an option to check it. Questions from every NCERT topic in this chapter, from easy to hard.
Q1Introduction to Respiration
Glycolysis occurs in the:
Not quite — the answer is D.
Glycolysis is a cytoplasmic process requiring no membrane-bound organelle — this is why it is common to both aerobic and anaerobic organisms. All subsequent aerobic steps occur inside mitochondria.
Q2Introduction to Respiration
Anaerobic respiration in yeast produces:
Not quite — the answer is A.
Yeast ferments pyruvate to ethanol and CO₂ via alcoholic fermentation. Lactic acid is the anaerobic product in animal muscle, not yeast — a classic NEET trap. Water is not a direct product of fermentation.
Q3Glycolysis
The net gain of NADH molecules during glycolysis per glucose molecule is:
Not quite — the answer is A.
Two molecules of G3P are oxidized (one from each triose), each reducing one NAD⁺ to NADH — yielding 2 NADH total per glucose. 4 NADH is a common wrong answer from students who confuse glycolysis yield with Krebs cycle yield.
Q4Glycolysis
Pyruvate kinase catalyzes the conversion of phosphoenolpyruvate (PEP) to pyruvate, resulting in:
Not quite — the answer is B.
PEP donates its phosphate to ADP forming ATP (substrate-level phosphorylation) and pyruvate. Option A reverses the reaction — PEP is the substrate, not the product. This is the second substrate-level phosphorylation step per triose.
Q5Glycolysis
Which step of glycolysis is considered the major regulatory and rate-limiting step?
Not quite — the answer is C.
PFK-1 is the primary regulatory enzyme of glycolysis — it is allosterically inhibited by ATP and citrate, and activated by AMP. Option D (pyruvate kinase) is also irreversible and regulated, but PFK-1 is the committed, rate-limiting step. This distinction is the NEET trap.
Q6Fermentation
Fermentation occurs in the:
Not quite — the answer is B.
Fermentation is entirely cytoplasmic — both glycolysis and the subsequent fermentation steps use cytosolic enzymes. The mitochondrion is not involved at any stage of fermentation.
Q7Fermentation
During alcoholic fermentation, CO₂ is released at which step?
Not quite — the answer is C.
CO₂ is released specifically during the pyruvate decarboxylase step (pyruvate → acetaldehyde). It is NOT released during reduction of acetaldehyde to ethanol. Option D is a trap — glycolysis does not release CO₂ (all 6 carbons of glucose are conserved in two pyruvates).
Q8Link Reaction
The total NADH produced from the link reaction per glucose molecule is:
Not quite — the answer is C.
One glucose yields two pyruvate molecules; each pyruvate produces 1 NADH in the link reaction → 2 NADH per glucose. 4 NADH is the Krebs cycle yield — a frequent confusion in ATP/NADH accounting questions.
Q9Link Reaction
The enzyme complex that catalyzes the link reaction is:
Not quite — the answer is D.
The pyruvate dehydrogenase complex (PDC) catalyzes oxidative decarboxylation of pyruvate. Pyruvate kinase catalyzes the last step of glycolysis (PEP → Pyruvate) — the most dangerous distractor because it also acts on pyruvate, but produces it rather than processing it.
Q10Krebs Cycle
The total CO₂ released per glucose molecule from the Krebs cycle is:
Not quite — the answer is D.
Two CO₂ per turn × 2 turns per glucose = 4 CO₂ from Krebs cycle alone. Combined with 2 CO₂ from the link reaction, total CO₂ per glucose = 6 — matching the 6 carbons of glucose (complete oxidation). Option A is a trap for students who count only one turn.
Q11Krebs Cycle
The enzyme that catalyzes the first step of the Krebs cycle is:
Not quite — the answer is D.
Citrate synthase catalyzes condensation of acetyl-CoA + OAA → citrate. Aconitase acts in the second step (citrate → isocitrate) — the most plausible wrong answer since it also acts on citrate, just not to form it.
Q12Krebs Cycle
The oxidation of isocitrate to alpha-ketoglutarate produces:
Not quite — the answer is B.
Isocitrate dehydrogenase catalyzes both an oxidation (NAD⁺ → NADH) and a decarboxylation (one CO₂ released) simultaneously — making this step structurally analogous to the link reaction. Option D is the most dangerous distractor: students recall NADH but forget the CO₂.
