Water Potential Tendency of water to favor one side more than another. Water moves from an area of high potential to low potential. Predicts which way water diffuses in PLANT tissues using the Greek letter Psi.
Formula for Water Potential Water potential = pressure potential + solute potential
Pressure Potential Pressure exerted by the cell wall of a plant (limits water uptake)
Solute Potential • Effect of solute concentration • The more solute that is added to water, the more negative the potential. • Causes water potential to decrease
Note: Pure water has a solute potential of Zero (0) Unit of Measure for Water Potential = Bar
How do you calculate solute potential? • Solute Potential = - iCRT • i = Ionization Constant • C = Molar Concentration • R = Pressure Constant 0.0831liters bar/ mole K • T = Temperature in Kelvin (273 + ° C)
Why only in plant cells? Because the water diffuses into the cell and causes it to swell and not explode because of the cell wall. An increase in pressure on the cell wall is called Turgor Pressure.
Plasmolyzes If more solute is added to the water surrounding the plant cell, water will flow out of the cell causing it to lose turgor. The cell membrane shrinks away from the cell wall and plasmolyzes.
Example 1 Calculate the solute potential of a 0.1 M NaCl solution at 25°C. If the concentration of NaCl inside the plant cell is 0.15 M, which way will the water diffuse if the cell is placed into the 0.1 M NaCl solutions?
Answer 0.1 M outside of cell .15 M inside of cell Solute Potential = -iCRT - 2 (0.1 M) (0.0831 liters bar/mole K) (273+25) = - 4.95 bar Water will flow into cell