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biology module 5 > plant responses > Flashcards

plant responses Flashcards

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1
Q

outline 3 roles of hormones in plants

A
  • cellular communication
  • to respond to external stimuli
  • to signal to other plants or species nearby e.g. protecting themselves from pests/insects or producing chemical defences against herbivores
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2
Q

what are the 5 main plant hormones

A

gibberellins
ethene
auxins
cytokinins
abscisic acid - ABA

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3
Q

where are gibberellins found

A

plant seeds and apical portions of roots and shoots

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4
Q

what do gibberellins do in plants

A

when seeds absorb large amounts of water, gibberellin is released to start the process of germination - it stimulates enzymes to break down / metabolise food stores

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5
Q

what are gibberellins used for by humans

A

gibberellins are used to end seed dormancy, so seeds can be planted all year round
they are also used to control fruit ripening

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6
Q

where is ethene found

A

leaves, stems and young fruits

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7
Q

what does ethene do in plants

A

it promotes leaf fall in deciduous trees and causes fruit ripening

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8
Q

what is ethene used for by humans

A

since it affects plant growth, it can be used alongside gibberellins to prevent spoiling / ripening / overripening of fruit during transport, and then to promote fruit ripening when in stores

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9
Q

where are auxins found

A

found in shoot apical meristems and roots

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10
Q

what do auxins do in plants

A

auxins are growth factors, produced in tips of roots and shoots, in shoots they cause the stem to grow upwards while also stopping lateral buds from growing, promoting apical dominance
they also prevent leaf fall

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11
Q

why is apical dominance important in a plant

A

the higher up a plant grows the more light it has access to

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12
Q

how do changing auxin levels affect other hormones in a plant

A

if auxin levels / production is low, ethene is stimulated

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13
Q

give an example of a specific auxin

A

indoleacetic acid - IAA

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14
Q

what happens if the growing tip of a plant is removed

A

this is where the auxins are found / produced, so this means the source of auxins has also been removed, so apical dominance is no longer promoted - with time the lateral shoots will grow and curl towards the light

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15
Q

what are auxins used for by humans

A

they are used as selective weed killers - since they are growth hormones, they cause weeds to grow very quickly, meaning they absorb nutrients from soil at a faster rate, and so weed killer is also absorbed much faster

they are also used to promote growth of plant cuttings as they allow the roots to develop quickly so plants can self sustain

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16
Q

where are cytokinins found

A

they are produced in the roots and transported around the plant from there

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17
Q

what do cytokinins do in a plant

A

they work alongside auxins to stimulate cell division, and play a role in determining the course of differentiation

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18
Q

where is ABA found

A

in mature leaves, fruits and root caps

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19
Q

what does ABA do in a plant

A

it slows and inhibits growth, maintains seed dormancy and is involved in stomatal closure - it can start to accumulate when plants experience stresses, such as changes in temperature, water levels or salinity

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20
Q

outline how ABA could help a plant deal with water stress

A

low water levels are detected by the plant, causing ABA to accumulate and travel to leaves, where high levels of ABA cause the stomata to close, so less water is lost via transpiration

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21
Q

what is ABA used for by humans

A

it is used to prevent seed development, such as to produce seedless fruit, which is easier to sell

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22
Q

what are the 6 stages of life in a plant

A

seed dormancy
germination
growth to maturity
flowering
fruit development
leaf abscission

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23
Q

what hormones are involved in seed dormancy

A

ABA

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24
Q

what hormones are involved in germination

A

gibberellins

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25
Q

what hormones are involved in growth to maturity

A

gibberellins, auxins, cytokinins

26
Q

what hormones are involved in flowering

A

mostly gibberellins, auxins, cytokinins
also ethene

27
Q

what hormones are involved in fruit development

A

mostly cytokinins and ethene
also gibberellins and auxins

28
Q

what hormones are involved in leaf abscission

A

ethene and ABA

29
Q

what is the basic structure of a seed

A

a seed is a kind of capsule containing the plant embryo
it consists of an aleurone layer, which surrounds the endosperm (like the cytoplasm), which contains starch reserves, as well as the actual embryo

30
Q

outline how gibberellins control seed germination

A

1- water is absorbed by the seed
2- this causes gibberellins to be synthesised by the embryo
3- gibberellins stimulate aleurone layer cells to synthesise amylase
4- amylase hydrolyses starch to form maltose
5- maltose is converted to glucose
6- glucose is transported to the embryo providing energy for growth

31
Q

outline how hormones control stomatal closure

A

1- ABA binds to receptors on the guard cell membrane
2- Ca2+ ions enter guard cells via channels
3- K+ ions leave guard cells via channels
4- this causes water to leave the guard cells by osmosis to increase water potential inside
5- the guard cells become flaccid, and bend to close the stomata

