Explain what causes the Bohr shift to occur, and give one situation in which this is useful.

The Bohr Shift describes the movement of the oxygen dissociation curve to the right of normal. This occurs due to increased levels of carbon dioxide, such as when a person increases their exercise level, which causes an increased concentration of carbonic acid to be formed. Carbonic acid lowers the pH of the blood (making it more acidic) and meaning there are more H+ ions present., as the carbonic acid dissociates.
An increase in H+ concentration means haemoglobin has a lower affinity for oxygen (haemoglobin molecules are unable to bind as tightly to the oxygen and more likely to release it). This means more oxygen dissociates at the tissues (more oxygen is unloaded from the haemoglobin present in the red blood cells). More oxygen present at the tissues means more aerobic respiration can occur, producing more ATP that can be used to produce contraction of muscles during exercise.