chapter 9 Flashcards
(141 cards)
1
Q
transpiration
A
loss of water vapour vapour from stems or leaves of plants
2
Q
transpiration
A
light energy converts water in leaves to water vapour which evoporates from leaf via stomata
new water absorbed into soil via roots, creating difference in pressure between leaves and roots
water flows via xylem, along pressure gradient to replace water lost from leaves (=transpiration stream)
3
Q
stomata
A
pores on underside of leaf facilitating gas exchange (needed for photosynthesis)
as photosynthetic gas exchange requires stomata to be open, transpiration is affected by level of photosynthesis
therefore transpiration = consequence of gas exchange in leaf
4
Q
evaporation in plants
A
when water is lost from leaves of plant when its converted into vapour
5
Q
evaporation in leaves
A
some of light energy absorbed by leaves converted into heat which evaporates water within spongy mesophyll
vapour diffuses out of leaf via stomata creating negative pressure gradient within leaf
negative pressure creates tension force in leaf cell walls which draws water from xylem (transpiration pull)
water pulled from xylem under tension due to adhesive attraction between water +leaf cell walls
6
Q
transpiration rate regulated by
A
opening and closing of stomata
7
Q
transpiration rate regulation
A
guard cells flank stomata + can close opening by becoming increasingly flaccid in response to cellular signals
when plant begins to wilt from water stress, dehydrated mesophyll cells release plant hormone abscisic acid
loss of turgor makes stomatal pore close as guard cells become flaccid + block the opening
8
Q
transpiration rates = higher when stomatal pores = open than when closed
A
stomatal pores = responsible for gas exchange in leaf, so levels of photosynthesis will affect transpiration
other factors affecting transpiration = humidity, temp, light intensity + wind
9
Q
transpiration stream
A
flow of water via xylem from roots to leaf
water rises due to water properties: cohesion+adhesion
10
Q
cohesion vs adhesion
A
cohesion: water molecules stick together
adhesion: water molecules sticking to xylem wall
11
Q
cohesion
A
force of attraction between 2 particles of same subtance
water = polar and can form intermolecular association = hycrogen bond
cohesion +hydrogen bonds allow water molecules to be dragged up xylem
12
Q
Structure Xylem
A
xylem =specialised structure, functions to facilitate movement of water throughout plant
=tube composed of dead cells = hollow (no protoplasm)allowing free movement of water
as cells = dead, water movement =passive process + occurs in one direction only
cell wall contains numerous pits, enabling water to be transferred between cells
Walls have thickened cellulose + are reinforced by lignin, providing strength as water = transported under tension
12
Q
pits (ref cell wall
A
pores in cell wall of xylem
13
Q
vascular plants
A
plants w xylem + phloem (=vascular tissues)
14
Q
vessel element
A
cell type found in plant cell whose end walls become fused to form continuos tube, resulting in faster water transfer rate
15
Q
tracheid
A
tapered cells exchanging water solely via pits, leading to slower water transfer rate
16
Q
xylems may be composed of
A
tracheids (all vascular plants) and vessel elements (certain vascular plants)
17
Q
all xylem vessels reinforced by
A
lignin
18
Q
lignin may be deposited in different ways
A
annular vessels: lignin forms pattern of circular rings at equal distance from each other
spiral vessels: lignin present in helix or coil form
19
Q
in all vascular plants, xylems are composed of
A
tracheids
20
Q
in certain vascular plants, xylems are composed of
A
vessel elements/
21
Q
plants take up__________ via roots, thus needing maximal surface area to optimise this uptake
A
water and mineral ions
22
Q
root systems
A
some plants have fibrous highly branching root system, increasing surface area available for absorption
others have main tap root w lateral branches that penetrate soil to deeper water reservoirs
23
Q
root hairs
A
found on root epidermis increase surface area for absorption
24
material absorbed by root epidermis diffuse across cortex towards central stele where xylem located
stele surrounded by endodermis layer, impermeable to passive flow of water+ ions (casparian strip)
water + minerals = pumped across barrier by specialised cells, allowing uptake rate to be controlled
25
When drawing primary xylem vessels structure= important to remember the following features:
