Cell Biology


Diffusion & Osmosis


  • Diffusion is the spreading out of particles from an area of high concentration to an area of low concentration. 
  • Takes place in both solutions and gases because the particles are free to move about randomly. 
  • The bigger the concentraion gradient (the difference in concentraion), the faster the diffusion rate.
  • Higher temperature = faster diffusion rate (particles have more energy so they move around faster)


  • Osmosis is the movement of water molcules across a partially permeable membrane from a region of high water concentration to a region of low water concentration.
  • Partially permeable membrane has small holes that only water molecules can pass through and bigger molecules - e.g. sucrose - can't.
  • Water molecules pass both ways through the membrane. This happens because the molecules move around randomly all the time.
  • Osmosis is a type of diffusion.


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Active Transport

Active Transport

  • Active Transport is the movement of molecules across a cell membrane from a region of low concentration to a region of high concentraion, which goes aainst the concentration gradient.
  • Root hair takes in minerals using active transport.
  • Active Transport stops us from starving.
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