So, inside the cells of exercising tissues, these cells are continually undergoing different types of metabolic processes such as cellular respiration. And so the major waste byproduct that is produced in the process is carbon dioxide. Now, of course, carbon dioxide is a nonpolar molecule and so it will not readily diffuse in our blood plasma. Only about 5% of the carbon dioxide will exist in the blood plasma in its CO2 form. About 90% of the carbon dioxide, as we'll see in just a moment, actually exist in its bicarbonate ion form. Now, how exactly do we transform the carbon dioxide into its soluble bicarbonate ion form?