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Biology - Module 5 > Plant Responses > Flashcards

Plant Responses Flashcards

(58 cards)

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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

Study These Flashcards
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
describe the experimental evidence for movement of auxins
25
how does rate of growth change in response to light
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
are shoots positively or negatively geotropic
negatively geotropic
27
are roots positively or negatively geotropic
positively geotropic
28
main roles of auxins
cell elongation prevent lead fall - abscission maintain apical dominance involved in tropism involved in fruit ripening
29
describe the experimental evidence for geotropism
30
main roles of gibberellins
stem elongation trigger mobilisation of food stores in seeds at germination stimulate pollen tube growth
31
main roles of ethene
fruit ripening abscission in deciduous trees
32
main roles of ABA / abscisic acid
maintain dormancy of seeds + buds stimulates cold protective responses - antifreeze productions stimulates stomatal closing
33
state the hormones involved in seed germination
gibberellins ABA
34
what are gibberellins role in seed germination
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
how does the gibberellin molecules stimulate cells to make amylase
been shown that gibberellin does this by regulating genes = increase in transcription of mRNA coding for amylase
36
describe ABA's role in seed germination
has opposite effect to gibberellin – antagonist maintaining dormancy by inhibiting amylase production
37
how is seed germination controlled overall
determined by the balance of ABA + gibberellins
38
describe briefly how seed germination occurs
39
what is an endosperm
a starch-containing energy store surrounding the embryo
40
what is an aleurone layer
a protein-rich layer on the outer edge of the endosperm
41
state the hormone involved in leaf loss of deciduous plants
auxin ethene
42
describe how ethene is involved leaf loss occurs in deciduous plants
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
describe how auxin is involved leaf loss occurs in deciduous plants
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
state the hormones involved in stomatal closure
ABA
45
describe how stomatal closure occurs
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
how does auxins cause apical shoot growth
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
what is apical dominance
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
describe how auxins cause apical dominance
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
describe the experimental evidence for apical dominance
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
what is the experimental evidence for the role of gibberellins in stem elongation
when given gibberellic acid – grow taller
51
what is the experimental evidence for the role of gibberellins in germination
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
commercial use of ethene
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
commercial use of auxins
rooting powders + micropropagation hormonal weed killers unpollinated flower fruit development produce seedless fruit
54
how is auxin involved in rooting powders
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
how is auxin involved in hormonal weed killers
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
what is the commercial use of cytokinin
prevents ageing of ripened fruit
56
what is the commercial use of gibberellins
delay ripening make unpollinated flowers develop fruit

Biology - Module 5 (8 decks)

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