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Principles of plant physiologyPrinciples of plant physiology
Chapter TwoChapter Two
Plant-Water RelationsPlant-Water Re...
22
Water is absolutely essential for all livingWater is absolutely essential for all living
organisms.organisms.
Why is ...
33
Tom Robbins, “Tom Robbins, “ Even Cowgirls Get the Blues”Even Cowgirls Get the Blues”
• Water-the ace of elementsWater-...
44
1.1 Properties of water important to1.1 Properties of water important to
plantplant
 Life is absolutely dependent on t...
55
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II. Hydrogen bondsII. Hydrogen bonds
 A weak bond that forms between a hydrogen atomA weak bond that forms between a h...
77
B.B. high heat of vaporizationhigh heat of vaporization
 the energy needed to change the phase of a liquid to a
gas  ...
88
D. Capillary actionD. Capillary action
i.i. CohesionCohesion
 hydrogen bonds between water molecules makehydrogen bond...
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ii. Adhesionii. Adhesion
 the attraction of water molecules to non-waterthe attraction of water molecules to non-water...
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iii. Surface tensioniii. Surface tension
 Water has a very high surface tensionWater has a very high surface tension...
1111
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III. Universal solventIII. Universal solvent
 dissolves more different kinds ofdissolves more different kinds of
sub...
1313
Water is a versatile solvent owing to its polarityWater is a versatile solvent owing to its polarity
 Ionic compound...
1414
IV. Water is a liquid at physiologicalIV. Water is a liquid at physiological
temperaturetemperature
 high boiling an...
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VV. Transparent to Light. Transparent to Light
 Chloroplasts inside a cell areChloroplasts inside a cell are
surroun...
1616
VI. Chemically inertVI. Chemically inert ::
 water does not react unless enzymaticcallywater does not react unless e...
1717
Role of Water in plantsRole of Water in plants
 Solvent for the uptake and transport of moleculesSolvent for the upt...
1818
2.22.2 Concepts of water potentialConcepts of water potential
diverse multivarious role of water indiverse multivari...
1919
Defn.Defn. is the chemical potential of water in ais the chemical potential of water in a
solutionsolution compared ...
2020
Values of water potential:Values of water potential:
Pure water has a defined waterPure water has a defined water
p...
2121
Units of measurementUnits of measurement ::
measured in units of atmosphericmeasured in units of atmospheric
pressu...
2222
 Equation of water potentialEquation of water potential
 In a simple systemIn a simple system
• Pressure potential ...
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A. Solute potential / osmotic potential/A. Solute potential / osmotic potential/
 A measure of tendency for HA measu...
2424
 Addition of solute makes the value ofAddition of solute makes the value of
solute potential negativesolute potentia...
2525
Van’t Hoff equationVan’t Hoff equation
 Shows relationship of solute concentrationShows relationship of solute conce...
2626
For example,For example,
when a solute is dissolved in waterwhen a solute is dissolved in water
the water molecules a...
2727
regions
of higher
regions
of higher
water potential
water potential
•less
negative;
less
negative;
•high
free
energy;...
2828
B. Pressure potential (turgor pressure) (Ψp)B. Pressure potential (turgor pressure) (Ψp)
• the hydrostatic pressure p...
2929
• When a biological cell is in a hypotonicWhen a biological cell is in a hypotonic
environment (the cell interior con...
3030
Hypotonic
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C. Matric potentialC. Matric potential (Ψm)(Ψm)
• due to the force of attraction of water fordue to the force of attr...
3636
D.D. Gravitational potential ( ΨgΨg)
• The potential energy associated with movingThe potential energy associated wit...
3737
Basic principles of water potentialBasic principles of water potential
• Water potential of pure water is zero,Water ...
3838
• Plant cells will gain or lose water toPlant cells will gain or lose water to
intercellular fluids depending upon th...
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• Gives a measure of water statusGives a measure of water status
– Leaves of well-watered plants have waterLeaves of ...
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Effect on physiological changesEffect on physiological changes
Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM...
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2.3 Water movement in cells and tissues2.3 Water movement in cells and tissues
Mechanisms of movementMechanisms of mo...
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2. Diffusion2. Diffusion
• the net random movement of individualthe net random movement of individual
molecules drive...
4343
•Molecules move until they reach dynamic equilibrium
•At equilibrium the net movement stops
•the molecules continue t...
