Last Updated: May 2026
NEET 2027 — Respiration in Plants overview
For NEET 2027 Respiration in Plants (NCERT Class 11, Chapter 14), expect 1-2 questions in NEET-UG with high recall on enzyme names, reaction sites, ATP yield, and respiratory quotient. The chapter is one of the highest-leverage Plant Physiology units because much of the content overlaps with Human Physiology (cellular respiration in mitochondria) — meaning prep here pays off twice.
Stage Map of Aerobic Respiration in Plants
| Stage | Site | Substrate | Net ATP | Reduced Coenzymes |
|---|---|---|---|---|
| Glycolysis (EMP pathway) | Cytoplasm | Glucose → 2 Pyruvate | +2 ATP | 2 NADH |
| Pyruvate Oxidation | Mitochondrial matrix | 2 Pyruvate → 2 Acetyl-CoA | 0 | 2 NADH |
| Krebs / TCA Cycle | Mitochondrial matrix | 2 Acetyl-CoA → 4 CO₂ | +2 GTP/ATP | 6 NADH + 2 FADH₂ |
| ETS + Oxidative Phosphorylation | Inner mitochondrial membrane | NADH/FADH₂ → H₂O | +34 ATP (theoretical) | — |
| Total per glucose | — | — | ~38 ATP (theoretical) / 36 ATP (in eukaryotes due to NADH shuttle) | — |
Glycolysis — 10 Steps Compressed
- Glucose + ATP → Glucose-6-P (hexokinase)
- Glucose-6-P → Fructose-6-P (phosphoglucoisomerase)
- Fructose-6-P + ATP → Fructose-1,6-bisP (phosphofructokinase) [rate-limiting]
- F-1,6-BP → DHAP + G-3-P (aldolase)
- DHAP ↔ G-3-P (triose phosphate isomerase)
- 2 G-3-P + 2 NAD⁺ + 2 Pi → 2 1,3-BPG + 2 NADH
- 2 1,3-BPG → 2 3-PG + 2 ATP (substrate-level phosphorylation)
- 2 3-PG → 2 2-PG (phosphoglycerate mutase)
- 2 2-PG → 2 PEP + 2 H₂O (enolase)
- 2 PEP → 2 Pyruvate + 2 ATP (pyruvate kinase)
Net glycolysis: 1 Glucose → 2 Pyruvate + 2 ATP + 2 NADH (4 ATP gained, 2 ATP invested).
Krebs Cycle Quick Notes
- Acetyl-CoA + Oxaloacetate → Citrate (citrate synthase)
- Per acetyl-CoA: 3 NADH + 1 FADH₂ + 1 GTP/ATP + 2 CO₂
- Per glucose (2 acetyl-CoA): 6 NADH + 2 FADH₂ + 2 GTP + 4 CO₂
- Rate-limiting enzyme: isocitrate dehydrogenase
- Allosteric regulation by ATP (inhibits) and ADP/AMP (activates)
Electron Transport System (ETS)
| Complex | Function | Inhibitor |
|---|---|---|
| I (NADH-Q reductase) | NADH → Coenzyme Q | Rotenone |
| II (Succinate-Q reductase) | FADH₂ → Coenzyme Q | Malonate |
| III (Cytochrome bc₁) | Q → Cytochrome c | Antimycin A |
| IV (Cytochrome c oxidase) | Cyt c → O₂ | Cyanide, CO, Azide |
| V (ATP synthase) | Phosphorylates ADP | Oligomycin |
Per NADH oxidised: 2.5 ATP (some textbooks: 3 ATP, theoretical). Per FADH₂: 1.5 ATP (or 2 ATP theoretical). NCERT uses the older 3 ATP/NADH and 2 ATP/FADH₂ values, giving 38 ATP/glucose total — match this in MCQs unless specified.
Fermentation (Anaerobic)
- Alcoholic fermentation (yeast): Pyruvate → Acetaldehyde (pyruvate decarboxylase) → Ethanol + CO₂ (alcohol dehydrogenase)
- Lactic acid fermentation (muscle, bacteria): Pyruvate → Lactate (lactate dehydrogenase)
- Net ATP yield: 2 ATP per glucose (much lower than aerobic 36-38)
Respiratory Quotient (RQ)
RQ = Volume of CO₂ released / Volume of O₂ consumed
- Carbohydrates: RQ = 1.0
- Fats: RQ ≈ 0.7
- Proteins: RQ ≈ 0.9
- Organic acids (e.g., malic acid): RQ > 1
- Anaerobic respiration (alcohol fermentation): RQ = ∞ (no O₂ consumed)
Amphibolic Pathway
Respiration is amphibolic — both catabolic (breakdown) and anabolic (provides intermediates for biosynthesis). Examples: acetyl-CoA → fatty acid synthesis; α-ketoglutarate → glutamate (amino acid biosynthesis); succinyl-CoA → porphyrin synthesis.