32
Q

when + why does leaf loss occur in plants

A

it can occur during winter when absorption of water is difficult due to frozen soil

it can also occur in hot dry climates to minimise water loss

33
Q

how does leaf abscission occur

A

a layer of parenchyma cells - called the abscission layer - develops at the base of the leaf stalk, which have thin walls that are easily broken
ethene then stimulates the break down of cell walls in the abscission layer
this causes the leaves to drop off

  • in young plants auxins also play a role in leaf loss as they make leaf stalks insensitive to ethene
34
Q

what happens to auxin concentration in plants as they grow

A

as plants age the conc of auxins decreases

35
Q

how do auxins regulate growth

A

by controlling cell division and elongation

36
Q

how is growth regulated differently in the shoots and roots

A

in the shoots growth is stimulated
in the roots growth is inhibited

37
Q

how to tropisms work

A

movement and changes in concentrations of auxins allows plants to respond to environmental factors

38
Q

tropism definition

A

a directional response

39
Q

phototropism definition

A

a plants directional response to light

40
Q

what kind of phototropism is displayed in the shoots and roots

A

positive phototropism in the shoots, negative phototropism in the roots

41
Q

outline how shoots show positive phototropism

A

when a plant received light on on side, the auxins will move to the other side of the plant
this causes the shaded side to grow and elongate more
as a result the plant bends towards the light

42
Q

why is positive phototropism in shoots useful

A

this allows plants to face the sun, which increases rates of photosynthesis

43
Q

outline how roots show negative phototropism

A

when roots grow, the auxins move to the shaded bottom side, but here is inhibits growth
this means the top side nearer to the light elongates more
as a result roots grow down

44
Q

why is negative phototropism in roots useful

A

it increases the probability of roots growing into soil towards water

45
Q

gravitropism / geotropism definition

A

a plants directional response to the earths gravitational field

46
Q

outline how roots show positive geotropism

A

auxins in the root tips is pulled down towards the bottom side of the roots
this inhibits growth causing the top to bend downwards

47
Q

hydrotropism definition

A

a plants directional response to water - tendency to grow towards water

48
Q

chemotropism definition + example

A

a plants directional response to chemicals
e.g. pollen tubes grow down the style towards the ovary where fertilisation happens

49
Q

thigmotropism definition

A

the tendency of a plant to wind around other plants or solid structures to allow it to grow + support itself

50
Q

nastic movement definition

A

a non directional response

51
Q

what are 4 examples of abiotic stresses plants can response to

A

changing daylight hours
freezing
heat
water availability

52
Q

how have plants adapted to cope with daylight hours

A

seasonal changes in hours of daylight impacts the amount of photosynthesis possible
if the amount of glucose needed for respiration to maintain leaves is greater than the amount of glucose being produced, leaf fall will occur

53
Q

how have plants adapted to cope with freezing temperatures

A

decreasing temperatures can cause plant cells to freeze, which can disrupt cell surface membranes and kill cells
to prevent this, plant cells have lots of solutes in cytoplasm and cell sap which decreases the freezing point of the cells, and cells can also produce proteins that act antifreeze during winter

54
Q

how have plants adapted to cope with heat

A

stomatal opening/closing helps plants to deal with heat - if it is very hot stomata will open to allow water to cool down the plant as it evaporates out of leaves

55
Q

how have plants adapted to cope with water availability

A

stomatal opening/closing helps plants to deal with water - if water is scarce, stomata will close to conserve water, as a result if ABA production in roots which then travels to guard cells

56
Q

what are 2 ways that plants have adapted to biotic stresses

A

physical defences
chemical defences

57
Q

give 6 examples of a physical plant defence + its function

A

thorns, barbs, spikes, spines, inedible tissue, stings, etc
- these discourage herbivory, protecting plants

58
Q

give 4 examples of chemical defences in plants

A

tannins
alkaloids
terpenoids
pheromones

59
Q

what are tannins + how do they act as a plant defence

A

they are part of a group of compounds called phenols

they make up 50% of dry weight in the leaves, and are bitter tasting to animals, and toxic to microbes as they bind to and inhibit digestive enzymes in saliva - discourages herbivory

60
Q

what are alkaloids + how do they act as a plant defence

A

they are part of a large group of bitter tasting compounds

they can act as drugs, affecting the metabolism of animals or poisoning them
e.g. caffeine - toxic to fungi + insects, nicotine, morphine, cocaine

61
Q

what are terpenoids + how do they act as a plant defence

A

these are compounds which form essential oils, and they can often act as toxins to insects + fungi e.g. pyrethin in crysanthemums

they also repel insects

62
Q

what are pheromones

A

these are chemicals made by an organism which affect the social behaviours of other members of the same species

biology module 5 (7 decks)

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