PLANT RESPONSES Flashcards
what do plant need to respond to?
abiotic factors
herbivore
how do plant respond to herbivores?
physical and chemical defences and touch responses
list chemical defences and what do they do
alkaloids - their toxicity leads to animal death so enables plants to survive and reproduce
pheromones- release of this alerts nearby plants to produce more callose or toxins to harden leaves and make difficult for animals to feed from them, increased survival
tannins - toxic to herbivores
what is meant with tropism?
organism response in a particular direction as a response to stimulus
positive tropic response?
toward stimulus
negative tropic response?
away from stimulus
types of tropisms and what are they?
phototropism - directional response to sunlight (positive for shoots negative for roots)
geotropism - directional response to gravity (positive for roots and negative for shoots)
chemotropism -a movement of organs in growth due to a chemical stimulus
thigmotropism - when a plant responds to a movement or touch from another stimulus
hydrotropism - the movement or growth of a plant towards water.
aerotropism - a behavioural response in a plant that results in it growing towards the presence of air.
what is a nastic movement?
is a reponse not affected by direction of stimulus
what are the plant growth regulators/factors?
enable plants to respond to stimuli
list the plant growth regulators
auxins
gibberellins
abscisic acid ABA
cytokinins
ethene
AGACE
explain what AUXIN does
promotes cell elongation in shoots allowing APICAL DOMINANCE
inhibits lateral buds growth
inhibits leaf fall
explain what GIBBERELLINS does
stimulate seed germination, flowering and stem growth
explain what ABSCISIC ACID (ABA) does
inhibits seed germination /growth
causes stomatal closure during stressful periods
inhibits lateral bud growth,so support apical dominance
explain what CYTOKININS does
stimulate cell division and differentiation
delay leaf senescence
promote cell expansion
overcomes apical dominance by promoting lateral buds growth
explain what ETHENE does
stimulates flowering and fruit ripening
factors that increase effect of growth
SYNERGIC
factors that decrease effect of growth
ANTAGONISTIC
what does apical meristems allow?
lenghtening
what does lateral meristems allow?
widening
by what does the plant growth rate depend?
concentration of growth factor
tissue being acted on
developmental stage
plant species
explain the role of ethene and auxin in leaf loss
ethene- stimulates breakdown of cell wall in abscission layer, so leaf drop off
auxin - concentration of auxin decreases as the leaf ages
so as auxin level decreases, ethene level increases
disintegration of the abscission layer causes leaf to fall
explain the role of ABSCISIC ACID (ABA) in stomatal closure
ABA binds to receptor on guard cells membrane, causing Ca2+ channels to open allowing Ca2+ influx , this causes K+ channels to opne and K+ to leave the guard cells
water potential inside the cell increases, water moves out, cell becomes flaccid and closes stomata
ABA reduces transpiration
explain the role of GIBBERELLINS in seed germination
in right conditions, H2O absorption , germination occurs, embryo is stimulated, gibberellin is produced, gibberellin diffuses into the aleurone layer, this stimulates amylase synthesis , which hydrolyses starch into maltose,maltose is then rearranged into glucose and tranported to the embryo, which is used for respirarion, dormancy broken.
what are the 2 other growth factors involved in apical dominance and lateral bud growth inhibition?
ABA and CYTOKININS
ABA - may inhibit lateral bud growth as increased concentration of auxin may keep increased concentration of ABA, so when apex is cut off, ABA concentration drops so lateral bud growth is promoted
CYTOKININS - promotes lateral bud growth
high levels of auxin in the shoot makes the apex a cytokinins sink produced in the roots, so when the shoot is cut off auxin and ABA level drop, allowing cytokinins to spread evenly around the plant, causing lateral bud growth
what is the commercial use of auxin?
promotes flowering
root growth powder - encourages root growth
promotes seedless fruit growth
herbicide as too much shoot growthmakes the stem incapable of supporting itsel, dying
what is the commercial use of cytokinins
prevent yellowing of lettuce leaves after being picked
help mass-produce plants
promotes bud shoot growth of small pieces of plants , to then being grown separately
what is commercial use of gibberellins
delay senescense in citrus fruits,so can be left unpicked for longer so available for longer in shops
cytokinins+gibberelling allows apple shape elongation
allows grape stalk elongation so grape are less compacted so grow bigger
allows sugar cane stem elongation so more sugar can be stored
what are the commercial uses of ethene
speed up fruit ripenng in apples, tomatoes and citrus fruit
fruit drop in cotton, cherry and walnut
female sex expression in cucumbers, so reduce chances of self-pollination
what does IAA do and what is it?
type of auxin - stimulate cell elongation and division
