What is the Bohr effect and how does it affect oxygen unloading?

The Bohr effect describes the change in affinity for oxygen haemoglobin has as a result of an increased partial pressure of CO2. It occurs due to the reaction between CO2 and H20, catalysed by carbonic anhydrase, to form carbonic acid. The carbonic acid then dissociates (breaks down) into Bicarbonate and H+ ions. The decrease in blood pH as a consequence of increased H+ ion concentration causes the affinity of the haemoglobin for oxygen to decrease, which allows for easier oxygen unloading. This is handy because tissues which have higher respiratory requirements, such as during exercise, will produce more C02. The requirement of oxygen for aerobic respiration in these cells is higher, and the Bohr effect helps the demands of these cells to be met due to enhanced unloading of oxygen.