What is the primary function of iron in the body?

• A. Transports carbon dioxide.
• B. Regulates calcium absorption.
• C. Carries oxygen in hemoglobin.
• D. Stores fat.

Answer: (C)

Iron's job in the body centers on oxygen transport. It is part of the heme group in hemoglobin inside red blood cells, and the iron atom binds oxygen reversibly. Each hemoglobin molecule has four heme units, so it can carry up to four oxygen molecules from the lungs to tissues that need it. In tissues, oxygen is released for cellular respiration, powering energy production. Iron also helps in muscle by being part of myoglobin, which stores and releases oxygen there. Some carbon dioxide is transported back to the lungs, but that involves mostly other mechanisms and the protein part of hemoglobin rather than the iron itself, so the primary function of iron is oxygen transport. Calcium regulation and fat storage involve different pathways and nutrients, not iron.