LabBench Activity

Calculating Water Potential

Water potential is calculated using the following formula:

Water potential (Ψ) = pressure potential (Ψp) + solute potential (Ψs)

Pressure potential (Ψp):

In a plant cell, pressure exerted by the rigid cell wall that limits further water uptake.

Solute potential (Ψs):

The effect of solute concentration. Pure water at atmospheric pressure has a solute potential of zero. As solute is added, the value for solute potential becomes more negative. This causes water potential to decrease also.

In sum, as solute is added, the water potential of a solution drops, and water will tend to move into the solution.

In this laboratory we use bars as the unit of measure for water potential; 1 bar = approximately 1 atmosphere.