Final answer:
An increase in hemoglobin's affinity for oxygen corresponds to a leftward shift of the oxygen dissociation curve. A rightward shift, indicating a decreased affinity, can be caused by factors like elevated PCO2 and hyperthermia. Diseases affecting hemoglobin's structure or levels can also influence this affinity. The correct option is B. Shift to the left.
Step-by-step explanation:
An increase in hemoglobin affinity for oxygen occurs with a shift to the left on the oxygen dissociation curve. This leftward shift indicates that hemoglobin has a higher affinity for oxygen, allowing it to bind oxygen more readily. Conversely, a rightward shift in the curve signifies a decrease in oxygen affinity, as seen with factors like elevated levels of carbon dioxide (PCO2), lower blood pH, hyperthermia, and certain diseases like sickle cell anemia and thalassemia which affect hemoglobin's shape or oxygen-carrying capacity.
When the blood pH decreases due to increased carbon dioxide levels, it leads to the release of more oxygen from hemoglobin to the tissues, reflected as a rightward shift of the curve. Increased body temperature, seen during intense muscular activity for example, also decreases hemoglobin's oxygen affinity, causing a similar rightward shift. A leftward shift might occur when these conditions are reversed - lower body temperature, decreased carbon dioxide levels, and higher pH leading to an increased affinity for oxygen. The correct option is B. Shift to the left.