What is the primary function of red blood cells?

• A. Carry oxygen to tissues and provide the blood's red color
• B. Fight infections
• C. Transport carbon dioxide
• D. Clot blood

Answer: (A)

Red blood cells are specialized to move oxygen from the lungs to every tissue in the body. They contain hemoglobin, a protein with iron that binds oxygen in the lungs to form oxyhemoglobin and releases it to cells where it’s needed for energy production. This oxygen delivery is the primary job of RBCs, and it’s also why blood looks red—the iron-hemoglobin complex gives it that color. Red blood cells also carry a portion of carbon dioxide, a waste product of metabolism, back to the lungs to be exhaled, but that role supports oxygen transport rather than being the main purpose. Other blood components handle different tasks, like fighting infections or forming clots.