• All cells are surrounded by a cell membrane which is?partially permeable
• Water can move in and out of cells by?osmosis
• Osmosis is the?diffusion of water molecules?from a dilute solution to a more concentrated solution across a partially permeable membrane
  • In doing this, water is moving down its?concentration gradient

   

• The cell membrane is partially permeable which means it?allows small molecules (like water) through?but not larger molecules (like solute molecules)

Osmosis and the partially permeable membrane.

• Osmosis can also be described as the?net movement of water molecules?from a region of?higher water potential?to a region of?lower water potential, through a partially permeable membrane
• Water potential describes the tendency of water to move out of a solution. This term is used to avoid confusion between water concentration and concentration of a solution
  • A?dilute solution?has a?high water potential?(the right-hand side of the diagram below) and a?concentrated solution?has a?low water potential?(the left-hand side of the diagram below)

   

How osmosis works. The water moves from the region of higher water potential (dilute solution) to the region of lower water potential (concentrated solution).

• The?water potential?of?pure water?(without any solutes) at atmospheric pressure is?0kPa, therefore any solution that has solutes will have a water potential lower than 0kPa (it will be a?negative?value)