Aerobic respiration proceeds in a series of steps, which also increases efficiency-since glucose is broken down gradually and ATP is produced as needed, less energy is wasted as heat. This strategy results in the waste products H 2 O and CO 2 being formed in different amounts at different phases of respiration. CO 2 is formed in Pyruvate decarboxylation, H 2 O is formed in oxidative phosphorylation, and both are formed in the citric acid cycle.