diffusion

• net movement of particles from an area of high concentration to an area of low concentration
• molecules can diffuse both ways but the net movement will be to the area of lower concentration. continues until particles are evenly distributed through the liquid or gas
• concentration gradient is the path from an area of high to low concentration. particles diffuse down a concentration gradient
• passive process - no energy needed
• small, non polar molecules e.g. O2 and CO2 can easily diffuse through spaces between the phosoholipids
• water is also small enough to fit so is able to diffuse across the plasma membrane even though its polar ( osmosis )
• factors effecting rate :

  • concentration gradient - higher it is, faster the rate
  • thickness of exchange surface - thinner, faster rate
  • surface area - larger, faster rate
  • temperature - warmer, faster as particles have more kinetic energy