Rate of facilitated diffusion

• What does the rate of facilitated diffusion depend on?


  • the concentration gradient
  • the number of channel or carrier proteins
• Why does the rate of facilitated diffusion depend on the concentration gradient?


  • The higher the concentration gradient, the faster the rate of facilitated diffusion (up to a point)
  • As EQUILIBRIUM is reaches, the rate of FACILITATED DIFFUSION WILL LEVEL OFF
• Why does the rate of facilitated diffusion depend on the number of channel or carrier proteins?


  Once all the proteins in a membrane are in use, facilitated diffusion cannot happen any faster, even if you increase the conc gradient.

  So the greater the number of channel/carrier proteins in the cell membrane, the faster the rate of diffusion
• the greater the number of channel/carrier proteins in the cell membrane.......?


  ........ the faster the rate of diffusion!
• what happens once all the proteins in a membrane are in use?


  facilitated diffusion cannot happen any faster, even if you increase the concentration gradient!
• What is the effect of having more channel proteins?


  the rate of facilitated diffusion is increased
• what are Aquaporins?


  special channel proteins that allow the facilitated diffusion of water through cell membranes/
• give details about Aquaporins?


  • some kidney cells are adapted to have lots of aquaporins
• what do the aquaporins allow kidney cells to do?


  reabsorb a lot of the water that would otherwise be excreted by the body- about 180 litres need re-absorbing every day