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?

Answer: In the absence of oxygen, oxidative phosphorylation produces more ATP than does fermentation

Explanation:

ATP is a molecule that contains energy and it is used to carry out different cellular processes. This energy is obtained through cellular respiration, which can be carried out both in the presence and absence of oxygen. For this, the first step is the breakdown of glucose in a process called glycolysis, to form a molecula called pyruvate. Then, depending on whether or not oxygen is available, aerobic (with oxygen) or anaerobic (without oxygen) cellular respiration will take place. In both cases ATP is produced, but the amount obtained is significantly less in anaerobic respiration.

Fermentation is a catabolic process of incomplete oxidation, which does not require oxygen, and whose final product is an organic compound. The fermentation process is anaerobic, so it occurs in the absence of oxygen; this means that the final acceptor of the electrons of NADH produced in glycolysis is not oxygen, but an organic compound that will be reduced in order to reoxide NADH to NAD+.

While, oxidative phosphorylation is the final step of aerobic respiration and it converts ADP to ATP, to which a large protein molecule that protrudes throughout the internal mitochondrial membrane contributes. This is an ATPase called ATP synthetase. The high concentration of positively charged hydrogenions created between the two mitochondrial membranes and the large potential difference across the internal membrane causes hydrogenions to flow into the mitochondrial matrix through the ATPase. The energy released by this flow of hydrogen is used by the synthetase to phosphorylate the ADP into ATP which is transferred to the cytoplasm.

During oxidative phosphorylation, 30 and 36 ATPs are produced. While fermentation produces only 2 molecules of ATP.