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 tissues of the body and to transport carbon dioxide from the tissues back to the lungs for exhalation. This process is vital for maintaining the body's metabolic functions, as oxygen is essential for cellular respiration, which produces the energy needed by cells to perform their functions.

Red blood cells contain hemoglobin, a protein that binds to oxygen, allowing them to effectively transport oxygen throughout the bloodstream. Their unique biconcave shape increases their surface area, enhancing oxygen absorption and delivery. The efficient functioning of red blood cells is crucial to sustaining life, as oxygen is required for the energy production processes that power all bodily activities.

Other options pertain to different physiological functions: regulating body temperature involves mechanisms different from blood cell action, fighting infections is primarily the role of white blood cells, and hormone production is mainly a function of various glands and organs, not red blood cells. Therefore, the assertion that red blood cells primarily carry oxygen appropriately underscores their essential role in the circulatory system.