Vessel elements should be drawn as continuous tube (tracheids will consist of interlinking tapered cells)
remnants of fused end wall can be represented as indents (these forms perforated end plates)
xylem wall should contain gaps (pits), which enable the exchange of water molecules
Lignin can be represented by either spiral (coiled) or annular (rings) arrangement
26
xerophytes
desert plants that tolerate dry conditions due to adaptations
27
halophyte
plants that can tolerate salty conditions (eg marshlands) due to adaptations
28
xerophytes adaptations (to tolerate dryness)
Reduced leaves: reducing total number + size of leaves reduces surface area available for water loss
Rolled leaves: rolling up leaves reduces stomata exposure to air + therefore reduces evaporative water loss
Thick, waxy cuticle: leaves covered by thickened cuticle prevents water loss from leaf surface
Stomata in pits – stomata in pits, surrounded by hairs, traps water vapour therefore reduces transpiration
Low growth – low growing plants = less exposed to wind + more likely to be shaded, reducing water loss
CAM physiology – plants w CAM physiology open stomata at night, reducing water loss via evaporation
29
Halophytes adaptations (to tolerate saltiness)
Cellular sequestration (removal): halophytes can sequester toxic ions + salts within the cell wall or vacuoles
Tissue partitioning: plants may concentrate salts in particular leaves, leaves then fall (abscission)
Root level exclusion: plant roots may be structured to exclude ~95% of salt in soil solutions
Salt excretion: parts of the plant (e.g. stem) may contain salt glands which eliminate salt
Altered flowering schedule: halophytes may flower at specific times (e.g. rainy seasons) to minimise salt exposure
30
movement of water up xylem can be demonstrated by
capillary tubing, filter or blotting paper +porous pots
31
capillary tubing (ref: movement of water up xylem demonstration)
Water has the capacity to flow along narrow spaces in opposition to external forces like gravity (capillary action)
=bc of combination of surface tension (cohesive forces) + adhesion w walls of tube surface
thinner the tube or the less dense the fluid, the higher the liquid will rise (xylem vessels are thin: 20 – 200 µm)
32
filter paper (ref: movement of water up xylem demonstration)
absorbs water due to adhesive/cohesive properties
when placed perpendicular to water, water will rise up along paper
comparable to movement of water up xylem (paper+xylem wall made of cellulose)
33
porous pots
= semi permeable containers allowing free passage of certain small materials through pores
loss of water from pot = similar to evaporative water loss occuring in plant leaves
if porous pot attached by airtight seal to tube, water loss creates neg pressure which draws more liquid
34
potometer
device used to estimate transpiration rates by measuring rate of water loss + uptake
when plant affixed to potometer, transpiration can be directly identified by movement of water toward plant
water movement measured by change in meniscus level or movement of air bubble towards plant
starting position of meniscus/air bubble can be adjusted by introducing additional water reservoir
35
variables that affect transpiration rate
temperature, humidity, light intensity and wind exposure
36
Temperature: (ref: variable affecting transpiration rate)
Increasing ambient temperature = predicted to cause increase in the rate of transpiration
Higher temperatures = increase in the rate of water vaporisation in the mesophyll, leading to more evaporation
effect of temp variation can be tested experimentally by using heaters or submerging in heated water baths
37
humidity (ref: variable affecting transpiration rate)
Increasing humidity = predicted to cause decrease in the rate of transpiration
Humidity = amount of water vapour in air – less vapour will diffuse from the leaf if theres more vapour in air
effect of humidity tested experimentally by encasing plant in a plastic bag w variable levels of vapour
38
light intensity (ref: variable affecting transpiration rate)
Increasing the light intensity which plant is exposed is predicted to cause increase in rate of transpiration
Increasing light exposure causes more stomata to open to facilitate photosynthetic gas exchange
effect of light intensity can be tested experimentally by placing plant at variable distances from lamp
39
wind exposure (ref: variable affecting transpiration rate)
Increasing the level of wind exposure is predicted to cause an increase in the rate of transpiration
