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BIOLOGY A LEVEL > CHAPTER 16 - PLANT RESPONSES > Flashcards

CHAPTER 16 - PLANT RESPONSES Flashcards

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1
Q

What are tropisms

A

Directional growth in response to environmental cues

eg. Light and gravity

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2
Q

What are the key limitations of plants

A

They are rooted - hence not mobile
no rapid responding nervous system

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3
Q

How to plants communicate (cells and with other individuals) and respond to their environment

A

Hormones

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4
Q

Are most plant responses faster or slower than animal responses

A

Slower

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5
Q

What are the roles of the Auxin hormone group?

A

Control cell elongation
Prevent leaf fall (abscission)
Maintain Apical Dominance
Involved in tropisms
Stimulates release of Ethene

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6
Q

What are the roles of the Gibberellin hormone group?

A

Causes Stem elongation
Triggers mobilisation of food stores in a seed at germination
Stimulates pollen tube growth in fertilisation

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7
Q

What are the roles of Ethene

A

Causes Fruit ripening
Promotes abscission in deciduous trees

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8
Q

What are the roles of ABA (abscisic acid)

A

Maintains Dormancy of seeds and buds
Stimulates cold protective responses eg. Antifreeze production, stimulating stomatal closure

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9
Q

What is growth of plants controlled by

A

Plant hormones

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10
Q

Do plant hormones work at high or low concentrations?

A

Low

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11
Q

Why is it difficult for researchers to isolate the role of a single chemical in a response in plants

A

Multiple interactions between different chemical control systems
Plant hormones work at low concentrations

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12
Q

Describe the series of events in seed germination

A

Seed absorbs water, embryo is activated and produces gibberellins

Gibberellins stimulate the production of enzymes that break down the food stores found in the seed.

The food store is in the cotyledons in dicot seeds and the endosperm in monocot seeds

Embryo plant uses these food stores to produce ATP for building materials so it can grow and break out through the seed coat.

Evidence suggests that gibberellins switch on genes which code for amylase and proteases - the digestive enzymes required for germination

ABA acts as an antagonist to gibberellin to control rate of seed germination

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13
Q

What is the experimental evidence supporting the role of gibberellins in seed germination

A

Mutant seed varieties have been Breed which lack the gene to make gibberellins, so the seeds dont germinate. If Gibberellins are applied externally, they germinate normally

If gibberellin biosynthesis inhibitors are applied to seeds, they dont germinate as they cannot make the gibberellins needed for them to break dormancy. If inhibition is removed, or gibberellins are applied, the seed germinates

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14
Q

What is an example of an Auxin

A

Indoleacetic acid (IAA)

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15
Q

What is the general role of Auxins

A

Stimulates growth in plants

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16
Q

Where are Auxins made

A

Cells at tip of the shoots and roots, and in the meristems

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17
Q

What direction do auxins move

A

Down the stem and up the roots in transport tissue

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18
Q

What do Auxins stimulate the growth of

A

Main apical shoot

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19
Q

What effect do Auxins have upon the cell wall

A

Plasticity - causes a more stretchy cell wall

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20
Q

What affect do Auxins have upon the pH after binding to receptors?

A

Fall to about 5

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21
Q

Why is the fall in pH to 5 as a result of auxins affect necessary?

A

To keep cell walls flexible and plastic, as it is the optimum pH for enzymes that carry out this function

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22
Q

What happens to auxin as cells mature

A

It is destroyed

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23
Q

What affect do the destruction of auxins have upon the pH and cell plasticity

A

pH rises so
Enzymes become inactive so
Cell walls become rigid

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24
Q

What are the effects of auxins on plant growth

A

Stimulate growth of main apical shoot

Suppress growth of lateral shoots - prioritising apical shoot

Low concentrations promote root growth/High concs inhibit root growth

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25
Q

What do gibberellins do

A

Affect length of internodes - regions between the leaves on a stem

Involved in germination of seeds and important in elongation of plant stems during growth

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26
Q

What is the proof for gibberellin action

A

Seedlings infected from fungus in Gibberella genus grew tall and thin

Plants without gibberellins are short stemmed

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27
Q

What are the benefits of using gibberellins

A

Dwarf varieties of plants can be bred

Reduces waste, and makes plants less vulnerable to damage from weather and harvesting

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28
Q

What is synergism

A

Different hormones working together, complementing each other and giving greater response than they would on their own

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29
Q

What is antagonism

A

If the hormones have opposite effects eg. one for promoting root growth and one inhibiting it, the balance will determine the response of the plant