4444
Factors influencing the rate of diffusionFactors influencing the rate of diffusion
i. Concentration Gradienti. Concen...
4545
• The rate of diffusion is directly proportionalThe rate of diffusion is directly proportional
to the concentration g...
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ii. Molecular Speedii. Molecular Speed
• atoms and molecules are always in motion atatoms and molecules are always in...
4747
iii. Temperatureiii. Temperature
• increases the rate of molecularincreases the rate of molecular
movementmovement
• ...
4848
V. Solute effect on the chemical potential ofV. Solute effect on the chemical potential of
the solventthe solvent
• S...
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3.Osmosis3.Osmosis
• This is a specialized case of diffusionThis is a specialized case of diffusion
• the diffusion o...
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4. Dialysis:4. Dialysis:
• This is another specialized caseThis is another specialized case
of diffusionof diffusion
...
5252
Transport of water inTransport of water in
PlantsPlants
Levels of transport in plants:Levels of transport in plants:
...
5353
Water diffuse from theWater diffuse from the soilsoil to theto the plantplant
rootroot and then to theand then to the...
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• Physical state of waterPhysical state of water
– highest whenhighest when water is a liquid andwater is a liquid an...
5555
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Water Transport in the RootWater Transport in the Root
 Water is taken in to the root hairWater is taken in to the r...
5757
A.A. Apoplastic path wayApoplastic path way
 movement of water through intercellularmovement of water through interc...
5858
 blocked by the casparian strip atblocked by the casparian strip at
endodermisendodermis
Impermeable band of suberi...
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B. Syplastic path wayB. Syplastic path way
 the continuum of cytoplasm within athe continuum of cytoplasm within a
p...
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C. Transmembrane path wayC. Transmembrane path way
• Water sequentially moves from one cellWater sequentially moves f...
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Apoplast
Symplast
TransmembraneBeira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM
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The xylem pathwayThe xylem pathway
1. Root Pressure1. Root Pressure
• This a push forceThis a push force
• Generated ...
6565
 water flows into the roots through osmosis andwater flows into the roots through osmosis and
osmotic pressureosmoti...
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(A)
(B)
Mineral
ions
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2. TACT Mechanism2. TACT Mechanism
 The transpirational pull on the xylem sapThe transpirational pull on the xylem s...
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i. Transpirationi. Transpiration
 involves the pulling of water upinvolves the pulling of water up
through the xylem...
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ii. Adhesionii. Adhesion
 is the attractive force between wateris the attractive force between water
molecules and o...
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iii. Cohesioniii. Cohesion
 is the attractive force between molecules of theis the attractive force between molecule...
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iv. Tensioniv. Tension
a stress placed on an object by a pulling force.a stress placed on an object by a pulling for...
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Soil factors affecting water absorptionSoil factors affecting water absorption
Reading AssignmentReading Assignment
...
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1.1. What is the importance of the water potentialWhat is the importance of the water potential
concept in plant phys...
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Plant water relations

  1. 1. 11 Principles of plant physiologyPrinciples of plant physiology Chapter TwoChapter Two Plant-Water RelationsPlant-Water Relations Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  2. 2. 22 Water is absolutely essential for all livingWater is absolutely essential for all living organisms.organisms. Why is water importantWhy is water important ?? –Living cells are composed of 70-95 % waterLiving cells are composed of 70-95 % water –Life absolutely depends on the properties ofLife absolutely depends on the properties of water.water. –Life probably evolved in water.Life probably evolved in water. –water covers ¾ of the earthwater covers ¾ of the earth –When organisms go dormant, they loose most ofWhen organisms go dormant, they loose most of their watertheir water –Limiting resource for crop productivityLimiting resource for crop productivity Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  3. 3. 33 Tom Robbins, “Tom Robbins, “ Even Cowgirls Get the Blues”Even Cowgirls Get the Blues” • Water-the ace of elementsWater-the ace of elements – Water dives from the clouds withoutWater dives from the clouds without parachute, wings orparachute, wings or safety netsafety net – Water runs over the steepest precipiceWater runs over the steepest precipice and blinks not aand blinks not a lashlash – Water isWater is buried and rises againburied and rises again ; water; water walks on firewalks on fire and fireand fire gets the blistersgets the blisters – Stylishly composed in any situation - solid, gas or liquidStylishly composed in any situation - solid, gas or liquid – speaking in penetrating dialects understood by all things -speaking in penetrating dialects understood by all things - animal, vegetable or mineralanimal, vegetable or mineral – water travels intrepidly through three dimensions:water travels intrepidly through three dimensions: • sustaining,sustaining, • destroying, anddestroying, andBeira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  4. 