Now, in the process of glycolysis, we also produce two ATP molecules. And these two ATP molecules can be used by other processes of the cells that actually require energy. Now, even though glycolysis actually does produce a net amount of ATP molecules, glycolysis only collects a very small portion of that usable energy that is stored in the chemical bonds of the glucose molecules. So it only harvests a very small amount of potential energy that is stored in the bonds of glucose. And to actually be able to collect the remaining energy stored in the chemical bonds of glucose, we have to undergo aerobic cell respiration. And this only takes place in the presence of oxygen and if we have mitochondria in the cells of our body, because remember, certain cells don't actually have mitochondria.