D2.3.8 - Higher Level

• The concept of water potential helps to understand movement of water in living systems, especially plants.
• Water potential is a measure of the potential energy per unit volume.
• The symbol for water potential is the Greek letter psi and the units for measurement are Kilopascals (kPa) or megapascals (MPa).
• The absolute quantity of potential energy cannot be determined, so all values are relative.
• Pure water at standard atmospheric pressure and 20°C has been assigned a water potential of zero.
• Many factors influence water potential, but in living systems only two contributors vary in such a way that they need to be considered: solute concentrations and hydrostatic pressure.
• Rises or falls in hydrostatic pressure change the potential energy of water.
• The higher the pressure, the more potential energy water has.
• When solutes dissolve, the potential energy of water is reduced.
• The higher the solute concentration, the less potential energy water has.