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A2 Biology > 5.1.5 Plant Responses > Flashcards

5.1.5 Plant Responses Flashcards

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1
Q

define cell signalling

A

communication and coordiantion between cells to trigger a reaction in the cell

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2
Q

why do plants need to respond to their environment

A

to avoid abiotic stress- cold, heat, dryness and humidity
to maximise photosynthesis by obtaining more light and water
to avoid herbivory

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3
Q

what are the roles of auxins

A

control cell elongation, involved in tropisms and stimulate the release of ethene

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4
Q

what are the roles of gibberellins

A

cause stem elongation

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5
Q

what are the role of ethene

A

causes fruit ripening, promotes senescence

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6
Q

what is the role of ABA

A

stimulates stomatal closing

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7
Q

name 3 similarities between plant hormones and hormones in mammals

A
  • hormones bind to receptors which cause enzyme reaction inside cells
  • act on several target tissues
  • may involve in switching genes on and off
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8
Q

name 3 differences between plant and mammals hormones

A

plants- produced by many tissues
animals- produced by endocrine tissues

p- move in xylem and phloem
a- move in bloodstream

p-act on most tissues
a- act on specific target tissues only

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9
Q

what is the food store in a
dicot
monocot

A

2x cotyledons

endosperm

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10
Q

explain the process of seed germination

A

1) seeds absorb water
2) water activates the embryo to start making the gibberelin
3) gibberelin activates genes to make protease, converts protein into amino acids, this is converted into amylase which converts starch into maltose, maltose is converted into maltase which converts maltose into glucose
4) these are used to respire and produce atp for building roots and shoots

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11
Q

what are the two pieces of evidence which shows that gibberelins are responsible

A

1:
plant species without the gene to make protease do not germinate

2:
if gibberellin biosynthesis inhibitors are applied to seeds they do not germinate

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12
Q

what are meristems

A

groups of immature cells which can divide and differentiate

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13
Q

what are apical meristems

A

tips of roots and shoots making them grow longer

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14
Q

what are lateral bud meristems

A

buds that could form a side shoot

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15
Q

what are lateral meristems

A

circular bands that make roots and shoots get wider

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16
Q

what are intercalary meristems

A

between the nodes, helps the shoots get longer

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17
Q

where are auxins made and what do they cause

A

made in the cells at the tips of shoots and tips of roots
(move down from the shoot top and up from the root tip via diffusion)
travel to the zones of elongation
stimulate elongation here

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18
Q

describe exactly how the auxins cause stem cell elongation

A

auxins bind to specific receptors in the cell surface membrane

they cause the active transport of H+ by an ATPase enzyme into the cell wall

low PH optimal for expansin enzymes that loosen cell walls

the expansin enzymes break bonds between microfibrils present in cellulose

allows for cell elongation

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19
Q

explain how positive phototropism occurs

A

1) shoot tip produces auxin, auxin diffuses down from shoot tip or is moved by active transport
2) light causes movement of auxin from light side to shaded side
3) higher auxin concentration on shaded side causes cell wall loosening and greater elongation of cells on shaded side
4) grows faster and causes shoot to bend towards the light

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20
Q

what happens if their is a high concentration of auxin in the root

A

high concentration of auxin inhibit elongation of cells in the root

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21
Q

what is apical dominance

A

high concentrations of auxins suppress growth of lateral shoots

22
Q

what happens if the apical shoot was removed

A 
auxin production stops
apical dominance stops
lateral buds develop
side shoots grow
plant becomes bushy
23
Q

what effect on the stem do gibberellins have

A

affect the length of internodes (regions between leaves)

24
Q

define tropism

A

directional growth of plants determined by the direction of external stimuli

25
Q

what is the difference between positive and negative tropism

A

a positive tropism is one that grows towards the stimulus

a negative tropism is one that grows away from the stimulus

26
Q

why do plants grow more rapidly in the dark

A

to grow upwards to reach light in order to photosynthesise, auxin is not destroyed by the light so more is present causing elongation

