Carbon dioxide reacts with haemoglobin in body cells to form carbaminohemoglobin compound. Carbaminohemoglobin comes from the compound body cells to the walls of the alveoli. The compound breaks down in the walls of the alveoli and turns into carbon dioxide and haemoglobin. Carbon dioxide is then released from the body.
CO2 + HbNH2 → HbNHCOOH
Haemoglobin acts as the sole carrier for transporting oxygen and carbon dioxide in the human body. That is, oxygen and carbon dioxide transport is not possible without red blood cells.