Respiration In Plants

The energy yield of aerobic respiration is tabulated in NCERT Class 11, Chapter 14 (Respiration in Plants). When one molecule of glucose is completely oxidised through glycolysis, the citric acid cycle and the electron transport system, the conventional theoretical calculation gives a net total of thirty-eight ATP molecules. This arises from a small direct yield by substrate-level phosphorylation in glycolysis and the Krebs cycle, plus a large contribution from oxidative phosphorylation as NADH and FADH2 are reoxidised in the electron transport chain. The option two represents the net ATP from glycolysis alone or the yield of fermentation, not complete oxidation. Fifteen does not correspond to any standard step total in this pathway. Thirty-six is the figure often quoted when the cost of shuttling cytoplasmic NADH into the mitochondria is deducted, but the classic NCERT-style maximum yield assumed under ideal conditions is thirty-eight. A numerical sanity check supports the answer: the bulk of ATP comes from roughly ten NADH and two FADH2 feeding the electron transport chain, which together account for the large majority of the thirty-eight total, while only four ATP arise directly through substrate-level phosphorylation in glycolysis and the Krebs cycle combined.