Turgor and plasmolysis

• what does it mean if the water potential of the external solution is less negative (higher) than the solution inside the cell?

  it means that the external solution is hypotonic to the cell and water flows into the cell
• what does it mean if the water potential of the external solution is more negative (lower) than the solution inside the cell?

  it means that the external solution is hypertonic to the cell and water flows out of the cell
• what does it mean if the cell has the same water potential as the surrounding solution?

  it means that the external solution and cell are isotonic and there will be no net water movement
• what happens to a plant cell in a hypertonic solution?

  • they lose water by osmosis
  • vacuole shrinks and cytoplasm draws away from the cell (plasmolysis-when complete, the cell is flaccid)
  • if the external concentration is high enough that the cell has lost just enough water that its membrane begins to be pulled away from the cell wall, the cell is at incipient plasmolysis
  • cell wall doesn’t exert any pressure on cytoplasm and so theres no pressure potential - this means the cell’s water potential = the solute potential of the external solution
• what does ’flaccid mean‘?

  it means ‘floppy’ and such cells can’t provide support so when a plant loses too much water and its cells become flaccid, the plant wilts
• what does plasmolysis mean?

  the reaction of the cytoplasm and the cell membrane from the cell wall as a cell loses water by osmosis
• whats incipient plasmolysis?

  cell membrane and cytoplasm are partially detached from the cell wall due to insufficient water to make cell turgid
• what happens to plant cells in a hypotonic solution?

  • takes in water until prevented by the opposing pressure from the cell wall
  • as water enters the cell, the contents expand and push out more on the cell wall, increasing pressure potential
  • pressure potential rises until its equal and opposite to the pull inwards of the solute potential
  • no more water can enter, and as theres no tendency for the cell to absorb water, its water potential is 0
• how do you know if a cell is turgid?

  it can’t take in any more water
• why is turgor important to plants, especially young seedlings?

  as it provides support, maintains their shape and holds them upright
• what is this a diagram of?

  a turgid cell

  
• what is this a diagram of?

  a plasmolysed cell

  
• what is this a diagram of?

  incipient plasmolysis on a cell