So for instance, the lipids and the proteins inside the cell membrane are held together by non covalent interactions, intermolecular bonds. And what that means is, although these intermolecular bonds are weaker than the covalent bonds, because we have so many of these intermolecular bonds, the collective aggregate of all these bonds basically makes that membrane an effective barrier. So the individual lipid and protein molecules are held together by intermolecular bonds. And although they are weak compared to the covalent bonds that actually hold the atoms in any one of these molecules. The collective aggregate of older forces make the membrane an effective barrier. Or property number five is the membrane is not rigid, it is not stationary, it is fluidlike.