Why is the highest percentage of co2 transportes by RBCs as compared to plasma
As СO2 diffuses from the tissues into the blood, most of it is taken up by the RBCs', while some of it remains dissolved in the plasma. In the RBCs' an enzyme known as Carbonic anhydrase acts upon the CO2 and H2O molecule to give H2CO3 and H+. H2CO3 formed diffuses into the plasma acting as a pH buffer and the H+ binds to the hemoglobin for the release of O2 into the tissues. Therefore, simple answer would be; the higher concentration of CO2 in the RBCs' is required for the buffering of blood plasma and release of O2 to tissues.