? 2017 Pearson Education, Inc. Lecture Presentations byNicole Tunbridge and Kathleen Fitzpatrick Chapter 7Membrane Structure and Function 1 Life at the Edge The plasma membrane is the boundary that separates the living cell from its surroundings The plasma membrane exhibits selective permeability, allowing some substances to cross it more easily than others Transport proteins are often responsible for controlling passage across cellular membranes ? 2017 Pearson Education, Inc. 2 Concept 7.1: Cellular membranes are fluid mosaics of lipids and proteins Phospholipids are the most abundant lipid in the plasma membrane Phospholipids are amphipathic molecules, containing hydrophobic (?water-fearing?) and hydrophilic (?water-loving?) regions