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?

A. The rate of proton pumping across the inner mitochondrial membrane is lower in the sample without oxygen. B. Electron transport is reduced in the absence of a plasma membrane. C. In the absence of oxygen, oxidative phosphorylation produces more ATP than does fermentation. D. In the presence of oxygen, glycolysis produces more ATP than in the absence of oxygen.