Which factor will shift the O2 dissociation curve to the left?

The shift of the oxygen dissociation curve to the left indicates an increased affinity of hemoglobin for oxygen. This means that hemoglobin holds onto oxygen more tightly, making it less available to tissues. Alkalosis, which is a condition characterized by increased blood pH (i.e., more basic), promotes this leftward shift. In an alkaline environment, hemoglobin tends to bind oxygen more effectively due to the changes in the structure of the hemoglobin molecule and the reduced release of oxygen to the tissues.

In contrast, factors such as anemia, hyperthermia, and hypercapnia typically shift the curve to the right, indicating a decreased affinity of hemoglobin for oxygen, which enhances oxygen delivery to tissues under certain conditions. In the case of alkalosis, the combination of increased pH and lower concentrations of hydrogen ions results in hemoglobin retaining more oxygen, which is key to understanding how pH affects oxygen transport and delivery in the body.