4. 44 1.1 Properties of water important to1.1 Properties of water important to plantplant  Life is absolutely dependent on the properties of water  Pure water: Colourless and has no smell and taste  The hidden qualities of water make it a most interesting: Physicochemical properties of water I. Water is polar  Water's unique properties due to its simple composition and structure  hydrogen atoms are "attached" to one side of the oxygenhydrogen atoms are "attached" to one side of the oxygen atomatom  Positive and negative chargePositive and negative charge  The separation between negative and positive chargesThe separation between negative and positive charges creates a polar moleculecreates a polar molecule Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  5. 5. 55 Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  6. 6. 66 II. Hydrogen bondsII. Hydrogen bonds  A weak bond that forms between a hydrogen atomA weak bond that forms between a hydrogen atom and electronegative atomand electronegative atom  Water can bond both to itself and to other moleculesWater can bond both to itself and to other molecules  responsible for theresponsible for the thermal properties of waterthermal properties of water A.A. Water's high specific heat capacityWater's high specific heat capacity  the amount of heat energy that must bethe amount of heat energy that must be added oradded or lostlost to change the temperature of one gram of waterto change the temperature of one gram of water by 1°Cby 1°C  water can absorb a lot of heat before waterwater can absorb a lot of heat before water molecules can move faster or begin to get hotmolecules can move faster or begin to get hot  much more energy is needed disrupt the hydrogenmuch more energy is needed disrupt the hydrogen bonds in liquid waterbonds in liquid water • water resists rapid temperature fluctuationswater resists rapid temperature fluctuations • adding stability to earth's environmentsadding stability to earth's environmentsBeira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  7. 7. 77 B.B. high heat of vaporizationhigh heat of vaporization  the energy needed to change the phase of a liquid to a gas  (44 kJ/mole)  it takes a great deal of energy to break a molecule free of its liquid partners – water resists evaporation – causes a cooling effect on plants C. High latent heat of fusionC. High latent heat of fusion  takes lots of energy to convert from solid to a liquidtakes lots of energy to convert from solid to a liquid statestate  lot of energy must be released by water to freezelot of energy must be released by water to freeze  Thus water resists freezingThus water resists freezing Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  8. 8. 88 D. Capillary actionD. Capillary action i.i. CohesionCohesion  hydrogen bonds between water molecules makehydrogen bonds between water molecules make liquid water self-stickyliquid water self-sticky  The hydrogens of one water molecule are attractedThe hydrogens of one water molecule are attracted to the oxygen from other water moleculesto the oxygen from other water molecules  makes water bead up more on a surfacemakes water bead up more on a surface Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  9. 9. 99 ii. Adhesionii. Adhesion  the attraction of water molecules to non-waterthe attraction of water molecules to non-water hydrophilic substanceshydrophilic substances  This property of water gives it the ability to climbThis property of water gives it the ability to climb the wall of any container it is inthe wall of any container it is in  The top of the water column assumes aThe top of the water column assumes a uu-shape-shape Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  10. 10. 1010 iii. Surface tensioniii. Surface tension  Water has a very high surface tensionWater has a very high surface tension  the cohesion of water molecules to eachthe cohesion of water molecules to each other and to the water molecules below at theother and to the water molecules below at the surface of a body of watersurface of a body of water  It is a measure of how difficult it is to breakIt is a measure of how difficult it is to break the surface of a liquidthe surface of a liquid  Thus water acts as thought it has a skinThus water acts as thought it has a skin because of cohesionbecause of cohesion  Plants take advantage of capillary action toPlants take advantage of capillary action to pull water from the root into themselvespull water from the root into themselves Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  11. 11. 1111 Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  12. 12. 1212 III. Universal solventIII. Universal solvent  dissolves more different kinds ofdissolves more different kinds of substances than any other solventsubstances than any other solvent  Hydrogen bonds make water anHydrogen bonds make water an excellent solventexcellent solvent  wherever water goes, either through thewherever water goes, either through the ground or through plant body, it takesground or through plant body, it takes along valuable chemicals, minerals, andalong valuable chemicals, minerals, and nutrients.nutrients. Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  13. 13. 1313 Water is a versatile solvent owing to its polarityWater is a versatile solvent owing to its polarity  Ionic compounds dissolve in water.Ionic compounds dissolve in water. • Charged regions of polar water moleculesCharged regions of polar water molecules have an electrical attraction to charged ionshave an electrical attraction to charged ions • Water surrounds individual ions, separatingWater surrounds individual ions, separating and shielding them from one anotherand shielding them from one another  Polar compounds in general, are water-soluble.Polar compounds in general, are water-soluble.  Charged regions of polar water molecules have anCharged regions of polar water molecules have an affinity for opposite charged regions of other polaraffinity for opposite charged regions of other polar moleculesmolecules Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  14. 14. 1414 IV. Water is a liquid at physiologicalIV. Water is a liquid at physiological temperaturetemperature  high boiling and melting point when compared tohigh boiling and melting point when compared to other similar sized moleculesother similar sized molecules  Life exists between 0 and 100Life exists between 0 and 100oo CC  <0<0oo C too low to permit significant chemistry forC too low to permit significant chemistry for metabolismmetabolism  >> 100 oC tends to disrupt bonds100 oC tends to disrupt bonds Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  15. 15. 1515 VV. Transparent to Light. Transparent to Light  Chloroplasts inside a cell areChloroplasts inside a cell are surrounded by watersurrounded by water Photosynthesis if water werePhotosynthesis if water were opaque ????opaque ????  the penetration of light in waterthe penetration of light in water determines the distribution of aquaticdetermines the distribution of aquatic plantsplants Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  16. 16. 1616 VI. Chemically inertVI. Chemically inert ::  water does not react unless enzymaticcallywater does not react unless enzymaticcally designed to reactdesigned to react VII. Affect the shape, stability andVII. Affect the shape, stability and properties of biological molecules.properties of biological molecules. Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  17. 17. 1717 Role of Water in plantsRole of Water in plants  Solvent for the uptake and transport of moleculesSolvent for the uptake and transport of molecules  Water is major component of cellsWater is major component of cells  Good medium for biochemical reactionsGood medium for biochemical reactions  React in many biochemical reactionReact in many biochemical reaction  Provide structural support via turger pressure in leavesProvide structural support via turger pressure in leaves  The medium for the transfer of plant gameteThe medium for the transfer of plant gamete  Plant movements are the result of water moving in toPlant movements are the result of water moving in to and out of those plantsand out of those plants  Temperature stabilizationTemperature stabilization  Plays a role in cell elongation and growthPlays a role in cell elongation and growthBeira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  18. 18. 1818 2.22.2 Concepts of water potentialConcepts of water potential diverse multivarious role of water indiverse multivarious role of water in plant functionplant function Consider bothConsider both the state of water andthe state of water and rate of movement of water in plantsrate of movement of water in plants determined by values of water potentialdetermined by values of water potential or gradient in water potentialor gradient in water potential Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  19. 19. 1919 Defn.Defn. is the chemical potential of water in ais the chemical potential of water in a solutionsolution compared tocompared to pure waterpure water at the sameat the same temperature and pressuretemperature and pressure a measure of the free energy of watera measure of the free energy of water the energy available to movethe energy available to move waterwater from onefrom one place to anotherplace to another with out temperature changewith out temperature change Determines direction of water movementDetermines direction of water movement Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  20. 20. 2020 Values of water potential:Values of water potential: Pure water has a defined waterPure water has a defined water potential of zero.potential of zero. However it is possible for the waterHowever it is possible for the water potential to bepotential to be positivepositive oror negativenegative Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  21. 21. 2121 Units of measurementUnits of measurement :: measured in units of atmosphericmeasured in units of atmospheric pressure:pressure:  Pascal (MPa)Pascal (MPa)  Pounds force/square inchPounds force/square inch  BarsBars  dynes/square cmdynes/square cm Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  22. 22. 2222  Equation of water potentialEquation of water potential  In a simple systemIn a simple system • Pressure potential (Ψp)Pressure potential (Ψp) • Osmotic potential(Ψπ) or solute potentialOsmotic potential(Ψπ) or solute potential (Ψ(Ψss).). Ψ = Ψp + Ψπ (Ψs)Ψ = Ψp + Ψπ (Ψs)  Complex SystemsComplex Systems  Gravity potential (Ψg)Gravity potential (Ψg)  Matric potential (Ψm)Matric potential (Ψm) Ψ = Ψπ + Ψp + Ψg + ΨmΨ = Ψπ + Ψp + Ψg + ΨmBeira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  23. 