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Biology > C16 - Plant Responses > Flashcards

C16 - Plant Responses Flashcards

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1
Q

Define Tropism

A

A growth response by a plant in response to a unidirectional stimulus

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2
Q

Define phototropism

A

A growth response by a plant in response to a unidirectional light

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3
Q

Define geotropism

A

A growth response by a plant in response to gravity

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4
Q

Define hydrotropism

A

A growth response by a plant in response to water

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5
Q

Define node

A

Point at which a petiole/leaf attaches to stem

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6
Q

Define internodal length

A

Length between two adjacent nodes

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7
Q

Define lateral shoots

A

Side shoots, those below the apical shoot/bud

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8
Q

Define apical shoot

A

The topmost shoot

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9
Q

Define apical dominance

A

When the main central stem grows more strongly than the side stems

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10
Q

Define abscission

A

Leaf drop

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11
Q

Define synergism

A

When several hormones work together to give a greater response

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12
Q

Define antagonism

A

When hormones have opposite effects (one promotes, one inhibits)

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13
Q

Define meristem

A

tissue of undifferentiated stem cells

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14
Q

Define deciduous

A

A plant that looses its leaves in autumn/winter

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15
Q

Why do plants need hormones

A 
Movement (tropism)
Seed germination
Fruit ripening
Abscission
Growth
Protection (herbivores and abiotic stress)
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16
Q

What makes a tropism positive or negative

A

Positive - towards stimulus

Negative - away from stimulus

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17
Q

Name the 4 plant growth hormones we study

A

Gibberellins
Ethene
Auxins
ABA (abscisic acid)

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18
Q

What are the roles of gibberellins?

A
  • cause stem elongation
  • trigger metabolism of food stores at germination
  • stimulate pollen tube growth in fertilisation
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19
Q

Describe how gibberellins are used in seed germination

A

Seed absorbs water, embryo activated and gibberellins produced
Gibberellins switch on genes that code for amylases and proteases
Stimulates enzymes to break down food stores in seed
ATP produced, grows and breaks out of the seed coat

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20
Q

What is the experimental evidence for the role of gibberellins

A
  • seeds bred to not produce gibberellins do not germinate
    (if applied to seeds externally they will then germinate)
    -inhibitors of gibberellins applied they do not germinate
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21
Q

Name an application of gibberellins in industry

A

Affect length of internode (few gibberellins = short stems)
Dwarf plants made
-reduces waste
- reduced vulnerability (eg. wind)

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22
Q

What is the role of auxins?

A
  • responsible for geotropism and phototropism

- Stimulates elongation in shoots and inhibits elongation in roots

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23
Q

Describe how auxins cause cell elongation

A

1) auxins bind to receptors on cell surface membrane
2) Stimulates H+ ions to be actively pumped across cell membrane into cell wall
3) H+ ions lower pH to 5
4) Expansins activated
5) Loosen cellulose cell wall - more plastic
6) water diffuses into vaculole, causing it to expand, along with the rest of the cell

24
Q

Describe how the concentrations of auxins change ina shoot in response to unilateral light

A

Auxin produced in the tip
Diffuses down stem
Diffuses to shady side
Causes shaded side cells to elongate thus bending it towards the light

25
Q

Evidence for phototropism:
How would the growth a plant shoot change if…
exposed to unilateral light

A

Grow towards the light

Positive phototropism

26
Q

Evidence for phototropism:
How would the growth a plant shoot change if…
Shoot tip removed and exposed to unilateral light

A

no response as auxins produced in the tip

27
Q

Evidence for phototropism:
How would the growth a plant shoot change if…
Lightproof cover placed over shoot tip and exposed to unilateral light

A

No response

Ausins act on tip in response to light

28
Q

Evidence for phototropism:
How would the growth a plant shoot change if…
Thin layer of mica placed on sunny side and exposed to unilateral light

A

Bends towards light

Hormone still able to diffuse along shaded side and act on those cells causing elongation

29
Q

Evidence for phototropism:
How would the growth a plant shoot change if…
Thin later of mica place on shaded side and exposed to unilateral light

