Now, the thing about CO2 molecules is they're non polar molecules and they can easily move across the cell membrane of the tissue. Cells move into our blood system and then move into the red blood cells because they don't have a charge and they can easily pass across the cell membrane. Along with that, we also have special protein transporters in the cell membrane that allow the carbon dioxide to basically be brought into the red blood cell. Now, once the CO2 is inside the red blood cell, it reacts with water. And with the help of a special enzyme known as carbonic and hydrase, we transform CO2 and water into carbonic acid. And then, because carbonic acid is a relatively good acid, it will dissociate into H plus ions and into bicarbonate ions.