40 Practice MCQs
- Glycolysis occurs in the — (A) mitochondrial matrix (B) cytoplasm (C) inner membrane (D) ribosome
- The end product of glycolysis is — (A) glucose (B) pyruvate (C) lactate (D) acetyl-CoA
- Net ATP yield in glycolysis is — (A) 2 (B) 4 (C) 6 (D) 8
- Rate-limiting enzyme of glycolysis — (A) hexokinase (B) PFK (C) pyruvate kinase (D) aldolase
- Pyruvate to acetyl-CoA reaction occurs in — (A) cytoplasm (B) mitochondrial matrix (C) Golgi (D) chloroplast
- Krebs cycle is also called — (A) Calvin cycle (B) TCA cycle (C) Cori cycle (D) Urea cycle
- How many CO₂ are released per turn of TCA — (A) 1 (B) 2 (C) 3 (D) 4
- Krebs cycle takes place in — (A) cytoplasm (B) mitochondrial matrix (C) chloroplast (D) inner membrane
- Total NADH per glucose in aerobic respiration — (A) 2 (B) 6 (C) 8 (D) 10
- FADH₂ produced per glucose — (A) 1 (B) 2 (C) 4 (D) 6
- Cyanide blocks — (A) Complex I (B) Complex II (C) Complex III (D) Complex IV
- Total ATP per glucose (NCERT theoretical) — (A) 30 (B) 36 (C) 38 (D) 42
- RQ of carbohydrate is — (A) 0.7 (B) 0.9 (C) 1.0 (D) ∞
- RQ of fat is approximately — (A) 0.7 (B) 1.0 (C) 1.5 (D) ∞
- Alcoholic fermentation produces — (A) lactate (B) ethanol + CO₂ (C) acetate (D) butyrate
- Substrate-level phosphorylation in TCA produces — (A) ATP (B) GTP (C) NADH (D) FADH₂
- The first stable C6 compound in glycolysis — (A) Glucose-6-P (B) Fructose-6-P (C) F-1,6-BP (D) Pyruvate
- Aerobic respiration uses — (A) NAD⁺ (B) O₂ (C) Cyt c (D) all of the above
- The terminal electron acceptor in ETS — (A) NAD⁺ (B) FAD (C) Cyt c (D) O₂
- ATP synthase is on — (A) outer mitochondrial membrane (B) inner mitochondrial membrane (C) matrix (D) intermembrane space
- Anaerobic respiration in muscle produces — (A) ethanol (B) lactate (C) acetate (D) succinate
- The “amphibolic pathway” means — (A) only catabolic (B) only anabolic (C) both (D) neither
- Photorespiration occurs in — (A) C3 plants (B) C4 plants (C) CAM plants (D) all plants equally
- Rubisco’s affinity for O₂ vs CO₂ leads to — (A) photorespiration (B) C4 cycle (C) CAM (D) Krebs
- Photorespiration is highest at — (A) low temperature (B) high temperature, low CO₂ (C) low light (D) low temp, high CO₂
- Mitochondrion’s inner membrane is folded into — (A) thylakoids (B) cristae (C) granum (D) matrix
- Number of carbon atoms in pyruvate — (A) 2 (B) 3 (C) 4 (D) 6
- Number of carbon atoms in acetyl-CoA — (A) 2 (B) 3 (C) 4 (D) 6
- Citrate is a — (A) C4 (B) C5 (C) C6 (D) C7
- α-ketoglutarate is a — (A) C4 (B) C5 (C) C6 (D) C7
- The chemiosmotic hypothesis was proposed by — (A) Calvin (B) Mitchell (C) Krebs (D) Lipmann
- NADH in cytoplasm shuttles into mitochondria via — (A) malate-aspartate shuttle (B) citrate-pyruvate shuttle (C) glycerol-3P shuttle (D) both A and C
- Each NADH yields how many ATP (NCERT) — (A) 1 (B) 2 (C) 3 (D) 4
- Each FADH₂ yields how many ATP (NCERT) — (A) 1 (B) 2 (C) 3 (D) 4
- In yeast, alcoholic fermentation enzyme — (A) lactate dehydrogenase (B) alcohol dehydrogenase (C) hexokinase (D) PFK
- The number of ATP produced in fermentation per glucose — (A) 0 (B) 2 (C) 6 (D) 38
- The H⁺ pumping in ETS creates — (A) electrochemical gradient (B) osmotic gradient (C) chemical gradient only (D) no gradient
- ATP synthase requires — (A) ADP + Pi (B) AMP + Pi (C) ADP only (D) Pi only
- The largest ETS complex — (A) I (B) II (C) III (D) IV
- Decoupling of oxidative phosphorylation is caused by — (A) DNP (2,4-dinitrophenol) (B) NaCN (C) Rotenone (D) Oligomycin
Answer Key
1-B, 2-B, 3-A, 4-B, 5-B, 6-B, 7-B, 8-B, 9-D, 10-B, 11-D, 12-C, 13-C, 14-A, 15-B, 16-B, 17-A, 18-D, 19-D, 20-B, 21-B, 22-C, 23-A, 24-A, 25-B, 26-B, 27-B, 28-A, 29-C, 30-B, 31-B, 32-D, 33-C, 34-B, 35-B, 36-B, 37-A, 38-A, 39-A, 40-A
FAQ
How many questions from Respiration in Plants in NEET 2027?
Typically 1–2 questions, often combined with cellular respiration overlap from Class 11. NCERT one-line statements are tested heavily.
Should I memorise all 10 steps of glycolysis for NEET?
Memorise enzyme names of rate-limiting (PFK), substrate-level phosphorylation steps (1,3-BPG → 3-PG and PEP → Pyruvate), and ATP-investment vs ATP-yield steps. Full step-by-step is rarely tested.
What is the difference between RQ and TR for NEET?
RQ = CO₂/O₂ ratio; varies with substrate (1.0 for carbohydrate, 0.7 for fat, ~0.9 for protein, >1 for organic acids, ∞ for anaerobic).
Total ATP per glucose for NEET — 36 or 38?
NCERT uses 38 ATP (theoretical, with 3 ATP per NADH and 2 ATP per FADH₂). Modern textbooks revise to 30–32 ATP, but NEET marks 38 unless the question specifies otherwise.