What makes the structure of Haemoglobin good for the transport of oxygen to tissues? (3 marks)

Haemoglobin (Hb) is comprised of 4 polypeptide chains (2 alpha, 2 beta). Each polypeptide chain has a prosthetic group capable of picking up oxygen, therefore one Hb molecule can transport 4 oxygen molecules. Oxygen binds the Hb reversibly so that it may be released at the level of the respiring tissue where the partial pressure of oxygen is lower (moves down the concentration gradient).