Module 5: Plant responses Flashcards
What two types of stimuli do plants respond to
Herbiovary and aboitic stimuli
abiotic stimuli can be things like water stress
heribory is when they are being eaten by insects
Give examples of physical plant responses
Thorns, spikes, hairy leaves
What are the chemical defences
Tannins: Bitter taste, toxic to insects
Alkaloids: bitter taste, poisonous to animals which can affect metabolism (nicotine and tobacco)
Pheromones: affect social behaviour of other members of the same species (callose deposition)
(top three on spec)
Terpenoids: toxic to insects and fungi (neurotoxins, repellants)
Volatile organic compounds: same as pheromones but affect other species, an example being attracting parasitic wasps which lay eggs on catapillars which kills them)
What is the folding response
Mimosa pudioca
- fold leaves when they are touched
- this scares animals off
- or insects can slide or the fly of if they land on the leaves to prevent them from being eaten
(from the spec)
What are the 4 stages of plant growth and development
Seed germination
cell elongation
apical dominance
stem elongation
How does a seed germinate
- Water being absorbed stimulates creation of gibberellin
- this stimulates breakdown of proteins
- amalyse is made which breaks starch into maltose which breaks down into glucose
What chemical is involved in
seed germination and what does it do
Gibberellins stimulate production of digestive enzymes which release glucose from food stores
energy released fro seedling growth
What happens during cell elongation and what chemical is involved
Meristemic cells realises auxin at the tip of the shoot
auxin binds to receptor, which allows hydrogen ions to be pumped into the cell
hydrogen ions cause ph to be lowered, which helps make the cell wall more flexible, which allows it to elongate
auxin leaves the receptor and is broken down by enzymes
protein channel closes and no more hydrogen can come in
so the cell wall becomes rigid again
What happens during apical dominance and what hormone is involved
Auxins promote apical shoot growth going upwards
Auxins limits lateral shoot growth (stem that grows horizontally)
This allows all the shoots to better compete for light
What happens during stem elongation and what hormone is involved
Gibberellins concentration is increased This promotes stem elongation which means we get a taller plant this helps it better compete for light (more light, more photosynthesis)
Why don;t farmers want plants with long stems
want to reduce waste
and it can prevent crop damage
What kind of relationship does auxin and gibberlien have
synergic and antagonsit relationship
What is phototropism
Growth of plant in response to light,
How does phototropism occur
Unilateral light causes auxins to move laterally to the shaded side
higher auxin conc on shaded side
rate of growth higher on shade side
this means shoots are postively phototropic and they grow towards the light
Why is phototropism important
ensures max rate of photosynthesis
What is geotropism
plant growth in response to gravity
How does geotropism occur
Auxins found on the bottom part of the root
conc of auxins mean less root growth so the top of the plant faster
this ensures that the roots grow downwards
Name three other types of tropism
Hydrotropisms: plant growth towards the water
thermotropism: plant growths in response to temperature
thigmotropism: plant growth in response to contact with an object
What are IAA and what parts of plant growth or delvelopment are they are part of
An auxin that is produced in tips of shoots and roots (meristem)
- help with cell elongation
- maintain apical dominance (promotes apical growth so the vertical stem, and it inhibits the lateral shoots
- involved in phototropism and geotropism
How did they find out about IAA
check the textbook
What do auxins inhibit?
- Can inhibit fruit ripening (high level of auxins, the fruit won’t be ripe)
- can inhibit abscission (the falling fo leaves)
How does ethene promote leaf loss in decidous plants
- proudced by aging leaves
- phyotchons dtect low levelsof light
- auxin conv decreases, ethene increase
- layer of cells called absicion layer develops at the bottom of the stalk
- the absiccion layer seperates leaf from the rest of the plant
- ethene stimulates cells in the abscission layer to produce digestive enzymes which breaks the cell wall, causes leaf to fall off
What does ethene promote
- promotes abscission (leaf loss)
- promotes fruit ripening
What kind of realtionship does auxins and ethene have
antagonistic realtionship
What is the role of gibberrelins
- Promotes stem elongation (helps plant grow upwards)
- can promote seed germination
- stimulate pollen tube growth during fertilisation
What is the role of abscisic acid (ABA)
- maintain dormancy of seeds (stops seed from germinating)
- stimulates protective measures or responses
- antifreeze
- stomatal closure (to prevent water loss)
How does ABA trigger stomatal closure
- ABA binds to recpectors on guard cell membranes
- causes ion channels to open
- calcium ions enter cytosol from vacoule
- increased conc of calcium ions in cytosol causes other ion channels to open (pottassium channels)
- raises water potential of the cell
- Water leaves gaurd cells vai osmosis
- guard cells become flaccid and stomata close
What evidence have scientists found to find plant hormones
mutate genes that make a hormone
disrupt production pathway
cut shoot tip
What are the commerical uses of plant hormones
Ethene is used to rippen fruit (an example is bannas they are picked when they are unripe, so when they arrive at peoples home they are ripe)
Auxins
- can be used a weed killers, this makes weeds proudce long stems and less leaves which means they die due to a lack of food)
- can be used a rooting hormone (can use cuttings with rooting powder to grow many new plants)
