This document discusses diffusion pressure deficit (DPD), water potential, and related concepts in plant cells. It defines DPD as the difference between the diffusion pressure of a pure solvent and a solution. Water moves from areas of low DPD to high DPD. Water potential is the difference in free energy of water between pure water and other systems like plant cells. It depends on matric, solute, and pressure potentials. Plasmolysis occurs when cells are placed in hypertonic solutions, causing water to move out by exosmosis. Deplasmolysis is the reverse process when cells return to hypotonic solutions.

1. DIFFUSION PRESSURE DEFICIT
(DPD)
&
WATER POTENTIAL
By: Dr. Sunita Sangwan
Assistant professor, Dept of Botany
Higher education Dept. Haryana

2. Plant cell as Osmotic system
Turgor Pressure(TP): It is the pressure
exerted on the cell wall from the inner side by
the cell inclusions and cell organelles through
the entry of water. Such swollen cell are called
Turgid cells and the stage of cell is called
turgidity.
Wall pressure (WP) : Pressure exerted by wall
against protoplasm in opposite direction to the
turgor pressure.
In fully rigid cell TP=WP

3. Plant cell as Osmotic system
 Osmotic pressure (OP): As a result of the separation of two
solutions by semi permeable membrane, a pressure is developed in
solution due to the presence of dissolved solutes in it. This is called
osmotic pressure.
 Osmotic pressure α concentration of solutes.
 The term osmotic potential or solute potential also used for OP.
 Osmotic potential or solute potential are equal to osmotic pressure
but has negative valve.

4. Diffusion Pressure Deficit (DPD)
 Diffusion pressure of
pure solvent > Solution
so the difference in the diffusion pressure of solvent to the solution is called diffusion
pressure deficit (DPD) or
The quantities amount of diffusion pressure of solution, in measured unit, which is less
than the diffusion pressure of its solvent is called DPD.
Ex. Let, Diffusion pressure (DP) of solvent = 30 atm
Diffusion pressure of solution = 20 atm
DPD of solution = DP of solvent – DP of solution
DPD of solution = 30-20= 10 atm

5. Diffusion Pressure Deficit (DPD)
 DPD of cytoplasm is more than the DPD of water.
 So when a cell is placed in pure water the water start entering in to the cell due to high
DPD of the cytoplasm. Since the DPD of any cell is the measurement of water absorbing
capacity of that cell, it is also called Suction Pressure (SP).
DPD (SP)= OP-WP But WP=TP
DPD (SP) = OP-TP
As water enters into cell OP decrease and TP increases and at equillibrium
OP=TP (when cell is fully turgid)
DPD (SP) = OP-OP
DPD (SP) = TP-TP
DPD (SP) =0

6. Diffusion Pressure Deficit (DPD)
 When a cell is placed in hypertonic solution:
The water from the cell goes out by the process of exosmosis resulting an increase in OP and
decrease in TP of cell cytoplasm. This phenomenon is called plasmolysis . Such a cell is
called plasmolysed cell . When the cell is completely plasmolysed that stage is call flaccid
stage. At this stage:
TP=0
So DPD (SP)= OP-TP, DPD= OP-0, DPD=OP
So DPD is not directly proportional to the OP it depends upon TP and WP.
Water water move from low DPD to high DPD as sometimes it happens that OP and TP of a
cell is high than OP and TP of other cell, even than water does not enter in to it that is due
to low DPD of that cell.

7. Water Potential
 The water molecules possess free energy and “ the difference between free energy of
water molecules in pure and in any other system is called water potential.” any other
system like water in a solution or plant cell or tissue.
 It is designated by Ψ (psi) symbol
 Water potential is measured in terms of pressure e.g. bars or atm.
 Movement of water cannot be explained in terms of differences in concentration only or
a linear expression but spontaneous movement of water from one system to another can
be best expressed in terms of difference in free energy of water between the two systems.
 The water moves from the system having higher free energy towards the system having
lower free energy and free energy of pure water is greater than the free energy of other
solutions prepared in water.

8. Water Potential
 The water potential of a solution is usually measure using pure water as standard. The
water potential of pure water at atmospheric pressure is zero (0).
 When solute particle added to the pure solvent it decreases its water potential so water
potential of the solution is always less than Zero.
 Movement of water always take place from system having higher water potential (less
concentrated) towards the system having less water potential (more concentrated).
 The movement of water will continue till the water potential of the two systems become
equal and a stage of equilibrium is reached. At this stage net movement of water will
stop.

