USA Biology Olympiad (USABO) Practice Exam

During glycolysis, glucose is broken down into two molecules of pyruvate, along with a net gain of ATP and NADH. In aerobic respiration, when oxygen is present, the pyruvate produced in glycolysis must be transported into the mitochondria where it undergoes further processing.

Once in the mitochondria, pyruvate is converted into Acetyl-CoA, which then enters the Krebs cycle (also known as the citric acid cycle). This conversion is essential as Acetyl-CoA serves as a key metabolic intermediate, linking glycolysis to the aerobic pathway of ATP production.

Glucose is not transported directly to the mitochondria during aerobic respiration; it is metabolized through glycolysis first. Lactate, produced under anaerobic conditions, primarily occurs in muscle cells when oxygen levels are low and does not enter the mitochondria for ATP production in the presence of oxygen. Acetyl-CoA, although a product of pyruvate conversion that enters the Krebs cycle, is not the final product of glycolysis itself; rather, it is produced after the transport of pyruvate into the mitochondria.

Thus, the transport of pyruvate to the mitochondria is a crucial step in enabling the cell to utilize aerobic