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Biology OCR A A level > Plant Hormones > Flashcards

Plant Hormones Flashcards

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1
Q

Define ‘plant hormones’

A

Chemicals that are produced in one region of the plant and transported both through transport tissues and from one cell to another

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2
Q

What are the 6 roles of auxins?

A 
Control cell elongation
Abscission
Maintain apical dominance
Involved in tropisms
Stimulate release of ethene
Involved in fruit ripening
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3
Q

What are the 3 roles of gibberellins?

A

Causes stem elongation
Trigger the mobilisation of food stores in a seed at germination
Stimulate pollen tube growth in fertilisation

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4
Q

What are the 2 roles of ethene?

A

Causes fruit ripening

Promotes abscission in deciduous trees

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5
Q

What are the 3 roles of ABA?

A

Maintains dormancy of seeds and buds
Stimulates cold protective responses
Stimulates stomatal closing

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6
Q

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

A

Plant hormones work at low concentrations so isolating them and measuring changes is difficult
Multiple interactions between chemical systems so difficult to isolate one chemical system

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7
Q

Explain the process of how germination is triggered

A

Seed absorbs water and the embryo is activated
Gibberellins start to be produced
Stimulates production of enzymes that breakdown the food stores of the seed
Embryo plant uses the food stores to produce ATP for building materials so they can grow and break out seed coat
Gibberellins switch on genes which code for amylases and proteases which are key for germination

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8
Q

Give 2 pieces of evidence that support the role of gibberellins in the germination of seeds

A

Mutant varieties of genes have been produced without gibberellins and they do not germinate. When fertilised with gibberellins externally they germinate.
Gibberellin biosynthesis inhibitors are applied to seeds, they don’t germinate as they cannot break dormancy

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9
Q

Give an example of an auxin

A

IAA- indoleacetic acid

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10
Q

Where are auxins produced?

A

Tips of roots and shoots and in the meristems

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11
Q

How does lateral growth in a plant occur?

A

Apical bud removes

Decrease in the concentration of auxins leads to the growth of lateral shoots

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12
Q

How does apical dominance occur?

A

High concentrations of auxins inhibit the growth of lateral shoots and apical shoots is stimulated

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13
Q

Explain the mechanism of action of auxin

A

Auxin binds to receptors on the cell membrane
H+ ions are actively pumped across the membrane into the cell wall
Build up of H+ ions lowers the pH to 5
Decrease in pH activates proteins called expansins
Cellulose cell wall becomes more plastic and there is cell expansion

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14
Q

What are the benefits of having low levels of gibberellins?

A

The plants are less vulnerable to damage by weather and harvesting

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15
Q

Define synergism

A

Different hormones working together, complimenting each other and giving a greater response than they would have individually

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16
Q

Define antagonism

A

Substances have opposite effects, the balance between them determining the response

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17
Q

Give 5 abiotic stresses

A 
Seasonal changes in day length
Temperature changes
Lack of water
Too much water
High wind
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18
Q

Why is not efficient for plants to continue photosynthesizing through winter?

A

As plants need to produce enough glucose to support respiration in leaves
Glucose required for chlorophyll based process that protect the plant against freezing

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19
Q

How do deciduous trees combat seasonal changes and the inefficiency of photosynthesis?

A

Lose all of their leaves in the winter and remain dormant until the days lengthen and temperatures rise

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20
Q

Explain the phenomenon that is ‘wind rock’

A

Trees in full leaf are top heavy
During winter months there are often heavy winds
Heavy winds can cause uproot which damages the roots.
Stems may break which damages the xylem and phloem tissue in the stem.

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21
Q

How do trees respond to ‘wind rock’?

A

Losing all their leaves in winter months to make them less vulnerable as less heavy

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22
Q

Explain how ethene triggers abscission

A

Ethene is produced when the days get shorter
Ethene triggers the genes to switch on
Enzymes produced
Enzymes digest and weaken the cell walls of the cells in the separation zone
Vascular bundles supplying the leaf are sealed off and the cells bellow the abscission zone swell
Leaves are pushed off

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23
Q

How does the plant respond to leaf loss via abscission?

A

Fatty material deposited in the cells on the stem side of the separation layer

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24
Q

What is the abscission zone?

A

Two layers of cells that are sensitive to ethene

25
Q

Define photoperiodism

A

Physiological response to the length of the night/dark period

26
Q

What process are affected by the photoperiod?

