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George Biology > Plant responses chp 16 > Flashcards

Plant responses chp 16 Flashcards

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1
Q

what are some general functions of auxins within plants

A
  • control cell elongation
  • prevent abscission (leaf fall)
  • maintain apical dominance
  • important for tropisms
  • stimulates the release of ethene
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2
Q

what are some functions of gibberellins

A
  • causes stem elongation
  • triggers mobilisation of food stores in seed at germination
  • stimulate pollen tube growth in fertilisation
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3
Q

what are some functions of ethene

A
  • causes fruit ripening
  • promotes abscission
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4
Q

what are some functions of ABA, what does ABA stand for

A

abscisic acid

  • maintains dormancy of seeds and buds
  • stimulates cold protective responses (antifreeze production)
  • stimulates stomatal closing
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5
Q

What occurs when a seed germinates

A

seed absorb water
embryo is activated and starts producing gibberellins
^stimulates production of amylase and protease that breakdown food stores
plant uses to produce ATP for metabolic activites

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6
Q

what is some evidence that supports the role of gibberellins in the germination of seeds

A
  • if mutant seeds do not produce gibberlins they do not germinate but once given do germinate
  • if gibberelin inhibitors are applied to seeds do not germinate if taken off they do germinate
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7
Q

where can auxins be mainly found In the plants

A

inthe cells at the tip of roots, shoots and in meristem

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8
Q

explain effect of auxins on plant cell walls

A
  • effect elasticity of cell walls - more auxins means stretches more easily
  • stimulates fall in pH, optimum for enzymes that maintain elasticity
  • as cell mature auxins destroyed, pH rises again so elasticity is removed from the cell wall and become rigid
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9
Q

what are the 3 zones that can be found in the apical shoot

A
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10
Q

explain effect of auxin on lateral shoots

A
  • high concentrations of auxins suppress lateral shoots
  • ^results in apical dominance
  • further down stem auxin concentration is lower and so lateral shoots grow
  • if you removed apical shoot lateral grow starts
  • ^if you artificially replace it with auxins apical dominance is reasserted
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11
Q

explain how auxins effect root growth

A
  • low concentrations of auxins promote root growth
  • more auxin that reaches the roots the more they grow (up to a point)
  • if apical shoot is removed then amount of auxin reaching roots is reduced and root growth slows
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12
Q

Explain how gibberellins effect stem length

A
  • influences length of the internodes - the region between the leaves on a stem
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13
Q

what is meant by antagonism when talking about hormones

A

substances have opposite effects, e.g promoting and inhibiting growth

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14
Q

what is photoperiodism

A

the response to changes in daylength that enables plants to adapt to seasonal changes in their environment

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15
Q

what allows plants to be sensitive to day length/dark length

A

results from light-sensitive pigment called phytochrome

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16
Q

How does leaf abscission actually work

A
  • abscission zone (base of leaf stalk) made up of protective and seperation layer
  • Ethene initiates production of enzyme (turn genes on/off)
  • enzymes digest cell walls of abscission zone
  • vascular bundles going to and from stalk sealed off
  • fatty material deposited in cells at abscission zone
    ^scar, prevents pathogens entering
  • cells in separation zone retain water and swell putting strain on outer layers
  • abiotic factors help leaves fall
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17
Q

how do plants prevent damage from freezing

A
  • cytoplasm of cells and sap contain solutes which lower freezing point - such as sugars, amino acids & proteins

controlled by gene experession

18
Q

How do the lengths of days actually cause abscission

A
  • falling light levels causes auxin concentration to fall
  • plants produce ethene in response to less auxin
  • abscission zone is sensative to ethene (begins breaking down)
19
Q

what hormone influences stomatal opening and closing and how does it do it

A
  • ABA
  • binds to receptors on cell membranes of guard cells
  • activates changes in ionic concentrations of guard cells,
    ^reduces water potential and therefore turgor
  • ^as result of less turgor, guard cells close the stomata
  • water loss Is reduced
20
Q

what are some commons plant physical defences

A
  • throws, bards, spikes, spiny leaves, fibrous and inedible tissue and stings
21
Q

what are some common plant chemical defences

A
  • tannins
  • alkaloids
  • terpenoids
  • pheromones
22
Q

how do alkaloids acts as plant defences

A
  • very bitter tasting
  • act as drugs that affect metabolism of animals
  • caffeine, morphine, nicotine, cocaine
23
Q

how do phermones act as plant defences

A
  • chemical made by organism which affects behaviour of same species
  • can alert others of things like insects or water stress
24
Q

How do VOC’s link to phermones and how do they act as plant defences

A
  • act like pheromones but effect the behaviour of other animals
  • diffuse in the air around plants
  • cabbages release VOC’s after being attacked by caterpillars
  • VOC’s attract wasps that lay eggs inside of the caterpillars, killing them
25
Q

what is phototropism

A

plants response to light which comes from one direction only

26
Q

what is geotropism

A

plant response to gravity

27
Q

what is meant by positive and negative phototropism

A
  • positve phototropism is when something grow towards light and negative is when something grows away from light
  • shoots are positvely phototropic and roots are negatively phototropic
28
Q

What would be observed if the top of a plant was to be cut off with light coming from one direction and what does it tell us about how plants grow

A
29
Q

What would be observed if a lightproof cover was placed over the top of a plant and what do we learn from this

A
30
Q

what would be observed if an impermeable barrier is placed halfway through a plant shoot with light coming from one direction
what do we learn from this experiment

A
  • if placed on side of direction of light plant grows towards light
  • if in shaded side no repsone
  • tells us that hormone diffuses down shaded side and causes it to grow
31
Q

what would be observed if the tip of a shoot was removed and a a gelatinous block was then inserted with the tip being replaced
what does this tell us

A
32
Q

what plant hormone is responsible for plant growth in complete darkness

A
  • gibberellins are responsible for extreme elongation of the internodes when a plant is grown in the dark.
  • once exposed to light the level of gibberellins fall
33
Q

what is etiolation

A

rapid upward growth which takes place in the dark

34
Q

what is meant by positive and negative geotropism

A

roots are positivly geotropic as they grow towards gravity
shoots are negatively geotropic s they grow away from the direction of gravity

35
Q

what piece of equipment is used to illustrate geotropism in shoots

A
36
Q

what plant hormone is involved in the ripening fruits

A

the gaseous plant hormone ethene

37
Q

what are climateric fruits

A

fruits that continue to ripen after they have been harvested
e.g.bananas, tomatoes, mangos and avocados

38
Q

When are climateric fruits harvested and why is this

A
  • once they are fully formed but long before they are ripe
  • the are harder and therefore much harder to damage during transport
39
Q

how can auxin be used to influence root growth

A
  • application of auxin to cut shoots stimulates the production of roots (makes it much easier to propagate new plants from plant cuttings)
  • dipping the cut stem into hormone rooting powder increases the chances of roots forming
40
Q

what plant hormone can be used as weedkillers

A
  • most weeds are broad-leaved dicots
  • if synthetic dicot auxins are applied and absorbed by the broad-leaved, their growth rate increases and becomes unsustainable, so they die
  • the narrow leaved crops are not affected
41
Q

what are some uses of plant hormones

A
  • auxins can be used to produce seedless fruit
  • ethene is used to promote fruit dropping
  • cytokinins used to prevent ageing of ripened fruit
  • gibberellins can be used to delay ripening and ageing in fruit
42
Q

why is the purpose of the scar at the abscission zone after abscission has taken place

A
  • to prevent entry of pathogens

George Biology (71 decks)

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