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Get RankUp on Google PlayQ13Electron Transport Chain
During the electron transport chain, protons are actively pumped into the:
Not quite — the answer is B.
Complexes I, III, and IV function as proton pumps, translocating H⁺ from the matrix into the intermembrane space, creating the electrochemical gradient. Complex II does NOT pump protons — this is a critical distinction. The proton gradient (matrix = low H⁺, intermembrane space = high H⁺) drives ATP synthase.
Q14Electron Transport Chain
The immediate driving force for ATP synthesis by ATP synthase is:
Not quite — the answer is C.
The proton motive force — combining the pH gradient and membrane potential — drives protons through ATP synthase, powering ATP synthesis. Electrons do not flow through ATP synthase itself. Oxygen is the terminal electron acceptor at Complex IV, not a direct driver of ATP synthase.
Q15Electron Transport Chain
Which of the following correctly distinguishes Complex I from Complex II in the ETC?
Not quite — the answer is A.
Complex I (NADH dehydrogenase) oxidizes NADH and pumps 4H⁺ per electron pair into the intermembrane space. Complex II (succinate dehydrogenase) oxidizes FADH₂ but does NOT pump any protons — this is why FADH₂ yields less ATP than NADH. This is the most commonly confused distinction in ETC questions.
Q16Respiratory Balance Sheet
Total CO₂ molecules released per glucose during complete aerobic respiration is:
Not quite — the answer is D.
Two CO₂ are released per pyruvate during the link reaction (2 pyruvate × 1 CO₂ = 2), and four CO₂ are released per glucose during two turns of the Krebs cycle (2 turns × 2 CO₂ = 4), totaling 6 CO₂. No CO₂ is released during glycolysis.
Q17Respiratory Balance Sheet
As per NCERT Class 11 respiratory balance sheet, oxidation of one FADH₂ in the ETC yields how many ATP?
Not quite — the answer is A.
NCERT Class 11 uses the older P/O ratio: 1 FADH₂ = 2 ATP. The revised chemiosmotic value is 1.5 ATP, but NCERT balance sheet uses 2 ATP. Since FADH₂ enters at Complex II (bypassing Complex I), fewer protons are pumped, yielding less ATP than NADH.
Q18Respiratory Balance Sheet
The actual ATP yield in living cells is lower than the theoretical maximum because:
Not quite — the answer is C.
The theoretical yield assumes 100% coupling efficiency and no proton leakage. In reality, some protons leak across the inner mitochondrial membrane without passing through ATP synthase, and cytoplasmic NADH requires shuttle systems (malate-aspartate or glycerol-3-phosphate) that have energy costs. These reduce actual yield to ~30–32 ATP.
Q19Amphibolic Nature of Respiration
A metabolic pathway that serves both catabolic and anabolic functions is called:
Not quite — the answer is A.
An amphibolic pathway participates in both breakdown (catabolism) and synthesis (anabolism). Option B (anaplerotic) refers specifically to reactions that replenish Krebs cycle intermediates — it is a subset concept, not a synonym for amphibolic.
Q20Amphibolic Nature of Respiration
Fatty acids are integrated into the respiratory pathway after being converted into:
Not quite — the answer is C.
Fatty acids undergo β-oxidation in the mitochondrial matrix, progressively cleaved into 2-carbon units released as acetyl-CoA, which then enters the Krebs cycle. Option B is a trap — pyruvate comes from glucose catabolism, not fatty acid breakdown. Fatty acids do not produce pyruvate.
Q21Amphibolic Nature of Respiration
Succinyl-CoA, an intermediate of the Krebs cycle, is a precursor for the synthesis of:
Not quite — the answer is A.
Succinyl-CoA is a key precursor for porphyrin biosynthesis — including heme (in hemoglobin and cytochromes) and chlorophyll. This is a high-value amphibolic connection. Option B is a trap — succinyl-CoA cannot directly enter gluconeogenesis in animals as it cannot yield net oxaloacetate.
Q22Respiratory Quotient
If equal volumes of CO₂ are evolved and O₂ are consumed during respiration, the substrate being utilized is most likely:
Not quite — the answer is C.
