In the presence of oxygen, one glucose molecule has the energy to make up to 38 ATP. The ATP production is determined by the following steps, (-2 ATP) glycolysis preparatory phase, (7-9 ATP) glycolysis pay-off phase, (5 ATP) oxidative decarboxylation of pyruvate and (20 ATP) Krebs cycle. One glucose which has 38 ATP hence was the summation of all the process mentioned that took place. All these process take place under the cellular function of cellular respiration.
