Final answer:
CO2 is produced during the stages of cellular respiration when pyruvate is oxidized to acetyl-CoA and during the Krebs cycle. The Krebs cycle is where most of the CO2 waste is generated as pyruvate is fully oxidized, and FADH2 is one of the energy carriers produced in this cycle.
Step-by-step explanation:
During cellular respiration, CO2 is produced during the oxidation of pyruvate to acetyl-CoA and the Krebs cycle. Specifically, CO2 is released when pyruvate, a product of glycolysis, is converted into acetyl-CoA before entering the Krebs cycle, and additionally, CO2 is produced as a waste product during the Krebs cycle itself. The Krebs cycle, a major part of cellular respiration, takes place in the matrix of a mitochondrion and plays a crucial role in the biochemical pathway of aerobic respiration. It is during the Krebs cycle that the carbon atoms from the acetyl group in acetyl-CoA are fully oxidized to CO2. On the other hand, glycolysis does not produce CO2, and while the electron transport chain uses products from the Krebs cycle, it does not generate CO2, since it focuses on the transfer of electrons to ultimately produce ATP.
To address a related question, the molecule FADH2 is specifically produced only in the Krebs cycle during the catabolism of glucose. This molecule, alongside NADH, later donates electrons to the electron transport chain.