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30
Q

Why are chemicals so important in coordinating the growth of plants

A

Plants are multicellular and often large so need coordination

plants don’t appear to have nervous systems so no electrical coordination system

chemicals can be carried in plant transport systems and move from cell to cell to coordinate responses

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31
Q

Give three examples of plant hormones and for each give one function in the plant

A

Auxins - Control cell elongation etc…

Gibberellin - causes stem elongation

Ethene - fruit ripening

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32
Q

Why are hormones such as auxins and gibberellins described as plant hormones

A

Analogous to animal hormones

involved in coordination and control of the plant

made in one place

and carried through the transport system to another region where they have an effect

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33
Q

What are some abiotic stresses a plant faces

A

Day length, cold and heat, lack of water, excess water, high winds, and changes in salinity

34
Q

How do deciduous trees deal with the lack of photosynthesis in colder months

A

Amount of glucose required for respiration to maintain the leaves, producing chemicals from chlorophyll may be too high

Drops leaves and remain dormant

35
Q

What is photoperiodism

A

Plants that are sensitive to lack of light in their environment

36
Q

How do plants deal with a lack of light in the environment

A

Some plants drop leaves

Make other pigments called phytochrome, each absorbing different levels of light

37
Q

How does abcission occur

A

Falling light levels = fewer levels of auxins

Responds to less auxins by producing ethene, which creates an abcission zone, made up of two layers of cells sensitive to ethene

Initiate gene switching in these cells, resulting in production of enzymes, digesting and weakening cell walls in outer layer called the seperation zone

The vascular layer is sealed off, and fatty material is deposited to form a protective layer, finished my wind and low temps
(pg 446)

38
Q

How to plants prevent freezing

A

Cytoplasm of plant cells and the sap in the vacuoles contain solutes which lower the freezing point

Some plants produce sugars, polysaccharides, amino acids and proteins which act as an anti-freeze to prevent cytoplasm from freezing

39
Q

How and why do plants hormonally control their stomata

A

Either to cool down as water evaporates or to conserve water

opening and closing of stomata usually controlled by hormone ABA. Leaf cells release ABA under abiotic stress causing stomatal closure,

Plant roots give an indication to a level of soil water falling hence producing ABA, activating changes in concentration of compounds in guard cells, reducing water poteintial, and turgor, closing the stomata

40
Q

Why is it important for plants to be able to respond to their surroundings

A

They are rooted to the ground so cannot move their bodies

therefore very important that they
are sensitive so they can grow in the right direction and make the best of the circumstances where they have germinated

41
Q

Why do many trees in temperature climates lose all of their leaves in winter

A

The amount of photosynthesis that can take place decreases as day length is reduced and
temperatures fall

so the amount of glucose produced by photosynthesis falls

the amount of glucose needed for respiration to maintain leaves through the winter

and produce chemicals to prevent freezing damage increases

it becomes more efficient to lose the leaves and become
dormant until the days lengthen and temperatures increase again

42
Q

Explain how plant hormones are involved in protecting the plant cells from damage in freezing conditions

A

Falling light levels  decreased concentration of auxin leaves produce hormone ethene 
ethene initiates gene switching in abscission zone at base of leaf stalk  gene switching causes
production of new enzymes  new enzymes digest and weaken cell walls in outer layer of abscission
zone (separation layer)  vascular bundles sealed off, fatty material deposited in cells on stem side
of separation layer  layer forms protective scar when lead falls preventing pathogen entry  cells in
separation zone respond to hormonal cues by retaining water and swelling putting more strain on
outer layer  further abiotic factors finish process  strain is too much and leaf separates from plant
leaving neat waterproof scar

43
Q

Give two more adaptions by which plant cells may be protected against damage by freezing during the winter

A

Chemicals such as abscisic acid

trigger gene switching

so plants make chemicals such as
sugars or proteins

which lower the freezing point of the cytoplasm

or protect the cells against
damage by ice crystals if they do freeze

44
Q

If there is a sudden spell of freezing weather early in the autumn, many plants which can normally survive winter may be killed. Similarly, if there is a late frost several weeks after warm spring weather, plants that have already survived a harsh winter can die. Explain the difference in the response of the plants in these circumstances compared with the winter months

A

Protection mechanisms include leaf loss, production of chemicals to act as antifreeze or ice
protection depend on gene switching, and production of new compounds in response to triggers of day length and temperature which take place over several weeks (2);

sudden early frost – cold
protection mechanisms not in place so cells damaged and plant may be killed

late frost – reverse gene switching has occurred as plants move into summer mode

so levels of protection have fallen

and can’t respond to freezing temperatures so cells destroyed

45
Q

What are some physical defences of plants

A

Thorns, barbs, spikes, spiny leaves, fibrous and inedible tissue, hairy leaves and stings

