The document summarizes key aspects of cell membranes. It notes that membranes form specialized compartments through selective permeability, creating concentration gradients and differences in pH and charge. Membranes contain proteins and lipids that give membranes structure and allow for functions like selective transport and cell signaling. The lipid bilayer is composed of phospholipids with hydrophobic tails inside and hydrophilic heads outside, and integral and peripheral proteins embed within or attach to the surface of the bilayer.