Diffusion & Osmosis

Diffusion and osmos notes, biology aqa AS unit one

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  • passive movement of molecules down a concentration gradient
  • small uncharged molecules such as O2 and CO2
    -can pass through phospholipids

Rate of diffusion depends on:

  • Concentration gradient- larger the faster
  • thickness of exchange surface - thinner the faster
  • surface area - larger the faster 
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Facilitated Diffusion

Diffusion of larger/charged molecules.

1) Carrier Proteins facilitate large molecules

  • molecule attatches to protein which changes shape and releases on other side of membrance

2) Channel Proteins facilitate diffusion of charged particles

  • via pores in the membrane
  • different channel proteins for different charged particles 
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The diffusion of water moelcules across a partially permeable membrane from an area of high water potential to an area of lower water potential.

Water Potential: potential of water molecules to diffuse in or out of a solution

Isotonic: Same water potential

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