. . one answer at a time. The main function of the respiratory system is to discard waste in the form of carbon dioxide and to take in oxygen. Carbon dioxide is carried to the lungs in erythrocytes (red blood cells) and released, then the erythrocytes collect oxygen and deliver this essential gas to our bodies.he function of the respiratory system is to allow gas exchange it, taking oxygen into the blood and removing carbon dioxide from the blood. The oxygen absorbed is used by the ….