Flashcards in Class 3 Deck (112):
1
simplest index of water status
relative water content
2
relative water content = -- / (saturated mass - dry mass) x 100%
fresh mass - dry mass
3
one weakness of RWC is that it is not very -- for measuring drought responses
sensitive
4
leaves can show strong responses to -- change in RWC
less than 2 percent
5
one weakness of RWC is that it tells us nothing about the -- for water movement
forces
6
-- is another index of water status, that is correlated with RWC but lacks RWC's weaknesses
water potential
7
an overall, average water potential of the whole leaf, as the collection of all the leaf cells
leaf water potential
8
leaf water potential can be measured with the --
pressure bomb
9
for leaves of well watered plants, leaf water potential ranges from --
-0.2 MPa to -2 MPa
10
plants of arid climates of saline environments can function at much lower leaf water potential down to below -- due to accumulating solutes in the cells, producing a very negative solute potential
-5 MPa
11
plant growth requires that cells have -- turgor pressure
positive (pressure potential > 0)
12
as cells lose water, pressure potential -- quickly until turgor is lost (solute potential declines linearly)
drops
13
T/F: as water potential declines further, different functions cease, and eventually plants die
true
14
at zero turgor, unlignified tissues collapse and plants --
wilt
15
plot of leaf water potential versus RWC
(or sometimes - 1/leaf water potential vs RWC, or vs 100%-RWC), and sometimes includes plots of leaf osmotic (solute) potential and pressure potential versus RWC
pressure-volume curve
16
plotting the PV curve allows extraction of 4 main parameters: the --, determined from the intercept of the solute potential versus RWC
osmotic potential at full turgor
17
osmotic potential at full turgor is an index of the -- of cell sap in hydrated tissue
saltiness
18
plotting the PV curve allows extraction of 4 main parameters: -- which is the leaf water potential corresponding to the point at which the pressure potential = 0 or when the leaf water potential = solute potential
osmotic potential at turgor loss point
19
osmotic potential at turgor loss point is also known as -- or simply turgor loss point
water potential at turgor loss point
20
because stomata close and cells may lose function at turgor loss, osmotic potential at turgor loss point is a -- of cell, leaf and plant drought tolerance
predictor
21
plotting the PV curve allows extraction of 4 main parameters: -- determined as the slope of pressure potential versus RWC
modulus of elasticity
22
modulus of elasticity is an index of the -- of cell walls
rigidity
23
some drought tolerant plants have -- elastic modulus values, but not always
high
24
plotting the PV curve allows extraction of 4 main parameters: -- is the x-intercept of the -1/leaf water potential versus RWC curve
apoplastic function
25
apoplastic function represents the -- in the apoplast in a hydrated leaf
% of water stored
26
of all the PV curve's parameters, -- is the strongest predictor of drought tolerance
osmotic potential at turgor loss point (water potential at turgor loss point, turgor loss point)
27
-- of cell sap is a strong predictor of drought tolerance across plant species
saltiness
28
water diffuses from the leaf due to a -- between leaf and air
water vapor concentration gradient (vapor pressure deficit)
29
the diffusion of water from the cell walls inside the leaf causes stretching of -- which generates a tension, pulling water from the xylem
air-water interfaces
30
the resulting tension, from the stretching of air-water interfaces, in the xylem pulls water by -- from the roots
bulk flow
31
water moves through soil by -- driven by pressure gradients, and dependent on soil hydraulic conductivity
bulk flow
32
soil hydraulic conductivity depends on -- and structure and how wet the soil is
soil type
33
clay = -- particles
small
34
sand = -- particles
large
35
water moves through channels between particles or as -- adhering to particles
film
36
soil saturated with water, with excess water drained away
field capacity
37
field capacity occurs when water stops dripping and water potential = --
0
38
soil solute potential is usually close to -- unless soil is very salty
0
39
for wet soils, pressure potential is close to --
0
40
as soil dries, air-water interfaces becomes stretched between soil particles generating a negative pressure because of -- so pressure potential becomes negative
surface tension
41
in drier soils, as the films around particles become thinner, smaller radii of curvature are generated = -- of the interface = stronger tension
greater distortion
42
when soils are -- soil water potential = pressure potential = -2MPa or lower
dry
43
as soil dries, soil hydraulic conductivity -- as channels in the soil empty of water
declines
44
water is more difficult to remove from drier soil both because the soil water potential is lower and because the -- is lower
soil hydraulic conductivity
45
water moves into the root principally through --
root hairs
46
root hairs constitute -- of root surface area and principally near the root apex
> 60%
47
roots need in contact with -- to absorb water and nutrients
soil
48
disturbance of root's contact with soil (new root hairs needed)
transplant shock
49
T/F: roots also need contact with air
true
50
during flooding, airspaces are filled with water --> roots can't respire and lose function --> plants --
wilt
51
water moves in the root via the apoplast, transmembrane and symplast pathways until reaching the --
endodermis
52
at the endodermis, the -- has suberized radial cell walls, and the apoplastic path is blocked; water enters the symplast
Casparian strip
53
after entering the symplast, the water moves to the --
xylem
54
