5.1.5 Plant Responses Flashcards
define cell signalling
communication and coordiantion between cells to trigger a reaction in the cell
why do plants need to respond to their environment
to avoid abiotic stress- cold, heat, dryness and humidity
to maximise photosynthesis by obtaining more light and water
to avoid herbivory
what are the roles of auxins
control cell elongation, involved in tropisms and stimulate the release of ethene
what are the roles of gibberellins
cause stem elongation
what are the role of ethene
causes fruit ripening, promotes senescence
what is the role of ABA
stimulates stomatal closing
name 3 similarities between plant hormones and hormones in mammals
- hormones bind to receptors which cause enzyme reaction inside cells
- act on several target tissues
- may involve in switching genes on and off
name 3 differences between plant and mammals hormones
plants- produced by many tissues
animals- produced by endocrine tissues
p- move in xylem and phloem
a- move in bloodstream
p-act on most tissues
a- act on specific target tissues only
what is the food store in a
dicot
monocot
2x cotyledons
endosperm
explain the process of seed germination
1) seeds absorb water
2) water activates the embryo to start making the gibberelin
3) gibberelin activates genes to make protease, converts protein into amino acids, this is converted into amylase which converts starch into maltose, maltose is converted into maltase which converts maltose into glucose
4) these are used to respire and produce atp for building roots and shoots
what are the two pieces of evidence which shows that gibberelins are responsible
1:
plant species without the gene to make protease do not germinate
2:
if gibberellin biosynthesis inhibitors are applied to seeds they do not germinate
what are meristems
groups of immature cells which can divide and differentiate
what are apical meristems
tips of roots and shoots making them grow longer
what are lateral bud meristems
buds that could form a side shoot
what are lateral meristems
circular bands that make roots and shoots get wider
what are intercalary meristems
between the nodes, helps the shoots get longer
where are auxins made and what do they cause
made in the cells at the tips of shoots and tips of roots
(move down from the shoot top and up from the root tip via diffusion)
travel to the zones of elongation
stimulate elongation here
describe exactly how the auxins cause stem cell elongation
auxins bind to specific receptors in the cell surface membrane
they cause the active transport of H+ by an ATPase enzyme into the cell wall
low PH optimal for expansin enzymes that loosen cell walls
the expansin enzymes break bonds between microfibrils present in cellulose
allows for cell elongation
explain how positive phototropism occurs
1) shoot tip produces auxin, auxin diffuses down from shoot tip or is moved by active transport
2) light causes movement of auxin from light side to shaded side
3) higher auxin concentration on shaded side causes cell wall loosening and greater elongation of cells on shaded side
4) grows faster and causes shoot to bend towards the light
what happens if their is a high concentration of auxin in the root
high concentration of auxin inhibit elongation of cells in the root
what is apical dominance
high concentrations of auxins suppress growth of lateral shoots
what happens if the apical shoot was removed
auxin production stops apical dominance stops lateral buds develop side shoots grow plant becomes bushy
what effect on the stem do gibberellins have
affect the length of internodes (regions between leaves)
define tropism
directional growth of plants determined by the direction of external stimuli
what is the difference between positive and negative tropism
a positive tropism is one that grows towards the stimulus
a negative tropism is one that grows away from the stimulus
why do plants grow more rapidly in the dark
to grow upwards to reach light in order to photosynthesise, auxin is not destroyed by the light so more is present causing elongation
suggest how hormones alter a plants growth in response to overcrowding by other plants
auxin causes positive phototropism, plant shoot bends towards the light
plants grow taller
what tropic are shoots/roots
shoots- negatively geotropic
roots- positively geotropic
what happens if there is a high concentration of auxin in the roots
elongation is inhibited
what happens to the shoots when the plant is attached to the rotating drum
shoots grow straight
gravitational stimuli is applied evenly
name three abiotic stresses to plants
lack of water
high winds
temperature
what happens to deciduous trees in winter
trees lose all their leaves and remain dormant until the temperature rises and the day lengthens
why do deciduous trees lose their leaves in winter
amount of sunlight decreases, less photosynthesis, the amount of glucose required to maintain the leaves and stop chlorophyll freezing exceeds the amount of glucose produced
define plant senescence
the process of aging in plants, chlorophyll degrades and carotenoids revealed (which gives leaves this orange colour in autumn)
explain the process of leaf loss
1) cytokinins inhibit senescing by making leaf a sink for nutrients
2) in autumn cytokinins production stops, senescing begins
3) auxin concentration reduces in the abscission zone
4) low auxins mean increased production of ethene
5) ethene causes the production of cellulase enzyme
6) cellulase enzymes break down cell wall in abscission zone
7) petiole and stem separates
what is deposited on either side of the separation layer, what does this do
fatty material, forms a protective scar preventing the entry of pathogens
what prevents plants from freezing
the cytoplasm of cells and vacuoles contain solutes which lower the freezing point of water
polysaccahrides siuch as amino acids and proteins act as antifreeze
the genes that make these products are activated by a decrease in temp over a sustained period of time
what hormone controls stomatal closing/opening
ABA
how does ABA control stomata
1) levels of soil water fall, plant makes ABA
2) ABA transported to leaves by xylem and phloem
3) ABA binds to receptors on the plasma membrane of guard cells
4) k+ actively transported out the guard cell, high WP in guard cell so water moves by osmosis out of the cell
5) cells become less turgid and the stomata closes
name three physical defences of plants
thorns
hairy leaves
stings
what are tannins
a part of a chemical group called phenols
have a BITTER TASTE which putd animals off eating them
this is TOXIC TO INSECTS
what are alkaloids
bitter tasting compounds: niccotine, caffeine, cocaine…
what are terpenoids
toxins to insects and fungi
eg citronella
some disrupt insect nervous systems
what are pheremones
a chemical made by one organism that affect the social behaviour of other members
what are volatile organic compounds
act like chemical signals
eg in cabbages when caterpillars, attack they produce a VOC to attract a parasitic wasp which lets its eggs into the caterpillar and is eaten alive
why do some plants fold at touch
to scare off larger organisms
what is the name to fruits that ripen after being picked
what is the advantage of this
what does ethene do
climacteric fruits
eg bananas
prevents damage during trasnport and lives on shelves for longer
triggers a higher rate of respiration, ripens fruit
what is the effect of adding auxins to cut shoots
causes the production of roots, makes it easier for them to grow and develop
why are weeds bad
they outcompete useful plants for space light etc
what is applied to weeds and what effect does this have
the synthetic auxin dicots are applied to weeds, promotes unsustainable growth and eventually death
what are the advantages of auxin based weedkillers
cheap to make and low in toxicity to other animals
