What is the primary function of red blood cells?

The primary function of red blood cells is to transport 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, where it is released for use in 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, where it can be exhaled. This dual role of oxygen transport for cellular energy production and carbon dioxide removal for maintaining acid-base balance is vital for the proper functioning of bodily systems.

Other options describe important yet distinct roles that are fulfilled by different types of blood cells or bodily systems; for instance, white blood cells are primarily involved in fighting infections, platelets play a crucial role in blood clotting, and hormone production is primarily the domain of endocrine glands rather than red blood cells.