Plant-Water-Transport | uksir-notes |Plant- Physiology
Plant Physiology:
Transport In Plants:
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| water Transport |
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The transportation may start from root (Water and mineral) or
from Leaves (Food).
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The transporting tissue is Xylem and phloem.
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Plants also need Transpiration and Guttation like process for
transport of water.
Type of Transportation:
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It is of 3 type in Plants :
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I) Cellular Transport – With in a cell
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Ii) Short distance Transport-
One cell to another
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Iii) Long distance transport- Water and sugar transport
through Xylem and Phloem.
Cellular Transport:
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In a cell, as the Plasma membrane is selectively permeable,
there are various type of transport system can be seen. They are of following
types:
Membrane Transport:
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| Transport Type |
As the Plasma membrane is selectively permeable, there are various type of transport system can be seen. They are of following types:
1. Passive Transport:
- Do not need any kind of energy for transport of material.
- Mostly transport occurs from high conc. Area to low conc. Area.
- Transport mainly dependent on simple diffusion or Osmosis process.
- Diffusion occurs directly or through the Channel and Carrier proteins(Facilitated diffusion)
- Neutral Solutes or Lipid soluble substances can directly pass through membrane.
- There are some open channel protein and Ion channels for facilitated diffusion.
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Presence of Aqua porins for water transport.
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| Passive Transport |
2. Active Transport:
- In Active transport there is use of Energy.
- Here the transport of material occurs from lower conc. To Higher conc. i.e. against the Osmosis law.
- Active transport is of two type
- A)Primary active transport: Direct use of ATP as energy source
- B)Secondary Active transport: ATP is not used directly. Other sources for energy.
- Primary Active transport- Example- H+ ATpase Present in Mitochondria, Calcium pump ATpase in RBC and Muscle cells.
- Secondary Active transport mostly done by various carrier proteins, also called as pumps.
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| Types |
- Pumps are of 3 types- Uniport (1 molecule to one direction at a time )
Symport (2 Molecule transport to the same direction)
Antiport (2 molecule transport to opposite direction)
- Uniport Pumps – K+/potassium Pump, Cl- pump etc.
- Antiport Pump - Sodium Potassium Pump, Na + ca2+ exchanger in plasma membrane etc.
- Symport Pumps - K+ H+ pump symporter in root, Na+ Cl – symporter, K+ Cl – symporter loop of henle.
3. Bulk Transport:
- When cell need material in Group/bulk/in Large number, it perform bulk transport.
- It is of Two Type-
- A) Endo Cytosis: Inner ward transport of material with help of Carrier Vesicle.
- B) Exo Cytosis: Outer ward transport of material with help of Carrier Vesicle.
- Endo Cytosis is either -
- i) Phago Cytosis- Cell eating or ii) Pino Cytosis/ Poto Cytosis- Cell Drinking
- Sometime Receptor / Ligand mediated endocytosis can be seen.
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| Bulk transport |
Diffusion:
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The movement of particles from their higher conc to their
lower conc, it is called as diffusion.
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The particles may be Gas, liquid or solid.
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They maintain equllibrium through diffusion.
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Generally diffusion occurs due to – Particle’s kinetic energy and difference in
conc. Of particular areas.
Diffusion pressure: (DP)
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Due to diffusion of particles a pressure is developed called
as the DP.
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Maximum DP is of Pure Water : ~1336.40 Atm at 200C
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It decraes when solute is added.
Imbibition :
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When a solid particle absorb water but donot form solution, its
called as imbibition.
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The water absorbtion may increase their size.
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Imbibants: the solid particle which absorb water
(Hydrophillic in nature).
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Imbibate: The liquid which is absorbed.
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Due to imbibtion wetting heat may generate, and the
imbibition pressure is really high.
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Ex: Wooden door swell in rainy season, seed swell up before
germination etc.
Osmosis:
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Osmosis process was
discovered by Nollet (1748)
Definetion:
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| osmosis |
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Osmosis may be defined as the flow of solvent or water
molecule from less conc. Solution area to high conc. Solution Through a semipermeable
membrane.
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Or
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Osmosis is the flow of solvent from its high conc. To
its lower conc. Area through a semipermeable
membrane.
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Or
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When water pass from its high water potential area to its
lower water potential area is called as the Osmosis process.
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Both pressure gradient and conc. Gradient decide the
direction and rate of osmosis.
Osmotic Conc.:
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It is the amount of dissolved solute in solution per unit
volume.
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It can be of 3 types:
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Hypotonic solution: if osmotic conc. Is lower then the cell
sap or another solution.
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Hyper tonic Solution: If osmotic conc is higher then the cell
sap or another solution.
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Isotonic Solution: If osmotic conc. Is equal to the cell sap conc.
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| solution-type |
Osmosis Types:
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Generally of 2 type-according to water movement.
