Each of the subunits of the haemoglobin molecule contains a haem group that is necessary for the binding of oxygen.

Haemoglobin is an excellent acid-base buffer because the iron binds bicarbonate.

Haemoglobin from erythrocytes that have been removed from the circulation is degraded into bilirubin and other compounds.

Males have a haemoglobin concentration of around 16 g per 100 ml of whole blood and females around 14 g per 100 ml of whole blood.           

The human erythrocyte contains haemoglobin, a respiratory pigment based on the iron atom.