Cells have a high level of internal organization largely due to membranes. Eucaryotic cells are full of specialized organelles bound by membranes. Procaryotic cells are organized internally by the properties of their plasma membranes. Membranes have the intrinsic property of organizing a region because they are able to couple an energy source to the transport of substances from one place to another. Membranes may be the most significant organizing structures in the biological world.