But glycolysis doesn't regenerate these molecules once it takes place. And that's precisely why under aerobic conditions, when we have plenty of oxygen inside the cell, that Pyruvate enters the mitochondria and we form more ATP molecules. And we also regenerate those NAD plus molecules from the breakdown of Pyruvate under aerobic conditions. Now, sometimes in those cells that don't have mitochondria, or in those cells that are experiencing hypoxia, so a lack of oxygen, they cannot actually break down the Pyruvate in the citric acid cycle of the mitochondria. So instead of using that, they switch to anaerobic respiration. So in anaerobic respiration, which takes place entirely in the cytoplasm, we essentially undergo glycolysis to form the ATP molecules and the Pyruvate molecules.