Water Potential

Water Potential
Teacher: What is the formula for water?
Student: H, I, J, K, L, M, N, O
Teacher: That's not what I taught you.
Student: But you said the formula for water was...H to O.

Prepared by

Lower concentration of solute

Water potential
– the ability of water move out of the solution through osmosis.

Solute molecule Equal concentration of solute

Higher concentration of solute

H2O

Selectively permeable membrane
Water
molecule

Solute molecule with cluster of water molecules
Net flow of water

ψcell

Water potential of cell (ψcell) – the ability of H2O molecules to move out of cell by osmosis. nwk ψsol

Water potential for solution (ψsol) – the ability of
H2O molecules to move out of solution by osmosis. nwk

ψs

Solute potential (ψs) = osmotic potential
– the ability of solution causing H2O molecules to enter by osmosis because presence of solute/osmotic substances. nwk Distilled water separated by a partiallypermeable membrane:

Water molecules are moving from one side of the membrane to the other but there is no net osmosis. nwk If a substance is dissolved in water, the kinetic energy of the water molecules is lowered.
This is because some water molecules aggregate on the surfaces of the other molecules.

nwk

 For osmosis, it talks about the potential water molecules have to move.
 Distilled water has the highest potential
(zero):
ψ of pure water = 0 kPa
 When water has another substance dissolved in it, the water molecules have less potential to move. The potential is NEGATIVE. ψsol = always -ve kPa nwk 

osmotic potential;

 Less - ve of ψ out. water potential.
H2O more energy to move

 Water molecules always move from less negative to more negative water potential.

Ψ = -0.5 kPa

nwk

Ψ = -0.9 kPa

ψp
Pressure potential (ψp) – the pressure that derives from the cell wall to the cell.
Ψp = always +ve kPa nwk Ψcell

nwk

=

Ψs +

Water potential
=
of plant cell

Solute potential Ψp
+

Pressure potential Summary
ψcell