Osmosis

• Osmosis = the new movement of water molecules from an area of high water potential to an area of low water potential across a partially permeable membrane
• Water potential:

  • addition of a solute to water will lower the water potential
  • the water potential of a solution is always negative
• Hypotonic: solute concentration inside the cell is higher, water is transported into the cells so they eventually burst
• Isotonic: amount of water outside the cell is equal to the amount of water inside the cell
• Hypertonic: solute concentration inside the cell is greater than outside it. Water is transported outside the cell so the cells shrink
• Osmosis in animal cells:

  • If water enters the cell it has been placed in a higher water potential than the cell and the cell will burst (cytosine)
  • If water leaves the cell the water potential is lower than the cell and it will shrink and shrivel
• Osmosis in plant cells:

  • If water enters the cell it has been placed in a higher water potential than the cell. The protoplast will expand and push against the cell wall.
  • The cell wall prevents the cell from bursting
  • When a plant cell is full of water it is turgid