So the black curve describes the condition in which we don't have any carbon dioxide present and we have a normal PH of 7.4, which is the PH found inside our lungs. The blue curve describes the conditions in which we don't have any carbon dioxide, but we decrease our PH. So we increase the hydrogen ion concentration, the PH decreases to about 7.2 and the rec curve describes the condition under which we have about 40 mercury of carbon dioxide present in that surrounding area and we also decrease the PH to 7.2. So once again, we increase the hydrogen ion concentration as compared to this case here. And notice that when we don't have any CO2 present but we lower the PH, the black curve actually shifts to the blue position. And when we keep the PH a 7.4 and we add carbon dioxide, the blue curve shifts to where the red curve is.