Samacheer Class 11 Bio Botany - Transport in Plants

High salt concentration results in high be osmotic potential of the soil solution, so the plant has to use more energy to absorb water. Under extreme salinity conditions, plants may be unable to absorb water and will wilt even if the surrounding soil is thoroughly irrigated. This is also referred to as the osmotic or water deficit effect of salinity.

* The discovery of enzyme phosphorylase in guard cells by Hanes (1940) greatly supports the starch-sugar interconversion theory.
* The enzyme phosphorylase hydrolyses starch into sugar and high PH followed and the opening takes place during the night.
Day:
1.
2. Photosynthesis occur
3. pH – increased
4. Movement of water from
5. subsidiary cells to guard cells
6. Guard cells become turgid
7. Opening of stomata
Night:
1.
2. No Photosynthesis
3. pH – lowered
4. Movement of water from guard cells
5. Guard cells become flaccid
6. Closure of stomata

1. Slatyer and Taylor (1960) introduced the concept of water potential.
Definition – water potential is the potential energy of water in a system – compared to pure water when temperature and pressure are kept constant.
2. It is also a measure of how freely water molecules can move in a particular environment or system. Water potential is denoted by the Greek symbol Ψ (psi) and measured in Pascal (Pa). At standard temperature, the water potential of pure water is zero
3. Addition of solute to pure water decreases the kinetic energy thereby decreasing the water potential, from zero to negative.
4. So, Comparatively a solution always has low water potential than pure water. In a group of cells with different water potential, a water potential gradient is generated.
5. Water will move from higher water potential to lower water potential.
When potential ( Ψ) can be determined by. Solute concentration or Solute potential ( Ψ s ) Pressure potential ( Ψ p )
By correlating two factors, water potential is written as (Ψ w =Ψ s )+Ψ p
a) Solute potential (Ψ s ) or Osmotic potential
* Denotes the effect of dissolved solute on water potential.
* In pure water, the addition of solute reduces its free energy and lowers the water potential value from zero to negative.
* Thus the value of solute potential is always negative. In a solution at standard atmospheric pressure, water potential is always equal to solute potential (Ψ w = Ψ s ).
b) Pressure Potential (Ψ p )
* Pressure potential is a mechanical force working against the effect of solute potential.
* Increased pressure potential will increase water potential and water enters cells and cells become turgid.
* This positive hydrostatic pressure within the cell is called Turgor, pressure likewise, withdrawal of water from the cell decreases the water potential and the cell becomes flaccid.

Water absorbed from roots must travel up to leaves by xylem for food preparation by photosynthesis. Likewise, food prepared from leaves has to travel to all parts of the plant including roots.

It is a special type of diffusion almost same like simple diffusion but has a selectively permeable membrane is here, through which osmosis occur.
(OR)
It is the movement of water molecules from a place of its higher concentration, to the place of its lower concentration through a semipermeable membrane.

The net movement of molecules from a region of their higher concentration to a region of their lower concentration along a concentration gradient until an equilibrium is attained.

• In the ‘Touch me not’ plant the touching act as stimulus, and it closes the leaves.
• When we touch the plant, at that time the stem releases some chemicals, which force water to move out of the cell leading to the loss of Turgor pressure and the leaves droop down However after sometime they become normal.

• The potential energy of water in a system compared to pure water when both temperature and pressure are ketp same.
• It is a measure of how freely water molecules can move in a given environment
• Water potential of pure water is = 0

• Termed by Meyer (1938)
• The difference between the Diffusion pressure of the solution and its solvent at a particular temperature and atmospheric pressure of the solution and its solvent at a particular temperature and atmospheric pressure is called DPD.

SDT
LDT
1. Cell to cell Transport
Involve few cells ni lateral direction
Transport with in the network of xylem and
phloem
2. Connecting link to xylem bind phloem from root hairs to leaf tissues
Direct vertical – main Transport
3. Eg. Diffusion, Osmosis etc
4. Eg. Ascent of sap & Translocation of solutes.

PT
AT
1. Down hill Transport (Phyical)
Up hill Transport (Biological)
2. Occur According to concentration gradient
Occur against concentration gradient
3. No expenditure of energy
There is expenditure of energy obtained from Respiration
4. Eg. Diffusion – Facilitated Diffusion osmosis etc.
Eg. Na + K + ATP are pump.

two examples for the phenomenon of Imbibition:
* The swelling of dry seeds.
* The swelling of wooden windows, tables, doors due to high humidity during the rainy season.

• Soil solution act as a medium of ion-exchange
• The CO 2 released by roots combine with water to form carbonic acid (H 2 CO 3 )
• Carbonic acid dissociates into H + + HCO 3 in the soil solution.
• H + ions exchange with cations adsorbed on clay particles and cations from micelles get released int c.

