Transcript 03 Water - goldsword.com

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
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
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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)

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
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10

Plant cells – generally ≤ 0
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
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
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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
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18
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Within cell walls: -0.8 to -1.2 Mpa

Apoplast: -0.1 to 0.0 Mpa
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In general
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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
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20
Cells with rigid cell walls – larger changes in
turgor pressure (per volume change) than cells
with more elastic cell walls
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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