Which piece of evidence explains the cause of most of the ATP generation that occurs in cellular respiration? A Glycolysis can also occur without oxygen, a process called anaerobic respiration, or fermentation. When this happens, cells make small amounts of ATP.

B These molecules are converted into a slightly different compound, which is known as acetyl coenzyme A (acetyl CoA). Then, the citric acid cycle can begin.

C During the citric acid cycle, two ATP molecules are also produced. The cycle also produces two compounds called NAD and FAD.

D Ultimately, ATP is produced by oxidative phosphorylation, a process by which enzymes (substances that speed up reactions) combine with oxygen.