23. 2323 A. Solute potential / osmotic potential/A. Solute potential / osmotic potential/  A measure of tendency for HA measure of tendency for H22 O to cross aO to cross a selectively permeable membraneselectively permeable membrane  from low concentration to highfrom low concentration to high concentration of soluteconcentration of solute  Pure water has a solute potential ofPure water has a solute potential of zerozero Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  24. 24. 2424  Addition of solute makes the value ofAddition of solute makes the value of solute potential negativesolute potential negative  decreasesdecreases the free energy of waterthe free energy of water  Negative contribution to water potentialNegative contribution to water potential Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  25. 25. 2525 Van’t Hoff equationVan’t Hoff equation  Shows relationship of solute concentrationShows relationship of solute concentration (in molality) to solute potential(in molality) to solute potential Ψπ = − miRTΨπ = − miRT  m,m, concentration of the soluteconcentration of the solute  ii , ionization constant of the solute (1 for, ionization constant of the solute (1 for glucose, 2 for NaCl)glucose, 2 for NaCl)  RR , ideal gas constant, ideal gas constant  TT , temperature (K), temperature (K) Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  26. 26. 2626 For example,For example, when a solute is dissolved in waterwhen a solute is dissolved in water the water molecules are less likely tothe water molecules are less likely to diffuse away via osmosis than whendiffuse away via osmosis than when there is no solutethere is no solute SSSSSS WWWW SSSSSS WWWW SSSSSS WWWW High free energy of water ????? A B Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  27. 27. 2727 regions of higher regions of higher water potential water potential •less negative; less negative; •high free energy; high free energy; •m ore positive; m ore positive; •less solute) less solute) Regions of lower water Regions of lower water potential potential •m ore negative, m ore negative, •less free energy, less free energy, •less positive, less positive, •high solute high solute Water movement Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  28. 28. 2828 B. Pressure potential (turgor pressure) (Ψp)B. Pressure potential (turgor pressure) (Ψp) • the hydrostatic pressure produced by athe hydrostatic pressure produced by a solution in a space divided by asolution in a space divided by a differentially permeable membranedifferentially permeable membrane • due to a differential in the concentrationsdue to a differential in the concentrations of soluteof solute • is increased as water enters a plant cellis increased as water enters a plant cell • It is usually positiveIt is usually positive • may be negative (tension) as in the xylemmay be negative (tension) as in the xylem Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  29. 29. 2929 • When a biological cell is in a hypotonicWhen a biological cell is in a hypotonic environment (the cell interior contains aenvironment (the cell interior contains a lower concentration of water)lower concentration of water) • water flows across the cell membrane intowater flows across the cell membrane into the cellthe cell • expand due to an increases in the totalexpand due to an increases in the total amount of water inside the cellamount of water inside the cell • exerts a pressure on the cell wallexerts a pressure on the cell wall Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  30. 30. 3030 Hypotonic Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  31. 31. 3131 Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  32. 32. 3232 Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  33. 33. 3333 Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  34. 34. 3434 Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  35. 35. 3535 C. Matric potentialC. Matric potential (Ψm)(Ψm) • due to the force of attraction of water fordue to the force of attraction of water for colloidal, charged surfacescolloidal, charged surfaces • It is negative because it reduces the ability ofIt is negative because it reduces the ability of water to movewater to move • In large volumes of water it is very small andIn large volumes of water it is very small and usually ignoredusually ignored • Water adheres electrostatically to solidWater adheres electrostatically to solid hydrophilic surfacehydrophilic surface • Capillary rise is associated with matrix potential.Capillary rise is associated with matrix potential. Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  36. 36. 3636 D.D. Gravitational potential ( ΨgΨg) • The potential energy associated with movingThe potential energy associated with moving water to heightwater to height • when referring to the top of tall treeswhen referring to the top of tall trees ΨgΨg== ρghρgh = 1000kg/M= 1000kg/M33 *9.8 m/S*9.8 m/S22 *h(m)*h(m) = 0.01Mpa/m= 0.01Mpa/m water in leaves at the top of a 100m tall treewater in leaves at the top of a 100m tall tree suck water.suck water. Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  37. 37. 3737 Basic principles of water potentialBasic principles of water potential • Water potential of pure water is zero,Water potential of pure water is zero, open to the atmosphereopen to the atmosphere • Water potential in intact plant tissue isWater potential in intact plant tissue is usually negative because of the largeusually negative because of the large quantities of dissolved solutes in cellsquantities of dissolved solutes in cells • The addition of solute decreases waterThe addition of solute decreases water potentialpotential • The addition of pressure increases waterThe addition of pressure increases water potentialpotential Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  38. 