ch. 36 Flashcards
1
Q
what does the stem do
A
- conduits for water and nutrients
- supports structures for leaves
2
Q
what do shoot length and branching pattern affect?
A
light capture
3
Q
what is there a tradeoff between?
A
growing tall and branching
- more energy invested into branching, less energy available for growth in height
4
Q
what is there a positive correlation between?
A
water availability and leaf size
5
Q
phyllotaxy
A
arrangement of leaves on the stem
- phyll - leaf
- tax - movement toward/away
6
Q
phyllotaxy of most angiosperms
A
leaves arranged in spiral
7
Q
angle between leaves
A
137.5 degrees, likely minimizes shading of lower leaves
8
Q
what does leaf orientation affect
A
light absorption
9
Q
low light conditions
A
horizontal leaves capture more sunlight
10
Q
high light conditions
A
vertical leaves less damaged by sun and allow light to reach lower levels
11
Q
why are stomatal pores necessary
A
diffusion of CO2 into the photosynthetic tissues of leaves
12
Q
how is over 90% of water lost by plants
A
evaporation from stomatal pores
13
Q
what do shoot adaptations represent compromises against
A
enhancing photosynthesis and minimizing water loss
14
Q
what can root growth adjust to?
A
local conditions
- roots branch extensively into pockets with high nitrate and grow straight through pockets of low nitrate availability
15
Q
roots and competition
A
roots from same plant less competitive than roots from dif plants
16
Q
mycorrhizae
A
roots and hyphae of soil fungi form mutualistic associations
- mycorrhizal fungi increase surface area for absorbing water and minerals, especially phosphate
17
Q
3 transport routes for water and solutes
A
- apoplastic
- symplastic
- transmembrane
18
Q
apoplastic route
A
through cell walls and extracellular spaces
19
Q
symplastic route
A
cross plasma membrane once and then travel through cytosol
- use plasmodesmata
20
Q
transmembrane route
A
repeatedly cross plasma membranes as they pass from cell to cell
21
Q
apo
A
away, furthest point
22
Q
sym
A
with, in company
23
Q
trans
A
cross
24
Q
plastic
A
to grow or form, capable of being deformed without rupture
25
plasma membrane permeability controls what?
short-distance movement of substances
26
what types of transport occur in plants
both active and passive
27
establishment of membrane potential in plants
pumping H+ by proton pumps
28
potential =
voltage
29
establishment of membrane potential in animals
pumping Na+ by sodium=potassium pumps
30
different types of energy conversion
1. H+ and membrane potential
2. H+ and cotransport of neutral solutes
3. H+ and cotransport of ions
4. ion channels
31
osmosis
diffusion of water into or out of a cell that is affected by solute concentration and pressure
32
water potential =
solute potential + pressure potential
- determines direction of movement of water
- higher to lower
33
definition of potential
ability to do work
34
solute potential of a solution is inverse to what?
its molarity
35
what is solute potential also called?
osmotic potential
36
pressure potential
physical pressure on a solution
37
positive pressure potential
pushing
- solution being expelled from syringe
38
negative pressure potential
sucking
- solution withdrawn by syringe
39
turgor pressure
positive pressure exerted by plasma membrane against the cell wall and the cell wall against the protoplast
40
protoplast
living part of the cell, which includes plasma membrane
41
what does water potential affect?
uptake and loss of water by plant cells
42
what happens when a flaccid/limp cell is placed in an environment with a higher solute concentration
the cell will lose water through negative pressure and undergo plasmolysis
43
aquaporins
transport proteins in the cell membrane that facilitate the passage of water
44
what do the opening/closing of aquaporins affect the rate of
osmotic water movement across the membrane
45
bulk flow
movement of a fluid driven by a pressure gradient
46
what does efficient long-distance transport of fluid require
bulk flow
47
where do water and solute move together?
tracheids and vessel elements of xylem and sieve-tube elements of phloem
48
what do branching veins within leaves ensure
that all living cells are within a few cells of the vascular tissue
49
what is bulk flow enhanced by
structural adaptations of xylem and phloem cells
- mature tracheids/vessel elements have no cytoplasm
- sieve-tube elements have few organelles in cytoplasm
- perforation plates connect vessel elements
- porous sieve plates connect sieve-tube elements
50
where does most water and mineral absorption occur
near root tips
- where root hairs are located and epidermis is permeable to water
51
what accounts for much of the surface area of roots?
root hairs
52
what happens after soil solution enters the roots?
the extensive surface area of cortical cell membranes enhances uptake of water and selected minerals
53
what does active transport enable in the roots
essential minerals to accumulate at much higher concentrations in roots compared to the surrounding soil
54
endodermis
innermost layer of cells in the root cortex
- surrounds vascular cylinder and is last checkpoint for selective passage of minerals from cortex into the vascular tissue
55
water can cross the cortex via what?
symplast or apoplast
56
Casparian strip
waxy strip in endodermal wall that blocks apopastic transfer of minerals from the cortex to the vascular cylinder
57
what must water/minerals cross to enter the vascular cylinder of roots
the plasma membrane of an endodermal cell
58
what do endodermal cells discharge?
water and minerals from their protoplasts into their own cell walls
59
what are involved in the movement from symplast to apoplast
diffusion and active transport
60
once in the apoplast after the endodermis, what do water and minerals do?