Wind / air circulation will function to remove water vapour from near the leaf, effectively reducing proximal humidity
The effect of wind can be tested experimentally by using fans to circulate the air around a plant
39
wind exposure (ref: variable affecting transpiration rate)
Increasing level of wind exposure = predicted to cause increase in rate of transpiration
Wind / air circulation function to remove water vapour from near leaf, effectively reducing proximal humidity
effect of wind can be tested experimentally by using fans to circulate air around plant
40
translocation
movement of organic compounds (amino acids, sugars, etc) from sources to sinks
41
source
where organic compounds = synthesised: photosynthetic tissues (leaves)
sink = where compounds delivered to for use/storage: includes roots, fruits, seeds
42
organic compounds transported from sources to sinks by vascular tube system ______
phloem
43
materials transported by phloem
sugars transported as sucrose (disaccharide) as = soluble but metabolically inert
nutrient rich viscous fluid of phloem = plant sap
44
phloem sieve tubes made up of two main cell types:
sieve element cells + companion cells
phloem also contains schlernchymal + parenchymal cells which fll additional spaces + provide support
45
sieve element cells
long narrow cells connected to form sieve tube
connected by sieve plates at transverse ends- which = porous to enable flow between cells = porous to enable flow between cells
have no nuclei + reduced numbers of organelles to maximise space for translocation of materials
sieve elements have thick + rigid cell walls to withstand hydrostatic pressures which facilitate flow
46
Companion Cells
Provide metabolic support for sieve element cells + facilitate loading + unloading of materials at source + sink
Possess an infolding plasma membrane which increases SA:Vol ratio to allow more material exchange
Have many mitochondria to fuel active transport of materials between sieve tube + source or sink
Contain appropriate transport proteins in plasma membrane to move materials in or out of sieve tube
47
Sieve elements unable to sustain independent metabolic activity without support of companion cell
bc sieve element cells have no nuclei + fewer organelles (to maximise flow rate)
Plasmodesmata exist between sieve elements + companion cells in relatively large numbers
These connect cytoplasm of 2 cells + mediate symplastic exchange of metabolites
48
Stem monocotyledons
vascular bundles = found in scattered arrangement throughout stem
Phloem vessels will be positioned externally (towards outside of stem) – remember: phloem = outside
49
Stem dicotyledons
vascular bundles = arranged in circle around centre of stem (pith)
Phloem + xylem vessels will be separated by cambium (xylem on inside ; phloem on outside)
50
roots monocotyledons
stele = large and vessels will form a radiating circle around central pith
Xylem vessels will be located more internally + phloem vessels will be located more externally
51
roots dicotyledons
stele is very small and the xylem is located centrally with the phloem surrounding it
Xylem vessels may form a cross-like shape (‘X’ for xylem), while phloem = situated in surrounding gaps
52
Xylem and phloem vessels are grouped into
bundles that extend from roots to shoots in vascular plants
53
Differences in distribution and arrangement exist between plant types
(e.g. monocotyledons vs dicotyledons)
54
Xylem + phloem vessels can usually be differentiated by diameter of their cavity
xylem have larger cavities
55
oraganic compounds produced at source =
actively loaded into phloem sieve tubes by companion cells
Materials can pass into sieve tube via interconnecting plasmodesmata (symplastic loading)
or, materials can be pumped across intervening cell wall by membrane proteins (apoplastic loading)
56
Apoplastic loading of sucrose into phloem sieve tubes
active transport process requiring ATP expenditure
57
Apoplastic loading of sucrose into the phloem sieve tubes
Hydrogen ions (H+) = actively transported out of phloem cells by proton pumps (involving hydrolysis of ATP)
concentration of hydrogen ions consequently builds up outside of cell, creating proton gradient
Hydrogen ions passively diffuse back into phloem cell via co-transport protein, (requires sucrose movement)
= results in build up of sucrose in phloem sieve tube for subsequent transport from source
58
At Source
active transport of solutes (eg sucrose) into phloem by companion cells makes sap solution hypertonic
