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A Level Biology OCR A > 16 - Plant Responses > Flashcards

16 - Plant Responses Flashcards

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1
Q

What is a tropism?

A

The directional growth of a plant in response to a directional stimulus

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2
Q

What is an abiotic stress?

A

Stress caused by a non-living factor i.e. lack of water

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3
Q

What is a biotic stress?

A

Stress caused by a living thing i.e. a pathogen

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4
Q

What is a herbivory stress?

A

Stress caused to a plant by being eaten

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5
Q

What is phytochrome?

A

A light-sensitive pigment in plants which exists in two variants, the balance of which can invoke a change

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6
Q

What is photoperiodism?

A

A plant’s response to seasonal changes in length of night and day due to sensitivity to light availability

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7
Q

What are the two key limitations of plants in terms of responses?

A

They are rooted and do not have a rapidly responding nervous system

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8
Q

What are 4 important plant hormones?

A
  1. ABA 2. Ethene 3. Gibberellins 4. Auxins
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9
Q

What happens to auxin levels in plants as a result of low light levels?

A

They are also low

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10
Q

What does the plant do in response to low auxin levels caused by low light availability?

A

Produces the hormone ethene

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11
Q

How does ethene cause abscission?

A

It switches on plant digestive enzymes. This causes a fatty layer to be laid down in the abscission zone, and also causes the cells on the separation side to swell. This weakens the joint of leaf to stem, causing the leaf to fall off

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12
Q

What is abscission?

A

When plants shed fruits, leafs, flowers, and seeds.

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13
Q

What is the abscission zone?

A

Layer of cells at base of petiole that weakens and allows leaf to drop off

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14
Q

Why is it important that plants avoid freezing?

A

Expanding, frozen water can damage cell walls

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15
Q

What is an adaptation that most plants have to prevent freezing?

A

The vacuole and cytosol contain certain solvents which lower the freezing temperature of water

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16
Q

What is a specific adaptation which carrots have to prevent freezing?

A

They produce a protein which binds to ice crystals, stopping them from freezing

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17
Q

What hormone causes closure of guard cells?

A

ABA

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18
Q

What causes ABA to be released?

A

When the roots detect low water concentration

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19
Q

How does ABA work?

A

It causes Ca²⁺ and K⁺ ions to leave the guard cells, increasing the water potential and thus causing water to leave the cells, causing the stomata to close

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20
Q

What are 2 known roles of ethene in plants?

A

Promotes abscission and fruit ripening

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21
Q

What hormone can stimulate antifreeze production in plants?

A

ABA

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22
Q

What are 5 known roles of auxins in plants?

A
  1. Stimulate ethene production 2. Involved in tropisms 3. Control cell elongation 4. Prevent abscission 5. Maintain apical dominance
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23
Q

What are 3 known roles of gibberellins in plants?

A
  1. Cause stem elongation 2. Trigger mobilisation of food stores in seeds at germination 3. Stimulate pollen tube growth in fertilisation
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24
Q

What are 3 known roles of ABA in plants?

A
  1. Stimulate stomatal closure 2. Stimulate cold protective response 3. Maintains dormancy of seeds and buds
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25
Q

What is a positive tropism?

A

Growth towards a stimulus

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26
Q

What is a negative tropism?

A

Growth away from a stimulus

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27
Q

What is the stimulus for geotropism?

A

Gravity

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28
Q

What is the stimulus for thigmotropism?

A

Touch

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29
Q

What is the stimulus for electrotropism?

A

Electric fields

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30
Q

What are the only 2 places in a plant where growth can occur?

A

Shoots and meristems

31
Q

How do gibberellins affect stem length?

A

More gibberellins mean a longer stem

32
Q

What stimulates a plant seed to start producing gibberellins?

A

Absorption of water

33
Q

What do gibberellins do when produced in seeds?

A

Produce proteases and amylases

34
Q

What do the proteases and amylases do in seeds?

A

Cause a store of protein to be built up, which helps growth and energy release in the seed

35
Q

What acts as an antagonist to gibberellins in seeds?

A

ABA

36
Q

What determines when a seed will germinate?

A

The relative levels of ABA and gibberellins

37
Q

What 2 pieces of experimental evidence indicate that gibberellins are involved in seed germination?

A
  1. Mutant seeds with no gibberellin production gene do not germinate 2. If gibberellin biosynthesis inhibitors are applied to seeds, they do not germinate
38
Q

What is an example of an auxin?

A

Indoleacetic acid (IAA)

39
Q

Where are auxins produced?

A

Tips of shoots and roots, meristems

40
Q

What shoot do auxins stimulate the growth of?

