ninja icon


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

Osmosis is the net movement of water molecules across a semi-permeable membrane from a region of low solute concentration to a region of high solute concentration (until equilibrium is reached)

  • Water is considered the universal solvent – it will associate with, and dissolve, polar or charged molecules (solutes)
  • Because solutes cannot cross a cell membrane unaided, water will move to equalise the two solutions
  • At a higher solute concentration there are less free water molecules in solution as water is associated with the solute
  • Osmosis is essentially the diffusion of free water molecules and hence occurs from regions of low solute concentration

Relationship between Solute Concentration and Levels of Free Water Molecules