I) Exomosis
Endomosis
The osmotic outflow of water, when cell placed in hypertonic solution
Osmotic inflow into the cell when placed in hypotonic solution or water
Eg. Preservation of Jam, Jellies, pickles
Eg. Swelling of Dry grapes placed in water
II) Apoplast
Symplast
System of adjacent cell walls – continuous throughout except at the asparian strips of endodermis in the roots
System of interconnected protoplasts of neighbouring cells in plants
III) Cohesion
Adhesion
Attraction between molecules of a similar kind
The attraction between molecules of different kind
IV) Influx
Efflux
The entry of ion into the cell is known as Influx
The exit of ion from the cell into outside is known as Efflux
It can be active or passive
It can be active or passive.

When a solution and its solvent (pure water) are separated by a semipermeable membrane, the pressure is developed in the solution, due to the presence of dissolved solutes. This is called osmotic pressure (OP).

• Stephen Hales – coined the term
• Stoking (1956) Defined the term.
• A pressure developing in the tracheary elements of the xylem as a result of metabolic activities of the root.

Osmosis (Latin: Osmos – impulse, urge) is a special type of diffusion. It represents the movement of water or solvent molecules through a selectively permeable membrane from the place of its higher concentration (high water potential) to the place of its lower concentration (low water potential).

Name
Type
Properties
1.Starch
Polysaccharide (non reducing sugar)
Insoluble in water cann’t be transport
2. Glucose & Fructose
Monosaccharides (reducing sugar)
Soluble in water but less efficient in energy storage & reactive
3. Sucrose
Disaccharide(non reducing sugar)
Soluble in water, even at high concentration, low viscosity, more efficient in energy storage no reducing ends make it inert than glucose & Fructose.

Ascent of sap
Translocation of solute
The upward transport of water along with dissolved minerals from roots to the aerial parts is called as Ascent of sap.
The transport of food from the site of synthesis to the site of utilization or from source to sink is known as Translocation of organic solutes (a dissolved substance)
Occur through Xylem
Occur through Phloem

Two objections to starch – sugar interconversion theory:
* In monocots, the guard cell does not have starch.
* There is no evidence to show the presence of sugar at a time when starch disappears and stomata open.

Cuticular Transpiration
Lenticular Transpiration
Loss of water through cuticle is known as cuticular Transpiration
Some pores
It is only about 5 to 10% of the total Transpiration
Present on the woody surface of stem (bark) are known as Lenticels
The thicker the cuticle, the lesser will be the Transpiration. Eg. xerophytes
The loss of water from the lenticel is Lenticular Transpiration – It is only about 0.1 % of the total.

Two uses of anti – transpirants:
* Anti – transpirants reduce the enormous loss of water by transpiration in crop plants.
* Useful for seedling transplantations in nurseries.

* Water pore – Aquaporin in KBC was discovered by Peter Agre (Nobel Prize for chemistry – 2003)
* Water channel protein is present in PM.
* Regulate the massive amount of water transport across PM
* 30 types of Aquaporins are known from maize
They also transporter
* glycerol
* urea
* CO 2
* NH
* metalloids & Reactive oxygen species (ROS)
Function:
* They increase the permeability of the membrane of water
* They confer drought and salt, stress tolerance.

A.
Cohesion
Adhesion
The strong mutual attraction between water molecules is called cohesion or cohesive force.
The Attraction between a water molecule and the wall of the xylem element is called adhesion.
B. The cohesive and Adhesive forces work together to form an unbroken continuous water column in xylem.
The magnitude of cohesive force is much high (350 atm) and is more than enough to ascent sap in the tallest
trees.
III. 3 Mark Questions

Diffusion
Osmosis
1. The net movement of molecules from a region of their higher concentration to a region of their lower concentration along a concentration gradient until an equilibrium is attained
It is a special type of diffusion – There is movement of water or solvent molecules through a selectively permeable membrane from a place of its higher concentration to its lower concentration until an equilibrium is attained.
2. it is independent of the living system
It is also independent of the living system
3. Passive process
Passive process
4. Obvious in solids gases & liquids Only in liquid molecules Eg. diffusion of sugar in water
Eg. Dry grapes, when kept in water swells, & becomes turgid.

Osmotic pressure
Osmotic potential
1. The hydrostatic pressure developed in a solution. due to the presence of dissolved solutes when it is separated from a pure solvent by a semi-permeable membrane.
The ratio between the number of solvent particles and the number of solute particles in a solution or (lowering of free energy of water in a system due to the presence of solute particles
2. develops only in a confined system.
develops in confined or an open system
3. The value is positive, though it is numerically equal to osmotic potential
The value is negative though it is numerically opposite to osmotic pressure.

