Best for O-level Biology, NEET Biology and Degree Level

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