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Chapters 3-4 Polar Excellent solvent Distinctive thermal properties Specific heat Heat of vaporization 2 Specific Heat Specific heat – amount of energy absorbed for given temperature rise (measured in J/g/°C) Specific Heat Gold Silver Copper Paraffin 3 0.13 0.23 0.38 2.5 Specific Heat Water (18) H2S (34) NH3 (17) CO2 (44) CH4 (16) C2H6 (30) CH3OH (32) C2H5OH (46) 4.2 -5.0 ---2.6 2.4 Melting and Vaporizing Heat of fusion -- melting Heat of vaporization Heat Heat of of Vaporization Fusion Water (18) H2S (34) Water Gold Silver Copper Heat of Fusion Heat of Vaporization NH3 (17) 335 64.5 88.3 134 2452 1578 2336 5069 CH4 (16) CO2 (44) C2H6 (30) CH3OH (32) C2H5OH (46) 335 70 452 180 58 96 100 109 2452**** -1234 301 556 523 1226 878 4 5 Can measure the attraction via contact angle Capillarity – combines adhesion, cohesion and surface tension 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 7 Water resists pressures more negative than -20 MPa 8 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) 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 http://www.phschool.com/science/biology_pl ace/labbench/lab1/factors.html 12 13 14 15 16 17 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) Leaves Well watered herbs: -0.2 to -1.0 Mpa Trees & shrubs: -2.5 Mpa Desert plants: -10.0 Mpa 18 Within cell walls: -0.8 to -1.2 Mpa Apoplast: -0.1 to 0.0 Mpa In general 19 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 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 20 Cells with rigid cell walls – larger changes in turgor pressure (per volume change) than cells with more elastic cell walls 21 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! Physiological processes are affected by “plant water status” 22 Increase root volume Solute accumulation Turgor pressure affects growth & mechanical rigidity