Membrane Structure and Function Chapter 7 Overview: 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 ? 2011 Pearson Education, Inc. Figure 7.1 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 and hydrophilic regions The fluid mosaic model states that a membrane is a fluid structure with a ?mosaic? of various proteins embedded in it ? 2011 Pearson Education, Inc. Membrane Models: Scientific Inquiry