how is oxygen transported

• oxygen is absorbed into the blood as it passes the alveoli in the lungs. Oxygen molecules diffusing into the blood plans enter the erythrocytes. here they become associated with the haemoglobin molecules.
• When the oxygen is associated with the haemoglobin, it is bonded reversibly to haemoglobin. this takes oxygen molecules out of solution and so maintains a steep concentration gradient to allow more oxygen to enter the blood from the lungs and diffuse into the cells.
• the blood carries the oxygen from the lungs back to the heart before travelling around the body to supply the tissues.
• In the body tissues, cells need oxygen for aerobic respiration. therefore the oxyhaemoglobin must be able to release the oxygen in a process known as dissociation.