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  • Created by: Olivia
  • Created on: 30-04-13 10:11

Osmosis is a special case of diffusion

Osmosis is the net movement of water molecules across a partially permeable membrane from a region of high water concentration to a region of lower water concentration

  • A partially permeable membrane is just one with very small holes in it. So, small in fact that only tiny molecules (like water) can pass through them, and bigger molecules (e.g. sucrose) can't. A cell membrane is a partially permeable membrane.
  • The water molecules actrually pass both ways through the membrane during osmosis. This happens because water molecules move about randomly all the time
  • But because there are more water molecules on one side that the other, there's a steady net flow of water into the region with fewer water molecules, e.g. into the sucrose solution
  • This means the sucrose solution gets more dilute. The water acts like its trying to even up the concentration either side of the membrane

Water moves in and out of cells by osmosis

  • Tissue fluid surrounds the…


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