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AP Biology
Water Potential Notes
Jeffrey
Water Potential:
A measure of the tendency of water to leave one place in favor
of another place.
Greek letter psi () is used to represent water potential
Water will move from an area of higher water potential to
lower water potential.
Water potential can be positive, zero, or negative.
Distilled water in an open beaker has water potential of "zero".
Factors which affect water potential:
Solute potential (amount of solute added to a solution)
As solute concentration increases, water potential decreases.
Solute and water potential are inversely related.
It is always a negative number since pure water has a water
potential of zero.
An increase in solute potential makes water potential value
more negative.
Pressure potential (physical pressure)
As the pressure increases, water potential increases.
Water movement is directly proportional to the pressure on
a system.
It is usually positive in living cells.
An increase in pressure potential makes the water potential
more positive.
Water Potential formula

=
Water
Potential
p
+
Pressure
Potential
S
Solute
Potential
Dynamic equilibrium is reach when the water potential inside the
cell equals the water potential outside the cell.
Why is it important to know about water potential?
Biologists use this term when predicting the movement of water into or
out of plant cells