Which energy system uses glucose in long-duration exercise and depends on oxygen?

• A. oxidative system
• B. glycolysis
• C. ATP-PC
• D. anaerobic

Answer: (A)

Aerobic energy production powers long-duration exercise. This system uses glucose as fuel and requires oxygen to fully convert it into ATP. Glucose is first broken down through glycolysis to pyruvate, which enters the mitochondria and becomes acetyl-CoA. The acetyl-CoA feeds the Krebs cycle and the electron transport chain, where oxygen accepts electrons and helps drive the production of a large amount of ATP (about 30–32 ATP per glucose). Because it relies on oxygen, this system is sustainable for extended efforts, matching the demands of endurance activity. The other options describe energy paths that are either anaerobic (no oxygen) or for short bursts, so they don’t fit long-duration, oxygen-dependent energy needs.