Final answer:
Highly active tissues during exercise would have an oxygen saturation of hemoglobin of less than 50% due to the increased demand for oxygen and other factors like elevated temperature, which promote faster oxygen dissociation from hemoglobin.
Step-by-step explanation:
Oxygen-Hemoglobin Dissociation Curve and Active Tissues
During exercise, highly active tissues such as skeletal muscle have a higher demand for oxygen to produce ATP. This heightened activity lowers the partial pressure of oxygen in the tissue to about 20 mm Hg, while the partial pressure inside capillaries is about 100 mm Hg.
The significant difference in pressure facilitates a greater number of oxygen molecules to dissociate from hemoglobin and be used by the tissues. According to the oxygen-hemoglobin dissociation curve, the oxygen saturation of hemoglobin in highly active tissues during exercise would decrease.
This process is enhanced by factors such as increased temperature in actively working muscles, causing an even faster dissociation of oxygen from hemoglobin. Therefore, the level of saturation you might expect in highly active tissues during exercise is less than 50%, corresponding to option D.