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Ex-osmosis : When water comes out of the cell due to placing
it in Hypertonic solution, its called ex-osmosis. Due to ex-osmosis cell loose
turgidity and become flaccid.
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Endosmsis : When water is absorbed by cell due to placing it
in Hypotonic solution, then its called as endosmosis. In this case cell become
more turgid.
Turgid
cell:
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| turgid-cell |
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When a cell attains, its maximum size due to fully hydrated
condition, it is called as Turgid cell.
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Now this property is called as Turgidity.
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Here the pressure developed by cell membrane against cell
wall is called as Turgor Pressure (TP).
Osmotic pressure: (OP)
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When a solution is separated by one semipermeable membrane
from its pure solvent (water), then the solution develops a pressure – called
as osmotic pressure.
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OP is directly proportional to the Conc. Of the solution and
the temperature.
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It also depends on the solute particle (Ionization and
hydration).
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OP of plant generally varies from- 4 to 5 Atm.
Significance:
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Help in absorption of water by cell.
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Help in maintaining the turgidity of Cell.
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Help in movement of plant parts.
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Help in opening and closing of stomata.
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Some time provide resistant to cold stress.
Plasmolysis:
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Due to excess exosmosis in cell, cytoplasm become dehydrated.
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Cytoplasm shrink from the cell wall, become jelly like
semisolid condition.
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Thus due to exosmosis, shrinkage of protoplast is called as Plasmolysis
process.
The cell show plasmolysis process is called as Plasmolysed cell.
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| plasmolysis |
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It may be of 3 stages:
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Limiting Plasmolysis:
starting stage where water loss starts, vacuole and cytoplasm starts
shrinking. (Here TP= 0)
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Incipient Plasmolysis: Due to continuous exosmosis, cytoplasm
shrinks. (Here TP= less -ve)
- Evident plasmolysis: Last stage of shrinkage, protoplast become rounded.
(Here TP = extremely -ve). A cell can’t survive in this
condition.
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De-plasmolysis:
when a plasmolysed cell placed in water and again come to its original
size, by getting hydrated.
Plant water relationship:
As
water content in a plant cell is 75- 95%, there is a plant water relationship
develops. To define this we use dome term like- Water potential, pressure
potential, solute potential, matric potential etc.
Chemical potential:(ᴪ)
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According to thermodynamics- free energy represents the
potential of performing work.
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So the quantitative expression of free energy present in any chemical in a
system is called as Chemical potential.
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It’s a relative quantity.
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Larger the chemical potential = greater chance of chemical
reaction.
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Chemical potential Unit is = energy in per mole
of substance (J/ mole)
Osmotic / Solute Potential: (ᴪs)
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It is the potential of water molecule to move from less conc.
Solution to high conc. Solution through a semipermiable membrane.
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Osmotic potential decrease
due to addition of solute in pure water.
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There for osmotic potential always carry a –ve sign.
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Formula:
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ᴪs = C×R×T
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Here C= conc. Of solute in mole/L
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R = Universal gas constant (0.083)
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T= Temp in absolute degree.
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OP is less –ve at 00C and more –ve in warmer
solution.
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This result the flow of water from colder to warmer condition.
Turgor Pressure (ᴪp):
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The pressure of cell membrane or protoplast against cell wall
is called Turgor pressure.
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Also called Hydrostatic pressure or Pressure potential. (ᴪp)
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Normally in a normal condition cell Wall pressure and Turgor
pressure are almost equal.
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TP = WP
Metric Potential (ᴪm):
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Expression of water absorption by matrix, colloidal particle
or surface in plant cell.
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Macrix potential show almost negligible value, which do not
considered in calculation.
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Also called as
Chemical potential of water.
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Or
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It’s the difference between the free energy present in
solution to that of pure water.
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Water potential of Pure water is maximum i.e. 0 Mpa. (1 Mpa =
10 bars.)
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Water potential of solution is –ve as solute is added.
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Water potential formula
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ᴪw = ᴪs + ᴪp
+ ᴪm
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Here ᴪw = water potential
ᴪs = solute potential, ᴪp
= pressure potential, ᴪm = matric potential.
But ᴪm is negligible
So ᴪw =ᴪs + ᴪp
Diffusion Pressure Deficit (DPD):
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I is the difference between diffusion pressure od solution to
its pure solvent. (at particular temp, and pressure.)
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The term was coined by Meyer (1938).
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It determine the direction of water movement. (Water move
from High DPD to Low DPD.)
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DPD have +ve sign.
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DPD is directly related to conc. Of solution. (DPD α Conc. Of solution)
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DPD is the measure of ability of cell to absorb water, therefore
also called as Suction pressure (SP).
DPD/ SP = OP – WP
But, WP =
TP (in turgid cell)
S0, DPD =
OP – TP
In fully turgid cell :
OP =TP, So, DPD = 0 (Zero)
In fully
Plasmolyzed cell : TP = 0, So,
DPD = OP /
SP = OP
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