Cellular respiration
Acetyl CoA joins with oxaloacetate to form a compound with six carbon atoms. This is the first step in the ever-repeating Krebs cycle. Because two acetyl-CoA molecules are produced from each glucose molecule, two cycles are required per glucose molecule. Therefore, at the end of two cycles, the products are: two ATP, six NADH, two FADH, and four CO2. The ATP is a molecule which carries energy in chemical form to be used in other cell processes.  This process is also known as the TCA cycle (Tricarboxylic (try-car-box-ILL-ick) acid cycle), the citric acid cycle, or the Krebs cycle after the biochemist who elucidated its reactions.