University of Central Florida (UCF) BSC2010C Biology I Practice Exam 2

During cellular respiration, the production of carbon dioxide occurs primarily during the citric acid cycle, also known as the Krebs cycle. This process takes place in the mitochondrial matrix, where acetyl-CoA, derived from carbohydrates, fats, and proteins, enters the cycle and undergoes a series of enzymatic reactions.

Throughout these reactions, carbon skeletons are transformed, leading to the release of carbon dioxide as a byproduct. Specifically, during the decarboxylation reactions within the cycle, carbon atoms are released in the form of carbon dioxide. For every acetyl-CoA molecule that enters the cycle, two molecules of carbon dioxide are produced.

While glycolysis occurs in the cytoplasm and involves the breakdown of glucose into pyruvate, it does not release carbon dioxide. Similarly, the electron transport chain, which takes place in the inner mitochondrial membrane, is primarily responsible for the production of ATP and the reduction of oxygen to water, without generating carbon dioxide. Fermentation, a form of anaerobic respiration, occurs in the absence of oxygen and also does not produce carbon dioxide as a direct result of the major metabolic pathways involved.

Thus, the citric acid cycle is uniquely responsible for producing carbon dioxide during cellular respiration, making it the correct answer