Equal CO₂ and O₂ volumes give RQ = 1, which is the hallmark of carbohydrate oxidation. Option A (fat) gives RQ ~0.7; Option B (protein) ~0.8; Option D (organic acid) > 1.
Q23Respiratory Quotient
RQ value greater than 1 indicates respiration of:
Not quite — the answer is D.
Organic acids are already partially oxidized and oxygen-rich; they require less external O₂ relative to the CO₂ released, giving RQ > 1. Option C (carbohydrates) is wrong — RQ for carbs = 1 exactly.
Q24Respiratory Quotient
The balanced equation for oxidation of tripalmitin (a fat) is: 2C₅₁H₉₈O₆ + 145O₂ → 102CO₂ + 98H₂O. The RQ of tripalmitin is approximately:
Not quite — the answer is B.
RQ = CO₂/O₂ = 102/145 ≈ 0.703 ≈ 0.7. This is the standard NEET PYQ calculation for fat RQ. Option A (1) is the carbohydrate trap; Option D (0.5) represents an even more reduced substrate.
ELITE question · AIR under 50 level
This chapter has 31 ELITE questions for students aiming at the very top. They are only in the app.
Unlock ELITE questions in the appRespiration: where, what and how much
Quick revision: most questions in this chapter test these facts.
| Step | Key fact |
|---|---|
| Glycolysis (EMP pathway) | Embden, Meyerhof and Parnas; in the cytoplasm; glucose → 2 pyruvate; net 2 ATP and 2 NADH |
| Alcoholic fermentation | Yeast: pyruvic acid decarboxylase and alcohol dehydrogenase → ethanol + CO₂; yeast is poisoned at about 13% alcohol |
| Lactic acid fermentation | Muscles: lactate dehydrogenase reduces pyruvate to lactic acid |
| Link reaction | In the mitochondrial matrix; pyruvate dehydrogenase needs Mg²⁺, NAD⁺ and coenzyme A; makes acetyl CoA, CO₂ and NADH |
| Krebs (TCA) cycle | Acetyl CoA + oxaloacetic acid → citric acid (citrate synthase); per turn: 3 NADH, 1 FADH₂, 1 ATP/GTP, 2 CO₂ |
| Electron transport system | Inner mitochondrial membrane; complex I (NADH dehydrogenase), complex II (FADH₂), ubiquinone, cytochrome c, complex IV (cytochrome c oxidase); oxygen is the final acceptor |
| ATP synthase | Complex V with F₀ (proton channel) and F₁ (makes ATP) |
| ATP yield (NCERT) | NADH → 3 ATP; FADH₂ → 2 ATP; net 38 ATP per glucose in aerobic respiration |
| Amphibolic pathway | Respiration both breaks down (catabolism) and supplies building blocks (anabolism) |
| RQ of carbohydrates | 1 |
| RQ of fats | Less than 1 — tripalmitin about 0.7 |
| RQ of proteins | About 0.9 |
| RQ of organic acids | More than 1 |
What the app covers in this chapter
441 questions in total, each with a detailed explanation.
| Introduction to Respiration | 20 |
| Glycolysis | 40 |
| Fermentation | 21 |
| Link Reaction | 19 |
| Krebs Cycle | 19 |
| Electron Transport Chain | 20 |
| Respiratory Balance Sheet | 21 |
| Amphibolic Nature of Respiration | 21 |
| Respiratory Quotient | 21 |
| Mixed practice and chapter tests | 239 |
Questions students ask
Is Respiration in Plants important for NEET?
Yes. It is a numbers-heavy Botany chapter. Most questions test the site of each step, the count of NADH, FADH₂, ATP and CO₂ per glucose, the enzymes of fermentation and the RQ of different substrates.
Which topics should I revise first?
Start with where each step happens and what it produces (use the table on this page), then the electron transport system and ATP count, and finish with the amphibolic pathway and respiratory quotient.
How many questions from this chapter are on RankUp?
The RankUp app has 441 questions on Respiration in Plants, including 31 ELITE questions written for students aiming at AIR under 50. Every question has a detailed explanation.
Can I download these questions as a PDF?
Yes. The free PDF on this page has all 24 questions with the answer key and explanations. No signup is needed.
