What is the primary function of red blood cells?

• A. Transport oxygen using hemoglobin
• B. Fight infections
• C. Clot blood
• D. Transport carbon dioxide

Answer: (A)

Oxygen transport by hemoglobin is the primary function of red blood cells. Hemoglobin binds oxygen in the lungs, where oxygen is abundant, and releases it in tissues that need it for cellular respiration and energy production. The iron-containing heme groups in hemoglobin enable each molecule to carry up to four oxygen molecules, making delivery efficient as blood circulates. Red blood cells also help move carbon dioxide from tissues back to the lungs for exhalation, but that role is secondary to delivering oxygen. Other cells handle immune defense and clotting: fighting infections is the job of white blood cells, and clotting involves platelets.