4.2 - Diffusion

• Definition of diffusion ?

  The net movement of molecules or ions from a region of high conc to a lower conc until evenly distributed
• Difference between net movement and normal motion ?


  All particles are constantly moving in all directions but the net movement is the overall movement
• What kind of process is diffusion ?


  Passive
• 3 factors that increase diffusion rate ?


  higher conc gradient, larger surface area, shorter distance for diffusion
• What 3 properties do particles need to have to be able to diffuse through a phospholipid bilayer ?


  Small, non-polar, lipid soluble
• What kind of process is facilitated diffusion ?

  Passive
• What molecules can move through membranes due to facilitated diffusion ?

  Polar molecules, lipid insoluble, large
• What component of a cell membrane does facilitated diffusion require ?

  Transmembrane proteins (channel and carrier)
• Does facilitated diffusion occur against a conc. gradient ?


  No, it occurs down a conc. gradient
• What are channel proteins specific to ?

  Specific to a particular ion, if it’s not present then the channel won’t open
• How does a carrier protein allow molecules through the membrane ?

  When the specific molecule is present it binds with the protein, it changes shape and the molecule is released to the inside of the cell
• What factor can limit the rate of facilitated diffusion ?

  The number of transmembrane proteins
• When will the rate of facilitated diffusion level off ?

  When all available transmembrane proteins are fully saturated with molecules