What is the primary function of red blood cells?

Red blood cells, also known as erythrocytes, have the primary function of transporting oxygen from the lungs to the rest of the body. They accomplish this through a specialized protein called hemoglobin, which binds to oxygen molecules. This enables red blood cells to carry oxygen efficiently, ensuring that vital organs and tissues receive the necessary oxygen to function properly. Additionally, red blood cells also help transport carbon dioxide, a waste product of metabolism, back to the lungs for exhalation. This dual role in gas exchange is critical for maintaining the body's overall respiratory and metabolic health.

The other options describe functions associated with different types of cells or biological processes. For example, fighting infections is primarily the role of white blood cells, while stopping bleeding involves platelets and the clotting process. Digesting nutrients is primarily a function of cells in the digestive system rather than red blood cells. Thus, the selection of the transport of oxygen as the main function reflects an accurate understanding of red blood cell physiology.