 Phospholipids  Membrane Proteins

 Maintains fluidity in the membrane!!! (think about the cotton plant!)

 Maintains shape, act as enzymes, transport in/out of cell, cell communication (receptors)

© 2012 Pearson Education, Inc. Animation: Membrane Selectivity Right click on animation / Click play

 Only small, non-polar molecules move through the bilayer (ex: O2, CO2, H2O, Lipid- Hormones, Fatty Acids)  **Ionic, Charged, Large, Polar (hydrophilic) molecules CANNOT cross the membrane without help!)**

 Inactive structural supports composed of polysaccharides  Plants (cellulose), Fungi (chitin), Many Prokaryotic cells (peptidoglycan)

Figure 5.3A Molecules of dye Membrane Pores Net diffusion Equilibrium

Figure 5.3B Net diffusion Equilibrium

 Measurement of the relative concentrations of solute between two solutions (inside and outside of cell)  Hypertonic – More solute/less solvent  Hypotonic: Less solute/More solvent  Isotonic: Equal concentrations **These terms are COMPARATIVE**

Figure 5.4 Osmosis Solute molecule with cluster of water molecules Water molecule Selectively permeable membrane Solute molecule H2OH2O Lower concentration of solute Higher concentration of solute Equal concentrations of solute