9. The Components of Water Potential
 Major three components of Water potential (Ψ)
 Matric potential (Ψm): This is also called surface potential and in case of plant tissue &
cell it is insignificant.
 Solute potential (Ψs): this is also called osmotic potential. The amount of solute present
in water is called solute potential. Solute potential is always negative i.e. less than zero.
 Pressure potential (Ψp): It is the pressure exerted by the cell wall on the Cytoplasmic
content of cell which resulting in the development of hydrostatic pressure termed as turgor
pressure.
Ψ = Ψm + Ψs + Ψp
Ψm- neglected as it is insignificant in osmosis
So Ψ = Ψs + Ψp

10. Osmotic relations of cell acc. to Water
Potential
In fully turgid
cell
 Net movement of
water into cell stops
Ψ = Ψs + Ψp
Ψs = Ψp
But Ψs has negative
valve
So Ψ = 0
So the water potential
become zero
In fully flaccid
cell
 The turgor pressure
is zero
So Ψ = Ψs + Ψp
Ψ = Ψs
 The water
potential is equal
to the osmotic
potential of the cell
In plasmolysed
cell
 The pressure
potential has
negative valve i.e
cell shows –ive
turgor pressure is
zero
So Ψ = Ψs + Ψp
Ψ = Ψs + (- Ψp)
So the water potential
become more negative.

11. Problem regarding osmotic entry of water
Problem 1: There are two adjacent living cell A and B. cell A has an osmotic
potential (Ψs) of -10 bars and pressure potential of 5 bars, where as cell B has
an osmotic potential (Ψs) of -5 bars and pressure potential of 2 bars. What will
be the direction of flow of water in the cell.
Solution: Cell A Cell B
Ψs = -10
Ψp = 5
Ψs = -5
Ψp = 2
Ψ = Ψs + Ψp
Ψ = -10 +5 = -5
Ψ = -5
Ψ = Ψs + Ψp
Ψ = -5+2 = -3
Ψ = -3

12. Problem for your practice
 Problem 2: There are two adjacent living cell A and B. cell A has an osmotic
potential (Ψs) of -7 bars and pressure potential of 4 bars, where as cell B has an
osmotic potential (Ψs) of -8 bars and pressure potential of 3 bars. What will be the
direction of flow of water in the cell.
 Problem 3: There are two adjacent living cell A and B. cell A has an osmotic
potential (Ψs) of -12 bars and pressure potential of 4 bars, where as cell B has an
osmotic potential (Ψs) of -15 bars and pressure potential of 9 bars. What will be the
direction of flow of water in the cell.

13. Difference b/w DPD & Water potential
DPD
1. Difference b/w the diffusion
pressure of any solution and its pure
solvent in atm.
2. The direction of water movement is
from lower DPD to higher DPD.
3. Measured in atm
4. DPD= OP-TP
Water potential
1. It is the difference in the free energy
of water molecules in pure water &
in a solution. It is equivalent to
DPD with –ive sign.
2. The direction of water movement is
from higher water potential to lower
water potential.
3. Measured in bars
4. Ψ = Ψm + Ψs + Ψp

14. PLASMOLYSIS AND DEPLASMOLYSIS

15. Plasmolysis & Deplasmolysis
 Plasmolysis: when a cell is placed in
hypertonic solution exosmosis of cell sap starts
which reduces the tension of cell wall and result
in contraction of protoplasm due to continuous
loss of water. This phenomenon id called
plasmolysis.
 Deplasmolysis: if completely plasmolysed cell
is placed in the hypotonic solution the proceess
of endosmosis starts and cell protoplasm
regains its stage and shape and the cell again
become turgid. This phenomenon is just reverse
of plasmolysis and known as deplasmolysis.

16. Stages of plasmolysis

17. Difference b/w different stages of plasmolysis
Incipient Plasmolysis Evident Plasmolysis Final Plasmolysis
1. No morphological
symptoms appears
in plants
2. The plasma
membrane
separates at only
the corner of the
cell wall.
3. It is reversible.
1. Wilting of leaves
appears
2. Plasma membrane
completely detach
from cell wall.
3. It is reversible.
1. Severe wilting and
dropping of leaves
appear
2. Plasma membrane
completely detach
from cell wall with
maximum shrinkage
of volume.
3. It is irreversible.

18. Advantages of Plasmolysis
1. Plasmolysis confirms the semi-permeable nature of plasma membrane.
2. The phenomenon of plasmolysis is used to find out the OP of the cell- sap.
3. Plasmolysis is used in the separation of flesh from bones.
4. Plasmolysis is also used to protect the jam & jelly from fungal and bacterial
infection jam & jellies posses high concentration of sugar which plasmolysis
the fungal hyphae and bacterial cell.
5. The rate of entry of water in the cell can be measured by plasmolysis.

19. Imbibition
 Some material like gum, starch, cellulose, gelatin, agar and protein etc. when
placed in water they absorb it and swell up. This phenomenon is called
Imbibition. Ex. Swelling of dryness, wooden windows, table etc.
Significance of Imbibition:
1. Imbibition initiate seed germination
2. It causes increase in the volume of seeds and ultimately bursting of testa or
seed coat.
3. It helps in initiation of water absorption by roots.
4. It helps in ripening of ovules into the seeds.
5. During imbibition heat energy is released which further increases the
activities of cells of the living seeds.

20. THANKS