Explain how oxygen and carbon dioxide are transported within the blood?

Oxygen diffuses through the alveolar wall into the capillary beds surrounding the lungs, and here it enters the red blood cells (erythrocytes). It binds to protein contained within the red blood cell called haemoglobin, and specifically interacts with Fe2⁺ (iron ion) contained within a prosthetic haem group. Haemoglobin is a 4 chained polypeptide comprised of 2 alpha and 2 beta polypeptide chains, each containing a prosthetic haem group, therefore 4 molecules of 0₂ can be carried by each haemoglobin protein. The affinity of haemoglobin for O₂ increases with each subsequent O₂ molecule binding.
Carbon dioxide however is carried in multiple forms. The majority (around 70%) is transported within the blood as bicarbonate ions. These HCO₃- ions are produced within the erythrocytes, through a reaction catalysed by the enzyme carbonic anhydrase (CO₂ + H₂O ⇌ H₂ CO₃ ⇌ H⁺ + HCO₃ ^_ ). These HCO₃ ^_ ions are then exchanged for Cl^_ ions and are transported in the plasma, however the H⁺ ions are retained within the erythrocyte to prevent a decrease in blood PH. 20% of CO₂ is carried through binding with haemoglobin within the erythrocyte in a similar mechanism to oxygen. Lastly, the remaining 10% of CO₂ is directly dissolved into the blood plasma and carried in aqueous solution.