46
Q

What are some chemical defences of plants to herbivory

A

Tannins - bitter taste to put animals off eating the leaves, toxic to insects, binding to digestive enzymes produced in saliva and inactivating them eg. phenols

Alkaloids - Affecting metabolisms and poisoning them, or acting as toxins in animals. Prevents seed germination in plants eg. tobacco, nicotine, morphine and cocaine

Terpenoids - Essential oils for a plant but often act as (neuro) toxins to insects and fungi that might attack the plant, or repellant eg. pyrethrin

Pheromones - Affect social behaviour of same species - ON ANOTHER FLASHCARD

47
Q

What do pheromones do

A

Affects social behaviour of same species

Maple tree releases pheromone when attacked, leaves absorbed which producing callose to protect from attack, as well as warning other trees

Can tell neighbour it is under water stress

when Cabbages are attacked by capterpillars, it sends out a signal, attracting wasps to come and lays its eggs in the catepillars, which are then eaten alive, protecting the plant

If apple trees are attacked by spider mites, they produce VOCs attracting predatory mites which eat the pests

48
Q

What does the minosa pudica do as well has having common defences (alkaloids and prickles) and how does it work

A

Leaves fold sown and collapse, frightening off herbivores and dislodging insects

Recovers over 10-12 minutes as a result of K+ movement into specific cells, followed by osmotic water movement

49
Q

what is herbivory

A

Herbivory is the process by which herbivores eat plants

50
Q

Describe two examples of chemical defences against herbivory by animals, explaining how they protect the plant and how they are used by people

A

Eg. tannins
bitter taste puts animals off eating leaves OR toxic to insects
flavour tea and red wine

Alkaloids
affect metabolism, often poison animals OR prevent
germination in plants OR stop roots of neighbouring plants spreading OR taste bitter

insecticide
terpenoids; toxic to insects OR repel insects; used as insect repellent

51
Q

Why are the chemicals sometimes known as plant pheromones not strictly pheromones

A

A pheromone is a chemical made by an organism which affects the social behaviour of other members of the same species

plants are not mobile and do not behave socially so pheromones are not entirely appropriate

52
Q

Why is it so important that these chemicals are volatile

A

They must travel through the air inside or outside of the plant to carry their message

so they must be in the form of a gas or vapour

52
Q
A
52
Q

Give two examples of how these chemicals may be used to protect a plant against herbivory, including a discussion as to whether your examples are pheromones or not

A

For example, pheromone produced by maple tree when attacked by insects that is absorbed by leaves on other branches and nearby trees
that make protective
chemicals such as callose (1); pheromone because acts between members of the same species to
affect their behaviour (1); OR not a pheromone as does not affect behaviour, only biochemistry.

Apple
tree attacked by spider mites produce chemicals that attract predatory mites (1); that come and
destroy the spider mites attacking the tree (1); NOT a pheromone as affects the social behaviour of a
different species (the predatory mites) not the same species (apple trees)

53
Q

What is phototropism

A

The growth of plants in response to light which comes from one direction

54
Q

What is gravitropism

A

The growth of plants in response to gravity

55
Q

Why must the root grow upwards towards the light source

A

maximise photosynthesis

56
Q

Why must a plants root grow downwards

A

To provide support, minerals and water

57
Q

Why is most of the tropisms research conducted on young seedlings

A

Easy to work with, manipulate, and growing and responding rapidly - so changes show up quickly

58
Q

Why are dicot seeds harder to manipulate than a monocot

A

Monocots emerge as the shoot is a single spike with no apparent leaves

59
Q

What is the result of unilateral light from the side of a plant shoot, and an explanation

A

Shoot bends towards light

Shoot is positively photographic, bending occurs behind the tip
(pg 452)

60
Q

What is the result of light from the side of a plant shoot with a shoot tip removed, and an explanation

A

No response

Tip must either detect the stimulus or produce the messenger as its removal prevents any response
(pg 452)

61
Q

What is the result of light from the side of a plant shoot with a light proof cover placed over the intact tip of shoot, and an explanation

A

No response

The light stimulus must be detected by the tip
(pg 452)

62
Q

What is the result of light from the side of a plant shoot with a thin, impermeable barrier of mica on the light side , and an explanation

A

Bends towards the light - movement of chemical down shaded side

Mica on illuminated Side of the shoot allows the hormone to pass, only down the shaded side where increases growth and causes, bending
(pg 452)

63
Q

What is the result of light from the side of a plant shoot with mica inserted on shaded side, and an explanation

