Which component of blood carries oxygen to body cells?

• A. Serum
• B. Plasma
• C. Red blood cells
• D. White blood cells

Answer: (C)

Oxygen is carried to body cells mainly by red blood cells because of the protein hemoglobin they contain. Hemoglobin binds oxygen in the lungs, where oxygen levels are high, and releases it in tissues where it’s needed, where oxygen levels are lower. This reversible binding lets oxygen be picked up and delivered efficiently as blood circulates. The liquid part of blood, plasma (and serum when clotting factors are removed), mainly transports nutrients, hormones, and wastes but does not carry oxygen in any meaningful amount. White blood cells are involved in immune defense, not oxygen transport. The red blood cells’ biconcave shape also increases their surface area for gas exchange, aiding rapid loading and unloading of oxygen.