So we have the membrane. Let's say this is the outside and this is the inside of the cell. So we only have two types of molecules that we're going to consider. We have the purple molecules and we have these orange molecules. Now, let's say on the outside of the membrane, we have a high concentration of these purple molecules and a high concentration of these orange molecules. On the inside, we have a low concentration of the purple and a low concentration of these orange molecules.