So ion specificity is the ability of the ion channel. In this case, it's the potassium ion channel to basically move specific ions. In this case, it's the potassium ions across the cell membrane, while at the same time preventing the movement of all other ions. So the question is, how is this property actually achieved by that potassium ion channel? And in general, how is it that these ion channels are so specific to types of ions that they move across the cell membrane? Well, to answer this question, let's take a look at the following diagram.