A

No response

Movement of chemical down shaded side is prevented by mica

Auxins travel up and down shaded side
(pg 452)

64
Q

What is the result of light from the side of a plant shoot with tip removed, gelatine block inserted and tip replaced, and an explanation

A

Bends towards the light - movement of chemical down shaded side

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
(pg 452)

65
Q

Describe the result of the experiment where a shoot is split down the middle and one isn’t, and their auxins responses to light

A

Describe following data
Kept in dark:
Intact shoot: 25.5
Split shoot: 24.1

Unilateral light:
I: 26.2
S: 23.4

Shoot in unilateral light but undivided:
I: 31.0 : 12.5
S: 23.0 : 24.7
(pg 453)

66
Q

Why do plants grow quicker in the dark

A

In the dark, the biological imperative grow up was rapidly to reach the light to be able to photosynthesise. The seedlings that break through the soil first will not have to compete with the other seedlings for light

Evidence suggests that gibberellins are responsible for the extreme elongation of the internodes, where the plant is grown in the dark.

What is a plant as exposed to the light a slowing of upward growth is valuable resources can be used for synthesising leaves, extend an overall growth, hence the gibberellin level will fall

67
Q

What is an etiolated plant and what are its key features

A

The rapid upward growth, which takes place in a plant grown in the dark

They are thin and pale, because the plant is deprived of little light chlorophyll that develops in the leaves

68
Q

What are shoots and roots in respect to gravity

A

Shoots: negatively gravitropic
Roots: positively gravitropic

69
Q

What is a tropism

A

Plant growth responses to a directional stimulus

70
Q

Explain what is meant by phototropism and geotropisms

A

Phototropisms: Plant responses to unilateral light

Geotropisms: Plant responses to gravity

71
Q

Describe the different phototropic and geotropic responses in shoots and roots

A

Shoots positively phototropic and negatively geotropic

roots negatively phototropic and positively geotropic

72
Q

If a block of butter is used in auxin phototropisms experiment instead of the gelatine block, there is no response in the decapitated shoot. Explain how this informs scientists that the message is water soluble

A

Water soluble substances will pass through gelatin as it is made up of water

butter is a fat so water soluble substances will not pass through it, but fat soluble substances will

gelatine allows auxin to pass through it and so the response to unilateral light is maintained

butter prevents auxin moving through it so the response to unilateral light is lost

indicating that auxin is water soluble and not fat soluble

73
Q

Originally scientists thought geotropisms were the result of auxin movements in response to gravity. Investigate current models of how do you tropisms occur and write a brief report

A

the importance of space flight in the investigation of geotropism should be mentioned for full marks (1);

the role of the root cap (1);

gravity perceiving cells (1);

amyloplasts and sedimentation under gravity

role of calcium ions

work in space to remove gravity

possibility of magnetic gradients

role of auxin

74
Q

How are plant hormones used commercially

A

Auxins can produce seedless fruit

Ethene promotes fruit dropping

Cytokinins are used to prevent ageing of ripened fruit and products such as lettuces, and in micropropagation to control tissue development

Gibberellins can be used to delay ripening and ageing in fruit to improve the size and shape of fruits and in beer brewing to speed up the malting process

75
Q

How are plant hormones used to control the ripening of fruit

A

Ethene involved in natural fruit ripening

used to ripen fruit such as bananas, mangos, tomatoes etc. at desired time

cytokinins and gibberellins can be used to delay fruit ripening

76
Q

Why is it commercially important to be able to control fruit ripening

A

Ripe fruit is easily damaged in transport

once fruit is ripe it has a finite life before it goes off

If fruit is transported unripe and hard

much less likely to be damaged and doesn’t start to go off

controlled ripening when needed gives uniform product

and minimises waste

77
Q

How do synthetic weedkillers work and why are they important

A

Weeds interfere with crop plants, competing for light, space, water and minerals, with low toxicity to animals

Hormone Imbalance can interrupt metabolism of the plant and lead to death.

If synthetic dicot auxins are applied as weedkiller, they are absorbed by broad leaved plants (weed), increasing growth so it is unsustainable so they die. Narrow leaved (monocot usually) crop plants (crop) are not affected and continue to grow normally

78
Q

What are climacteric fruits

A

plants that continue to ripen after the are picked

79
Q

How do hormone rooting powders propagate new plants from plant cuttings

A

A cutting is a small piece of stem with some leaves on

If this is placed in compost or soil, roots may appear

Dipping the cut stem into hormone rooting powder increases the chances of root forming

BIOLOGY A LEVEL (24 decks)

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