Diffusion

• Diffusion

  The net movement of molecules or ions from an area of high concentration to an area of low concentration, until equilibrium is reached
• What can diffuse through the Phospholipid Bilayer?


  • Lipid-soluble
  • Non-polar
  • Very small
• Since diffusion is passive...


  no energy is involved because substances move down a concentration gradient
• Diffusion cannot be controlled
• Fick's Law


  Diffusion$\alpha$ SA x Concentration Gradient/Diffusion Distance
• Factors that effect rate of diffusion


  • Difference in concentration
  • High temperature
  • Large Surface Area
  • Smaller molecule or ion
  • Shorter distance of diffusion
• Facilitated Diffusion


  Allows water-soluble, charged and larger ions across a plasma membrane
• Protein Channels


  Water filled hydrophilic channels that span the phospholipid bilayer. They're selective and will only open in the presence of a specific molecule or ion
• Carrier Proteins


  Change shape when a particular molecule or ion binds to it. The comformational change allows for the molecule or ion to be passed to the other side
• Facilitated Diffusion is passive, no energy as it goes down a concentration gradient