What is the primary function of red blood cells?

The primary function of red blood cells is to transport gases, specifically oxygen and carbon dioxide, throughout the body. These cells contain hemoglobin, a protein that binds to oxygen in the lungs and carries it to the tissues and organs where it is needed for cellular respiration. Simultaneously, red blood cells pick up carbon dioxide, a waste product of metabolism, from the tissues and transport it back to the lungs for exhalation. This gas exchange is crucial for maintaining the body's overall function and health.

While fighting infections, transporting hormones, and clotting blood are important bodily functions, they are primarily associated with other types of cells and mechanisms within the body. White blood cells are responsible for the immune response, platelets play a key role in blood clotting, and hormones are generally transported by the bloodstream, but not specifically by red blood cells. Therefore, their primary role centers on gas transport, making this the correct answer.