Now, lipid bilayer membranes consist of two major biological molecules lipids and proteins. Now, the lipids have two functions. Function number one is to actually create a semipermeable barrier, a barrier that separates the inner aqueous environment from the outer aqueous environment. And function number two of lipids is to actually create a medium, an environment in which the proteins can actually dissolve in, because ultimately, it's the proteins that carry out nearly all the other functions of that particular membrane. So, remember, the proteins greatly diversify the functionality of cell membranes. They basically carry out processes such as signal transduction pathway, communication pathways.