Students able to understand that who helps to transport in plants, Mechanism of transport in plants, physical forces involved in transport, Behavior with different solutions.

1. ABSORPTION OF WATER
Dr. K. GANESH KUMARI,
ASSISTANT PROFESSOR,
DEPARTMENT OF BOTANY,
SRIMAD ANDAVAN ARTS AND SCIENCE COLLEGE (AUTONOMOUS),
TRICHY - 5

2. Introduction
– Moving from one place to another
– C Co2 Stomata Leaves
H
o Water
N
S
P Soil Root

3. Who helps to transport in plants ?
Vascular Bundle – Xylem – which conducts water
Phloem – which conducts food

4. Think…
How xylem transports?
How Phloem transports? How water moves up the Plant?

5. Mechanism of transport in Plants
• Diffusion
• Osmosis
• Plasmolysis short distance
• Imbibition
• Root Pressure Long distance
• Transpiration Pull

6. Diffusion
What is diffusion ?
• Net movement of a substance from a region of
higher concentration towards a region of
lower concentration
• Extremely important for gaseous movement
within a plant

7. Factors affecting Diffusion
• Concentration gradient
- Movement from higher to lower concentration
• Membrane permeability
- Increases if the membrane is permeable to the particles
• Temperature
- Increases with increase in temperature

8. • Pressure
- Decreases with increase in pressure
• Mobility
- Decreases with increase in size and mass of particle

9. Osmosis
• Diffusion of water across a semi permeable membrane
• The diffusion of solvent takes place from the less
concentrated solution into more concentrated solution
• Equilibrium have to be reached
• Semi permeable membrane allows only solvent to pass
through it and not the solute

10. Water potential
• Measure of tendency of water to move from one region to
another
• Where ever the water is more the kinetic energy is more
• If kinetic energy is more the water potential is more
• Denoted by ψw
• Expressed in units of pressure (Pa, Bar, KPa)
Components of Water Potential
Ψw = Ψs + Ψp
Ψw = water potential
Ψs = solute potential
Ψp = pressure potential

11. Solute Potential
• Magnitude of lowering of water potential due
to dissolution of solute
• Denoted by Ψs
• Always be negative
Salt
NaCl
Cl- Cl-
Cl- Cl-
Na+Na+
Na+Na+
Pure H2O
-
ᵟᵟ
ᵟ- ᵟ-
ᵟ-
ᵟ-
ᵟ+
ᵟ+
ᵟ+ᵟ+
Ψs
Ψw = 0
Ψw = <0

12. Pressure Potential
• Component of water potential due to hydrostatic pressure
exerted in a cell
• Denoted by Ψp
• can be positive / negative
Osmotic pressure
• Pressure required to prevent water from diffusing in
• Positive pressure applied
Ψw = 0
Pure H2O

13. What is Plasmolysis ?
• Plasma – cytoplasm
• Lysis – cut down
• Process in which plant cell cytoplasm is separated
from cell wall due to severe water loss
• Cytoplasm get shrinked when looses water
• Before After

14. Behavior with different solutions
1. Hypertonic solution
• Hyper - more
• Water concentration in the solution is lesser than that inside the cell
• The cytoplasm is said to be shrinked
2. Hypotonic solution
• Hypo - less
• Water concentration in the solution is higher than that inside the cell
• The cytoplasm is said to be turgid (turgor pressure)
3. Isotonic solution
• Water concentration in the solution is same as that inside the cell.
• If movement is present it will happen in both the side
• Both the movement was balanced

15. What is Imbibition ?
• Absorption of water by colloids / porous solids
causing them to swell
• Special form of diffusion
• Eg. Almonds, Raisins

16. Diffusion pressure deficit [DPD] or
suction pressure [SP]
• The amount by which the diffusion power of the solution is less
than its pure solvent
• It is the ability of the cells to absorb water
• DPD = OP – WP
Cell Sap / Hypo
DPD – higher
OP – higher
Water deficit
Pure water
DPD – zero
OP – lower
TP – higher
Unable to
absorb water
Hyper water
DPD – higher
OP – higher
TP - lower
DPD = OP – TP
DPD = [OP – OP] – TP
DPD = 0
DPD = OP

17. Long distance transport mechanisms
Will get dried

18. Translocation
• Bulk movement of substances through conduction tissues of
plants
• Mass flow will be happen in plants
• It will happen due to pressure
• Eg : river, straw
Transport in Plants
Important needs of plants:
- water: from soil through root hairs
- Food: in leaves by photosynthesis
- Xylem: always unidirectional
- Phloem: always bidirectional

19. • Means xylon in greek – wood
• Mostly dead cells
• Made up of no. of elements
Tracheids & Vessels
• Tubular structures
• Conducts water and minerals vertically
Xylem Parenchyma
• It does not help in conducting
• Store food
Xylem fibres
• support
Tracheid Vessel Xylem parenchyma

