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

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

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

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_place/labbench/lab1/factors.html

12

13

14

15

16

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: -10.0 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