A

The main, apical shoot

41
Q

What do auxins affect about the cell wall?

A

They make it more plastic and stretchy

42
Q

How do auxins make cell walls more plastic?

A

They bind to receptors and cause a fall in pH to around 5, the optimal pH for enzymes which keep the cell wall plastic

43
Q

What happens to auxins as cells mature and what does this cause?

A

They are destroyed, causing the enzymes maintaining cell wall plasticity to be destroyed and meaning that the cell wall becomes more rigid and fixed in place

44
Q

High levels of auxins suppress the growth of what?

A

Lateral shoots

45
Q

How do auxins cause apical dominance?

A

At the top of the shoot there are high levels of auxins which inhibit lateral shoot growth, causing the apical shoot to grow better and be dominant. As you move further down the plant auxin levels fall and the lateral shoots become more pronounced

46
Q

What experimental evidence is there for the role of auxins in maintaining apical dominance?

A

If the apical shoot is removed, apical dominance stops due to a lack of auxins, and this can be reversed by applying auxins to the cut shoot tip

47
Q

What do low levels of auxins promote except lateral shoot growth?

A

Root growth

48
Q

What are 4 types of plant defence against herbivory?

A
  1. Physical defences 2. Chemical defences 3. Pheromones 4. Folding in response to touch
49
Q

What plant is used folding its leaves in response to touch as a defence strategy?

A

Mimosa pudica

50
Q

How does folding its leaves help defend Mimosa pudica against herbivory?

A

Can knock insects off and startle larger predators

51
Q

What are 4 examples of plant physical defences against herbivory?

A
  1. Barbs/thorns 2. Hairy leaves 3. Stings 4. Fibrous and inedible tissue
52
Q

What are 3 types of plant chemical defences against herbivory?

A
  1. Tannins 2. Alkaloids 3. Terpenoids
53
Q

How do tannins protect plants against herbivory?

A

They are very bitter and astringent tasting, and are also toxic to insects

54
Q

How do alkaloids protect plants against herbivory?

A

Bitter tasting, affecting metabolism of animals

55
Q

How do terpenoids protect plants against herbivory?

A

Can act as toxins to insects and fungi which attack the plant

56
Q

What is a pheromone?

A

A chemical made by an organism which affects the social behaviour of other members of the species

57
Q

Why do plants not use pheromones much?

A

They do not behave socially

58
Q

What are 2 examples of plants using pheromones?

A
  1. Some plants can release chemicals in their root systems to tell their neighbours that they are suffering from water stress 2. When attacked by insects, maple trees release a pheromone which causes other leaves on the tree to prepare chemical defences such as callose
59
Q

What are VOCs and how do plants use them?

A

Chemicals which act as pheromones for other organisms, particularly insects. Plants can use these in a variety of ways- they can attract their attackers’ predator, or create chemicals to repel their attackers

60
Q

What form at nodes on plant stems containing meristems?

A

Branches

61
Q

What type of phototropism do shoots and roots display?

A

Shoots positive, roots negative

62
Q

How do auxins cause cell elongation?

A

The plasticity of cell walls which they create allows the cell to expand as they absorb water

63
Q

What do increased light levels do to auxins?

A

Cause the auxins to diffuse away from the light source

64
Q

What causes plants to grow more quickly in the dark?

A

Gibberellins

65
Q

Why does it make sense that plants grow more quickly in the dark?

A

Would allow them to move towards light more quickly

66
Q

How does ethene cause fruit ripening?

A

Increased ethene levels cause increased respiration and increased carbon dioxide levels, causing ripening

67
Q

Why is it advantageous for fruit to be unripe during transport?

A

It is harder, as starch is converted to sugar during ripening

68
Q

What type of plant hormone does rooting powder contain?

A

Auxins

69
Q

How is rooting powder used?

A

You dip a cut stem in it and it increases the chances of roots forming

70
Q

What type of plant cloning are hormones especially vital in?

A

Micropropagation

71
Q

What are 4 advantages of hormonal weedkillers?

A
  1. Cheap 2. Can be plant species-specific 3. Non-harmful to animals 4. Can be used in fields of monocot crops to kill dicot weeds
72
Q

How do hormonal weedkillers often work?

A

They use synthetic auxins to stimulate unsustainable growth in the weeds

73
Q

What is Synergism

A

This is where two hormones work together, complementing each other causing a greater response than they would on their own.

74
Q

What is Antagonism

A

This is where two hormones have an opposite affect on each other e.g. one promoting plant growth and one inhibiting it. The balance between the response will determine the plant response.

A Level Biology OCR A (23 decks)

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