Water potential.

Water moves across a selectively permeable membrane from higher water potential to lower by osmosis.

Water potential (MegaPascal, or Ψ) is the sum of pressure potentialP) and solute potentialS):

Ψ = ΨP + ΨS.

  1. The addition of solutes reduces water potential (to a negative value).

  2. Application of physical pressure increases water potential.

  3. The increased physical pressure can reverse the effects of the solutes .

  4. A negative pressure reduces water potential (on the other side).