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Biology - Module 5 > Plant Responses > Flashcards

Plant Responses Flashcards

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1
Q

what are some plant responses to abiotic stress

A

leaf loss in deciduous plants

daylength sensitivity

leaf fall

preventing freezing

stomatal control

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2
Q

describe how leaf loss in deciduous plants is beneficial for the plant

A

Trees in temperate climates – great environmental changes in year

Glucose required for respiration to maintain leaves + to produce chemicals from chlorophyll to protect against freezing > glucose produced from respiration

Leaf tree more likely to be damaged + blown over

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3
Q

how do plants prevent freezing + why is this necessary

A

Cytoplasm + sap in vacuoles – have solutes = lower freezing point

Produce sugars / polysaccharides / amino acids – act as antifreeze

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4
Q

how do plants control stomata + why is this necessary

A

Shut stomata for drought – reduce transpiration

Controlled by ABA

Open stomata – cool plant

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5
Q

what are the physical defences to herbivory

A

thorns

barbs

spiny leaves

fibrous + inedible tissue

hairy leaves

folding in response to touch

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6
Q

what is an example of a plant that folds in response to touch

A

Mimosa pudica plant

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7
Q

how does the Mimosa pudica plant fold in response to touch

A

leaflets of touch-sensitive leaves fold in rapidly when touched

caused by rapid water uptake (+ therefore increase in volume) in cells at the base of each leaflet and rapid loss of water from (+ therefore collapse of) adjacent cells

maybe local bioelectrical signal

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8
Q

what are the chemical defences in response to herbivory

A

tannins

alkaloids

terpenoids

pheromones

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9
Q

what are tannins and how are they a chemical defence

A

part of phenols – water soluble carbon compound

stored in vacuoles

bitter taste

toxic to insects – bind to digestive enzymes produced in saliva + inactivate them

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10
Q

what are alkaloids and how are they a chemical defence

A

nitrogenous compound

bitter taste

caffeine – toxic to fungi / insects

nicotine – toxin produced in tobacco plants

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11
Q

what are terpenoids and how are they a chemical defence

A

toxin to insect + fungi

neurotoxin = disrupts nervous system

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12
Q

what are pheromones and how are they a chemical defence

A

chemical made by organism that affects social behaviour of other members of same species

if tree attacked – produce pheromones

absorbed by leaves on other branches + other trees

leaves make callose to protect

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13
Q

what is tropism

A

growth movement of a part of a plant in response to a directional stimulus

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14
Q

what type of tropism occurs when the plant grows towards stimulus

A

positive tropisms

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15
Q

what type of tropism occurs when the plant grows away from stimulus

A

negative tropism

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16
Q

what is phototropism in response to + why is it beneficial

A

light

Ensures plants get max light – max photosynthesis

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17
Q

what is geotropism in response to + why is it beneficial

A

gravity

Ensures shoots/roots from germinating seeds grow in the right direction regardless of the orientation of the seed – positive + negative

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18
Q

what is hydrotropism in response to + why is it beneficial

A

moisture

Root tips normally grow towards damper areas in soil – increase access to water

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19
Q

what is thigmotropism in response to + why is it beneficial

A

touch

Important in climbing plants – adapted to climb as it provides greater access to light etc. allows these plants to detect living/non-living support + curl around it

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20
Q

what is chemotropism in response to + why is it beneficial

A

chemicals

Pollen tubes grow down the flower’s stigma towards the ovules

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21
Q

are shoots positively or negatively phototrophic

A

positively phototrophic

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22
Q

describe the experimental evidence for phototropism

A
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22
Q

are roots positively or negatively phototrophic

A

negatively phototrophic

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23
Q

describe how phototropism occurs

A

high conc of auxins supress growth of lateral shoots

diffuses to shaded side of shoot tip

causes active transport of H+ into cell wall

disruption of H bonds between cellulose molecules

make cell more permeable

cells on shaded side elongate faster due to higher turgor pressure

Once growing directly towards light = transport of auxin stops

grows straight towards light

24
Q

describe the experimental evidence for movement of auxins

A
25
Q

how does rate of growth change in response to light

A

in dark p reach surface fast to get light

gibberellins – responsible for extreme elongation of internodes (region between leaves on cell)

when exposed to light – growing slower

26
Q

are shoots positively or negatively geotropic

A

negatively geotropic

27
Q

are roots positively or negatively geotropic

A

positively geotropic

28
Q

main roles of auxins

A

cell elongation

prevent lead fall - abscission

maintain apical dominance

involved in tropism

involved in fruit ripening

29
Q

describe the experimental evidence for geotropism

A
30
Q

main roles of gibberellins

A

stem elongation

trigger mobilisation of food stores in seeds at germination

stimulate pollen tube growth

31
Q

main roles of ethene

A

fruit ripening

abscission in deciduous trees

32
Q

main roles of ABA / abscisic acid

A

maintain dormancy of seeds + buds

stimulates cold protective responses - antifreeze productions

stimulates stomatal closing

33
Q

state the hormones involved in seed germination

A

gibberellins

ABA

34
Q

what are gibberellins role in seed germination

A

When seed is shed from the parent plant = dormant – little water + metabolically inactive