- causes water to be drawn from xylem via osmosis (water moves towards higher solute concentrations)
bc incompressibility of water, build up of water in phloem causes hydrostatic pressure increase
this hydrostatic pressure increase forces phloem sap to move to areas of lower pressure (mass flow)
then phloem transports solutes away from source (+ towards sink)
59
at sink
solutes in phloem unloaded by companion cells + transported into sinks (roots, fruid seeds etc)
sap solution at sink = becomes increasingly hypotonic
water = drawn out of phloem + back in xylem by osmosis
therefore hydrostatic pressure in sink is ALWAYS lower than source
so phloem sap will always move from source to sink
when organic molecules transported into sink, either metabolised or stored in tonoplast of vacuoles
60
aphids
group of insects = primarily feed on phloem sap
61
aphids eating
protruding mouthpiece (=stylet) pierces plants sieve tube to allow extraction of sap
penetration of stylet aided by digestive enzymes, softening intervening tissue layers
id stylet severed sap continues ti flow from plant bc hydrostatic pressure in sieve tube
62
measuring phloem transport
aphids can provide measure of phloem transport rates when collecting sap
63
experiment measuring phloem transport
plant grown in lab w leaves sealed in glass chamber of radioactive CO2
leaves convert CO2 into radioactively labelled sugars (by photosynthesis) , which transported by phloem
aphids positioned on plants + encouraged to eat sap
once feeding, stylet severed + sap flows from sap at select positions
sap analysed for presence of radioactively labelled sugars
rate of phloem transport/translocation rate may be calculated based on time taken for radioisotope to be detected at different positions on plants length
64
Factors Affecting Translocation Rate
rate of phloem transport determined mainly by concentration of dissolved sugars in phloem
65
concentration of dissolved sugars in phloem sap affected by (+ factors affecting it)
rate of photosynthesis (light, co2, temp)
rate of cellular respiration (CO2 concentration)
rate of transpiration (water)
diameter of sieve tubes (hydrostatic pressure)
65
concentration of dissolved sugars in phloem sap affected by (+ factors affecting it)
rate of photosynthesis (light, co2, temp)
rate of cellular respiration (CO2 concentration)
rate of transpiration (water)
diameter of sieve tubes (hydrostatic pressure)
66
meristems (basic def)
tissues in plant consisting of undifferentiated cells capable of intermediate growth
67
meristems properties
=analagous to totipotent stem cells in animals, except they have specific regions of growth + development
Meristematic tissue can allow plants to regrow structures/even form new plants (vegetative propagation)
68
apical meristems
occur at shoot + root tips + are responsible for PRIMARY growth (i.e. plant lengthening)
give rise to new leaves and flowers
69
Lateral meristems
occur at cambium + are responsible for SECONDARY growth (i.e. plant widening / thickening)
responsible for the production of bark
70
primary growth (apical meristems)
lengthening, occurs at tips of roots +shoots
growth at these regions = bc of combination of cell enlargement + repeated cell division (mitosis/cytokinesis)
DIFFERENTIATION of dividing meristems gives rise to variety of stem tissues/structures (leaves, flowers)
71
nodes
growth in sections called nodes in stem: w remaining meristem tissue forming axillary bud
72
axillary (lateral bud)
have potential to form new branching shoots, complete w leaves + flowers
73
plant hormones
control growth in shoot apex
74
growth of stem +formation of new nodes controlled by
plant hormones released in shoot apex
75
1 of main groups of plant hormones involved in shoot + root growth
auxin
76
when auxins produced by shoot apical meristem it promotes
growth in shoot apex via elongation + division
77
apical dominance
when production of auxins prevents growth in lateral (axillary) buds
ensures a plant will use energy to grow up towards light to outcompete other plants
As distance between terminal bud + axillary bud increases, inhibition of axillary bud by auxin diminishes
Different species will show different levels of apical dominance
78
auxin
group of hormones produced by tip of shoot or root (eg apical meristem) that regulate plant growth
79
auxin efflux pumps
can set up concentration gradients within tissues, changing distribution of auxin in plant
can control direction of plant growth by determining which plant tissue regions have high auxin levels
