B5 - Process of Osmosis

• Osmosis 


  The movement of water from a dilute solution to a more concentrated solution through a selectively permeable membrane (image)

  
• Osmosis example 


  Part 1 (image)

  
• Osmosis example 


  Part 2 (image)

  
• Osmosis and plants 


  Normally a plant cell is more concentrated than its surroundings:

  • water enters cell through osmosis
  • vacuole expands, pushing the cell membrane against the cell wall
  • this causes the Turgor necessary for support
  • the cell wall stops the membrane expanding too far to cause damage and therefore limits the water intake

  Turgor is the state of a plant cell when it has gained enough water by osmosis for the cell membrane to push against the cell wall, making cell firm
• Plasmolysis 


  If a plant cell is surrounded by a more concentrated solution, the cell loses water by osmosis

  • The cell loses turgor and the membrane pulls away from the cell wall as the vacuole shrinks. This is called plasmolysis
  • Plasmolysis is when a plant cell is plasmolysed when it has lost water by osmosis and its membrane separates from cell wall
• Why do plants need water

  • For support (Turgor)
  • For transpiration - the movement of water up through a plant, its evaporation from leaf cells followed by diffusion out if the stomata
  • For transport - as the water moves up through the plant, it carries minerals
  • as a raw material in photosynthesis
• Isotonic Point

  • Labelled Q
  • Where the line crosses the x axis