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A-Level Biology > 16.1 Plant Hormones And Growth In Plants > Flashcards

16.1 Plant Hormones And Growth In Plants Flashcards

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1
Q

What is a tropism?

A

Directional growth in response to environmental cues

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2
Q

What are the two key limitations on plants?

A

Immobile

No nervous system

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3
Q

What is the role of auxin in plants?

A

CONTROL cell elongation

PREVENT abscission

Apical dominance maintenance

Fruit ripening

Stimulate the release of ethene

Involved in tropisms

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4
Q

What are the names of some plant hormones?

A

Auxin

Gibberelin

ABA Abscisic Acid

Ethene

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5
Q

What is the role of gibberellins in plants?

A

Causes STEM ELONGATION

Stimulate POLLEN TUBE GROWTH in fertilisation

Mobilisation of FOOD STORES in a seed at GERMINATION

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6
Q

What is the role of ethene in plants?

A

Causes FRUIT RIPENING

PROMOTES abscission in deciduous trees

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7
Q

What is the role of ABA in plants?

A

Maintains DORMANCY of seeds and buds

Stimulates STOMATAL CLOSURE

Stimulates cold protective responses
E.g. antifreeze production

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8
Q

Why are scientists still unsure about the details of many plant responses?

A

Plant hormones work at very low concentrations SO
isolating them and measuring changes in concentration is not easy

Multiple interactions between different CHEMICAL CONTROL systems makes it difficult to isolate role of a single chemical in a specific response

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9
Q

How does a seed germinate because of plant hormones?

A
  1. Seed absorbs water
  2. Embryo is activated and begins to produce gibberellins
  3. Gibberllins stimulate PRODUCTION OF ENZYMES that break down food stores found in seed
  4. Embryo plant uses food stores to produce ATP
  5. Build materials
  6. Grows and breaks out through seed coat
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10
Q

What determines whether a seed will germinate?

A

Relative levels of gibberellins and ABA

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11
Q

Where is the food store found in dicot seeds?

A

Cotyledons

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12
Q

Where is the food store found in monocot seeds?

A

Endosperm

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13
Q

What does evidence suggest about gibberellins involved in seed germination?

A

Switch on genes coding for digestive enzymes for germination

E.g. amylases and proteases

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14
Q

What is an antagonist?

A

Substance which interferes with action of another

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15
Q

What is an example of an antagonist in plant hormones?

A

ABA is an antagonist of GIBBERELLINS

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16
Q

What is ABA?

A

Abscisic acid

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17
Q

What is experimental evidence supporting the role of gibberellins in the germination of seeds?

A

Mutant varieties of seeds lacking genes which produce gibberellin do not germinate
They germinate normally if gibberellins are applied externally

Seeds with GIBBERELLIN BIOSYNTHESIS INHIBITITOR applied to not germinate
Germinate if inhibitor is removed OR gibberellins applied

18
Q

What is an example of an auxin?

A

IAA indoleacetic acid

19
Q

What does IAA stand for?

A

Indoleacetic acid

20
Q

Wher are auxins made in a plant?

A

Tips of roots and shoots

Meristems

21
Q

How does auxin move through a plant?

A

Down the stem

Up the roots

TRANSPORT TISSUE and from CELL TO CELL

22
Q

What does auxin do?

A

Stimulates growth of main, apical shoot

23
Q

What does evidence suggest about auxin and cell walls?

A

Auxin causes cell walls to stretch more easily

24
Q

How does auxin cause cell elongation?

A
  1. Auxin molecules bind to receptors in plant cell membrane
  2. pH falls to around 5
  3. Optimum pH for enzymes to keep cell flexible and plastic
  4. Cells mature
  5. Auxin destroyed
  6. pH rises and plasticity enzymes become inactive
  7. Cell wall becomes rigid again
25
Q

What does high concentrations of auxin do?

A

Suppress growth of LATERAL shoots

26
Q

What is something else high leves of auxin does?

A

Stimulates growth in MAIN shoot

27
Q

What happens if the apical shoot is removed?

A
  1. Auxin-producing cells removed so NO AUXIN
  2. Lateral shoots freed from dominance of apical shoot
  3. Lateral shoots grow faster
  4. Applying auxin artificially to apical shoot reasserts apical dominance and lateral shoot growth is suppressed
28
Q

What does low concentrations of auxin do?

A

Low concentrations of auxin a promote root growth

29
Q

What happens to the roots UP TO A GIVEN CONCENTRATION of auxin?

A

The more auxin that reaches the roots, the more they GROW

30
Q

How does the root get auxin?

A

Low concentrations from growing shoots

31
Q

What happens to the ROOTS if the apical shoot is removed?

A
  1. Apical shoot is removed
  2. Amount of auxin reaching roots is greatly REDUCED
  3. Root growth slows and STOPS
  4. Replacing auxin artificially AT CUT APICAL SHOOT restores root growth
32
Q

What does high auxin concentrations do to the roots?

A

High auxin concentration inhibits root growth

33
Q

What is something else gibberellins are responsible for in plants?

A

Elongation of plant stems during growth

34
Q

What are ‘internodes’?

A

Regions between leaves on a stem

35
Q

What do gibberellins affect?

A

Length of plant internodes

36
Q

What do plants that have short stems produce?

A

FEW or NO gibberellins

37
Q

What does interrupting the gibberellin synthesis pathway do?

A

Makes plant stems much shorter

38
Q

What does shorter plant stems allow?

A

Reduces waste

Makes plants LESS VULNERABLE to DAMAGE by WEATHER and harvesting

39
Q

What does growing seedlings ‘hydroponically’ mean?

A

In nutrient solution rather tha soil

40
Q

How should the data from each experimental group measuring the effects of the concentrations of plant hormones be measured?

A

Standard deviation

41
Q

What is synergism?

A

When two factors’ actions are greater than the sum of their total actions

42
Q

What is antagonism in plants (compared to synergism)?

A

Substances have opposite effects

A-Level Biology (35 decks)

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