Respiration in Plants: Core NEET Facts

Overall equation: $C_{6}H_{12}O_{6}$ + $6O_{2}$ → $6CO_{2}$ + $6H_{2}O$ + 38 ATP (or 36 ATP with glycerol-3-phosphate shuttle)
Glycolysis: Cytoplasm; 10 steps; no $O_{2}$ required; common to all cells; net yield = 2 ATP + 2 NADH per glucose; rate-limiting enzyme = phosphofructokinase (PFK); substrate-level phosphorylation at steps 7 and 10
Fermentation (anaerobic): Cytoplasm only; yields only 2 ATP per glucose (from glycolysis); purpose = regenerate N $AD^{+}$ $A D^{+}$ from NADH
- Alcoholic (yeast/Saccharomyces): pyruvate → ethanol + C $O_{2}$ (enzymes: pyruvate decarboxylase, alcohol dehydrogenase)
- Lactic acid (muscles/Lactobacillus): pyruvate → lactate (enzyme: lactate dehydrogenase)
Oxidative decarboxylation: Mitochondrial matrix; pyruvate dehydrogenase complex (requires TPP, N $AD^{+}$ , CoA); per glucose = 2 C $O_{2}$ + 2 NADH + 2 acetyl CoA
TCA cycle: Mitochondrial matrix; 8 steps; per glucose (2 turns) = 6 NADH + 2 $FADH_{2}$ + 2 GTP + 4 C $O_{2}$ ; first product = citrate; amphibolic pathway
ETS: Inner mitochondrial membrane; NADH enters at Complex I (→ 3 ATP); $FADH_{2}$ enters at Complex II (→ 2 ATP; bypasses Complex I); final electron acceptor = $O_{2}$ ; water formed at Complex IV; proton pumping by Complexes I, III, IV
Mobile carriers in ETS: Ubiquinone/CoQ (lipid-soluble, between CI/CII and CIII); cytochrome c (water-soluble, between CIII and CIV)
Chemiosmosis: Proton gradient across inner mitochondrial membrane drives $F_{0}$ - $F_{1}$ ATP synthase; proposed by Peter Mitchell (1961, Nobel 1978)
ATP yield: Glycolysis = 2 ATP; link reaction (via 2 NADH) = 6 ATP; TCA (via 6 NADH + 2 $FADH_{2}$ + 2 GTP) = 24 ATP; Grand total = 38 ATP
TCA cycle intermediates (8): Citrate → Isocitrate → α-Ketoglutarate → Succinyl CoA → Succinate → Fumarate → Malate → OAA (mnemonic: "Can I Keep Selling Succulent Fruits Making Oranges")
C $O_{2}$ released: Glycolysis = 0; Link reaction = 2 C $O_{2}$ ; TCA cycle = 4 C $O_{2}$ ; Total = 6 C $O_{2}$ per glucose
RQ values: Carbohydrates = 1.0; Fats ≈ 0.7; Proteins ≈ 0.8; Organic acids ≈ 1.33; CAM plants (night) = ∞
Amphibolic pathway: TCA cycle — both catabolic (energy) and anabolic (OAA → aspartate; α-KG → glutamate; acetyl CoA → fatty acids)