• Yes / No – R.O. is working on the principle of osmosis. but in the reverse direction.
• In regular osmosis water moves from its higher concentration to its lower concentration through the selectively permeable membrane but here water moves from lower concentration to higher concentration through selectively permeable membrane.
• Since against concentration gradient, there is the expenditure of energy, to apply pressure, to force water in a reverse direction.
• Eg- Desalination plants to purify seawater also work like R-O-Purifiers Movement of Water in house hold usage.

Antitranspirant is any material applied to plants to retard or reduce the rate of transpiration – without disturbing the process of gaseous exchange, for respiration and photosynthesis.
Eg. Colourless plastics silicone oil and low viscosity waxes.

* Natural antitranspirants usually induce stomatal closure
Eg. CO 2 – inhibits photorespiration – thereby induces stomata! closure
* Some chemicals, when applied as a foliar spray can induce stomatal closure for 2 – 3 weeks.
Eg. (PMA) Phenyl Mercuric Acetate & (ABA) Abscisic Acid.

Capillary theory: Boehm (1809) suggested that the xylem vessels work like a capillary tube. This capillarity of the vessels under normal atmospheric pressure is responsible for the ascent of sap. This theory was rejected because the magnitude of the capillary force can raise water level only up to a certain height. Further, the xylem vessels are broader than the tracheid which actually conducts more water and against the capillary theory.

Definition:
The products of Photosynthesis from the Mesophyll of leaves to sieve elements of phloem is known as phloem loading. (Just like the cement sack manufactured in a factory being loaded in a vehicle to be transported the respective site)
It involves 3 steps.
Step I:
* The chloroplast has photosynthate in the form of starch or Trlose phosphate
* It is transported to the cytoplasm, where it is converted into Sucrose.

Von Mohl (1856) observed that stomata open in light and close in the night. According to him, chloroplasts present in the guard cells photosynthesize in the presence of light resulting in the production of carbohydrate (Sugar) which increases osmotic pressure in guard cells. It leads to the entry of water from other cells and the stomatal aperture opens. The above process vice versa in the night leads to the closure of stomata.
Demerits:
* The chloroplast of guard cells is poorly developed and incapable of performing photosynthesis.
* The guard cells already possess much amount of stored sugars.
IV. 5 Mark Questions

1. Definition:
The epidermis of leaves and green stems possess many small pores called – Stomata
2. Length & Breadth
The length – 10- 40μ The Breadth – 3 – 10μ
Number Mature leaves contain 50- 500 stomata / mm 2
3. Structure
a. Guard Cells – A pair of Kidney shaped cells (semilunar) surrounded a small opening called stoma
b. Subsidiary Cells – Guard cells attached to surrounding epidermal cells known as subsidiary cells or accessory cells.
* The inner wall of guard cell is thicker
* The stoma open into an interior substomatal cavity.

Aim: To demonstrate osmosis by Potato osmoscope
Apparatus used: Potato tuber, beaker containing water, sugar solution and pin.
Definition:
Diffusion of water or solvent from the region of higher water potential to a region of lower water potential
is known as osmosis.
Procedure:
Take a peeled potato tuber and make a cavity inside with the help of a knife fill the cavity with concentrated sugar solution and mark the initial level.
Place this set up in a beaker containing pure water After 10 minutes observe the sugar solution level and record your observation.
Observation:
There is rise in the level of the solution. in the cavity of the tuber due to osmosis
Inference: Osmosis has occured, through the potato osmoscope

Aim: To measure the rate of Transpiration with Ganong’s Potometer
Apparatus needed: Ganong’s Potometer, a twig, beaker, water, split rubber cork, and vaseline.
Procedure:
* Ganong’s Potometer is a horizontal graduated tube which is bent in opposite directions at the ends.
* A reservoir is fixed to the horizontal tube hear the wider end Reservoir has stop cock to regulate water flow.
* A twig is fixed to the wider arm through the split cork. The apparatus is filled with water with water from reservoir.
* The apparatus is made air tight by applying vaseline.
* The other bent end of the horizontal tube is dipped into a beaker containing coloured water.
An air bubble is introduced into the graduated tube at the narrow end. Keep the apparatus in bright sunIght
and observe
Observation:
As the twig transpires, the air bubble move towards the twig.
This loss is compensated by water ohsorption from the beaker.
inference:
By the experiment we can study the rate of Transpiration and rate of transpiration is equal to the rate of water absorption.

