Anatomy and Physiology II Practice Test

The correct answer is the Citric Acid Cycle, which relies on oxygen to function effectively. This step in carbohydrate metabolism occurs in the mitochondria of the cells and is part of aerobic respiration, where the Krebs cycle oxidizes acetyl-CoA derived from carbohydrates, fats, and proteins. Oxygen is crucial here because it serves as the final electron acceptor in the electron transport chain, which is directly linked to the Citric Acid Cycle. The oxidation process generates ATP, the energy currency of the cell, and carbon dioxide, which is eliminated from the body.

Other processes in carbohydrate metabolism, such as glycolysis and fermentation, can occur without the presence of oxygen. Glycolysis takes place in the cytoplasm and converts glucose into pyruvate, producing a small amount of ATP anaerobically. Fermentation, on the other hand, is an anaerobic process that occurs in the absence of oxygen and converts pyruvate into lactate or ethanol, allowing for ATP production under anaerobic conditions. Glycogenesis, the formation of glycogen from glucose, also does not require oxygen. Thus, it is the Citric Acid Cycle that distinctly requires oxygen for its processes to continue efficiently.