During aerobic respiration, molecular oxygen (o2) is used between the citric acid cycle and the electron transport chain to move nadh and fadh2 at the end of glycolysis to switch from the fermentation pathway between glycolysis and the citric acid cycle to split a carbon from pyruvic acid at the end of the citric acid cycle to cycle back to citric acid at the end of the electron transport chain to accept electrons and form h2o