Q. Normal functioning of blood?

The sixth position marked by X is either occupied by H₂0 or 0₂ molecules. Impotant thing to note is that Fe²⁺ in hemoglobin does not get oxidised to Fe³⁺. On the ottier, tiahd if gaseous 0² is bubbled into an aqueous solution containing heme, the Fe²⁺ gets oxidised to Fe³⁺. It is believed that the oxidation of Fe²⁺ to Fe³⁺ is prevented by the bulky protein in the hemoglobin. Each helnoglobin can bind four 0² molecules to give a bright red complex.  When oxygen molecules are replaced by water molecules it gives a bluish coloured complex which is characteristic of venous blood. Both CO and CN^- can form more stable complexes with Fe²⁺ ion than molecular oxygen. Thus they can destroy the normal functioning of blood as in oxygen carrier.