AP Biology- Chapter 7: Membrane Structure and Function Plasma Membrane 8 nm thick Controls all cell traffic Separates cell from surroundings Selective permeability Allows some substances to cross easier than others Earliest evolution- formation of membrane than allowed a cell to enclose a solution different from its surroundings Ability of cell to discriminate in exchange with the environment Concept 7.1- Cellular Membranes are fluid mosaics of lipids and proteins Plasma Membrane Made mostly of lipids and proteins and has some carbohydrates Made of phospholipids Amphipathic Contain both hydrophilic and hydrophobic substances Phospholipids and most membrane proteins are amphipathic Fluid Mosaic Model Membrane is FLUID structure with embedded and attached proteins Gorter and Grendel