38. 3838 • Plant cells will gain or lose water toPlant cells will gain or lose water to intercellular fluids depending upon theirintercellular fluids depending upon their water potentialwater potential – A flaccid cell placed in a hyperosmoticA flaccid cell placed in a hyperosmotic solution (low Ψw)solution (low Ψw) – lose water by osmosislose water by osmosis – the cell will plasmolyzethe cell will plasmolyze – protoplast moves away from cell wallprotoplast moves away from cell wall Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  39. 39. 3939 • Gives a measure of water statusGives a measure of water status – Leaves of well-watered plants have waterLeaves of well-watered plants have water potential ranging from -0.2 and -0.6Mpapotential ranging from -0.2 and -0.6Mpa – Leaves of plants in arid climates posesLeaves of plants in arid climates poses water potential between -2 and -5water potential between -2 and -5 Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  40. 40. 4040 Effect on physiological changesEffect on physiological changes Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  41. 41. 4141 2.3 Water movement in cells and tissues2.3 Water movement in cells and tissues Mechanisms of movementMechanisms of movement 1.1. Bulk (or Mass) FlowBulk (or Mass) Flow • mass movement of molecules in responsemass movement of molecules in response to ato a pressure gradientpressure gradient • The molecules move from high to lowThe molecules move from high to low pressurepressure • functions in long-distance transportfunctions in long-distance transport • is usually along the vertical axis of theis usually along the vertical axis of the plantplant Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  42. 42. 4242 2. Diffusion2. Diffusion • the net random movement of individualthe net random movement of individual molecules driven by random thermal motionmolecules driven by random thermal motion • is rapid over short distancesis rapid over short distances a region of higha region of high concentrationconcentration // high chemicalhigh chemical potentialpotential area of high free energy low free energy region of lowregion of low concentrationconcentration// low chemicallow chemical potentialpotential Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  43. 43. 4343 •Molecules move until they reach dynamic equilibrium •At equilibrium the net movement stops •the molecules continue to move randomly Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  44. 44. 4444 Factors influencing the rate of diffusionFactors influencing the rate of diffusion i. Concentration Gradienti. Concentration Gradient • Solutes move from an area of highSolutes move from an area of high concentration to one of lowerconcentration to one of lower concentrationconcentration • Fick’s Law : relates the rate of diffusion toFick’s Law : relates the rate of diffusion to the concentration gradient (C1–C2) andthe concentration gradient (C1–C2) and resistance (r)resistance (r) Js = (C1-C2)/r Js= flux densityJs = (C1-C2)/r Js= flux density Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  45. 45. 4545 • The rate of diffusion is directly proportionalThe rate of diffusion is directly proportional to the concentration gradientto the concentration gradient • The greater the difference in concentrationThe greater the difference in concentration between two areas, the greater the rate ofbetween two areas, the greater the rate of diffusiondiffusion • if the gradient is zero, there will be no netif the gradient is zero, there will be no net diffusiondiffusion • The greater the resistance to diffusion, the lowerThe greater the resistance to diffusion, the lower the rate of diffusionthe rate of diffusion Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  46. 46. 4646 ii. Molecular Speedii. Molecular Speed • atoms and molecules are always in motion atatoms and molecules are always in motion at temperatures above absolute zerotemperatures above absolute zero • Molecular speed is directly proportional toMolecular speed is directly proportional to temperaturetemperature • At room temperature, the average velocity of aAt room temperature, the average velocity of a molecule is =2 km/secmolecule is =2 km/sec • indirectly related to molecular weightindirectly related to molecular weight Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  47. 47. 4747 iii. Temperatureiii. Temperature • increases the rate of molecularincreases the rate of molecular movementmovement • therefore, increases the rate of diffusiontherefore, increases the rate of diffusion iv. Pressureiv. Pressure increases speed of moleculesincreases speed of molecules increase the rate of diffusionincrease the rate of diffusion Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  48. 48. 4848 V. Solute effect on the chemical potential ofV. Solute effect on the chemical potential of the solventthe solvent • Solute particles decrease the free energySolute particles decrease the free energy of a solventof a solvent • factor is the number of particlesfactor is the number of particles • Mole fraction of solventMole fraction of solvent = Number of solvent= Number of solvent molecules/total number of solvent molecules + solutemolecules/total number of solvent molecules + solute moleculesmolecules  Water moves from an area of higher moleWater moves from an area of higher mole fractionfraction Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  49. 