27
Q

suggest how hormones alter a plants growth in response to overcrowding by other plants

A

auxin causes positive phototropism, plant shoot bends towards the light
plants grow taller

28
Q

what tropic are shoots/roots

A

shoots- negatively geotropic

roots- positively geotropic

29
Q

what happens if there is a high concentration of auxin in the roots

A

elongation is inhibited

30
Q

what happens to the shoots when the plant is attached to the rotating drum

A

shoots grow straight

gravitational stimuli is applied evenly

31
Q

name three abiotic stresses to plants

A

lack of water
high winds
temperature

32
Q

what happens to deciduous trees in winter

A

trees lose all their leaves and remain dormant until the temperature rises and the day lengthens

33
Q

why do deciduous trees lose their leaves in winter

A

amount of sunlight decreases, less photosynthesis, the amount of glucose required to maintain the leaves and stop chlorophyll freezing exceeds the amount of glucose produced

34
Q

define plant senescence

A

the process of aging in plants, chlorophyll degrades and carotenoids revealed (which gives leaves this orange colour in autumn)

35
Q

explain the process of leaf loss

A

1) cytokinins inhibit senescing by making leaf a sink for nutrients
2) in autumn cytokinins production stops, senescing begins
3) auxin concentration reduces in the abscission zone
4) low auxins mean increased production of ethene
5) ethene causes the production of cellulase enzyme
6) cellulase enzymes break down cell wall in abscission zone
7) petiole and stem separates

36
Q

what is deposited on either side of the separation layer, what does this do

A

fatty material, forms a protective scar preventing the entry of pathogens

37
Q

what prevents plants from freezing

A

the cytoplasm of cells and vacuoles contain solutes which lower the freezing point of water

polysaccahrides siuch as amino acids and proteins act as antifreeze

the genes that make these products are activated by a decrease in temp over a sustained period of time

38
Q

what hormone controls stomatal closing/opening

A

ABA

39
Q

how does ABA control stomata

A

1) levels of soil water fall, plant makes ABA
2) ABA transported to leaves by xylem and phloem
3) ABA binds to receptors on the plasma membrane of guard cells

4) k+ actively transported out the guard cell, high WP in guard cell so water moves by osmosis out of the cell
5) cells become less turgid and the stomata closes

40
Q

name three physical defences of plants

A

thorns
hairy leaves
stings

41
Q

what are tannins

A

a part of a chemical group called phenols
have a BITTER TASTE which putd animals off eating them
this is TOXIC TO INSECTS

42
Q

what are alkaloids

A

bitter tasting compounds: niccotine, caffeine, cocaine…

43
Q

what are terpenoids

A

toxins to insects and fungi
eg citronella
some disrupt insect nervous systems

44
Q

what are pheremones

A

a chemical made by one organism that affect the social behaviour of other members

45
Q

what are volatile organic compounds

A

act like chemical signals
eg in cabbages when caterpillars, attack they produce a VOC to attract a parasitic wasp which lets its eggs into the caterpillar and is eaten alive

46
Q

why do some plants fold at touch

A

to scare off larger organisms

47
Q

what is the name to fruits that ripen after being picked

what is the advantage of this

what does ethene do

A

climacteric fruits
eg bananas

prevents damage during trasnport and lives on shelves for longer

triggers a higher rate of respiration, ripens fruit

48
Q

what is the effect of adding auxins to cut shoots

A

causes the production of roots, makes it easier for them to grow and develop

49
Q

why are weeds bad

A

they outcompete useful plants for space light etc

50
Q

what is applied to weeds and what effect does this have

A

the synthetic auxin dicots are applied to weeds, promotes unsustainable growth and eventually death

51
Q

what are the advantages of auxin based weedkillers

A

cheap to make and low in toxicity to other animals

A2 Biology (8 decks)

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