Which component transports oxygen?

Erythrocytes, commonly known as red blood cells, are the specialized cells responsible for transporting oxygen throughout the body. They contain large quantities of hemoglobin, a protein composed of four globin chains each attached to a heme group containing an iron atom. Oxygen binds reversibly to this iron in the lungs, where partial pressure of oxygen is high, and is released at peripheral tissues where oxygen tension is lower. Erythrocytes also assist in transporting carbon dioxide back to the lungs, partly as bicarbonate ions formed within the red cell by carbonic anhydrase. Leukocytes are white blood cells whose primary function is immune defense — identifying and destroying pathogens — not gas transport. Platelets are small anucleate cell fragments derived from megakaryocytes that function in primary hemostasis by forming platelet plugs at sites of vascular injury; they do not transport gases. Lymphocytes are a specific subset of leukocytes involved in adaptive immunity, including antibody production by B cells and cell-mediated immunity by T cells; they have no gas-transport function. Understanding that oxygen transport is exclusively dependent on erythrocyte hemoglobin is foundational to interpreting conditions like anemia, where reduced erythrocyte mass or hemoglobin concentration impairs tissue oxygenation.