enter the tracheids and vessel elements
61
xylem sap
water and dissolved minerals transported from roots to leaves by bulk flow
62
what does the transport of xylem sap involve?
transpiration
63
transpiration
evaporation of water from a plant's surface
64
how is transpired water replaced
as water travels up from the roots
65
what do root cells do at night?
continue pumping mineral ions into the xylem of the vascular cylinder, lowering the water potential
66
root pressure
a push of xylem sap as water flows in from the root cortex
67
what does root pressure sometimes result in?
guttation
68
guttation
exudation of water droplets on tips or edges of leaves
69
positive root pressure is relatively...
weak
- minor mechanism of xylem bulk flow
70
cohesion-tension hypothesis
transpiration and water cohesion pull water from shoots to roots
71
what is xylem sap normally under
negative pressure, or tension
72
transpirational pull
- water vapor in air spaces of leaf diffuses down water potential gradient and exits leaf via stomata
- as water evaporates, air-water interface retreats into the mesophyll cell walls
- surface tension of water at air-water interface creates a negative pressure potential
73
what lowers water potential?
negative pressure potential
74
how are water molecules pulled from more hydrated areas of the leaf
by the negative pressure potential created at the air-water interface
75
what transfers the pulling forces to the water in the xylem
the cohesion of water molecules
76
how are water molecules attracted to each other
cohesion
- water molecules exiting xylem tug on adjacent water molecules down the column
77
what does adhesion do in the xylem
offset the force of gravity
78
why do vessel elements and tracheids not collapse under negative pressure
thick secondary walls
79
what can cause a break in the chain of water
drought stress or freezing
- causes cavitation
80
cavitation
formation of a water vapor pocket
81
how can transport of xylem sap continue after cavitation
- move between adjacent xylem cells through pits
- move from xylem to phloem tissue and back again
- cavitation can be repaired
- new xylem is added by secondary growth
82
what is blue flow in xylem sap ascent driven by
water potential difference at opposite ends of xylem tissue
- driven by transpiration
83
what does bulk flow require energy from
not from plant, but is solar powered like photosynthesis
84
how does bulk flow differ from diffusion
- driven by differences in pressure potential, not solute potential
- occurs in hollow dead cells, not across membranes of living cells
- moves entire solution, not just water or solutes
- much faster
85
do leaves have higher or lower surface area compared to volume
higher
86
what happens when high surface areas of leaves increase the rate of photosynthesis
increase in water lost through stomata
87
what do guard cells do
open and close stomata to help balance water conservation with gas exchange for photosynthesis
88
what controls stomatal density
genetic and environmental control
89
what happens to guard cells when they are turgid
guard cells bow outward and pore between them opens
90
what happens to guard cells when they are flaccid
become less bowed and pore closes
91
what do changes in turgor pressure result from
reversible uptake and loss of potassium ions by guard cells
92
what are required to move K+ across the plasma membrane?
(under guard cell slides)
proton pumps that generate membrane potential
93
when do stomata generally open and close
open during day, close at night
94
what is stomatal opening triggered by?
1. light
2. CO2 depletion
3. internal clock in guard cells
95
circadian rhythms
24-hour cycles - internal clocks of eukaryotic organisms
96
abscisic acid (ABA)
hormone produced in response to water deficiency and causes closure of stomata
97
what do sunny, warm, dry, and windy conditions cause?
evaporation and increased transpiration rates
98
true or false, some evaporative water loss occurs through the cuticle when stomata are closed
true
99
what happens if uptake/transport of water not sufficient to replace lost water
plant will wilt
100
evaporative cooling
- another result of transpiration
- can lower temperature of leaf
101
xerophytes
plants adapted to arid climates
102
xero
dry
103
when do some desert plants complete their life cycle
- during the rainy season
- others have fleshy stems that store water or leaf modifications that reduce rate of transpiration
104
crassulacean acid metabolism (CAM)
stomatal gas exchange occurs at night
105
translocation
products of photosynthesis are transported through phloem
106
elements for translocation in angiosperms
sieve-tube elements
107
phloem sap
aqueous solution that is high in sucrose
108
where does phloem sap travel
from sugar source to sugar sink
109
sugar source
organ that is net producer of sugar, such as mature leaves
110
sugar sink
organ that is net consumer or depository of sugar, such as roots, buds, and fruits
111
true or false: A storage organ can be a sugar sink in the summer and sugar source in the spring
true
112
where must sugar be loaded before being exported to sinks
sieve-tube elements
113
does sugar move by symplastic of apoplastic pathways
depends on species
114
what do companion cells do
enhance soul movement between apoplast and symplast
115
what kind of transport does phloem loading require in many plants
active transport
116
what enables the cells to accumulate sucrose
proton pumping and contransport of sucrose and H+
117
what occurs at the sink
sugar molecules diffuse from the phloem to sink tissues and are followed by water
118
how does phloem sap move
through a sieve tube by bulk flow driven by positive pressure called pressure flow
- flows from high pressure sources to low pressure sinks
119
self-thinning
dropping of sugar sinks such as flowers, seeds, or fruits
- occurs when there are more sugar sinks than the sources can support
120
symplast
continuum of cytosol linked by plasmodesmata
121
apoplast
water-filled cell walls and intercellular spaces
