What are erythrocytes?

• A. Platelets
• B. Red blood cells that contain hemoglobin
• C. White blood cells that fight infection
• D. Plasma

Answer: (B)

Erythrocytes are red blood cells that contain hemoglobin, the protein responsible for binding and transporting oxygen from the lungs to tissues throughout the body (and helping carry some carbon dioxide back to the lungs to be exhaled). This is what makes them distinct from the other blood components: platelets are small fragments involved in clotting, white blood cells are immune cells that fight infection, and plasma is the liquid portion that carries cells and nutrients. Hemoglobin’s iron-containing heme binds oxygen in the lungs and releases it where needed, while also picking up some carbon dioxide for removal. Mature erythrocytes in mammals typically lack nuclei to maximize space for hemoglobin, giving them their distinctive shape and enhancing gas exchange.