Two nutrient solutions are maintained at the same pH. Actively respiring mitochondria are isolated and placed into each of the two solutions. Oxygen gas is bubbled into one solution. The other solution is depleted of available oxygen. Which of the following best explains why ATP production is greater in the tube with oxygen than in the tube without oxygen?

Cellular respiration requires oxygen during the process of oxidative phosphorylation. Oxygen acts as the final electron acceptor, receiving the electrons that go through the electron transport chain. If this receiver was absent, the electron transport chain would stall. No protons would be pumped through the membrane, resulting in no electrochemical gradient. Without the gradient, ATP synthase would not be able to produce ATP.