Water Potential

Water potential

• a measure of water’s potential energy (to diffuse)

• distilled water has the greatest potential to move $\psi$ = 0

Adding solute

• decreases water potential

• water likes to be more negative and when you add more solutes the more negative the solution gets

  • water doesn’t want to leave

High —> Low water potential

Problem Statement

A plant cell has a solute potential of -7.5 bars and maintains a constant volume (no net water flow) when placed in an open-beaker solution with a solute potential of -4.0 bars. What is the pressure potential of the cell?

—> find Y_p of the cell

What we know

• open container

  • pressure of the solute = 0

• -7.5 Bars

  • solute potential in the cell

• No net water flow

  • at equilibrium —> water potential of the cell and solution are equal

• -4.0 Bars

  • solute potential in the solution

Total water potential of the cell = total water potential of the solution

Y_Solution = -4.0 + 0 = -4.0 Bars

Equation

Y_Cell = Y_{pressure potential in cell} + Y_{solute potential in cell}

-4.0 = -7.5 + Y_P,cell => Y_{p, cell} = 3.5