NACC PSW Practice Exam

Hemoglobin is the correct answer because it is a protein found in red blood cells that has a unique ability to bind to oxygen molecules. This binding is crucial for transporting oxygen from the lungs to the tissues throughout the body. Each hemoglobin molecule can carry four oxygen molecules, making it extremely efficient in its role. In contrast, white blood cells are primarily involved in the immune response, fighting infections and foreign substances in the body; they do not carry oxygen. Platelets play a role in blood clotting and wound healing, not oxygen transport. Plasma is the liquid component of blood that carries cells, nutrients, hormones, and waste products, but it does not have the capacity to transport oxygen on its own. Therefore, hemoglobin's function and structure make it essential for oxygen transport in the bloodstream.