Which transporter binds and carries oxygen in the blood from lungs to tissues?

• A. Haemoglobin
• B. Myoglobin
• C. Mitochondria
• D. Oxyhaemoglobin Dissociation

Answer: (A)

Oxygen is carried in the blood primarily by haemoglobin inside red blood cells. Haemoglobin has four heme groups with iron that bind oxygen reversibly. In the lungs, the high partial pressure of O2 promotes loading, forming oxyhaemoglobin so each haemoglobin molecule can carry up to four O2 molecules. As blood reaches tissues where O2 pressure is lower and CO2/H+ are higher, the affinity decreases and oxygen is released to support cellular respiration. Myoglobin stores oxygen in muscles but does not transport it in the blood. Mitochondria use oxygen for respiration and are not transporters. The term oxyhaemoglobin dissociation describes the release of oxygen from haemoglobin, not the transporter itself.