plant responses Flashcards
why do plants need to respond to their environment
avoid abiotic stress
maximise photosynthesis
avoid grazing
obtain more materials
why is it hard to examine plant hormones
they work at very low concs
multiple interactions between different chemical control systems means we cannot directly measure the effect of a hormone
give examples of physical defences
thorns
spikes
strings
give examples of chemical defences
tannins
bind to enzymes to inactivate them
alkaloids
pheromones
absorbed by leaves to stimulate cellulose formation
describe the action of ethene
speeds up ripening
promotes fruit drop
promotes lateral growth
describe the action of abscisic acid
stimulates stomata closing
maintains dormancy of seeds (antagonist to gibberellin)
describe the action of gibberellin
involved in seed germination
causes stem elongation
affects the length of the internodes
describe research support for gibberellins
mutant varieties bred to not produce gibberellin don’t germinate
if gibberellin inhibitors are applied, they don’t germinate
describe the action of auxins (indoleacetic acid)
made in tips of shoots and roots
promotes shoot growth and inhibit root growth (depending on its conc)
suppresses lateral shoot growth
describe the auxin mechanism of cell elongation
binds to receptors on the c.s.m causing a fall in pH so the optimal pH for enzymes to keep cell wall flexible
cells absorb water and vacuoles form and enlargen
as cells mature, auxin is destroyed
so pH rises, those enzymes denature and the cells become rigid
describe apical dominance caused by auxin
if the apical shoot is removed, there’s no auxin
so lateral shoots grow faster
if apical shoot is removed
amount of auxin reaching the root is reduced
root growth slows and stops
(high auxin conc inhibits root growth)
define synergism
different hormones work together and complement each other giving a greater response than on their own
define antagonism
describes hormones with opposite effects
the balance between them determines the response of the plant
describe the process of seed germination
seed absorbs water
embryo activates + produces gibberellins
stimulates producing enzymes that break down food stores in the cotyledons (dicot) or endosperm (monocot)
uses food stores to produce ATP to grow and break through seed coat
what do gibberellins switch on genes for
amylases and proteases
how does auxin cause cell elongation
binds to specific receptor sites in c.m.
causes a fall in pH
optimum pH for enzymes needed to keep the walls flexible
as cells mature, auxin is destroyed
so the pH rises and enzymes maintaining flexibily denature
wall becomes rigid
what does gibberellin affect in order
roots, lateral buds then apical bud
what are some abiotic stresses
day length
temperature
water
high wind
salinity
what is photoperiodism
plants are sensitive to lack of light
due to phytochromone
the ratio of Pr to Pfr changes depending on levels of light
how does abcission happen
as light levels fall, [auxin] falls
leads to ethene production
abscission zone is affected by ethene (gene switching)
producing enzymes which digest the cell walls in outer layer of abscission zone (separation layer)
vascular bundles sealed off
fatty material deposited in cells on the stem side to form a protective layer when the leaf falls
retaining water and swelling puts strain on outer layer
abiotic stresses put more strain, causing leaf separation
how do plants respond to freezing
cytoplasm + sap contain solutes
which lower freezing point
what does stomata do
cool the plant (in heat)
prevent water loss
what does ABA do
released under abiotic stress in the leaves
causes stomatal closure
ABA activates changes in [ionic] reducing the W.P. (and turgor) of cells
reduced turgor, guard cells close the stomata
