1 Water & Plant Cells: Chapter 3 Water & Plant Cells: Chapter 3 Why is water important? Why is water important? 1. 1. 1g organic material requires 500g water. 1g organic material requires 500g water. 2. 2. Roles of water in plants (97% is lost) Roles of water in plants (97% is lost) A. A. Solvent Solvent - Fluid medium for cytoplasm Fluid medium for cytoplasm B. B. Photosynthesis Photosynthesis C. C. Turgor Turgor pressure pressure D. D. Transpiration & Heat dissipation Transpiration & Heat dissipation E. E. Transport dissolved minerals Transport dissolved minerals 3. 3. Productivity Productivity Properties of Water Properties of Water 1. 1. Hydrogen bonding Hydrogen bonding 2. 2. Excellent solvent Excellent solvent – shells of hydration shells of hydration 3. 3. Specific heat = 4.187kJ kg Specific heat = 4.187kJ kg -1 (1c/g) (1c/g) 4. 4. Latent heat of vaporization = 44kJ mol Latent heat of vaporization = 44kJ mol -1 5. 5. Cohesion, adhesion & capillarity Cohesion, adhesion & capillarity 6. 6. Surface tension Surface tension 7. 7. Tensile strength > Tensile strength > -30MPa 30MPa 1 1 MPa MPa = 1 = 1 newton newton m -2 2 1 1 MPa MPa = 1 Joule m = 1 Joule m -3 3 1 1 MPa MPa = 9.9 atmospheres = 9.9 atmospheres 1 1 MPa MPa ≈ ≈ 145.5 145.5 psi psi 30 30 MPa MPa = 4351 lb in = 4351 lb in -2 2 1 Atmosphere = 14.7 lbs in 1 Atmosphere = 14.7 lbs in -2 2 1 Atmosphere = 760mm Hg 1 Atmosphere = 760mm Hg 1 Atmosphere = 0.1013 1 Atmosphere = 0.1013 MPa MPa 1 Atmosphere = 1.013 Bar 1 Atmosphere = 1.013 Bar 1 Atmosphere = 1.013 X 10 1 Atmosphere = 1.013 X 10 5 Pa Pa Major Processes Related to Water Movement in Plants Major Processes Related to Water Movement in Plants 1. 1. Short distance transport = Molecular Diffusion Short distance transport = Molecular Diffusion 2. 2. Long distance transport = Bulk Flow Long distance transport = Bulk Flow Short Distance Transport Long Distance Transport Processes of Water Movement in Plants Processes of Water Movement in Plants Short Distance Transport Short Distance Transport 1. 1. Molecular Diffusion Molecular Diffusion 1. 1. Fick Fick’s first law first law 2. 2. Importance: Identifies factors governing short distance transpor Importance: Identifies factors governing short distance transport: t: 1. 1. Concentration gradient Concentration gradient 2. 2. Distance Distance 3. 3. Medium through which something moves Medium through which something moves Js = rate of transport Ds = diffusion coefficient = how easily something moves in a medium c s = difference in concentration between two points = concentration gradient x = distance between two points/concentrations
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Processes of Water Movement in Plants Short Distance Transport€¦ · · 2007-02-041 MPa = 9.9 atmospheres ... Chapter 4 Water Balance of Plants Mechanisms & driving forces operating
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Why is water important?Why is water important?1.1. 1g organic material requires 500g water.1g organic material requires 500g water.2.2. Roles of water in plants (97% is lost)Roles of water in plants (97% is lost)
A.A. Solvent Solvent -- Fluid medium for cytoplasmFluid medium for cytoplasmB.B. PhotosynthesisPhotosynthesisC.C. TurgorTurgor pressurepressureD.D. Transpiration & Heat dissipationTranspiration & Heat dissipationE.E. Transport dissolved mineralsTransport dissolved minerals
3.3. ProductivityProductivity
Properties of WaterProperties of Water1.1. Hydrogen bondingHydrogen bonding2.2. Excellent solvent Excellent solvent –– shells of hydrationshells of hydration3.3. Specific heat = 4.187kJ kgSpecific heat = 4.187kJ kg--11 (1c/g)(1c/g)4.4. Latent heat of vaporization = 44kJ molLatent heat of vaporization = 44kJ mol--11
Major Processes Related to Water Movement in PlantsMajor Processes Related to Water Movement in Plants
1.1. Short distance transport = Molecular DiffusionShort distance transport = Molecular Diffusion2.2. Long distance transport = Bulk FlowLong distance transport = Bulk Flow
Short Distance Transport Long Distance Transport
Processes of Water Movement in PlantsProcesses of Water Movement in PlantsShort Distance TransportShort Distance Transport
1.1. Molecular DiffusionMolecular Diffusion1.1. FickFick’’ss first lawfirst law
2.2. Importance: Identifies factors governing short distance transporImportance: Identifies factors governing short distance transport:t:1.1. Concentration gradientConcentration gradient2.2. DistanceDistance3.3. Medium through which something movesMedium through which something moves
Js = rate of transport
Ds = diffusion coefficient = how easily something moves in a medium
cs = difference in concentration between two points = concentration gradient
x = distance between two points/concentrations
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1.1. Average time for a particle to diffuseAverage time for a particle to diffuse
2.2. Example: Glucose travels Example: Glucose travels 50um in 2.5 seconds50um in 2.5 seconds1 meter in 32 years1 meter in 32 years
3.3. Point: Diffusion Point: Diffusion rapid over short distancesrapid over short distancesvery slow over long distancesvery slow over long distances
Processes of Water Movement in PlantsProcesses of Water Movement in PlantsShort Distance TransportShort Distance Transport