A

No response

Hormone not able to diffuse down shadede side and have its effect

30
Q

Evidence for phototropism:
How would the growth a plant shoot change if…
tip removed, gelatin inserted and tip replaced and exposed to unilateral light

A

Movement of the chemical still possible, gelatin would stop electrical messages thus it must be a hormone

31
Q

Evidence for geotropism

A

Plant placed on a clinostat that rotates slowly
Evens out gravitational force and grows straight out
Plant replaced sideways not on clinostat - Shoot grows up and roots grown down

32
Q

Descibe the process of geotropism

A

Starch statoliths in root tip
Sink to the bottom of the cells in the roots in response to gravity
Causes downwards growth

33
Q

Describe what a plant with apical dominance will look like as opposed to a plant without apical dominance

A

Apical domincace - tall, thin, apical shoot leads the way

Without - bushy, fat, lateral shoots grow strongly

34
Q

What are the 3 wasy plants can respond to abiotic stress

A

Leaf loss
Preventing freezing
Stomatal control

35
Q

Why is leaf loss bebficial to a plant

A

In winter, less daylight = less photosynthesis

  • glucose required to prevent leaves from freezing becomes greater than the glucose able to be produced
  • greater surface area, more likely to be affected by high winds etc.
36
Q

What is photoperiodism?

A

Reponse to lack fo light caused by phytochrome - light sensitive pigment

37
Q

Descibe the process of abscission

A
  • falling auxin levels
  • ethene produced
  • triggers gene activation (enzymes produced)
  • enzymes digest cell wall in separation zone
  • vascular bundles sealed off
  • Cells below swell and push leaf off
    Fat deposited in cells acting as a scar
38
Q

Why is freezing dangerous for plant cells?

A

Water expand
Destroy membrane
Die

39
Q

How do plants respond to the risk of freezing?

A

produce solutes that dissolve in the vacuole, this lowers the freezing point

40
Q

How does stomatal control help a plant respond to it environment

A

Closed stomata - conserve water

Open stomata - allows CO2 in an helps coll the plant by evaporation of the water

41
Q

What hormone controls stomatal opening and closing

A

ABA (abscisic acid)

42
Q

How does ABA control the stomata

A

Increased ABA dereases the water potential of the stomata
Water moves out of the cells
Cells become flaccid and close (turgid means they open)

43
Q

What are the 3 types of plant responses

A

Chemical
Physics
Mechanical

44
Q

Give an example of a mechanical repsonse in plants

A

Thorns and hairs to deter herbinvores
Leaves that drop when touched
Mimicry

45
Q

Give a physical response in plants to stress

A

Cellulose cell walls
Tough waxy cuticle
Layers of dead cells around the stem

46
Q

What are tannins

A

Chemical response in plants

toxic to insects

47
Q

What are alkaloids?

A

Chemical repsonse in plants
nitrogenous
act as drugs

48
Q

What are volatile organic compounds (VOCs)

A

Chemical reposnse in plants

smelly repellents

49
Q

Names 4 types of chemical response in plants

A

pheromones
tannins
alkaloids
VOCs

50
Q

Name 3 commercial uses of plant hormones

A

ripening
hormone rooting powder
weed killers

51
Q

Describe how plant hormones can be used in artificial ripening

A

Ethene can be sprayed on to unripe plants to ripen them

52
Q

State an advantage of artificial ripening

A

Unripe plants can be transported more easily and produced less waste

53
Q

Outline the reaction that causes ripening fruits to become sweeter

A

Starch –> maltose (hydrolysed by amylase)

maltose –> glucose

54
Q

As ethene concentration increases what happens to CO2 prodcution

A

Increases as respiration increases, then decreases as starch hydrolyses

55
Q

What does hormone rooting powder do

A

Dipping cuttings into auxins

stimulate root growth from cut stem

56
Q

How do weed killers use plant hormones

A

Dicot auxins applied to area
Absorbed by broad leafed dicot weeds but not moncot crops
causes rapid and unsustainable growth —> death

Biology (17 decks)

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