Water Potential (Y)

Why can salt cause a water deficit in plants even
though the soil has plenty of water?
Given that the plant cell in the picture is
maintaining a constant volume, what can you
deduce about the water potential of the plant cell
and the solution in the beaker?
Water Potential
Plant cell in an aqueous solution. The water
potential of the cell equals that of surrounding
solution at dynamic equilibrium.
From AP Biology Exam Equation Sheet
Water Potential (Y)
• Y = Yp + Y s
• Yp = pressure potential
• Ys = solute potential
The water potential will be equal to the solute potential of a solution in an open
container, since the pressure potential of the solution in an open container is
The Solute Potential of the Solution
• Ys = –iCRT
• i = ionization constant (for sucrose this is 1.0 because sucrose does not ionize
in water)
• C = Molar concentration
• R = Pressure constant (R = 0.0831 literbar/moleK
• T = Temperature Kelvin (273 + °C)
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