A nurse is teaching a class about oxygen transport in the cardiopulmonary system. Which of the following transports oxygen in the blood?

Choice C rationale Hemoglobin is a complex protein found within red blood cells (erythrocytes) that is specifically responsible for oxygen transport. Each hemoglobin molecule contains four heme groups, each with an iron atom capable of binding reversibly with one molecule of oxygen. This allows oxygen picked up in the lungs to be efficiently transported to peripheral tissues where it is released for cellular use. Choice A rationale Platelets, also known as thrombocytes, are small, anuclear cells critical for hemostasis, the process of stopping bleeding. Their primary function involves aggregating at the site of vascular injury to form a platelet plug and releasing clotting factors to initiate the coagulation cascade. They have no role in oxygen transport. Choice B rationale Neutrophils are the most abundant type of white blood cell (leukocyte) and are a key component of the innate immune system. Their primary function is phagocytosis, engulfing and destroying invading pathogens like bacteria. Like other leukocytes, they are involved in immune defense, not oxygen transport. Choice D rationale Lymphocytes are a type of white blood cell crucial for adaptive immunity. They include T cells (involved in cell-mediated immunity) and B cells (responsible for producing antibodies in humoral immunity). Their function is centered on recognizing and destroying specific foreign antigens, not transporting respiratory gases.