Chapters 3-4

 Polar  Excellent solvent  Distinctive thermal properties  Specific heat  Heat of vaporization 2

3  Specific Heat  Specific heat – amount of energy absorbed for given temperature rise (measured in J/g/°C) Specific Heat Water (18)4.2 H 2 S (34)-- NH 3 (17)5.0 CO 2 (44)-- CH 4 (16)-- C 2 H 6 (30)-- CH 3 OH (32)2.6 C 2 H 5 OH (46)2.4 Specific Heat Gold0.13 Silver0.23 Copper0.38 Paraffin2.5

 Melting and Vaporizing  Heat of fusion -- melting  Heat of vaporization Heat of Fusion Heat of Vaporization Water (18) **** H 2 S (34) 70-- NH 3 (17) CO 2 (44) CH 4 (16) C 2 H 6 (30) CH 3 OH (32) C 2 H 5 OH (46) Heat of Fusion Heat of Vaporization Water Gold Silver Copper

 Can measure the attraction via contact angle  Capillarity – combines adhesion, cohesion and surface tension 5

 Force that a column of water can withstand before breaking  Push – positive pressure  Pull -- negative pressure 6

 Force that a column of water can withstand before breaking  Push – positive pressure  Pull -- negative pressure  Water resists pressures more negative than -20 MPa 7

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 Measure of the free energy of water per unit volume  Reference State -- pure water at ambient temp and standard pressure  Ψ w = Ψ s + Ψ p + Ψ g  Ψ w – water potential  Ψ s -- affect of solute or concentration  Ψ p – affect of pressure  Ψ g – affect of gravity (generally negligible) 9

 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 10

 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 11

ace/labbench/lab1/factors.html 12

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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) 17

 Leaves  Well watered herbs: -0.2 to -1.0 Mpa  Trees & shrubs: -2.5 Mpa  Desert plants: Mpa  Within cell walls: -0.8 to -1.2 Mpa  Apoplast: -0.1 to 0.0 Mpa 18

 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 19

 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 20

 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! 21

 Physiological processes are affected by “plant water status”  Increase root volume  Solute accumulation  Turgor pressure affects growth & mechanical rigidity 22