water enters cells mainly through protein channels called --
aquaporins
55
aquaporins can be open or -- in response to environmental factors
gated
56
water pulled through xylem conduits: tracheids and vessels
tension-driven flow
57
-- are universal in vascular plants but vessels are found only in angiosperms, a gymnosperm called Gnetum and some ferns
tracheids
58
xylem conduits are --, hollowed out cells (tubes with lignified cell walls)
dead
59
xylem conduits make up a series connected by --
pits
60
pits may be simple or in conifers, with a --
margo/torus
61
xylem tubes allow a high --
hydraulic conductance
62
because xylem acts as a tube system, flow are -- times faster than if water had to move cell-to-cell to the top of tall tress
10 billion
63
hydraulic conductance is related to the -- power of the radii of the conduit so vessels are MUCH more conductive than tracheids and allow much more rapid flows of water to the leaf
4th
64
water drawn up to the top of trees by tensions in the xylem
cohesion-tension theory
65
challenge to the plant: cavitation by --
air-seeding
66
air is drawn into xylem conduits through -- from surrounding airspaces
pits
67
Or during --, air may come out of solution
cooling/freezing
68
when air bubbles enter the xylem, they -- in the water under tension, and fill the xylem conduit, rendering it useless
expand
69
when air bubbles enter the xylem, they expand in the water under tension, and fill the xylem conduit --> xylem conduit must be -- or it loses function forever
refilled
70
T/F: water can move in conduits around the air-filled conduit
true
71
one way refilling takes place is by -- the stomata
closing
72
one way refilling takes place is by --
root pressure
73
root pressure is found in some, but not all plants, sometimes only --
seasonally
74
roots transport solutes into the xylem, which draws in water, which -- the pressure in the xylem
increases
75
the pressurized water in the xylem dissolves air bubbles, and when air is moist, and transpiration is low, water may eventually -- from hydathodes in the leaves
guttate
76
the tension in the xylem is produced by the -- of water from cells and surface tension
evaporation
77
the -- the radii of curvature the greater the deformation of the interface and the stronger the tension
smaller
78
water from the cell walls evaporates into -- and diffuses through the leaf and out of stomata
airspaces
79
only -- of water evaporates through the cuticle
less than 5 percent
80
leaf is full of airspace (up to 50% of leaf volume) to allow rapid diffusion of -- into the leaf and also allows rapid diffusion of water out of the leaf
CO2
81
the average water molecule evaporated in the leaf travels -- outside, which would take 0.04 s by diffusion calculation
1mm
82
the concentration gradient driving the diffusion of vapor out of the leaf is --
strong
83
leaves have large internal wet -- (up to 50 x external leaf area) so air inside the leaf is considered to be close to saturation (close to 100% relative humidity)
mesophyll surface
84
saturation water concentration increases exponentially with --
temperature
85
higher temperature -- leaf-to-air concentration gradient
higher
86
T/F: moist air is 'dry' enough to drive strong transpiration
true
87
at 20 degrees Celsius, air at RH = 95% is the equivalent of -- MPa
-7
88
when air is at RH = 50%, the driving force is equivalent of -- MPa
-94
89
transpiration occurs through the --
stomata
90
transpiration: the diffusion through pores depends on the concentration gradient (VPD), on the diffusion coefficient (D), and the --
diffusional resistance
91
diffusional resistance = -- + boundary layer resistance
stomatal resistance
92
stomatal resistance depends on the total area of --
stomatal pore
93
stomatal resistance -- as stomata close
increases
94
boundary layer resistance depends on leaf size and --
windspeed
95
a smaller leaf and higher windspeed lead to a thinner boundary layer with -- resistance
lower
96
leaf shape and -- can also influence boundary layer resistance
hairiness
97
at high windspeed, the boundary later is very thin and -- becomes the major influence on diffusional resistance and on transpiration
stomatal resistance
98
at low windspeed, the -- is the major influenceon diffusional resistance and on transpiration
boundary layer resistance
99
at low windspeed, transpiration is relatively -- stomatal resistance, except when this becomes very high because stomata are nearly closed
insensitive
100
T/F: stomata evolved once for all plants, in a distant ancestor
true
101
stomata are required for control of -- relative to CO2 gain
water loss
102
plants can thus open pores to fix carbon when water is abundant, but close pores to save water from the water supply is low, or when the leaf demand for CO2 is --
low
103
stomata are controlled via -- swelling
guard cell
104
guard cells are -- shaped in grasses and kidney-shaped in non-grasses
dumbbell
105
differential wall thickening and arrangement of -- dictates which parts of the guard cells will stay fixed
cellulose microfibrils
106
as the rest of the cell swells, pores open when guard cells are --
pressurized
107
guard cells are pressurized by increasing -- in the cell via ion uptake or creating new organic ions in the cells
solute potential
108
increasing solute potential in the guard cells, drives water uptake from the surrounding mesophyll, and pressure potential increases and the cells --
swell
109
guard cell turgor is sensitive to light, --, leaf water status, and CO2 concentration
temperature
110
the guard cells are kept isolated from surrounding cells (no plasmodesmata), so their aperture is -- dictated by the water status of surrounding cells
not directly
111
overall soil-plant-atmosphere continuum: water moves through soil and xylem by -- and out of leaves by diffusion
bulk flow
112