Influence of distanceInfluence of distance
L = distance traveled
D = diffusion coefficient
1.1. Molecules move in bulk driven by a pressure gradient.Molecules move in bulk driven by a pressure gradient.
2.2. Pressure driven bulk flow moves water long distancesPressure driven bulk flow moves water long distances
Processes of Water Movement in PlantsProcesses of Water Movement in PlantsLong Distance TransportLong Distance TransportBulk flow or Mass FlowBulk flow or Mass Flow
Volume flow rate = meters sec-1
r = radius of tubeη= viscosity of the liquid
ψp = pressure gradientx = distance between gradient points
1.1. Free energy per mole of waterFree energy per mole of water
2.2. Water potential Water potential ==
3.3. Units of chemical/water potentialUnits of chemical/water potentialEnergy: J molEnergy: J mol--11
Pressure: PascalPressure: Pascal
4. The Pascal: 1Pa = 0.000145 lb in4. The Pascal: 1Pa = 0.000145 lb in--22
Chemical Potential of WaterChemical Potential of Water Pressure UnitsPressure Units
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Water Potential and Its ComponentsWater Potential and Its Components1.1. Water Potential EquationWater Potential Equation
ψψ = = ψψss + + ψψpp + + ψψgg
ψψ == water potential in water potential in MPaMPa
ψψss = solute or osmotic potential= solute or osmotic potential
ψψpp = pressure potential= pressure potential
ψψgg = gravity potential= gravity potential
Solute or Osmotic PotentialSolute or Osmotic Potential
1.1. Represents effect of solutes on water potentialRepresents effect of solutes on water potential2.2. Solutes always decrease water potentialSolutes always decrease water potential
…… always reduce free energy of wateralways reduce free energy of water3. 3. vanvan’’tt Hoff equation Hoff equation
ψψss = = --RTcRTcss
ψψss = solute potential= solute potentialRR = gas constant (8.32 J mol= gas constant (8.32 J mol--11 KK--11))TT = temperature (degrees K)= temperature (degrees K)ccss == solute concentration solute concentration
((osmolalosmolal = moles solute per liter water)= moles solute per liter water)
4. Independent of solute identity4. Independent of solute identity
Values of Osmotic PotentialValues of Osmotic Potential
4.4. ψψpp = 0 in a standard state= 0 in a standard state
Pressure PotentialPressure Potential
Flaccid Turgid Tension
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1.1. Gravity causes water to move downwardGravity causes water to move downward2. ψgg = = ρρww g h g h
ρρww = density of water (1.0 kg/m= density of water (1.0 kg/m3 3 at 4C))h h = height (meters)= height (meters)gg = acceleration due to gravity (9.8 ms= acceleration due to gravity (9.8 ms--22))
ρρww g = 0.01 M Pa mg = 0.01 M Pa m--11
For a 100 meter tree: For a 100 meter tree: ψgg = 0.01 = 0.01 MPaMPa mm--11 X100 = 1.0 X100 = 1.0 MPaMPa1MPa = = 145 lb in1MPa = = 145 lb in--2 2
5. Here5. Here’’s the point: s the point: In cells: In cells: ψgg is negligible (no change in height)is negligible (no change in height)In tall trees (100 meters) = 1.0 In tall trees (100 meters) = 1.0 MPaMPa change in change in ψww
Gravity PotentialGravity Potential1.1. MatricMatric = surface which binds water= surface which binds water2.2. Can be strong or negligibleCan be strong or negligible
Examples: Examples: Dry seed Dry seed ψ ψ ≈≈ ––50 to 50 to --350 350 MPaMPa
Hydrated seed Hydrated seed ψ ψ ≈≈ 0 0 MPaMPa
3. Here3. Here’’s the point: s the point: In hydrated tissue: In hydrated tissue: ψmm is negligibleis negligibleIn dry tissue: In dry tissue: ψmm is very importantis very important
4. Application 4. Application Soil Soil matricmatric potential is a critical variable in crop yield , potential is a critical variable in crop yield , runoff, runoff, evapotranspirationevapotranspiration and irrigation scheduling.and irrigation scheduling.
