What is the primary function of red blood cells?

The primary function of red blood cells is to carry oxygen from the lungs to the rest of the body. This is accomplished through a protein called hemoglobin, which binds to oxygen and allows the red blood cells to transport it through the bloodstream. Once the oxygen reaches the tissues, hemoglobin releases it, enabling cells to perform their metabolic functions, which is critical for maintaining overall health and energy production.

Other options, while important processes in the body, do not describe the primary role of red blood cells. Fighting infection is primarily the role of white blood cells; clotting blood involves platelets and various clotting factors; and hormone production is typically the function of endocrine glands. Each of these plays a significant role in bodily functions, but they are not associated with the primary duty of red blood cells.