Which of the following is responsible for carrying carbon dioxide from the tissues to the lungs?
Hemoglobin
Plasma
Bicarbonate ion
Red blood cells
Red blood cells (RBCs) carry carbon dioxide (CO2) from tissues to the lungs through a process known as respiratory gas transport.
In the tissues, CO2 is produced as a waste product of cellular metabolism. It diffuses out of the cells and into the blood, where it combines with water to form carbonic acid (H2CO3) in a reaction catalyzed by the enzyme carbonic anhydrase. The carbonic acid then breaks into bicarbonate ions (HCO3-) and hydrogen ions (H+). The majority of the bicarbonate ions produced are transported out of the red blood cells and into the plasma, where they are carried to the lungs. In exchange, chloride ions (Cl-) from the plasma are transported into the red blood cells to maintain electrical neutrality.
Option 4 is the correct answer.