Once Oxygen reaches the blood via the lungs, it is taken in by a protein known as haemoglobin (Hb) in the red blood cells. Oxygen then binds to a heme group located within a subunit of the protein (Hb). A single heme group can bind 1 oxygen molecule, there are 4 heme groups all together meaning 4 oxygen molecules forming Oxyhaemoglobin. Oxygen is then diffused into local tissue by the Haemoglobin. - this was rushed sorry if it doesnt make alot of sense hope it helps tho
