What is the primary role of hemoglobin in the blood?

The primary role of hemoglobin in the blood is oxygen transport. Hemoglobin is a protein found in red blood cells that binds to oxygen molecules inhaled into the lungs. Once it has bound to oxygen, hemoglobin releases it in the tissues and organs throughout the body that require oxygen for metabolic processes. This transport of oxygen is crucial for maintaining cellular function and energy production.

The other options reflect important functions within the body, but they do not define the primary role of hemoglobin. Coagulation involves the process that helps blood to clot, which is primarily facilitated by platelets and numerous clotting factors, rather than hemoglobin. Nutrient transport pertains to the movement of various nutrients through the bloodstream, a function mainly performed by plasma and various proteins. Immune response relates to the body's defense against pathogens, involving white blood cells and antibodies rather than hemoglobin. Thus, while hemoglobin may be indirectly involved in some of these processes, its main purpose is the transport of oxygen.