Which blood component carries oxygen in the blood?

• A. white blood cells
• B. platelets
• C. plasma
• D. red blood cells

Answer: (D)

Oxygen is carried through the bloodstream primarily by red blood cells. These cells contain hemoglobin, a protein with iron that binds oxygen in the lungs where oxygen is plentiful and releases it to tissues where it’s needed. The biconcave shape of red blood cells increases their surface area for gas exchange, and their structure optimizes oxygen transport. A small portion of oxygen stays dissolved directly in plasma, but most of it travels bound to hemoglobin inside red blood cells. White blood cells are for immune defense, platelets help with clotting, and plasma is the liquid medium that carries nutrients, hormones, and waste. So the component responsible for transporting oxygen is the red blood cells.