The main source of energy for aerobic respiration is glucose. During this metabolic process, glucose is oxidized in the presence of oxygen to produce ATP, water, and carbon dioxide. The energy derived from glucose is harnessed in stages: glycolysis, the citric acid cycle, and oxidative phosphorylation, each contributing to ATP production. Aerobic respiration is much more efficient than anaerobic processes, generating significantly more ATP per glucose molecule. This energy is essential for a range of cellular activities, sustaining life.