So, the bicarbonate ion enters the blood plasma, and then it travels with the blood plasma all the way to the pulmonary capillaries. And once we find it in the pulmonary capillaries, what happens is the opposite process takes place. Now, in order to maintain electrical neutrality, when a single bicarbonate ion enters our red blood cell, a single chloride ion must leave that red blood cell so that we have a net charge of zero that essentially travels across the red blood cells. So one negative charge enters, and one negative charge leaves. Now, once our bicarbonate is inside our red blood cell, only then can it basically interact with the H ion and form our carbonic acid. And only then can our carbonic anhydrase catalyze the formation of CO2 and water by breaking this carbonic acid down.