Munch – Proposed it in 1930 Crafts – elaborated it in 1938
Definition: Organic substances (solute) move from a region of high osmotic pressure (mesophyll) to
region of low OP along TP gradient.
Example – Physical system:
Chamber ‘A’ & chamber ‘B’ made up of semi permeable membrane connected by a tube ‘T’
A – Contain highly concentrated sugar solution (hypertonic)
B – Contain dilute sugar solution (hypotonic)
A – draws water from the reservoir by Endosmosis – TP of chamber ‘A’ increased
* Continuous entry of water in to A – TP increased
* Flow of solute from chamber A to B thro TP gradient.
* The movement continues till both Aand B attain isotonic condition (equilibrium)
(However if new sugar solution added to A system will start to run again)
Example (Biological system)
* Chamber A (Source) – (Equivalent to) – Mesophyll cells of leaves (High concentration of soluble food)
* Chamber B (Sink) – (Equivalent to) – Cells of stem & Roots (Consumption end)
* TubeT – (Analogous to) – Sieve tube to phloem
Steps:
1. Xylem (Reservoir) – Movement of water (Endomosis) – Mesophyll cells (TP increase)
2. Mesophyll cells (High TP) Source – enmass movement of organic solutes through Phloem by TP Gradient – Cells of stem & Root (low TP) (Sink)

Introduction:
Levit (1974) – Proposed it
Raschke (1975) – Elaborated it
Steps:
This process of exchange of ions is called Actie ion exchange ( consume ATP) or Energy
* Increased K + ions in the Guard cells – balanced by CP ions
* Increase in solute concentration (Hypertonic) Decrease in water potential
* Water enters into Guard cells from subsidiary cells
* Wall pressure increase Turgor pressure, Turgid guard cells – fall apart & opens the stoma
* Exit of H +
* Intake of K +
* Exit of K +
* Loss of H 2 O
* Uptake of H 2 O +
* Turgidity of Guard Cells
* Accumulation of CO 2 – Lowering of pH
* Opening of Stoma.
* Activation of ABA
* Closure of Stoma.

Lunde gardth & Burstom (1933)- Proposed the Cytochrome
Pump theory:
* There is correlation between Respiration & Anion absorption.
* when a plant is transferred from water to salt solution, the rate of respiration increases – known as Anion respiration – or salt respiration
The Assumptions of Cytochrome pump theory:
* The mechanism of anion and cation absorption is different.
* Anion – absorption – through cytochrome pump or chain by Active process
* An oxygen gradient is responsible for oxidation at outer surface of the membrane and reduction at the inner surface.
Explanation:
* On the inner surface, the enzyme dehydrogenase Produces protons (W) and electrons (e)
* Anions are picked up by oxidized cytochrome oxidase and transferred to the other members of the chain.
* Theory assumes the passive movement of cations (C + ) along the electrical gradient created by the accumulation of anions (A – ) at the inner surface of the membrane.
Defects:
*
* Cations also induce respiration
* to fail to explain the selective uptake of ions
* It explains absorption of anions only.

i) Lloyd (1908)
According to him, turgidity of Guard cell is due to interconversion of starch → sugar
* Day time:
Guard cells have sugar → so turgid → opening of stomata
* Nighttime:
Guard cells have starch → so loose turgidity (become flaccid) → closure of stomata
ii) Sayre (1920)
According to him, the pH of Guard cell determine opening and closing of stomata
* Day time: Guard cells have high pH →so turgid → opening of stomata
* Nighttime: Guard cells have low pH → become flaccid → closure of stomata to be elaborate
* Day time: Utilisation of CO 2. in photosynthesis → Starch into sugar → high pH → high Turgor pressure→Opening of Stomata
* Night Time: No photosynthesis, so the accumulation of CO 2 → sugar to starch → low pH → decrease in TP → closure of stomata
iii) Hanes (1940)
According to Hanes – Enzyme phosphorylase is responsible for starch sugar conversion in the guard cells.

* Introduction
* Root hair & other epidermal cells – By imbibition absorb water from soil –
* By osmosis moves radically & centripetally – across
* cortex
* Endodermis
* Pencycle & Xylem
There are 3 Routes
* Apoplast
* Symplast
* Transmembrane route
I. Apoplast ( GK – Apo – Away) Everything external to PM
1. Cell walls
2. Extra Cellular Space
3. Interior of dead cells (vessel elements Tracheids)
Movement is continuous exclusively through the cell wall or nonliving part of the plant without crossing any membrane.
II. Symplast (GK – Sym = within)
Entire mass of cytosol of all the living cells in a plant + plasmo desmata + inter connecting cytoplasmic channel.
In the movement water has to cross PM, to enter cytoplasm of outer root cell; then move within adjoining
cytoplasm through plasmodesmata around the vacuoles without the necessity to cross more membrane it reaches xylem.
III. Trans – Membrane Route
* Water enters a cell on one side and exits from the other side.
* It crusses 2 membranes for each cell (also through to no plast).