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Diffusion is the spontaneous intermingling of the particles of two or more substances as a result of random thermal motion (1), usually leading to a motion from areas of high concentration to areas of low concentration that ends when the concentration becomes uniform. In essence, it tries to answer the laws of thermodynamics by maximizing entropy.

Rate of diffusion

  • four factors affect the rate of diffusion of a substance from one region of a solution to another.
  • Concentration gradient of the solute (proportional)
  • Temperature (proportional)
  • Molecular size of solute (inversely proportional)
  • Viscosity of medium (inversely proportional)
  • Illustration 1A graphical example of how much longer it would take for molecules to bridge 10cm than 10 micrometers
  • The approximate distance over which diffusion is an effective transport mechanism in a biological system is 20 - 40 µm