diffusion

• what is the definition of diffusion?

  the net movement of particles from an area of higher concentration to an area of lower concentration
• what is simple diffusion?

  the diffusion of particles/molecules directly through the phospholipid bilayer

  only small, non polar, lipid soluble particles/molecules

  BUT not water soluble due to hydrophobic tails
• e.g of simple diffusion molecules

  co2, oxgyen, small fatty acids and water molecules
• factors affecting simple diffusion

  • concentration gradient - bigger difference = faster rate. Slows as you move towards equilibrium.
  • thickness of exchange surface - thinner = shorter diffusion pathway and a faster rate
  • surface area - bigger surface area - quicker rate
• what is facilitated diffusion?

  the diffusion of larger particles/ molecules or ions through transport proteins in the phospolipid bilayer
• what do channel proteins move?

  ions - K+ or Na+ or Cl -
• what do carrier proteins transport?

  move large molecules - glucose - amino acids which attach to carrier protein that change their shape and are transported as a result.
• factors affecting facilitated diffusion

  • concentration gradient til the saturation of transport proteins
  • bigger difference between areas = faster rate but slows as you move towards equilibrium
  • the number of transport proteins - more channel proteins = higher rate of diffusion
• how to calculate diffusion from a straight line graph?

  change in y / change in x
• curved line graph

  draw a tangent with the centre on the section from the question and equal to either side

  then change in y/ change in x