plant responses Flashcards
plant go weeeeee brrrr
what is a tropism?
directional growth in response to a stimulus
what is phototropism?
growth in response to light
what is geotropism?
growth in response to gravity
what is hydrotropism?
growth in response to water
what is thigmotropism?
growth in response to touch
what is chemotropism?
growth in response to chemicals
what are 4 plant hormones?
- auxins (IAA)
- gibberellins
- ethene
- abscisic acid (ABA)
what is the role of auxins?
- cell elongation
- prevent abscission
- maintain apical dominance
- stimulate ethene
what would happen in the absence of auxins?
- no growth
- lack of photosynthesis due to not being able to reach the light
what is the role of gibberellins?
- germination
- pollen tube growth
- stem elongation
what would happen in the absence of gibberellins?
- couldnt reproduce sexually
- no growth
what is the role of ethene?
- ripening
- promotes abscission
what would happen in the absence of ethene?
- pollinators not attracted
- trees couldnt survive winter
what is the role of abscisic acid?
- maintains dormancy
- cold protection (antifreeze)
- stomatal closure
- abscission
what would happen in the absence of abscisic acid?
- sprout and not survive
- not survive winter
- water loss
how do auxins cause elongation?
- auxins synthesised in the meristems which inhibits synthesis in lateral stems
- diffuses out of meristem and binds to receptors on the CSM which activates a proton pump
- pH lowers as H+ ions are actively transported into the cell
- creates optimum conditions for expansin which breaks bonds in cellulose cell wall causing it to be more flexible
- elongation occurs
how do gibberellins affect germination?
- seed embryo is activated when water us absorbed which produces gibberellins
- turns on gene coding for amylases and proteases to break down food stores (endosperm in monocots, cotyledons in dicots)
- embryo uses food stores to produce ATP for building materials to grow
- ABA inhibits gibberellins to determine when germination occurs
what is the effect of IAA on roots and shoots?
- inhibits growth in roots
- promotes growth in shoots
what are the commercial uses of plant hormones?
- ethene used to control ripening of fruit during transport to commercial locations
- gibberellins used to increase size of fruit
- auxins used in herbicides to promote rapid growth in weeds so they die by cell elongation
- auxins used to stimulate root development for plant cuttings to clone plants rapidly and cheaply
what are abiotic factors that cause stress?
- temp
- water availability
- wind
- light
- glucose conc
how do plants respond to abiotic stress due to lack of light?
photoperiodism:
- use phytochromes which are leaf pigments used to detect light
- inactive phytochrome Pr converted to active form when it absorbs red light (daylight)
- active phytochrome Pfr broken down to inactive form to absorb red light
leaf abscission:
- low light causes decrease in auxins and increase in ethene which produces enymes to digest cell wall at abscission layer so leaf falls off
how do plants respond to abiotic stress due to lack of glucose?
when below requirement for respiration trees lose leaves and remain dormant
how do plants respond to abiotic stress due to lack of water?
- stomatal closure controlled by ABA under threat of drought
- ABA binds to receptors on guard cells which causes Ca2+ ion channels to open
- influx of calcium ions causes potassium ion channels to open so K+ leaves guard cells
- water potential increases in guard cells so water moves out by osmosis
- guard cells become flaccid and close
what was the effect of putting a cap on a coleoptile (Darwin’s experiment)?
- cut off the tip and placed a cap on
- there was no dir3ectional growth
- prevented phototropic response indicating that the tip is responsible for detecting light
