In the plot below, the y -axis represented fractional saturation ( Y ) and the x -axis represented partial pressure of oxygen ( pO 2 ) . If the binding curve represented by II was observed at pH 7.4 , then which of the following choices represents the binding curve that would be observed at pH 7.2 ? III It is not possible to predict II (it would not change from 7.4 to 7.2 ) .