What is the primary role of red blood cells in the human body?

Red blood cells, also known as erythrocytes, have the primary role of transporting oxygen from the lungs to the tissues and cells throughout the body. They contain a protein called hemoglobin, which binds to oxygen molecules when blood passes through the lungs. Once the red blood cells are oxygenated, they travel through the bloodstream to deliver this essential gas to various tissues, which is critical for cellular metabolism and energy production.

Additionally, red blood cells play a minor role in transporting carbon dioxide—produced as a waste product of cellular respiration—back to the lungs for exhalation. This dual function of oxygen delivery and carbon dioxide removal is vital for maintaining the body's overall respiratory and metabolic functions. Other options, such as regulating body temperature, fighting infections, and clotting blood, are functions performed by other components of the blood, such as plasma, white blood cells, and platelets. Thus, the primary role of red blood cells is clearly centered around oxygen transportation.