Osmosis

• Osmosis is the movement of water molecules across a partially permeable membrane from a region of high water concentration to a region of lower water concentration (down a concentration gradient)

  
• A partially permeable membrane is just one with very small holes in it. So small, that only tine molecules (like water) can pass through, and bigger molecules (e.g. sucrose) can't

  
• The water molecules actually pass both ways through the membrane during osmosis. This happens because water molecules move about randomly all the time

  
• Because there are more water molecules on one side than on the other, there's a steady net flow of water into the region with fewer water molecules, i.e. into the stronger sugar solution

  
• Due to osmosis, the strong sugar solution gets more dilute. The water acts like it's trying to 'even up' the concentration either side of the membrane

  
• Osmosis is a type of diffusion - passive movement of water particles from an area of higher water concentration to an area of lower water concentration