What component of blood carries oxygen?

• A. Platelets
• B. Hemoglobin in red blood cells
• C. Plasma proteins
• D. White blood cells

Answer: (B)

Oxygen transport in the blood is handled mainly by hemoglobin inside red blood cells. Hemoglobin binds oxygen in the lungs, where oxygen is abundant, and releases it in tissues where it’s needed and oxygen levels are lower. Each hemoglobin molecule can carry up to four oxygen molecules because of its four heme groups with iron that reversibly bind oxygen. Since oxygen isn’t very soluble in plasma, using hemoglobin as the carrier makes transport efficient as blood circulates. The red blood cells’ biconcave shape also aids gas exchange and flow through tiny vessels. Platelets, on the other hand, are responsible for clotting; plasma proteins perform other roles such as maintaining osmotic pressure and transporting various substances but do not primarily carry oxygen; white blood cells are involved in the immune response.