can change position in membrane (due to fluidity) + can be activated by various factors
80
auxin mechanism
different in roots and shoots
81
auxin mechanism roots
auxin inhibits cell elongation
thus high concentrations of auxin limit growth (cells become smaller)
82
auxin mechanism shoots
auxin stimulates cell elongation
thus high auxin concentrations promote growth (cells become large)
83
auxin = plant hormone that
influences cell growth rates by changing pattern of gene expression w plants cells
auxins mechanism of action different in roots/shoots as different gene pathways activated in each tissue
84
in shoots auxin
increases flexibility of cell wall to promote plant growth via cell elongation
auxin a
84
in shoots auxin (2)
Auxin activates proton pump in plasma membrane - causes secretion of H+ ions into cell wall
resultant pH decrease causes cellulose fibres in cell wall to loosen (by breaking bonds between them)
auxin upregulates expression of expansins, which increases elasticity of cell wall
w cell wall now more flexible, influx of water (to be stored in vacuole) causes cell to increase in size
85
tropisms
growth or turning movement of plant in response to directional external stimulus
86
phototropisms
growth movement in response to unidirectional light source
87
geotropism/gravitropism
growth movement in response to gravitational forces
88
shoots: high auxin concentrations promote cell elongation
dark side of shoot grow towards light: pos phototropism
lower side of shoot elongates + roots grow away from ground???/// im confused
89
roots: high auxin concentrations inhibit cell elongation
dark side of root becomes shorter + roots grow away from light (neg phototropism)
lower side of root becomes shorter + roots turn downwards into earth
90
micropropation
technique used to produce clones of selected stock plant
91
plants can reproduce asexually from meristems bc
they are undifferentiated cell capable of intermediate growth
92
vegetative propagation
when plant cutting used to reproduce asexually in native environment
93
micropropagation
when plant tissues = cultured in lab (in vitro) to reproduce asexually
94
micropropagation steps
specific plant tissue (usually undifferentiated shoot apex) selected from stock plant + sterilised
tissue sample (=explant) grown on sterile nutrient agar gel
explant treated w growth hormones (eg auxins) to stimulate shoot+root development
growing shoors can continuoslly divide to form new samples (multiplication phase)
once root+shoot = developed, clone plant may be transferred to soil
95
micropropagation
method to rapidly produce large n.o of cloned plants
96
rapid bulking
Desirable stock plants can be cloned via micropropagation to conserve the fidelity of selected characteristic
process = more reliable than selective breeding bc new plants = genetically identical to stock plant
technique = used to rapidly produce large quantities of plants created via genetic modification
97
Virus-Free Strains
plant viruses = potential to decimate crops, crippling economies + leading to famine
Viruses usually spread in infected plants via vascular tissue (–which meristems do not contain)
Propagating plants from non-infected meristems allows rapid reproduction of virus-free plant strains
98
Propagation of Rare Species
Micropropagation = used to increase n.o of rare/ endangered plant species
used to increase numbers of species that = difficult to breed sexually (e.g. orchids)
used to increase n.o of plant species that = commercially in demand
99
plant reproduction ways
vegetative propagation (asexual reproduction from plant cutting)
spore formations (eg mould, fern)
pollen transfer (flowering plants)
100
sexual reproduction in flowering plants
involves pollen transfer (male gamete) to ova (female gamete)
involves three stages: pollination, fertilisation, seed dispersal
101
pollination
transfer of pollen grains from anther (male structure) to stigma (female structure)
many plants possess male+female parts (monoecious) + can potentially self pollinate
evolution perspective: cross pollination preferable ( improves genetic diversity)
102
fertilisation
fusion of male gamete nuclei w female gamete nuclei to form zygote
male gamete stored in pollen gran + female game found in ovule
103
seed dispersal
fertilisation of gametes result in formation of see which moves away from parental plant
seed dispersal reduces competition of resources between parent + germinating seed
wind, water, fruit, animals = seed dispersal means
