Final answer:
Increasing blood pH or decreasing PCO₂ shifts the oxygen-hemoglobin dissociation curve to the left, indicating increased hemoglobin affinity for oxygen. A decrease in blood pH or increase in PCO₂ shifts the curve rightward, showing decreased affinity. This relationship is due to the Bohr effect.
Step-by-step explanation:
When blood pH increases or when there is a decrease in partial pressure of carbon dioxide (PCO₂), there is an increase in the affinity of hemoglobin for oxygen, which shifts the oxygen-hemoglobin dissociation curve to the left. This means that at a given partial pressure of oxygen, hemoglobin is more saturated with oxygen than it would be at a lower pH or higher PCO₂. Conversely, when blood pH decreases or PCO₂ increases, the curve shifts to the right, indicating a decrease in hemoglobin's affinity for oxygen, and thus more oxygen is required to reach the same level of hemoglobin saturation.
The Bohr effect describes this relationship, wherein a higher pH (more basic) inhibits oxygen dissociation from hemoglobin leading to a leftward shift in the curve, whereas a lower pH (more acidic) promotes oxygen dissociation from hemoglobin, causing a rightward shift in the curve. The oxygen-hemoglobin dissociation curve is a graphical representation that plots the percent saturation of hemoglobin against the partial pressure of oxygen. It is S-shaped because the binding of oxygen to hemoglobin is cooperative; once one oxygen molecule is bound, it becomes easier for subsequent oxygen molecules to bind.