Plant responses Flashcards
what is herbivory ?
plant being eaten by animals / insects
state ways plants respond to herbivory
- release toxic chemicals like tannins and alkaloids
- release pheromones
- fold up (knock off insects / scares off animal)
what are alkaloids and how do they help against herbivory ?
- chemicals w/ bitter tastes / noxious smells / poisons
e. g. tobacco produces nicotine which is poisonous to insects
what are tannins and how do they help against herbivory ?
- bitter tasting chemicals
- bind to proteins in gut, making hard to digest plant
(deterrence)
how do pheromones help against herbivory ?
- alarm pheromones causes nearby plants to produce chemicals like tannin
- may attract other organisms which will kill herbivore (attract wasps to kill caterpillars)
describe how carrots respond to cold conditions
- produce antifreeze proteins
- proteins bind to ice crystals and lowers the freezing point
- stops more ice crystals from forming
state what a tropism is
response of a plant to a directional stimulus
what are the meanings of positive / negative tropisms ?
positive - growth towards stimulus
negative - growth away from stimulus
state the 5 different tropisms
phototropism / geotropism / hydrotropism / thermotropism / thigmotropism
what is phototropism ?
plant growth in response to light
(shoots +ve as grown towards light)
(roots -ve as grow away from light)
what is geotropism ?
plant growth in response to gravity
(shoots -ve as grow away from gravity)
(roots +ve as grow towards gravity)
what is hydrotropism ?
plant growth in response to water
roots +ve as grow towards water
what is thermotropism ?
plant growth in response to temperature
what is thigmotropism ?
plant growth in response to contact with an object
what are the two growth hormones ?
gibberellin and auxins
what does gibberellin do ?
stimulates seed germination, stem elongation, side shoot formation and flowering
what do auxins do ?
stimulate growth of shoots and roots by cell elongation
state the name of the main auxin
Indoleacetic acid (IAA)
how does IAA affect shoots for phototropism ?
- moves to more shaded side
- cells elongate on this side
- shoot bends towards light
how does IAA affect roots for phototropism ?
- moves to more shaded side
- growth is inhibited on this side
- root bends away from light
how does IAA affect shoots for geotropism ?
- moves to underside of shoot
- cells elongate
- shoot grows upwards
how does IAA affect roots for geotropism ?
- moves to underside of root
- cell growth inhibited
- roots grows downwards
outline the process of testing phototropism
- 9 wheat shoots planted in separate pots
- cover tip of 3 w/ foil cap, wrap base of 3 with foil and leave 3 exposed
- set up in front of light source
- after two days, record amount of growth (mm) and direction of growth
state the variables to be controlled for phototropism test
length of shoots, soil type, distance from light source, light intensity, temp, moisture …
outline the process of testing geotropism
- three petri dishes with 10 cress seeds
- tape lid and wrap foil around each
- chose location with warm and constant conditions
- leave dishes, one at 90 degrees, 45 and flat for 4 days
- measure amount of growth of shoots and roots and angle of growth
what is apical dominance ?
growth of apical bud stimulated by auxins - growth of side shoots from lateral buds inhibited
what is the apical bud and lateral buds ?
apical bud - shoot tip at top of flowering plant
lateral buds - bud where side shoots grow from
what is the point in apical dominance ?
- energy used to grow tall faster to reach sun light
- also prevents side shoots from competing with shoot tip for light
what happens, in terms of apical dominance, if the apical buds is removed ?
side shoots grow by cell division and cell elongation
why do tall plants show more side shoots at bottom of plant ?
- auxins become less conc as apical bud moves further away
- bottom parts have lower auxin conc, so side shoots grow
how do you investigate apical dominance ?
- one set of plants w/ tip cut off but w/ auxin paste
- one set w/ tip cut off
- one set left as they are
- leave for few days and then count number of side shoots
how do gibberellins stimulate seed germination ?
- Gib stimulate production of protease enzymes
- protease hydrolyses storage proteins to aas
- Gib stimulates prod. of amylase
- amylase hydrolyses starch to maltose
what is the molecule that inhibits gibberellins ?
abscisic acid
why would seed germination be inhibited ?
- so seed develops fully first
- dispersed away from parent plant
what is seed dormancy ?
term for inhibition of seed germination
how do you investigate role of gibberellins in stem elongation ?
- several plants left as control
- several plants watered w/ dilute Gib solution
- those w/ Gib sol. will have grown taller
what is the term for gibberellins and auxins working together and give an example
synergistic
work together to make plant tall
what is the term for gibberellins and auxins opposing each other and give an example
antagonistic
Gib stimulate side shoot growth, auxins inhibit side shoot growth
state the term for a plant that loses all its leave in winter
deciduous plant
what is the term for leaf loss ?
abscission
what is the point in abscission ?
helps plants conserve water (hard to absorb frozen soil / little sunlight)
what is abscission triggered by ?
shortening day length in autumn
outline how abscission is carried out
- ethene produced by old leaves and builds up
- abscission layer forms and bottom of leaf stalk
- ethene stimulates abscission layer to expand
- cell walls break, leaf falls off
what inhibits abscission ?
auxins (produced in young leaves, less so in old leaves)
state the state of guard cells for open stomata
turgid
state the state of guard cells for closed stomata
flaccid
what controls opening/closing of stomata ?
abscisic acid (ABA)
outline process of how stomata close
- ABA binds to guard cell membrane receptors
- Ca ions move from vacuole to cytosol (cytoplasm)
- increase in Ca causes other ion channels to open
- K ions leave guard cells
- water pot. increases
- water leaves, cell becomes flaccid
state how plant hormone ethene is used commercially
- ethene stimulates enzymes that break down cells walls and chlorophyll, making fruit softer and riper
- fruit transported before ripe, then exposed to ethene
state how plant hormone auxin is used commercially as weed killers
- make weeds produce long stems w/out leaves
- weed grows too fast and dies
state how plant hormone auxin is used commercially as rooting hormones
make cuttings grow roots
