Selective permeability of membranes.
   Proteins  also  have  hydrophilic  and  hydrophobic  regions  and  are
   embedded in the bilayer.
   This  structure makes plasma membranes selectively permeable; allowing
   only some molecules to cross.
   Preview:  <A ClAsS=ACT Href="http://media.pearsoncmg.com/bc/bc_campbell_biology_7/media/activities/load.html?7&amp;B" oNClick="popact('http://media.pearsoncmg.com/bc/bc_campbell_biology_7/media/activities/load.html?7&amp;B');txtcolor('fluid_mosaic1','gray');return false;" Id=fluid_mosaic1><iMg sRc="/images/tutorial.gif" aLt='' boRDer=0></A>