Chapters 3-4. Polar Excellent solvent Distinctive thermal properties Specific heat Heat of...
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Transcript of Chapters 3-4. Polar Excellent solvent Distinctive thermal properties Specific heat Heat of...
Chapters 3-4
Polar Excellent solvent Distinctive thermal properties
Specific heat Heat of vaporization
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3
Specific Heat Specific heat – amount of
energy absorbed for given temperature rise (measured in J/g/°C)
Specific Heat
Water (18)
4.2
H2S (34) --
NH3 (17) 5.0
CO2 (44) --
CH4 (16) --
C2H6 (30) --
CH3OH (32)
2.6
C2H5OH (46)
2.4
Specific Heat
Gold 0.13
Silver 0.23
Copper 0.38
Paraffin 2.5
Melting and Vaporizing Heat of fusion -- melting Heat of vaporization
Heat of
Fusion
Heat of Vaporizat
ion
Water (18) 335 2452****
H2S (34) 70 -- NH3 (17) 452 1234CO2 (44) 180 301CH4 (16) 58 556C2H6 (30) 96 523CH3OH
(32)100 1226
C2H5OH (46)
109 8784
Heat of
Fusion
Heat of Vaporizat
ion
Water 335 2452Gold 64.5 1578Silver 88.3 2336Coppe
r134 5069
Can measure the attraction via contact angleCapillarity – combines adhesion, cohesion and surface tension
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Force that a column of water can withstand before breaking Push – positive pressure Pull -- negative pressure
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Force that a column of water can withstand before breaking Push – positive pressure Pull -- negative pressure
Water resists pressures more negative than -20 MPa
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Measure of the free energy of water per unit volume
Reference State -- pure water at ambient temp and standard pressure
Ψw = Ψs + Ψp + Ψg Ψw – water potential Ψs -- affect of solute or concentration Ψp – affect of pressure Ψg – affect of gravity (generally negligible)
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Solute (or osmotic) potential – effect of dissolved solutes Lowers free energy ∵ increases entropy Independent of nature of solute Total solute concentration – osmolality
Pressure – hydrostatic pressure of solution (i.e., turgor pressure when positive) Can be negative Deviation from atmospheric Pure water = 0MPa
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Plant cells – generally ≤ 0 Free energy less than pure water at ambient temp,
atmospheric pressure and equal height … why? Water enters/leaves the cell in response to
that water potential gradient Passive process No known metabolic pumps to drive water
against that gradient Can be co-transported
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http://www.phschool.com/science/biology_place/labbench/lab1/factors.html
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Varies with growth conditions (e.g., arid vs mesic)
Varies with plant location (e.g., leaves vs stems)
Varies with plant type (e.g., herbs, forbs, woody plants)
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Leaves Well watered herbs: -0.2 to -1.0 Mpa Trees & shrubs: -2.5 Mpa Desert plants: -10.0 Mpa
Within cell walls: -0.8 to -1.2 Mpa
Apoplast: -0.1 to 0.0 Mpa
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In general In xylem and cell walls dominated by pressure
potential (can vary 0.1 to 3 MPa depending on solute potential)
Wilt – turgor pressure approaches 0
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Small changes in cell volume large changes in turgor pressure Turgor pressure approaches 0 as volume
decreases Rigid cell walls lead to less turgor loss Elastic cells volume change larger
Cells with rigid cell walls – larger changes in turgor pressure (per volume change) than cells with more elastic cell walls
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Discovered in 1991 Channel proteins Alter the rate but not the direction Can be reversibly gated – plants may
actively regulate permeability of cell membranes to water!
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Physiological processes are affected by “plant water status” Increase root
volume Solute
accumulation Turgor pressure
affects growth & mechanical rigidity
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