Water potential

• Solvation


  The process by which a solvent interacts with and surrounds the molecules or ions of a solute
• Water as a solvent

  • It is a polar solvent, meaning that it has a partial negative charge at the oxygen end and a partial positive charge at the hydrogen end
• Polar solutes, positively charged ions, and negatively charged ions


  All dissolve in water due to their attraction to water's partial charges
• Water molecules


  • Form shells around ions and charged molecules, preventing them from clumping together
• Osmosis


  The movement of water from less concentrated to more concentrated solutions
• Water potential


  The potential energy of water per unit volume
• It is impossible to measure the absolute quantity of the potential energy of water, so values relative to pure water at atmospheric pressure and 20°C are used
• Solute potential (Ψs)


  Caused by dissolved solutes, lowers water's potential energy (more negative with higher solute concentration)
• Pressure potential (Ψp)


  Reflects water's potential energy due to pressure. Positive pressure (e.g.: turgor in plant cells) increases potential energy, while negative pressure (e.g.: lower pressure inside a cell) decreases it
• Water potential (Ψw)


  Ψw = Ψs + Ψp
• When plant tissue is bathed in a hypotonic solution


  Water moves from the solution into the cells, causing them to swell and become turgid
• When plant tissue is bathed in a hypertonic solution


  Water moves from the cells into the solution, causing them to shrink and become flaccid
• If the concentration of the hypertonic solution is high enough

  The cells may become plasmolyzed, where the plasma membrane detaches from the cell wall
• Hypertonic solutions dehydrate human cells, causing them to shrink and die
• Hypotonic solutions cause human cells to swell and burst due to the influx of water
• Isotonic solutions maintain the balance of water movement across the plasma membrane, keeping human cells healthy
• Medical applications of isotonic solutions

  • Intravenous (IV) therapy
  • Wound irrigation
  • Skin grafting
  • Eye drops