Simulation · Biology · Class 11

The ATP ledger for one glucose

From the lesson The respiratory balance sheet in Respiration in Plants. Change the values and watch what happens.

The idea behind it

NCERT §12.5

The net ATP from one glucose can be calculated, but only as a theoretical exercise resting on four assumptions.
Assumption one: the pathway runs as one orderly sequence, glycolysis then the TCA cycle then the ETS, each substrate forming the next.
Assumption two: the NADH made in glycolysis is moved into the mitochondria and undergoes oxidative phosphorylation.
Assumption three: no intermediate is drawn off to make another compound. Assumption four: only glucose is respired, with no other substrate entering at any intermediate stage.
None of these holds in a living cell: all the pathways run at once, substrates enter and leave as needed, ATP is used as needed, and enzyme rates are controlled in many ways.
On these assumptions the net gain is 38 ATP per glucose in aerobic respiration: 10 NADH × 3 = 30, 2 FADH₂ × 2 = 4, plus 2 net ATP from glycolysis and 2 from the TCA cycle.
Fermentation, by contrast, nets only 2 ATP per glucose.

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