ψψmm = = MatricMatric PotentialPotential
Numerical Examples of Water Potential & Its ComponentsNumerical Examples of Water Potential & Its ComponentsNumerical Examples of Water Potential and Its ComponentsNumerical Examples of Water Potential and Its Components
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Numerical Examples of Water Potential and Its ComponentsNumerical Examples of Water Potential and Its ComponentsHofflerHoffler diagram: Water Potential and Change in Cell Volumediagram: Water Potential and Change in Cell Volume
Major ideas…
As cell water potential decreases first 5%
1. In a turgid cell, Water potential drop results in sharp turgor drop with little change in cell volume.
2. As cell volume decreases below 90%, osmotic potential decreases faster than turgor (Turgor = 0) with further decline in water potential
Sensitivity of Various Physiological Processes to DehydrationSensitivity of Various Physiological Processes to Dehydration
END END Chapter 3Chapter 3
Water and Plant CellsWater and Plant Cells
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Chapter 4Chapter 4Water Balance of PlantsWater Balance of Plants
Mechanisms & driving forces Mechanisms & driving forces operating on water transport in operating on water transport in
plantsplants
Physical Characteristics of Soil
Field Capacity WetClay soil 40%Sand 3%
Relative Size of soil particles
ψsoil = ψs + ψp
ψp = about -2MPa in dry clay soil.Permanent Wilting Point = ψsoil > ψplant
Components of soil water potential Soil Hydraulic ConductivitySoil hydraulic conductivity ≈ how easily water moves through soil
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Role of Water Evaporation in Water MovementT = surface tension of water
= 7.28 X 10-8 MPa m
r = radius of curvaturerT
P2−
=Ψ
Water Uptake by the Root
Water Movement: Soil to Root
Root Hairs increase surface area.
Concave menisci form at soil-water interface..creating very negative matric potentials.
More water removedMore acute menisci
More negative ψsoil .
Water Absorption: Root
Epidermis Cortex
Aquaporins regulate water movement through endodermis.
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Role of Aquaporins in water transport Root Pressure and Guttation
How does water move up a tree?
1. Diffusion
2. Capillarity
3. It’s pushed up
4. It’s pulled up
1.1. Average time for a particle to diffuseAverage time for a particle to diffuse
2.2. Example: Glucose travels Example: Glucose travels 50um in 2.5 seconds50um in 2.5 seconds1 meter in 32 years1 meter in 32 years
3.3. Point: Diffusion Point: Diffusion rapid over short distancesrapid over short distancesvery slow over long distancesvery slow over long distances
Processes of Water Movement in PlantsProcesses of Water Movement in PlantsDiffusion is a very slow processDiffusion is a very slow process
L = distance traveled
D = diffusion coefficient
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Could capillarity generate the force needed to draw water up a tree?
To calculate the height liquid can be raised by capillarity:h = 2Tcosø ÷ dgr
h = height of capillary (meters)T = surface tension (@20C, T for water = 0.0728Nm-1)cos ø = lifting component of meniscus angle
(approx = 1)d = density of liquid (998kgm-3)g = gravitational constant (9.80 ms-2)r = radius of capillary (in meters)
Capillarity as a Mechanism of Long Distance Water Transport
Capillary diam (µm) height of water column (m)0.005 30001 15.310 1.5340 0.38
Point: Height to which a column of water can be lifted by a capillary is inversely related to the diameter of the capillary.
Capillarity as a Mechanism of Long Distance Water Transport
Xylem and Water Transport Circular Bordered Pits
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• Requires less pressure than movement through cells
• From Pouiseuille’s equation:• Rate = 4mm s-1
• Tube radius = 40um
Water Movement Through Xylem
0.02Xylem2 X 108Layer of cells
Pressure gradient (MPa m-1)Tissue
• Pressure gradient = 0.02 MPa m-1
• Tree height = 100 meters (a Redwood tree)• Total Pressure Needed = 2.0 MPa
• Weight of Water … added Pressure to overcome– 100 meters X 0.01MPa m-1 = 1MPa
Diurnal course of Relative Humidity over a deciduous forest1. Water Vapor diffuses from Leaf to Air = Transpiration2. Diffusion influenced by 2 factors
1. Water Vapor Concentration Gradient2. Diffusional Resistance
Water Movement from Leaf To Atmosphere
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Stomatal aperture and Boundary Layer Resistance at leaf surface Role of Water Evaporation in Water Up a Tree
Water Evaporation in a leaf generates Negative Pressure in the Xylem
Fig. 4.16 Soil-Plant-Atmosphere Continuum
Experimental Demonstration of Water Under Tension
1. Dye uptake in cut stems
2. Change in stem diameter (Fritts 1958 – Beech Trees)
3. Direct measurement – Pressure bomb
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Measuring Water Potential in Plants with a Pressure Bomb
1. Turgor increase in guard cell solute concentration … pores open2.Turgor decrease in guard cell solute concentration … pores close
Guard Cells Control Short Term Regulation of Water Loss
Physical Challenges of CohesionTracheary Elements are connected by Pits
1. Break strength of water is ≈ 30MPa << Pressure needed to raise water.
2. Water in a metastable state - 3MPa ≈ - 30 Atmospheres