What is the primary function of red blood cells?

The primary function of red blood cells is to transport oxygen and carbon dioxide. This is achieved through the molecule hemoglobin, which is found within red blood cells. Hemoglobin has a high affinity for oxygen, allowing red blood cells to pick up oxygen in the lungs and carry it to tissues throughout the body where it is needed for cellular respiration. Conversely, red blood cells also facilitate the removal of carbon dioxide, a waste product of metabolism, from the tissues and transport it back to the lungs for exhalation. This dual role is essential for maintaining proper respiratory function and overall metabolic balance in the body.

While other options present important functions within the body, they do not pertain to the primary role of red blood cells. Regulating body temperature involves a different set of physiological responses, fighting infections is primarily a function of white blood cells, and hormone production is mainly the responsibility of glands and other specialized cells.