plant responses Flashcards

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1
Q

auxin role

A
  • control cell elongation
  • prevents leaf abscission
  • maintain apical dominance
  • involved in tropism
  • stimulate ethene release
  • fruit ripening
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2
Q

gibberellin

A
  • cause stem elongation
  • mobilisation of food stores in a seed at germination
  • stimulates pollen tube growth in fertilisation
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3
Q

ethene

A
  • fruit ripening

- promotes abscission in deciduous tress

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4
Q

ABA

A
  • abscisic acid
  • maintain dormancy of seeds + buds
  • stimulates cold protective responses (antifreeze production + stomatal closure)
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5
Q

experimental evidence for role of gibberellins in seed germination

A
  • seeds that lack gene that enables them to make gibberellins do not germinate - if gibberellins are applied externally, they germinate normally
  • if gibberellin biosynthesis inhibitors applied to seeds they don’t germinate - if inhibition is removed/gibberellins applied the seeds germinate
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6
Q

auxin affect on pH and plant growth

A
  • auxins such as IAA are growth stimulants
  • tip of roots/shoots + meristems
  • stimulate growth of apical shoot
  • evidence : auxin affects plasticity of cell wall : CW stretches more easily
  • auxins binds to specific receptor sites in plant CM
  • pH decreases to 5
  • optimum pH for enzymes to keep CW flexible and plastic
  • when auxin conc = low (when cell matures)
  • pH rises
  • enzymes maintain plasticity inactive
  • CW becomes rigid
  • fixed in shape + size
  • cells can’t expand/grow
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7
Q

what is apical dominance

A
  • auxin suppresses growth of lateral shoots
  • results in apical dominance
  • growth of main shoot
  • stimulated by auxin produced at tip so grows quick
  • lateral shoots inhibited by auxin moving up and down the stem
  • down the stem = low conc of auxin = longer lateral shoots
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8
Q

evidence of apical dominance

A
  • apical shoot removed
  • auxin producing cells removed
  • no auxin
  • lateral shoots grow faster
  • auxin applied artificially = apical dominance is reasserted
    + lateral shoot growth = supressed
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9
Q

auxin and root growth

A
  • auxin conc = low
  • promotes root growth
  • more auxin in roots = more they grow
  • apical shoot removed = less auxin reaching roots = root growth slows
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10
Q

synergism

A
  • diff hormones work together

- greater response

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11
Q

antagonism

A
  • substances have opposite effects

- E.g one promoting growth + one inhibiting

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12
Q

abiotic stress

A
  • non-living stresses that affect plants
  • extreme temp
  • high winds
  • flood
  • natural disasters
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13
Q

biotic stress

A
  • stress to plants caused by living organisms
  • bacteria
  • fungi
  • virus
  • insects
  • weeds
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14
Q

plant Reponses to abiotic stress

- leaf loss

A
  • leaf loss in deciduous plants :
  • lose leaves in winter (damaged by wind)
  • remain dormant until temp rises
  • glucose needed for resp to maintain leaves is greater than glucose produced in photosynthesis
  • due to lack of light/low temp
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15
Q

plant response to abiotic stress

- preventing freezing

A
  • if cells freeze = membrane disrupted = die
  • cytoplasm + sap in vacuole have solutes which lower the freezing point
  • sugars/amino acids act as antifreeze
  • protect cells from damage
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16
Q

plant response to abiotic stress

- stomatal control

A
  • open stomata = cool the plant
  • water evaporates from cells in leaves in transpiration
  • close stomata = conserve water
  • close/open controlled by ABA
  • leaf cells release ABA when under abiotic stress = stomata close
17
Q

ABA and water stress

A
  • soil water conc fall
  • roots produce ABA
  • transported to leaves
  • binds to receptors on PM of stomata guard cells
  • ABA activated ionic conc changed of guard cells
  • reduced water potential
  • reduced turgor
  • guard cells close stomata
  • water lost by transpiration is reduced
18
Q

physical defence

A
  • thorns
  • spikes
  • hairy leaves
  • spiny leaves
19
Q

chemical defence

A

Tannins :

  • phenol
  • bitter taste
  • puts animals off eating plants
  • toxic to insects
  • bind to digestive enzymes in saliva and inactivate
  • in tea + red wine

alkaloids:

  • bitter
  • acts as drugs
  • affect metabolism of animals = poisoning them
  • caffeine, nicotine
20
Q

chemical defence - phermones

A
  • affects social behaviour of other members of same species
  • maples tree attacked by insects : releases pheromones absorbed by leaves on other branches
  • leaves make chemicals (callose) to help protect them
21
Q

folding in response to touch

A
  • Mimosa pudica
  • contain toxic alkaloid
  • stem has sharp prickles
  • when leaves touches fold downwards + collapse
  • scares larger herbivores
  • dislodges small insects
  • recover die to K+ ion and osmotic movements into specific cells
22
Q

phototropism

A
  • IAA moves to more shaded parts of the shoots + roots
  • uneven growth
  • cell elongates
  • shoot bends towards the light
  • if IAA in roots growth is inhibited
  • root bends away from light
23
Q

geotropism

A
  • IAA moves to underside of shoots + roots
  • uneven growth
  • cells elongate and shoot moves upwards
  • IAA in roots inhibits growth
  • root grows downwards
24
Q

commercial uses of plant hormones

A
  • ethene stimulates enzymes that break down CW
  • break down chlorophyll
  • convert starch into sugars
  • fruits = soft + ripe
  • auxins = selective weed killers
  • auxins make weeds
  • produce long stems instead of lots of leaves
  • makes weeds grow too fast
  • can’t get enough water/nutrients = die
  • auxins = rooting hormones
  • auxins make a cutting
  • planted and grown in a new plant
  • lots of the same plant can be grown quickly + cheaply from one plant.
  • auxins produce seedless fruit