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A schematic diagram. On the left-hand side of the diagram is a vertical row of five, pink, rectangular peripheral cells, one of which has CO2 written within it.

A yellow arrow shows CO2 leaving this cell; 10% of it is shown (by a blue arrow) as dissolved CO2 in the blood and tissue fluids. The remaining CO2 is shown as entering a stylised red blood cell. Yellow arrows within the cell show CO2 movement.

At the top of the red cell CO2 is shown binding to Hb (haemoglobin) to give Hb−CO2. At the bottom of the red cell CO2, after its combination with water and dissociation to give H+ and HCO3-, is shown as H+ with Hb to give protonated haemoglobin, Hb−H+, and HCO3- is shown leaving the cell, passing over a mauve circle which shows Cl- moving in the opposite direction. Blue arrows to the right of the diagram indicate that 30% of the CO2 is protein bound and 60% of the CO2 is chemically modified.

 4.3 Bicarbonate