Simple Diffusion

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•  Particles move across membranes by simple diffusion, facilitated diffusion, osmosis and active transport

Diffusion is the net movement of molecules from a region of high concentration to a region of low concentration

  • This directional movement along a gradient is passive and will continue until molecules become evenly dispersed (equilibrium
  • Small and non-polar (lipophilic) molecules will be able to freely diffuse across cell membranes (e.g. O2, CO2, glycerol)

The rate of diffusion can be influenced by a number of factors, including:

  • Temperature  (affects kinetic energy of particles in solution)
  • Molecular size  (larger particles are subjected to greater resistance within a fluid medium)
  • Steepness of gradient  (rate of diffusion will be greater with a higher concentration gradient)

Simple Diffusion Along a Concentration Gradient