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WATER• Plants' most important chemical• most often limits productivity
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WATER• Plants' most important chemical• most often limits productivity
• Often >90%% of a plant cell’s weight
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WATER• Plants' most important chemical• most often limits productivity
• Often >90%% of a plant cell’s weight• Gives cells shape
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WATER• Plants' most important chemical• most often limits productivity
• Often >90%% of a plant cell’s weight• Gives cells shape• Dissolves many chem
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WATER• Dissolves many chem• most biochem occurs in water• Source of e- for PS
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WATER• most biochem occurs in water• Source of e- for PS• Constantly lose water due to PS (1000 H2O/CO2)
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WATER• most biochem occurs in water• Source of e- for PS• Constantly lose water due to PS• Water transport is crucial!
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WATER• Water transport is crucial!• SPAC= Soil Plant Air Continuum• moves from soil->plant->air
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WATER Formula = H2O Formula weight = 18 daltons Structure = tetrahedron, bond angle 104.5˚
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WATER Structure = tetrahedron, bond angle 104.5˚ polar :O is more attractive to electrons than H
+ on H- on O
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WaterPolarity is reason for water’s properties water forms H-bonds with polar molecules
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WaterPolarity is reason for water’s properties water forms H-bonds with polar molecules
Hydrophilic = polar moleculesHydrophobic = non-polar molecules
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Properties of water1) Cohesion = water H-bonded to water
-> reason for surface tension
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Properties of water1) Cohesion = water H-bonded to water
-> reason for surface tension-> why water can be drawn from roots to leaves
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Properties of water1) Cohesion = water H-bonded to water2) Adhesion = water H-bonded to something else
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Properties of water1) Cohesion = water H-bonded to water2) Adhesion = water H-bonded to something else• Cohesion and adhesion are crucial for water movement in plants!
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Properties of water1) Cohesion = water H-bonded to water2) Adhesion = water H-bonded to something else• Cohesion and adhesion are crucial for water movement in plants!• Surface tension & adhesion in mesophyll creates force that draws water through the plant!
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Properties of water1) Cohesion = water H-bonded to water2) Adhesion = water H-bonded to something else3) high specific heat• absorb heat when break H-bonds: cools leaves
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Properties of water1) Cohesion = water H-bonded to water2) Adhesion = water H-bonded to something else3) high specific heat• absorb heat when break H-bonds• Release heat when form H-bonds
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Properties of water1) Cohesion = water H-bonded to water2) Adhesion = water H-bonded to something else3) high specific heat4) Ice floats
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Properties of water1) Cohesion = water H-bonded to water2) Adhesion = water H-bonded to something else3) high specific heat4) Ice floats5) Universal solvent
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Properties of water1) Cohesion = water H-bonded to water2) Adhesion = water H-bonded to something else3) high specific heat4) Ice floats5) Universal solvent•Take up & transport nutrients dissolved in water
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Properties of water5) “Universal” solvent•Take up & transport nutrients dissolved in water•Transport organics dissolved in water
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Properties of water1) Cohesion = water H-bonded to water2) Adhesion = water H-bonded to something else3) high specific heat4) Ice floats5) Universal solvent6) Hydrophobic bonds
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Properties of water1) Cohesion = water H-bonded to water2) Adhesion = water H-bonded to something else3) high specific heat4) Ice floats5) Universal solvent6) Hydrophobic bonds7) Water ionizes
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pH[H+] = acidity of a solutionpH = convenient way to measure aciditypH = - log10 [H+]pH 7 is neutral: [H+] = [OH-]
-> at pH 7 [H+] = 10-7 moles/l
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pHPlants vary pH to control many processes!
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Water movementDiffusion: movement of single molecules down ∆[ ] due to random motion until [ ] is even•Driving force?
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Water movementDiffusion: movement of single molecules down ∆[ ] due to random motion until [ ] is even • Driving force: lowers free energy•∆G = ∆H- T∆S
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Water movementDiffusion: movement of single molecules down ∆[ ] due to random motion until [ ] is even Bulk Flow: movement of groups ofmolecules down a pressure gradient
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Water movementDiffusion: movement of single molecules down ∆[ ] due to random motion until [ ] is even Bulk Flow: movement of groups ofmolecules down a pressure gradient• Independent of ∆ [ ] !
