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plant hormones Flashcards

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Biology 101 flashcards
1
Q

Tropisms

A

Directional growth responses in plants

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2
Q

Phototropisms

A

Growth in response to light
positve phototropism shoots grow towards light
negative phototropism grow away from light

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3
Q

explain phototropism

A
  1. Unilateral light causes auxins to move laterally in shoot tips to shaded side
  2. higher auxin conc on shaded side
  3. higher auxins conc promotes cell elongation on shaded side which grow faster
  4. shoot bends towards light
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4
Q

benefits of phototropism

A

ensures max rate of photosynthesis as shoots grow towards the light (+ve phototropism)

roots grow away from light (-ve phototropism)
get water and minerals in soil

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5
Q

Geotropism

A

Growth is response to gravity
positive geotropism roots grow towards gravity
negative geotropism shoots grow away from gravity

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6
Q

explain geotropism

A

auxins fall to the bottom parts of shoots and roots due to gravity

shoots negative geotropism
auxins prompt shoot growth. bottom part grows faster

roots positive geotropism
auxins inhibit root growth
top part of roots grow faster

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7
Q

benefits of geotropism

A

ensures shoots grow upwards for more light
ensures roots grow downwards to absorb more water and mineral ions

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8
Q

Thigmotropism

A

Influenced by touch

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9
Q

Chemotropism

A

Influenced by chemicals

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10
Q

Plant hormones

A

Cytokinins
Abscisic acid (ABA)
Auxins
Giberellins
Ethene

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11
Q

Effects of cytokinins

A

Promote cell divison
Delay leaf senescence - increases shelf life
Overcome apical dominance - lateral growth
Promote cell expansion

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12
Q

ABA

A

Maintain dormancy of seeds and buds ( prevent germination)
works against gibberellins
stimulate protective measures
antifreeze chemical release to prevent freezing
stimulate stomata closure to prevent water loss for example

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13
Q

auxins

A

inhibits fruit ripening and abscission
controls cell elongation
maintain apical dominance
produced by meristem produced by shoots
auxins favour the growth of apical shoots but inhibit the growth of lateral shoots

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14
Q

Effect of gibberellins

A

Promote seed germination - break bud dormancy (works against ABA)
Promote growth of stems - elongation of internodes
Develop seedless fruit and fruit setting
Acts synergistically w/ auxin

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15
Q

Effect of ethene

A

Promote fruit ripening - starch to sugar and breaks down chlorophyll and cell wall
Stimulates cells in abscission zone to expand and breaks cell wall causing leaf to fall off
Opp to auxin

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16
Q

How do plants avoid herbivores
5 chemical
3 physical

A

physical: thorns, spikes, hairy leaves

chemical
1. Tannis- bitter taste, toxic to insects
2. Alkaloids- bitter taste, poisonous to animals ( affect metabolism)
3. Terpenoids- toxic to insects and fungi ( neurotoxins, repellents)
4. pheromones- affect social behaviour of other members of the same species
5. Volatile organic compounds- same as pheromones but affect other species

Folding response in Mimosa pudica

17
Q

Abscission in deciduous plants

A
  1. Phytochromes detect falling light levels
  2. decrease in production of auxins
  3. ethene levels increase
  4. ethene activates genes in abscission zone to produce digestive enzymes
  5. enzyme digest cell wall in superstition zone and vascular bundles are sealed
18
Q

benefits of abscission

A
  1. reduce energy needed to maintain levels in winter
  2. fallen leaves insulate roots
  3. rotten leaves provide minerals to plants
19
Q

Mechanism of seed germination

A

gibberellins stimulate production. of digestive enzymes to release glucose from food stores
the glucose can be used in respiration for energy
energy released for seedling growth
the plant embryo in the seeds use the glucose to begin respiring and release energy it needs to grow

20
Q

Mechanism of stomatal closure

A

roots detect lack of water and produce ABA
ABA travel to leaves and bind to receptors on guard cells
ions move out of guard cells and affect water potential gradient
water leaves by osmosis
guard cells become flaccid and close stomata to decrease transpiration

21
Q

Proof of gibberellins causing seed germination

A

Mutant varieties that lack gibberellin do not germinate but w/ external gibberellin they do
When gibberellin inhibitors are addeed to normal seeds they dont grow

22
Q

Apical Dominance Effect

A

Auxin produced at the apex, inhibits growth of lateral buds

23
Q

Experimental evidence for apical dominance

A

Removal of apical buds allows lateral bud to grow
Auxin/synthetic auxin placed on cut tip continues to inhibit the growth of side shoots

Plant 30 plants of same type, age, genotype and weight in same soil
Remove tip of 10 and apply auxin paste
Remove tip of another 10 and add paste w/out auxin
Leave last 10 as control
Sig. increase of no. of side shoots grown in first 10

24
Q

Recent research on apical dominance

A

Auxin stimulates production of ABA (inhibits growth)
When apex is removed as is the source of auxin, ABA levels decrease
Most cytokinins go to tip so when tip is removed cytokinins spread evenly around plant promoting growth

25
Q

Where does growth occur in plants

A

Apical meristems

Lateral bud meristems

26
Q

Mechanism of cell elongation by auxin

A
  1. Meristematic cells produce auxins which diffuse down the shoot down a concentration gradient
  2. auxins bind to receptors in the cell which open protein channels on the plasm membrane that allows H+ ions to enter the cell
  3. low Ph causes cell wall to become more flexible
  4. cell absorbs water which expands the cell wall and the cell elongates
  5. cell wall becomes rigid when auxins are broken down
27
Q

Confirming auxin as the hormone that causes growth

A

Impregnated agar blocks w/ diff conc. of auxin
Placed them on cut shoot tips
Same effects as in reg. shoots
Curvature is directly proportional to conc of auxin used

28
Q

Research supporting geotropism in shoots

A

Plants are grown on a slowly rotating drum (clinostat) so gravitational stimulus is applied evenly
Plants grow straight in both light and dark

29
Q

Research supporting geotropism in roots

A

Seeds are placed in petri dishes w/ moist cotton wool that are rotated 90 degrees as seedlings grow
Cover lid w/ oil - ensure no light is coming in
All petri dishes should be in same environment
Geotropic response in the roots can be seen every 2 hours

30
Q

Investigating role of gibberellin in stem elongation

A

Plant 40 plants
Water 20 plants normally
Water other 20 w/ diluted solution of gibberellins
Let all 40 grow for 28 days, measuring height every 7
Calculate rate at which plants grew

31
Q

IAA

A

Natural form of auxin responsible for +ve phototropism so plant bends towards light to phostosynthesise and grow taller and grows roots to reach water and nutrients
Light stimulus detected by tip of plant

bio 2 (16 decks)

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