So the x axis is the intracellular PH, the PH inside the cell. And as we go from left to right, the PH increases. Now, the y axis describes the percentage of the DNA molecules that exist in their double helix form. So what exactly does this graph actually tell us? Well, we see that at a PH of seven, at a normal PH of seven, all the DNA molecules, 100% of the DNA molecules in the nucleus, exist in their double helix form. Now, as we begin to add a few drops of hydroxide ions, we begin to increase our PH.