When oxygen is present, aerobic cellular respiration takes place. This process can be divided into three main phases: glycolysis, the Krebs cycle (sometimes called the tricarboxylic acid, TCA cycle, or citric acid cycle), and the electron transport chain. As by-products, CO2 and H2O are produced, which leave the body via respiration, urination and perspiration. ATP are produced during all three of the phases, and the maximum yield for aerobic respiration is 38 ATP.

The general equation for the cellular respiration process is:

Glucose (C6H12O6) + 6 O2 + 38 ADP → 6 CO2 + 6 H2O + 38 ATP + heat

Steps in aerobic cellular respiration. Within a cell, carbohydrates are broken down to glucose. Glucose undergoes glycolysis to produce pyruvate, which enters the mitochondria. In the presence of oxygen, aerobic respiration proceeds. The pyruvate becomes acetyl Co A and enters the krebs cycle. Krebs cycle products carry over to the electron transport chain, where oxygen is the final electron receptor. NADH produced during glycolysis also enters the electron transport chain.

Figure: Overview of the aerobic cellular respiration process.