Water potential

• what is water potential?

  the tendency for water to move into a system; water moves from a solution with higher water potential (less negative) to one with a lower water potential (more negative)
• what decreases water potential?

  the addition of solutes
• whats the water potential of pure water?

  0
• what is water potential in terms of energy?

  a measure of the free energy of water molecules
• what is water potential measured in?

  kilopascals (kPa)
• why does pure water have a water potential of 0?

  as theres no tendency for water molecules to move into pure water
• how does the addition of a solute decrease water potential?

  • the addition of a solute to pure water tends to bring water molecules in
  • as the force pulls inwards, it has a negative sign and so the addition of a solute to pure water lowers the water potential and gives it a negative value
• how are water molecules pulled in based on concentration?

  the higher the concentration, the more strongly water molecules are pulled in, and the lower, i.e. the more negative, the water potential
• what happens when theres a high concentration of water molecules (e.g. a dilute solution)?

  the water molecules have a high potential energy as they are free to move
• what happens to water molecules in a solution?

  the water molecules are weakly bound to the solute so fewer are free to move - this system has a lower potential energy
• what happens to external water molecules with higher potential energy?

  they will move down an energy gradient to the lower potential energy - this is the pulling force they experience, which is the osmotic pull inwards (i.e. the water potential)
• what happens in a more concentrated solution?

  it has even fewer free water molecules so the pull on water molecules is greater so the water potential is more negative (i.e. lower)
• how do water molecules travel across cell membranes?

  they travel through specialised channels called aquaporins - a cell may have thousands of aquaporins and transfer billions of water molecules each second
• what do these symbols mean?

  they are different ways of saying water potential