Water Potential Concepts

This set of flashcards covers key concepts and definitions related to water potential in plant physiology, focusing on equations, factors affecting water movement, and calculations.

Water Potential (ψ)

A property predicting the direction of water flow by osmosis.

Two factors that determine water potential

1. Solute concentration 2. Pressure

Equation for water potential

ψ = ψs + ψp where ψs is solute potential and ψp is pressure potential.

Solute potential (ψs) of pure water

ψs = 0 bars.

Effect of solute concentration on ψs

ψs decreases as solute concentration increases; positive ψs is not possible.

Pressure potential (ψp)

The pressure placed on the solution; it can be positive (pushing water) or negative (pulling water).

ψp in an open container

In an open container, ψp = 0.

Net movement of water

Water moves from areas of higher ψ to areas of lower ψ.

Determining net flow of water

Net movement into the cell occurs when the inside solution has lower ψ than the outside solution.

iCRT equation variables

i = ionization constant, C = molar concentration, R = pressure constant (0.0831 L∙bar/mol∙K), T = temperature in Kelvin.

Calculating ψs with iCRT for NaCl solution

For 0.5 M NaCl at 300 K, ψs = -2(0.5)(0.0831)(300) = -24.93 bar.

Final water potential equation for solution

ψ = -24.93 bar + 0 bar = -24.93 bar.