Equilibrium in Living Systems There are numerous equilibrium systems in the human body which are essential to our everyday functioning. Case 1: Consider the equilibrium: haemoglobin + oxygen oxyhaemoglobin In an environment with a high oxygen concentration the equilibrium point is moved to the right and lots of oxyhaemoglobin is produced. This occurs in your lungs. The oxyhaemoglobin is then transported via your bloodstream to your bodies cells which need the oxygen for respiration. In the cells there is a low concentration of oxygen compared with oxyhaemoglobin and so the reverse reaction predominates, thereby releasing the oxygen for use. Case 2: Consider the equilibrium: haemoglobin + CO CO-haemoglobin This equilibrium system has a higher K value than the formation of oxyhaemoglobin considered above. If CO is introduced to the lungs it will consume haemoglobin at the expense of the oxyhaemoglobin reaction. A reduction in available haemoglobin drives the reaction in case 1 backwards. With insufficient oxygen reaching brain cells unconsciousness, or in severe cases death, results. Case 3: Consider the equilibrium: CO2(g) CO2(aq) Carbon dioxide gas is a product of the respiration reaction in cells. As more CO2(g) is produced it drives the CO2 into solution where it reacts with water in a two step process. CO2(aq) + H2O(l) H2CO3(aq) H+(aq) + HCO3-(aq) The equilibrium constant lies well to the right for these reactions. When the HCO3reaches the lungs the reverse reaction predominates as it is a CO2 low concentration environment. 49