49. 4949 3.Osmosis3.Osmosis • This is a specialized case of diffusionThis is a specialized case of diffusion • the diffusion of a solvent across a biologicalthe diffusion of a solvent across a biological selectively permeable membraneselectively permeable membrane • Movement is driven by the sum of aMovement is driven by the sum of a concentration gradient and pressure gradientconcentration gradient and pressure gradient • Osmosis to occur :Osmosis to occur : – two solutions of the same solventtwo solutions of the same solvent – separated with selectively permeable membraneseparated with selectively permeable membrane – pressure and concentration gradientpressure and concentration gradient Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  50. 50. 5050 Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  51. 51. 5151 4. Dialysis:4. Dialysis: • This is another specialized caseThis is another specialized case of diffusionof diffusion • it is the diffusion of solute acrossit is the diffusion of solute across a semi-permeable membrane.a semi-permeable membrane. High salt Low salt buffer Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  52. 52. 5252 Transport of water inTransport of water in PlantsPlants Levels of transport in plants:Levels of transport in plants:  Movement of water and solutes into and outMovement of water and solutes into and out of individual cellsof individual cells  Localized transport of material from cell toLocalized transport of material from cell to cell at the level of tissues and organscell at the level of tissues and organs  Long-distance transport of sap throughoutLong-distance transport of sap throughout the vascular tissues at the whole-plantthe vascular tissues at the whole-plant levellevel Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  53. 53. 5353 Water diffuse from theWater diffuse from the soilsoil to theto the plantplant rootroot and then to theand then to the airair ::  Water potential gradient is establishedWater potential gradient is established between the root cell sap and the soil solutionbetween the root cell sap and the soil solution Water potential may be established by:Water potential may be established by: • Increasing the concentration of solutesIncreasing the concentration of solutes .. – Water potential of soil solution isWater potential of soil solution is highest than airhighest than air Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  54. 54. 5454 • Physical state of waterPhysical state of water – highest whenhighest when water is a liquid andwater is a liquid and – lowest when water is a gas in airlowest when water is a gas in air .. intimate contact between root hairintimate contact between root hair and soil particlesand soil particles Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  55. 55. 5555 Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  56. 56. 5656 Water Transport in the RootWater Transport in the Root  Water is taken in to the root hairWater is taken in to the root hair  move into and within the plantmove into and within the plant root in a variety of routsroot in a variety of routs Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  57. 57. 5757 A.A. Apoplastic path wayApoplastic path way  movement of water through intercellularmovement of water through intercellular spaces and cell wallspaces and cell wall  continuum formed between the continuouscontinuum formed between the continuous matrix of cell wallsmatrix of cell walls  Water and solute move without entering aWater and solute move without entering a cellcell  involves the non-living vascular tissueinvolves the non-living vascular tissue Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  58. 58. 5858  blocked by the casparian strip atblocked by the casparian strip at endodermisendodermis Impermeable band of suberinImpermeable band of suberin inside walls of endodermal cellsinside walls of endodermal cells  regulates the quantity and type ofregulates the quantity and type of minerals and ions reach the xylemminerals and ions reach the xylem Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  59. 59. 5959 B. Syplastic path wayB. Syplastic path way  the continuum of cytoplasm within athe continuum of cytoplasm within a plant tissueplant tissue  formed by the plasmodesmataformed by the plasmodesmata which pass through pores in the cellwhich pass through pores in the cell walls.walls.  responsible in order water andresponsible in order water and minerals to reach the xylem.minerals to reach the xylem.  This path way involves the livingThis path way involves the living part of the cellpart of the cellBeira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  60. 60. 6060 C. Transmembrane path wayC. Transmembrane path way • Water sequentially moves from one cellWater sequentially moves from one cell to the next cellto the next cell • by repeatedly crossing plasmaby repeatedly crossing plasma membranes and cell walls.membranes and cell walls. • NB. Water and solute molecules canNB. Water and solute molecules can movemove – by any one of these routes orby any one of these routes or – a combination through switching from one toa combination through switching from one to anotheranother.. Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  61. 61. 6161 Apoplast Symplast TransmembraneBeira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  62. 