A

Breaking of dormancy

Time of flowering

27
Q

What causes the sensitivity of plants to dark length?

A

A light sensitive pigment called phytochrome

28
Q

How do plants prevent freezing?

A

Plants produce chemicals which activate the genes needed to produce sugars and amino acids
Substances dissolve in the cell sap of the vacuole
The sap lowers the freezing point preventing the sap from freezing

29
Q

What would occur if the sap of a cell froze?

A

The cell would expand and rupture the cell membrane

30
Q

What hormone causes stomatal closing?

A

ABA

31
Q

How does ABA cause stomatal closing?

A

ABA binds to receptors on the guard cell membranes.
Specific ion channels open causing calcium ions to enter the cytosol from the vacuole
Increased calcium ions cause other ion channels to open, K+ leaves the cell
Cells water potential increases so water leaves the cell by osmosis
Cell becomes flaccid ands stomata closes

32
Q

When is ABA produced and where?

A

Released in times of water shortage

Produced in roots and transported to the leaves

33
Q

What is herbivory?

A

The process by which herbivores eat plants

34
Q

Give 7 physical defences that plants tend to have

A 
Thorns
Barbs
Spikes
Spiny leaves
Fibrous and inedible tissue
Hairy leaves
Stings
35
Q

What are the 4 main types of chemical defence?

A

Tannins
Alkaloids
Terpenoids
Pheromones

36
Q

How do tannins act as chemical defences?

A

Bind to digestive enzymes produced in the saliva and inactivate them

37
Q

Give 2 examples of things rich in tannins

A

Tea

Red wine

38
Q

Give 4 examples of alkaloids

A

Caffeine
Nicotine
Morphine
Cocaine

39
Q

How do alkaloids work?

A

Act as drugs that affect the metabolism of the animals that take them in

40
Q

Give 2 examples of terpenoids

A

Citronella

Pyrethrin

41
Q

What a is a pheromone?

A

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

42
Q

What is a phototropism?

A

A plant response to light

43
Q

What is a geotropism?

A

A plant response to gravity

44
Q

What is a thigmotropism?

A

A plant response to touch

45
Q

What is chemotropism?

A

A plant response to chemicals

46
Q

What are phototropism’s the result of?

A

The movement of auxins across the shoot or root if exposed to light that is stronger on one side than the other

47
Q

What happens to the direction of plant growth if a plant is exposed to more light on one side than the other?

A

The shoots of the plant will grow towards the light

Roots of the plant will grow away from the light

48
Q

What happens to plant growth if a plant is exposed to light but the shoot tip is removed? Why?

A

No response

The tip must either detect the stimulus or produce the messenger as its removal prevents any response

49
Q

Compare the growth of plants in the dark with those in the light

A

The growth will be greater in the dark because plants are searching for light, and seedlings want to reach the light to prevent competition

50
Q

In normal conditions what type of gravitational stimulus do plants have?

A

A unilateral gravitational stimulus

51
Q

What are the typical geotropisms seen by roots and shoots?

A

Shoots- negatively geotrophic (grow away from gravitational pull)
Roots- positively geotrophic (grow towards gravitational pull)

52
Q

What are the two ways of investigating geotropisms?

A

Using a clinostat

Seeds in petri dishes stuck to the wall rotating every two hours

53
Q

What is a climacteric fruit?

A

A fruit that continues to ripen after it has been harvested

54
Q

How do plants continue to ripen after they’ve been picked?

A

Produce ethene which causes a series of chemical reactions

This can increase respiration rate

55
Q

How are fruits chemically ripened?

A

Sprayed with ethene

56
Q

Explain how auxins are used as hormone rooting powder

A

Propagates new plants
Small piece of stem cut from the plants
Dip end of cut stem into hormone rooting powder
Contains auxins
Which causes cell division and elongation

57
Q

Explain how auxins are used as weedkillers

A

Auxins are sprayed onto fields where they acts as selective weed killers
Dicots absorb
Auxin stimulates rapid apical growth in dicots so plants outgrow themselves

58
Q

What are gibberellins used for commercially?

A

Delaying ripening and ageing in fruit

Improve size and shape of fruits

59
Q

What are cytokinins used for commercially?

A

Prevent ageing of ripened fruit and micropropagation

Biology OCR A A level (17 decks)

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