For instance, sugar molecules. Sugar molecules are large enough and polar enough to not be able to pass across the membrane via simple diffusion. So in this case, if a molecule is polar and large, for example, sugars and sodium ions and so forth, they will not be able to simply dissolve inside that hydrophobic core. And in this particular case, they have to use another method. And what they use is these integral proteins, transmembrane proteins that exist inside our cells. So we have one integral protein shown here and another one shown here.