Cell Membranes


Cell Membranes

Types of movement


  • small and non-polar lipid soluble molecules
  • directly through phospholipid bilayer
  • passive
  • net movement down concentration gradient

Faciliated diffusion:

  • As diffusion but requiring a channel protein in the membrane to allow the diffusion of polar molecules, charged and water-soluble groups.


  • essentially the diffusion of free water molecules
  • net movement of free water molecules from a solution with lower solute concentraion to a solution with a higher solute concentration
  • movement through a partially permeable membrane.
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Cell Membranes

Active Transport:

  • all kinds of molecules possible
  • through carrier proteins
  • active- needs energy from the breakdown of ATP
  • up a concentration gradient

Exo-(out of cell) and endocytosis (into cell):

  • large particles of all kinds
  • bulk transport involving vesicles made from cell surface membrane in endocytosis, and fusing with the cell surface membrane in exocytosis. 
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