Cellular respiration consists of several stages, but the two main stages that produce carbon dioxide are the citric acid cycle, also known as the Krebs cycle, and pyruvate oxidation.
During pyruvate oxidation, which occurs in the mitochondria, pyruvate produced from glycolysis is converted into acetyl-CoA. This process releases one molecule of carbon dioxide for each pyruvate molecule. Since glycolysis produces two pyruvate molecules from each glucose, a total of two carbon dioxide molecules are released during this step.
The citric acid cycle further processes acetyl-CoA. Throughout this cycle, which takes place in the mitochondrial matrix, two additional carbon dioxide molecules are released for each acetyl-CoA that enters. Thus, for each glucose molecule, a total of four carbon dioxide molecules are produced: two from pyruvate oxidation and two from the citric acid cycle.
After carbon dioxide is produced, it is transported out of the cells into the bloodstream. From there, it moves to the lungs, where it is exhaled. This removal of carbon dioxide is essential, as high concentrations of carbon dioxide in the body can lead to respiratory acidosis and other health issues.