Water Potential of a Solution
What we already know...
•Osmosis will occur across a semi-permeable membrane
to balance the concentrations of two solutions
•Direction of water movement:
hypotonic hypertonic
low [solute];
high [free water]
high [solute];
low [free water]
Water Potential (Ψ):
A measure of water’s tendency to move
from one area to another
For movement of water to occur, there must be a
difference in water potential between two areas.
“psi” Ψ = Ψs+ Ψp
For a cell,
Solute potential (Ψs)
•measure of the solute
content
•always zero for pure water
•adding solutes lowers
solute potential
•value is always negative
Pressure potential (Ψp)
•the pressure a closed container or
a cell wall exerts on its contents
•value is usually positive
The rigid cell wall of
a plant exerts an
inward pressure on
its contents
