Final answer:
The oxidation of pyruvate releases carbon dioxide during pyruvate decarboxylation and the citric acid cycle. Glycolysis does not release carbon dioxide, and no carbon dioxide is released during the electron transport chain, which concludes cellular respiration.
Step-by-step explanation:
In cellular respiration, the steps in the oxidation of pyruvate that produce carbon dioxide are pyruvate decarboxylation and the citric acid cycle. Although glycolysis is the first step of cellular respiration and it produces pyruvate from glucose, no carbon dioxide is released during glycolysis itself. Instead, once pyruvate is formed, it is transported into the mitochondria where it undergoes a transformation into an acetyl group attached to coenzyme A, known as acetyl CoA—this is pyruvate decarboxylation. During this process, a molecule of carbon dioxide is released for each pyruvate molecule that is oxidized.
The acetyl CoA then enters the citric acid cycle, also known as the Krebs cycle, where it gets fully oxidized. More carbon dioxide is produced here as the acetyl group is broken down and combined with oxygen. The electron transport chain is the final stage of cellular respiration, and it does not release carbon dioxide but uses the electrons produced earlier to form ATP and water.