seed structure determines seed dispersal mechanism
104
cross pollination
involves transferring pollen grains from one plant yo ovule of other plant
pollen transfer: by wind, water, most commonly: animals (pollinators
105
pollinators
involved in mutualistic relationship w flowering plant = both benefit from interaction:
- flowering plant can sexually reproduce (pollen transfer between plants)
- animals gain nutrition(sugary nectar)
106
pollinations eg.s
birds, bats, insects
flowers may have structure to optimise access for certain pollinators
107
flowes
reproductive organs of angiospermophytes + develop from shoot apex
108
angiospermophyte
flowering plant
109
Changes in gene expression trigger enlargement of shoot apical meristem
then tissue differentiates to form different flower structures – sepals, petals, stamen and pistil
110
activation of genes responsible for flowering = influenced by
abiotic factors – typically linked to the seasons
111
Flowering plants will typically come into bloom when
a suitable pollinator is most abundant
112
The most common trigger for change in gene expression =
day/night length (photoperiodism)
113
monoecious
possess both male + female structures
(most plants)
114
dioecious
only possess one structure (male or female)
(some plants)
115
male part of flower called
stamen
116
stamen composed of
anther: pollen producing organ of flower
filament: slender stalk supporting anther (makes anther accessible to pollinator)
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female part of flower called
pistil or carpel
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pistil composed of
stigma: sticky receptive tip of pistil that = responsible for catching pollen
style: tube-shaped connection between stigma + ovule (elevates stigma to catch pollen)
ovule: structure containg female reproductive cells (post-fertilisation it will turn into seed)
119
non reproductive support structures in flower
petals: attract pollinators
sepal: outer covering - protects flower when in bud
peduncle: stalk of flower
120
flowering purpose
enabling plant to sexually reproduce via pollination, fertilisation, seed dispersal
flowers need to bloom where pollinators = most active + abundant (=dependent on seasons)
some plants bloom in long day conditions (summer), some in short day (autumn/winter)
121
critical factor responsible for flowering
length of light + dark periods
122
length of light + dark periods detected by
phytochromes
123
phytochromes
leaf pigments used by plants to detect light + dark periods
124
photoperiodism
response of plant to relative lengths of light + darkness
125
phytochrome forms
active + inactive
126
inactive phytochrome(Pr)
converted into active form when absorbs red light
127
active phytochrome(Pfr)
broken down into inactive form when absorbs far red light
128
active form phyto chrome will revert back to inactive form:
in absense of light (darkness reversion)
129
during day active phytochrome form predominant as
sunlight contains more red light than moonlight
vice versa (inactive =moonlight)
130
photoperiodism
only active form of phytochrome = capable of causing flowering- its action differs in certain plant types
131
plants can be classed as (ref: photoperiodism)
short day or long day plants (critical factor determining their activity = night length)
132
Short-day plants
flower when days = short – require night period to exceed critical length
Pfr inhibits flowering + so flowering requires low levels of Pfr (i.e. resulting from long nights)
133
Long-day plants
flower when days = long – hence require night period to be less than critical length
Pfr activates flowering + so flowering requires high levels of Pfr (i.e. resulting from short nights)
134
SID the LAD
Short Day pfr Inhibit (flowering)
Long Day pfr Activates (flowering)
135
Horticulturalists can manipulate flowering of short-day + long-day plants by
controlling exposure of light
(critical night length required for flowering response must be uninterrupted to be effective)
135
Horticulturalists can manipulate flowering of short-day + long-day plants by
controlling exposure of light
(critical night length required for flowering response must be uninterrupted to be effective)
136
Long-day plants require periods of darkness= less than uninterrupted critical length
plants will traditionally not flower in winter + autumn when night lengths = long
Horticulturalists trigger flowering in these plants by exposing plant to light source during night
Carnations = eg of long-day plant
