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A2 biology > plant responses > Flashcards

plant responses Flashcards

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1
Q

what do plants respond to?

A
  • competitors
  • temp
  • soil pH
  • light
  • gravity
  • pathogens
  • wind
    -water potential of soil
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2
Q

what is a tropism?

A
  • a directional growth response to a particular stimulus
  • can be positive or negative
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3
Q

examples of tropisms

A
  • phototropism : light
  • geotropism/gravitropism : gravity
  • chemotropism : chemicals
  • thigmotropism : physical content
  • hydrotropism : water
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4
Q

what is a nastic response?

A

non-directional response to an external stimuli (e.g. thigmotropism)

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5
Q

physical response of phototropism

A

shoot grows towards light

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6
Q

physical response of geotropism

A

root grows towards gravity

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7
Q

physical response of chemotropism

A

part of plant grows towards chemicals

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8
Q

physical response of thigmotropism

A

plant grows towards physical contact

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9
Q

survival advantage of phototropism

A

increases height of leaves for efficient photosynthesis

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10
Q

survival advantage of geotropism

A
  • helps to anchor plants
  • helps roots / plant get mineral ions and water
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11
Q

survival advantage of chemotropism

A
  • helps plant grow away from toxins
  • helps plant find minerals
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12
Q

survival advantage of thigmotropism

A

increases growth towards light for efficient photosynthesis

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13
Q

how does the plant ensure that the hormones only act on target tissue?

A
  • cell signals are sent out
  • target tissue has complementary receptor
  • specific hormones have specific shapes which can only bind to specific receptors
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14
Q

by what transport methods will the hormones be transported around the plant?

A
  • cell sap
  • diffusion
  • active transport
  • translocation in phloem
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15
Q

role of hormone ethene / ethylene in plants

A
  • fruit ripening
  • leaf abscission
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16
Q

role of hormone auxin

A
  • cell elongation (e.g. pollen tube growth)
  • inhibition if lateral roots and leaf abscission (cutting off)
  • apical dominance
  • phototropism
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17
Q

role of hormone gibberellins

A
  • germination
  • stem growth
  • stem elongation
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18
Q

role of hormone ABA (abscisic acid)

A
  • inhibits germination and seed growth
  • stomatal closure
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19
Q

role of hormone cytokinins

A
  • mitosis
  • delaying old age (senescence)
  • overcomes apical dominance
  • cell expansion
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20
Q

what is synergism?

A

when different hormones give a better response when working together than they would on their own

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21
Q

what is antagonism?

A

when the substances have opposite effects so the balance between them determines the response of the plant

22
Q

physical defenses to herbivory

A
  • calls elise plugs up phloem
  • bark
  • thorns / spikes
  • sap
  • tylose plugs xylem
  • lignin thickening
  • waxy cuticle
23
Q

chemical defences to herbivory

A
  1. tannins - taste bitter to herbivores
  2. alkaloids - nitrogen containing compounds
  3. terpenoids - antibacterial and anti fungal cells
  4. pheromones - influence social behaviours
24
Q

describe auxin (IAA)

A
  • produced at the apex (top) of the meristem
  • transported by active transport or diffusion to the “zone of elongation”
  • conc if auxin determines the effect
25
Q

describe auxin in geotropism

A
  • low conc of auxin in roots increase root growth
  • high conc inhibits cell elongation in the roots
26
Q

explain how auxin is transported via active transport

A
  1. auxin activates the H+ pump and is moved into the cell wall
  2. the pH lowers and activates expansin enzymes
  3. expansins break H bonds in cellulose fibrils
  4. water moves into cell, elongating it
27
Q

result of unilateral light shining towards plant shoot

A

shoot bends towards light
- as shoot is positively phototropic
-bending occurs behind the tip

28
Q

result of shoot tip removed when light is shone

A

no response
- as the top must either detect the stimulus or produce the messenger (or both) as it’s removal prevents any response

29
Q

result of lightproof cover placed over intact shoot tip

A

no response
- the light stimulus must be detected by the tip

30
Q

result of thin, impermeable barrier of mica on one side of tip when light is shone

A

movement of chemical down the shaded side
bends towards light
- mica on the illuminated side of shoot allows the auxin to only pass down the shaded side where it increases growth and causes bending

31
Q

result of mica inserted on shaded side

A

movement of chemical down its shaded side is prevented by mica
no response

32
Q

effect of tip separated by mica

A

-auxin is stuck in tip
- cant move down shady side

33
Q

result of gelatin block separating tip

A

movement of chemical down shaded side
bends towards light
- gelatin allows chemicals to pass through it but not electrical messages, the bending which occurs must be due to a chemical passing from the tip

34
Q

difference between gelatin and mica

A

mica is non porous
gelatin is porous

35
Q

what is apical dominance?

A

inhibition of side shoots

36
Q

cause of apical dominance

A

the presence of auxin

37
Q

what does abscisic acid do in apical dominance?

A

it inhibits bud growth.
- high levels of auxin maintain the high levels of abscisic acid in the bud, inhabiting the growth

38
Q

if the apex of the shoot is removed how might this effect apical dominance?

A
  • abscisic acid decreases
39
Q

effect of cytokinins on apical dominance

A
  • promote bud growth and can override the effect of apical dominance
  • high levels of auxins in tissues cause cytokinins to be transported to those tissues
40
Q

what does gibberellic acid cause?

A
  • stem elongation and therefore tall plants
  • seed germination
  • stimulate pollen tube growth in fertilisation
41
Q

explain how gibberellic acid causes stem elongation

A
  • dominant Le gene is expressed
  • produces enzyme that converts G20 to gibberellic acid (G1)
  • promoting stem elongation
42
Q

if you mutated the Le gene, what effects could you have on the phenotype of the plant and why?

A
  • shorter stem
  • enzyme not produced
  • cant convert G20 to G1
43
Q

why do seeds remain dormant until the right conditions occur for it to germinate?

A
  • so energy is not wasted trying to grow in bad conditions
  • as seeds need water and nutrients
44
Q

when seeds absorb water what is produced and transported? what is enabled?

A
  • gibberellin is produced and transported to the endosperm of the seeds
  • it enables the production of amylase
45
Q

what reaction does amylase catalyse?

A

starch into maltose

46
Q

why does the product of amylase being catalysed promote germination of the seed?

A

glucose is used as food for plants. the seed can grow a leaf

47
Q

6 commercial uses of plant hormones

A
  1. brewing
  2. sugar production
  3. decaying yellowing of leaves
  4. plant breeding
  5. ethene
  6. auxins
48
Q

what plant hormone is involved in the germination of seeds?

A

gibberellins

49
Q

what plant hormone is involved in stem elongation?

A

gibberellins + auxin

50
Q

what can cytokinins delay and why is this good?

A

delay leaf senescence so plants and vegetables remain green for longer

51
Q

what can be used for cell division, lateral shoot growth and lead growth?

A

cytokinins

52
Q

how can auxins be used a herbicide?

A

a high conc stop plants from growing
a low conc stop plants from growing

A2 biology (15 decks)

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