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communication, homeostasis and energy > plant responses > Flashcards

plant responses Flashcards

plant go weeeeee brrrr

1
Q

what is a tropism?

A

directional growth in response to a stimulus

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2
Q

what is phototropism?

A

growth in response to light

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3
Q

what is geotropism?

A

growth in response to gravity

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4
Q

what is hydrotropism?

A

growth in response to water

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5
Q

what is thigmotropism?

A

growth in response to touch

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6
Q

what is chemotropism?

A

growth in response to chemicals

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7
Q

what are 4 plant hormones?

A
  • auxins (IAA)
  • gibberellins
  • ethene
  • abscisic acid (ABA)
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8
Q

what is the role of auxins?

A
  • cell elongation
  • prevent abscission
  • maintain apical dominance
  • stimulate ethene
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9
Q

what would happen in the absence of auxins?

A
  • no growth
  • lack of photosynthesis due to not being able to reach the light
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10
Q

what is the role of gibberellins?

A
  • germination
  • pollen tube growth
  • stem elongation
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11
Q

what would happen in the absence of gibberellins?

A
  • couldnt reproduce sexually
  • no growth
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12
Q

what is the role of ethene?

A
  • ripening
  • promotes abscission
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13
Q

what would happen in the absence of ethene?

A
  • pollinators not attracted
  • trees couldnt survive winter
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14
Q

what is the role of abscisic acid?

A
  • maintains dormancy
  • cold protection (antifreeze)
  • stomatal closure
  • abscission
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15
Q

what would happen in the absence of abscisic acid?

A
  • sprout and not survive
  • not survive winter
  • water loss
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16
Q

how do auxins cause elongation?

A
  • auxins synthesised in the meristems which inhibits synthesis in lateral stems
  • diffuses out of meristem and binds to receptors on the CSM which activates a proton pump
  • pH lowers as H+ ions are actively transported into the cell
  • creates optimum conditions for expansin which breaks bonds in cellulose cell wall causing it to be more flexible
  • elongation occurs
17
Q

how do gibberellins affect germination?

A
  • seed embryo is activated when water us absorbed which produces gibberellins
  • turns on gene coding for amylases and proteases to break down food stores (endosperm in monocots, cotyledons in dicots)
  • embryo uses food stores to produce ATP for building materials to grow
  • ABA inhibits gibberellins to determine when germination occurs
18
Q

what is the effect of IAA on roots and shoots?

A
  • inhibits growth in roots
  • promotes growth in shoots
19
Q

what are the commercial uses of plant hormones?

A
  • ethene used to control ripening of fruit during transport to commercial locations
  • gibberellins used to increase size of fruit
  • auxins used in herbicides to promote rapid growth in weeds so they die by cell elongation
  • auxins used to stimulate root development for plant cuttings to clone plants rapidly and cheaply
20
Q

what are abiotic factors that cause stress?

A
  • temp
  • water availability
  • wind
  • light
  • glucose conc
21
Q

how do plants respond to abiotic stress due to lack of light?

A

photoperiodism:
- use phytochromes which are leaf pigments used to detect light
- inactive phytochrome Pr converted to active form when it absorbs red light (daylight)
- active phytochrome Pfr broken down to inactive form to absorb red light
leaf abscission:
- low light causes decrease in auxins and increase in ethene which produces enymes to digest cell wall at abscission layer so leaf falls off

22
Q

how do plants respond to abiotic stress due to lack of glucose?

A

when below requirement for respiration trees lose leaves and remain dormant

23
Q

how do plants respond to abiotic stress due to lack of water?

A
  • stomatal closure controlled by ABA under threat of drought
  • ABA binds to receptors on guard cells which causes Ca2+ ion channels to open
  • influx of calcium ions causes potassium ion channels to open so K+ leaves guard cells
  • water potential increases in guard cells so water moves out by osmosis
  • guard cells become flaccid and close
24
Q

what was the effect of putting a cap on a coleoptile (Darwin’s experiment)?

A
  • cut off the tip and placed a cap on
  • there was no dir3ectional growth
  • prevented phototropic response indicating that the tip is responsible for detecting light
25
Q

what was the effect of putting mica (impermeable) barrier and a gelatin barrier in a coleoptile (Boysen-Jensen experiment)?

A
  • placed mic barrier in first the shaded side (no phototropism) and then the lit side (phototropism occured)
  • cut off the tip and placed a gelatin block (permeable) between tip and plant
  • this restored the phototropic
    response
  • showed chemicals were responsible and they acted on the shaded side of the plant
26
Q

what was the effect of moving the tip of a coleoptile (Paals experiment)?

A
  • tip cut off and placed off centre in the dark
  • the side with the tip grew more
  • indicated that phototropic response was caused by a hormone stimulating growth
27
Q

what was the effect of a gelatin block with auxins in (Wents experiment)?

A
  • tip cut off and placed on top of a gelatin block
  • absorbed the hormones
  • block placed off centre on the plant
  • same results as paals experiment
  • more concentration of hormone meant more growth
28
Q

what is etiolation?

A
  • occurs in plants in partial or complete absence of light
  • long weak stems, smaller leaves, chlorosis
29
Q

what is herbivory?

A

feeding on plants

30
Q

what are the 4 main plant responses to herbivory?

A
  • physical defense
  • chemical defence
  • pheromones
  • folding on touch (mimosa pudica)
31
Q

what are plants chemical defences against herbivory?

A
  • alkaloids contain bitter tasting compounds and affect metabolism
  • tannins inhibit digestive enzymes
  • terpenoids are essential oils with antibacterial and antifungal properties
32
Q

what are plants physical defences against herbivory?

A
  • impenetrable waxy cuticle
  • cellulose cell wall
  • bark
  • thorns
  • casparian strip
33
Q

how are pheromones involved in plant defence?

A
  • affect social behaviour of the same species
  • when an organism is under attack, it signals to surrounding species to heighten defences
34
Q

what are volatile organic compounds (VOCs)?

A
  • compounds similar to pheromones
  • works between different organisms instead
35
Q

how do mimosa pudica defend themselves?

A
  • nastic movement whereby it folds under touch
  • electrical signals cause it uptake water so water is lost from adjacent cells and it collapses

communication, homeostasis and energy (6 decks)

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