Final answer:
Bicarbonate is pivotal for CO2 transport in blood, entering and leaving red blood cells through a process involving the enzyme carbonic anhydrase and a mechanism called the chloride shift, which is reversed in the lungs allowing the exhalation of CO2.
Step-by-step explanation:
Bicarbonate plays a crucial role in transporting carbon dioxide in blood. Within vertebrate red blood cells, an enzyme known as carbonic anhydrase (CA) facilitates the conversion of carbon dioxide and water into carbonic acid (H2CO3), which quickly dissociates into bicarbonate (HCO3−) and hydrogen (H+) ions. Consequently, bicarbonate accumulates in red blood cells.
To maintain ionic balance, the chloride shift occurs where bicarbonate is exchanged for chloride ions (Cl−), allowing bicarbonate to enter the blood plasma. Upon reaching the lungs, this process reverses; bicarbonate re-enters red blood cells in exchange for chloride ions. The H+ ions released from hemoglobin then recombine with bicarbonate to reform carbonic acid, which carbonic anhydrase converts back into carbon dioxide and water. This carbon dioxide is exhaled from the lungs during respiration.