What is the primary function of hemoglobin in blood?

Hemoglobin's primary function in blood is to transport oxygen from the lungs to the tissues throughout the body. This is essential for cellular respiration, as cells require oxygen to produce energy. Hemoglobin binds to oxygen molecules in the lungs, where the concentration of oxygen is high, and then releases it in areas where oxygen is needed, such as active tissues or muscles.

While hemoglobin is central to oxygen delivery, it also assists in transporting a small amount of carbon dioxide, a waste product of metabolism, from the tissues back to the lungs for exhalation. However, its primary role remains oxygen transport, making it vital for maintaining the physiological needs of the body's cells.

The other functions mentioned in the choices are important but are not related to hemoglobin. Fighting infections is primarily the role of white blood cells, clotting blood involves platelets and clotting factors, and removing waste is handled by organs such as the kidneys and liver. These roles are vital for overall health but do not pertain to the specific function of hemoglobin in the circulatory system.