Water potential is a measure of water's ability to do work. It is represented by the Greek letter psi and measured in pascals. Water potential is equal to the sum of solute potential and pressure potential. Solute potential decreases as solute concentration increases, making water potential more negative. Pressure potential increases with pressure, making water potential less negative. Water will always move from areas of higher water potential to lower water potential through semipermeable membranes.

1. By: Sanjay Kumar Lecturer

2.  Water potential (Ψ) is a measure of water’s
potential to do work.
 It is represented by Greek letter Psi (Ψ) .
 The value is measured in Pascal's (Pa).
 Water potentia Ψw in any living system is the
sum of Solute potential (Ψs )and Pressure
potential (Ψp).

3.  Both Pressure potential and solute potential
affect water potential.
 The solute potential (ψs) of a solution is
concentration of dissolved solutes.
 The pressure potential (ψp) is the hydrostatic
pressure on a solution or hydrostatic pressure
exerted on cell wall.

4.  Water potential in a plant cell or tissue can be
written as the sum of -
 the solute potential + pressure potential
 And gravitational potential ( due to gravity)
Ψw =Ψs +Ψp +Ψg
 Gravitational potential (YG) depends on the
position of the water in a gravitational field,
 Hence, the above given equation is written as
follows.
Ψw =Ψs +Ψp

5.  Pure water has the maximum water potential which by definition is
zero.
 Water always moves from a region of higherΨw to one of lowerΨw.
 All solutions have lower Ψw than pure water.
 Water always moves from the area of high water
 potential to the area of low water potential.
 Water potential of pure water at normal temperature and pressure
is zero.
 This value is considered to be the highest.
 The presence of solid particles reduces the free energy of water and decreases the
water potential.Therefore, water potential of a solution is always less than zero or
it has negative value.
 Osmosis in terms of water potential occurs as a movement of water molecules from the
region of higher water potential to a region of lower water potential through a semi
permeable membrane.

6.  When solute potential (Ψs) is increases than water
potential (Ψw )is decreases
 It is defined as the amount by which the water potential is
reduced as the result of the presence of the solute.
 due to concentration of dissolve solutes which by its effect
on the entropy components reduces the water potential
 Ψs are always in negative values.
 it is expressed in bars with a negative sign

7.  When pressure potential (Ψs) is increases than water
potential (Ψw )is decreases
 Due to hydrostatic pressure, which by its effect on energy
components increases the water potential
 Plant cell wall is elastic and it exerts a pressure on the
cellular contents. As a result the inward wall pressure,
hydrostatic pressure is developed in the vacuole it is
termed as turgor pressure.
 The pressure potential is usually positive
 And operates in plant cells as wall pressure and turgor
pressure.

8.  Solute was added to the solution on the left side of the
membrane
 This decreased the chances that water would move out of the
solution to the left of the membrane and into a solution to the
right of the membrane.
 This means that the water on the left side of the membrane has
less potential to do work than the water on the right side.
 What does this mean in terms of water potential?
 It means that the solution to the left of the membrane has a
more negative water potential than the solution to the right of
the membrane.
 Therefore, water will flow from the right side of the membrane
to the left.
 Water always moves towards a more negative water potential.

10. Osmotic Pressure:
 The pressure
applied by the
solution to
prevent inward
movement of
solvent/Water.
 Symbol: Pi
Osmotic Potential:
 The potential ofWater
molecules to move from
a Hypotonic to
Hypertonic Solution.
 It is represented by (Ψs).
 BothTerm Osmotic pressure
and Osmotic potential are
refers to Solution