And substrate level phosphorylation also occurs in the citric acid cycle, as we'll see in just a moment. Now, although aerobic respiration means we have oxygen present in the cell, glycolysis takes place regardless of whether or not we have oxygen present inside the cell. So that implies glycolysis is the first step of aerobic as well as anaerobic respiration. Now, once we actually synthesize our two pyruvate molecules via glycolysis, if we have oxygen present in the cell, those two pyruvate molecules will then be transported into the mitochondrial matrix of the mitochondria of aracel. And once inside the mitochondrial matrix of aracel, our two pyruvate molecules undergo a decarboxylation process in which we produce two carbon dioxide molecules, two NADH molecules, as well as two acetyl coenzyme A molecules. No ATP molecules are actually synthesized directly in the process of pyruvate decarboxylation.