62. 6262 Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  63. 63. 6363 Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  64. 64. 6464 The xylem pathwayThe xylem pathway 1. Root Pressure1. Root Pressure • This a push forceThis a push force • Generated as solute accumulates in the xylemGenerated as solute accumulates in the xylem Due to the root's active absorption of dissolvedDue to the root's active absorption of dissolved nutrientsnutrients the water in the soil tends to be lower inthe water in the soil tends to be lower in solutes than the water inside the root's cellssolutes than the water inside the root's cells solute potential gradient developssolute potential gradient develops Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  65. 65. 6565  water flows into the roots through osmosis andwater flows into the roots through osmosis and osmotic pressureosmotic pressure increasesincreases  called root pressurecalled root pressure a mechanism used by vascular plants to transporta mechanism used by vascular plants to transport water through the xylem to the plant's higherwater through the xylem to the plant's higher reachesreaches  only provide modest push water up the stemonly provide modest push water up the stem  is not enough to account for the movement ofis not enough to account for the movement of water to leaves at the top of treeswater to leaves at the top of trees Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  66. 66. 6666 (A) (B) Mineral ions Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  67. 67. 6767 2. TACT Mechanism2. TACT Mechanism  The transpirational pull on the xylem sapThe transpirational pull on the xylem sap is transmitted to the soil solutionis transmitted to the soil solution  Four forces combine to transport waterFour forces combine to transport water solutions from the roots through the xylemsolutions from the roots through the xylem elements, and into the leaveselements, and into the leaves  These TACT forces are:These TACT forces are: • TranspirationTranspiration • AdhesionAdhesion • CohesionCohesion • TensionTension Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  68. 68. 6868 i. Transpirationi. Transpiration  involves the pulling of water upinvolves the pulling of water up through the xylem of a plantthrough the xylem of a plant  Utilize the energy of evaporation andUtilize the energy of evaporation and the tensile strength of water.the tensile strength of water. Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  69. 69. 6969 ii. Adhesionii. Adhesion  is the attractive force between wateris the attractive force between water molecules and other substances.molecules and other substances. both water and cellulose are polarboth water and cellulose are polar moleculesmolecules there is a strong attraction for water to thethere is a strong attraction for water to the hydrophilic walls of xylem cellshydrophilic walls of xylem cells The small diameter of vessels andThe small diameter of vessels and tracheids is important to the adhesiontracheids is important to the adhesion Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  70. 70. 7070 iii. Cohesioniii. Cohesion  is the attractive force between molecules of theis the attractive force between molecules of the same substance.same substance.  high cohesive force due to the 4 hydrogen bondshigh cohesive force due to the 4 hydrogen bonds  water's cohesive force within xylem give it awater's cohesive force within xylem give it a tensile strength equivalent to that of a steel wiretensile strength equivalent to that of a steel wire of similar diameter.of similar diameter.  Cohesion of water allows for the pulling of waterCohesion of water allows for the pulling of water from the top of the plant without breaking thefrom the top of the plant without breaking the "chain"."chain". Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  71. 71. 7171 iv. Tensioniv. Tension a stress placed on an object by a pulling force.a stress placed on an object by a pulling force. is created by the surface tension whichis created by the surface tension which develops in the leaf's air spaces.develops in the leaf's air spaces.  The upward pull of sap causes tension (negativeThe upward pull of sap causes tension (negative pressure) in xylempressure) in xylem  decreases water potential anddecreases water potential and  allows passive flow of water from soil into steleallows passive flow of water from soil into stele Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  72. 72. 7272 Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  73. 73. 7373 Soil factors affecting water absorptionSoil factors affecting water absorption Reading AssignmentReading Assignment Until Next classUntil Next class Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
  74. 74. 7474 1.1. What is the importance of the water potentialWhat is the importance of the water potential concept in plant physiology? What are theconcept in plant physiology? What are the components of water potential?components of water potential? 2.2. List three unique properties of water thatList three unique properties of water that make it such a good for cellular functioningmake it such a good for cellular functioning 3.3. Can plant cells have negative turgorCan plant cells have negative turgor pressure values? Explainpressure values? Explain 4.4. Describe the casparian strip and its function.Describe the casparian strip and its function. Beira Hailu Meressa, JUCAVMBeira Hailu Meressa, JUCAVM 20082008
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