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Water movementDiffusion: movement of single molecules down ∆[] due to random motion until [ ] is even Bulk Flow: movement of groups of molecules down a pressure gradient•Independent of ∆[ ] !•How water moves through xylem
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Water movementDiffusion: movement of single molecules down [] due to random motion until [ ] is even Bulk Flow: movement of groups of molecules down a pressure gradient•Independent of ∆ [ ] !•How water moves through xylem•How water moves through soil and apoplast
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Water movementBulk Flow: movement of groups of molecules down a pressure gradient•Independent of ∆ [ ] !•How water moves through xylem•Main way water moves through soil and apoplast•Very sensitive to radius of vessel: increases as r4
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Water movementDiffusion: movement of single molecules down ∆[] due to random motion until [ ] is even Bulk Flow: movement of groups of molecules down a pressure gradient•Independent of ∆[ ] !•How water moves through xylem•Main way water moves through soil and apoplast•Very sensitive to radius of vessel: increases as r4
Osmosis: depends on bulk flow and diffusion!
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Water movementOsmosis: depends on bulk flow and diffusion!water crosses membranes but other solutes do notwater tries to even its [ ] on each side
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Water movementOsmosis: depends on bulk flow and diffusion!water crosses membranes but other solutes do notwater tries to even its [ ] on each sideother solutes can’t: result is net influx of water
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Water movementOsmosis: depends on bulk flow and diffusion!•Moves through aquaporins, so rate depends on pressure and [ ] gradients!
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Water movementOsmosis: depends on bulk flow and diffusion!•Moves through aquaporins, so rate depends on pressure and [ ] gradients!• Driving force = water's free energy (J/m3 = MPa)
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Water potentialDriving force = water's free energy = water potential w
• Important for many aspects of plant physiology
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Water potentialDriving force = water's free energy = water potential w
Water moves to lower its potential
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Water potentialDriving force = water's free energy = water potential w
Water moves to lower its potential
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Water potentialDriving force = water's free energy = water potential w
Water moves to lower its potentialDepends on:
1. [H2O]: s (osmotic potential)
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Water potentialWater moves to lower its potentialDepends on:
1. [H2O]: s (osmotic potential)
2. Pressure : p
• Turgor pressure inside cells
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Water potentialWater moves to lower its potentialDepends on:
1. [H2O]: s (osmotic potential)
2. Pressure : p
• Turgor pressure inside cells• Negative pressure in xylem!
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Water potentialWater moves to lower its potentialDepends on:• [H2O]: s (osmotic potential)
• Pressure p
• Gravity g
w = s +p + g
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Water potentialWater moves to lower its potentialDepends on:• [H2O]: s (osmotic potential)
• Pressure p
• Gravity g
w = s +p + g
w of pure water at sea level
& 1 atm = 0 MPA
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Water potentialw = s +p + g
w of pure water at sea level & 1 atm = 0 MPA
s (osmotic potential) is always negative
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Water potentialw = s +p + g
w of pure water at sea level & 1 atm = 0 MPA
s (osmotic potential) is always negative• If increase [solutes] water will move in
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Water potentialw = s +p + g
w of pure water at sea level & 1 atm = 0 MPA
s (osmotic potential) is always negative• If increase [solutes] water will move in
p (pressure potential) can be positive or negative
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Water potentialw = s +p + g
w of pure water at sea level & 1 atm = 0 MPA
s (osmotic potential) is always negative• If increase [solutes] water will move in
p (pressure potential) can be positive or negative
• Usually positive in cells to counteract s
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Water potentialp (pressure potential) can be positive or negative
• Usually positive in cells to counteract s
• Helps plants stay same size despite daily fluctuations in w
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Water potentialw = s +p + g
p (pressure potential) can be positive or negative
• Usually positive in cells to counteract s
• Helps plants stay same size despite daily fluctuations in w
• p in xylem is negative, draws water upwards
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Water potentialw = s +p + g
p (pressure potential) can be positive or negative
• Usually positive in cells to counteract s
• Helps plants stay same size despite daily fluctuations in w
• p in xylem is negative, draws water upwardsg can usually be ignored, but important for tall trees
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Water potentialMeasuring water potential
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Water potentialMeasuring water potentials (osmotic potential) is “easy”• Measure concentration of solution in equilibrium with
cells
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Water potentialMeasuring water potentials (osmotic potential) is “easy”• Measure concentration of solution in equilibrium with
cells g (gravity potential) is easy: height above ground• -0.01 Mpa/m
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Water potentialMeasuring water potentials (osmotic potential) is “easy”• Measure concentration of solution in equilibrium with
cells g (gravity potential) is easy: height above ground
P (pressure potential) is hard!• Pressure bomb = most common technique
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Water potentialMeasuring water potentials (osmotic potential) is “easy”• Measure concentration of solution in equilibrium with
cells g (gravity potential) is easy: height above ground
P (pressure potential) is hard!• Pressure bomb = most common techniqueOthers include pressure transducers, xylem probes
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Measuring water potentialP (pressure potential) is hard!• Pressure bomb = most common techniqueOthers include pressure transducers, xylem probesTherefore disagree about H2Otransport in xylem