20. How do plants absorb water ?
• Root hairs help in water absorption from soil
• It has very thin layer of cell wall
• Water absorption occurs by diffusion

21. How does water move into deeper root layers ?
• Apoplast pathway
• Symplast pathway

22. Apoplast pathway
• Apo means away from cytoplasm
• Water movements occurs through intercellular spaces and cell
walls
• No crossing of cell membrane
• Water flow occurs due to adhesive and cohesive properties of
water

23. Symplast pathway
• Sym means towards the cytoplasm
• Water movement occurs through cytoplasm
through plasmodesmata
• Crossing of cell membrane occurs very slowly
• Water flow occurs along a potential gradient

24. Apoplastic vs Symplastic pathway in Root

25. Transport of water from endodermis to xylem
• Active transport of Na+ by carrier proteins into xylem
• Water potential decreases in xylem
• Water moves by passive transport down the potential
gradient

26. How does water move up the plant from roots ?
Two mechanisms together makes
them possible
• Root pressure
• Transpiration pull
Root pressure
• Positive pressure developed in
roots due to water transported
into them
• Responsible for pushing water up
to some heights

27. Transpiration pull
• Upward movement of water through xylem is
primarily due to transpiration pull
• Water is being pulled up from below
• Cohesion tension model of water transport

28. Pressure creates during water
Movement
• Root pressure [RP]
• Osmotic pressure [OP]
• Turgor pressure [TP] or Wall pressure [WP]
• Diffusion pressure deficit [DPD] or suction
pressure [SP]

29. Mechanism of water absorption
The way in which water from soil enters
roots, particularly to the root xylem, is called
mechanism of water absorption.
Both Active and Passive absorption have been
proposed for mechanism of water absorption.

30. Mechanism of Absorption of Water
Water is absorbed through root hairs
which are in contact with soil water
and form a root hair zone a little
behind the root tips.
Root hairs are tubular hair like
prolongations arises from epidermal
layer (when epidermis bears root hairs
it is also known as piliferous layer) of
the roots.
The walls of root hairs are permeable
to water and solutes
The root consists of pectic and
cellulose substances.
It is strongly hydrophilic (water loving)
in nature.
Root hairs contain vacuoles filled with
cell sap.

31. Mechanism of water absorption is of two
types:
(1) Active Absorption of Water:
In this process, the root cells play active
role in the absorption of water and metabolic
energy released through respiration is
consumed.

32. Active absorption may be of two kinds:
(a) Osmotic absorption i.e., when water is ab-
sorbed from the soil into the xylem of the roots
according to the osmotic gradient.
(b) Non-osmotic absorption i.e., when water is
absorbed against the osmotic gradient.

33. (a) Active Osmotic Absorption of Water:
• First step in the osmotic absorption of water is the
imbibition of soil water by the hydrophilic cell
walls of root hairs.
• Osmotic Pressure (O.P.) of the cell-sap of root hairs
is usually higher than the O.P. of the soil water.
• Therefore, the Diffusion Pressure Deficit (D.P.D.)
and the suction pressure in the root hairs become
higher and water from the cell walls enters into
them through plasma-membrane (semi-
permeable) by osmotic diffusion.
• As a result, the O.P., suction pressure and D.P.D. of
root hairs now become lower, while their turgor
pressure is increased.

34. • Now, the cortical cells adjacent to root hairs
have higher O.P., suction pressure and D.P.D.
in comparison to the root hairs. Therefore,
water is drawn into the adjacent cortical cells
from the root-hairs by osmotic diffusion.

35. • In the same way, the water by cell to cell
osmotic diffusion gradually reaches the inner-
most cortical cells and the endodermis.
Osmotic diffusion of water into endodermis
takes place through special thin walled pas-
sage cells because the other endodermal cells
have casparian strips on their walls which are
impervious to water.

36. • Water from endodermal cells is drawn into
the cells of pericycle by osmotic diffusion
which now becomes turgid and their suction
pressure is decreased. In the last step, water is
drawn into xylem from turgid pericycle cells.

37. • When water enters into xylem from pericycle,
a pressure is developed in the xylem of roots
which can raise the water to a certain height
in the xylem. This pressure is called as root
pressure.

38. Active Non-Osmotic Absorption of Water:
• Sometimes, it has been observed that
absorption of water takes place even when
the O.P. of the soil water is higher than the
O.P. of cell-sap. This type of absorption which
is non- osmotic and against the osmotic
gradient requires the expenditure of
metabolic energy probably through
respiration.

40. Following evidences support this view:
• The factors which inhibit respiration also
decrease water absorption.
• Poisons which retard metabolic activities of
the root cells also retard water absorption.
• Auxins (growth hormones) which increase
metabolic activities of the cells stimulate
absorption of water.

41. Passive absorption of water

42. Thank You