What role does hemoglobin play in the blood?

Hemoglobin is a protein found in red blood cells that is crucial for transporting oxygen from the lungs to the tissues and organs throughout the body in vertebrates. This process is essential for cellular respiration, which is how cells generate energy. The oxygen binds to hemoglobin molecules, enabling efficient transport, as each hemoglobin molecule can carry four oxygen molecules at a time. This characteristic allows the blood to carry more oxygen than if it were dissolved in plasma alone.

While other options mention important functions related to blood, such as nutrient transport or blood clotting, they do not accurately describe the primary role of hemoglobin. Nutrients are carried by different components of the blood, like plasma, while blood clotting involves platelets and other proteins. The removal of carbon dioxide from the body is mainly facilitated by the bicarbonate system in blood and does not primarily involve hemoglobin, although it can play a role in transporting carbon dioxide back to the lungs for exhalation.