Which blood cell transports oxygen by binding it as oxyhemoglobin and has a lifespan of about 120 days?

• A. Erythrocytes
• B. Leucocytes
• C. Platelets
• D. Plasma

Answer: (A)

Oxygen is carried in the blood mainly by red blood cells because they contain hemoglobin, a protein that binds oxygen to form oxyhemoglobin in the lungs and releases it to tissues where it’s needed. These cells have a lifespan of about 120 days as part of their production in the bone marrow and removal in the spleen, reflecting steady turnover to maintain oxygen transport. Their distinctive biconcave shape increases surface area for gas exchange and allows them to squeeze through tiny capillaries. Other blood components don’t bind or transport oxygen: leucocytes are immune cells, platelets help with clotting, and plasma is the liquid matrix that carries dissolved nutrients and other substances.