What is the main function of red blood cells?

Red blood cells, also known as erythrocytes, have a primary function of carrying oxygen from the lungs to the tissues and organs throughout the body. This process is essential for maintaining cellular metabolism, as oxygen is crucial for the production of energy within cells.

Red blood cells contain a protein called hemoglobin that binds to oxygen molecules in the lungs. Once the red blood cells are saturated with oxygen, they travel through the bloodstream to deliver this vital gas to cells where it is utilized in various metabolic processes, particularly in the production of ATP, which cells use for energy.

While the other options mention important biological functions, they pertain to different types of cells or systems in the body. For instance, white blood cells are responsible for the immune response and fighting infections, hormones are typically produced by endocrine cells, and waste products in the body are removed primarily through the kidneys and other excretory mechanisms, not by red blood cells. Thus, the focus on the oxygen-carrying capacity of red blood cells underscores their critical role in maintaining overall physiological function.