(allows survival in harsh conditions)

when conditions are right - seed absorbs water

produces gibberellins

Gibberellin molecules diffuse into the aleurone layer + stimulate cells to make amylase

amylase hydrolyses starch molecules in the endosperm for monocot seeds
(or cotyledons in dicot seeds)

produces soluble maltose molecules

maltose is converted to glucose and transported to the embryo

respired by the embryo

breaking dormancy + providing energy for growth

35
Q

how does the gibberellin molecules stimulate cells to make amylase

A

been shown that gibberellin does this by regulating genes = increase in transcription of mRNA coding for amylase

36
Q

describe ABA’s role in seed germination

A

has opposite effect to gibberellin – antagonist

maintaining dormancy by inhibiting amylase production

37
Q

how is seed germination controlled overall

A

determined by the balance of ABA + gibberellins

38
Q

describe briefly how seed germination occurs

A
39
Q

what is an endosperm

A

a starch-containing energy store surrounding the embryo

40
Q

what is an aleurone layer

A

a protein-rich layer on the outer edge of the endosperm

41
Q

state the hormone involved in leaf loss of deciduous plants

A

auxin

ethene

42
Q

describe how ethene is involved leaf loss occurs in deciduous plants

A

Falling light levels – falling levels of auxin

Produce gas hormone ethene

Base of leaf stalk – abscission zone
(Has 2 layers of sensitive cells to ethene)

Ethene causes new enzyme production in there

Digest + weaken cell wall in outer layer of abscission zone // separation layer

Vascular bundles sealed off

Fatty material deposited on stem side of separation layer = form protective scar

Leaf separates from plant

43
Q

describe how auxin is involved leaf loss occurs in deciduous plants

A

inhibit leaf loss + produced in young leaves = leaf stalks insensitive to ethene

The concentration of auxins in leaves decreases as they age until leaf loss can once again occur in response to ethene

44
Q

state the hormones involved in stomatal closure

A

ABA

45
Q

describe how stomatal closure occurs

A

water stress = abscisic acid (ABA) produced

Guard cells have ABA receptors on cell surface membranes

ABA binds receptors

inhibits proton pumps
(stops active transport of H+ out of guard cells)

+ causes Ca2+ to move into cytoplasm of the guard cells via cell surface membranes

Ca2+ = second messengers:
- cause channel proteins to open
- negatively charged ions leave guard cells
- stimulates the opening of further channel proteins
- allow K+ ions to leave guard cells

loss of ions increases the water potential of the guard cells

Water leaves guard cells by osmosis

become flaccid = stomata close

46
Q

how does auxins cause apical shoot growth

A

auxins stimulated in meristem cells

diffuse away from tip

bind to receptor sites

vacuoles form + low pH develops

low pH of cells walls - keep flexible

allows cells to explain as they absorb water

vacuoles get bigger + cell walls stretch

large central vacuole forms

auxin destroyed by enzymes

cell walls rigid

no further cell elongation

47
Q

what is apical dominance

A

auxins produced at the growing tip at the apex of a plant stem cause the stem to grow upwards + stop lateral buds from growing

48
Q

describe how auxins cause apical dominance

A

high conc of auxins supress growth of lateral shoots

growth in apical shoot stimulated by auxin at tip

lateral shoots inhibited by hormone that moves back down – don’t grow well

further down stem – auxin conc is lower

lateral roots grow more strongly

49
Q

describe the experimental evidence for apical dominance

A

apical bud of the first test plant is removed (decapitated)

allows the lateral buds to grow

second (genetically identical) test plant is decapitated but this time the cut tip immediately replaced with an agar block containing auxin

restores the inhibition of lateral bud growth and no lateral buds grow

50
Q

what is the experimental evidence for the role of gibberellins in stem elongation

A

when given gibberellic acid – grow taller

51
Q

what is the experimental evidence for the role of gibberellins in germination

A

mutant varieties of seeds – lack gene that allows them to make gibberellins

seeds do not germinate

if applied externally – germinate normally

if gibberellin biosynthesis inhibitors applied – no germinate

52
Q

commercial use of ethene

A

stimulate fruit to ripen by increasing respiration rate

used for fruits that are delicate and soft when they are ripe (e.g. bananas) + that can be easily damaged during transport

53
Q

commercial use of auxins

A

rooting powders + micropropagation

hormonal weed killers

unpollinated flower fruit development

produce seedless fruit

54
Q

how is auxin involved in rooting powders

A

auxins = stimulate cuttings to grow new roots

cutting – small piece of stem

if cutting placed in soil + rooting powder – increases chance of roots forming + successful propagation

sold commercially in the form of rooting powders

55
Q

how is auxin involved in hormonal weed killers

A

weeds interfere with crop plant – compete for light / space / water / minerals

weeds – wide leaves

High conc auxin - rapid growth

become distorted and damage + allow pathogens to enter

normal plants fine – narrow leaved + do not absorb a lot of auxin

56
Q

what is the commercial use of cytokinin

A

prevents ageing of ripened fruit

56
Q

what is the commercial use of gibberellins

A

delay ripening

make unpollinated flowers develop fruit

Biology - Module 5 (8 decks)

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