Rate of simple diffusion

• What does simple diffusion depend on?


  • concentration gradient
  • thickness of the exchange surface
  • surface area
• Why does the rate of simple diffusion depend on the concentration gradient?


  • the higher the concentration gradient, the faster the rate of diffusion
  • As diffusion takes place, the difference in concentration between the 2 sides of the membrane decreases until it reaches an equilibrium
  • this means that diffusion slows down over time
• what does it mean when it reaches an equilibrium (in terms of conc)?


  the concentration on both sides of the membrane is equal
• Why does the rate of simple diffusion depend on the thickness of the exchange surface?


  the thinner the exchange surface (ie the shorter the distance the particles have to travel), the faster the rate of diffusion
• Why does the rate of simple diffusion depend on the surface area?


  the larger the surface area the faster the rate of diffusion
• what do microvilli do?


  increase the surface area for faster diffusion
• why do microvilli increase the surface area?


  for faster diffusion
• What are MICROVILLI?


  Projections formed by the cell-surface membrane folding up on itself
• What do microvilli give the cell?


  a larger surface area - in human cells they can increase surface area by approx. 600 times
• what does a larger surface area mean?


  That more particles can be exchanged in the same amount of time- increasing the rate of diffusion