The document summarizes the Krebs cycle, or citric acid cycle. It is a series of chemical reactions that occur in the mitochondria of cells to release stored energy through oxidation of carbohydrates, fats, and proteins into carbon dioxide. The cycle was discovered by Hans Krebs in 1937. It consists of a series of chemical reactions that generate energy carriers like NADH and FADH2. For each turn of the cycle, 12 ATP molecules are produced, resulting in a total of 24 ATP per cycle as it occurs twice to fully oxidize acetyl-CoA from carbohydrate, fat, and protein breakdown.