Which of the following is true of the oxygen dissociation curve?

a. The normal partial pressure of oxygen (PO2) at which hemoglobin is 50% saturated is 20 mm Hg.
b. A shift to the right or left in response to blood pH is called the Bohr effect.
c. A shift to the left results in lower oxygen affinity.
d. A shift to the right results in less effective delivery of oxygen to tissue.

ANS: B
The Bohr effect describes the shift in position of the oxygen dissociation curve in response to blood pH; a decrease in pH (acidosis) shifts the curve to the right and results in a decreased oxygen affinity and more effective oxygen delivery. A decrease in pH (alkalosis) is the reverse: the curve shifts to the left resulting in increased oxygen affinity and less effective delivery of oxygen to tissue.