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Water Potential WATER POTENTIAL • Water potential measures water’s tendency to leave one place in favor of another Calculating water potential • Ѱs + Ѱp = Ѱ • Solute potential – Adding solute decreases water potential • Pressure potential – Increasing pressure increases water potential Ѱs =-iCRT • i=ionization constant (number of ions solute forms in water) • C=concentration (mol/L) • R=pressure constant (.0831 liter bars/mol K) • T=temperature (C+273) Ѱp • Plant cells have cell walls • Turgor pressure pushes out on the cell wall • Limits expansion Equilibrium • Water moves until the water potential outside the cell is equal to the water potential inside the cell Practice problems • Calculate the water potential of a 1M sucrose solution at 22° C • Calculate the water potential of a cell that has a pressure potential of 4 and a solute potential of -5 • What would happen to the cell if it were placed in the 1M sucrose solution? • The initial molar concentration of the cytoplasm inside a plant cell is 2M and the cell is placed in a solution with a concentration of 2.5M. – Calculate the water potential of the cell and of the solution – Predict which direction water will move based on your calculations – Predict what will happen to the pressure potential of the cell – What will be the water potential of the cell once the system has reached equilibrium