What is the primary function of red blood cells?

The primary function of red blood cells is to transport oxygen throughout the body. This is achieved through a protein called hemoglobin, which binds to oxygen in the lungs and carries it to tissues and organs, where it is released to support cellular metabolism. Red blood cells also play a crucial role in transporting carbon dioxide, a waste product of metabolism, from the tissues back to the lungs for exhalation.

In the context of other options, while fighting infections is an important function of the immune system, it is primarily the role of white blood cells, not red blood cells. The production of hormones is carried out by various glands in the endocrine system, not red blood cells. Additionally, regulating body temperature is mainly managed by the circulatory system and specific physiological mechanisms rather than the direct action of red blood cells. Thus, the transportation of oxygen is the definitive and critical role of red blood cells, which highlights their importance in maintaining overall bodily function and health.