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Biology > Plant responses > Flashcards

Plant responses Flashcards

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1
Q

examples of nastic responses

A

Non-directional eg:
- photonasty - flowers/leaves opening due to light
- hydronasty - folding of leaves in response to drought
- thigmonasty - response to touch/vibration

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2
Q

examples of tropison responses

A

Directional eg:
- phototropism - growth towards/away from light
- chemotropism - growth towards/away from chemicals
- geotropism - growth towards/away gravity
- thigmotropism - growth towards/away contact stimulus

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3
Q

synergy

A

hormones amplifying each others’ effect or working together

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4
Q

antagonism

A

hormones cancelling out each others’ effects

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5
Q

action of gibberellin in seed germination

A
  • water absorbed and embryo activated
  • embryo starts to produce gibberellins which switch on gene for enzyme production such as protease and amylase
  • these enzymes break down food stores in seed eg. starch to maltose to glucose
  • energy available for growth of embryo - seed no longer dormant
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6
Q

abscisic acid action - seed dormancy

A
  • opposite effect to gibberellins
  • maintains seed dormancy by inhibiting amylase production
  • supresses growth
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7
Q

evidence of gibberellin action in germination

A
  • seeds with mutation to not make gibberellin don’t germinate
  • when gibberellins added to seeds externally, they germinate
  • if chemicals that inhibit gibberellins applied to seeds, they don’t germinate
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8
Q

action of gibberellin in stem elongation

A
  • stimulate cell division and elongation in stem
  • alters properties of cell wall, lowering water pot of cell and allowing water uptake and therefore increase in cell volume
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9
Q

evidence of gibberellin in stem elongation

A
  • dwarf plants have been found to have low levels of gibberellin
  • if dwarf plants treated with gibberellins, they grow to same height as normal plants
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10
Q

action of auxins on growth of shoots

A
  • auxin molecules bind to receptor site in plant cell membrane, causing pH to fall to 5
  • pH 5 is optimal for enzymes needed to pump protons into cells wall causing bonds between microfibres to loosen - cell wall flexible
  • K+ channels open and K+ enters cytoplasm
  • water moves down water pot grad and enters cytoplasm
  • when cells mature, auxin levels fall
  • therefore pH rises so enzymes stop working so the cell wall becomes more fixed and can no longer grow and expand
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11
Q

apical dominance meaning and reasoning

A
  • apical dominance - auxins produced at growing tip of apex causing stem to grow upwards
  • high conc auxin - suppresses lateral growth
  • further down stem - less auxin so buds can grow laterally
  • if apical shoot removed - auxin producing cells removed and apical dominance stops
  • best for plants to grow upwards towards light to maximise energy for photosynthesis
  • sideways growth not so useful - apical dominance caused by auxins ensures growth is upwards
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12
Q

phototropism

A
  • +ve shoot grows towards light - needs light for photosynthesis
  • -ve roots grows away from light - anchors plant into ground
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13
Q

geotropism

A

+ve roots grows towards gravity - anchors plant into ground
-ve shoot grows away from gravity - more light further up

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14
Q

thigmotropism

A

+ve shoot grows towards a stimulus eg. wrapping around bamboo
-ve growing away from a stimulus eg. root growing away from a rock

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15
Q

hydrotropism

A

+ve roots grow towards water source
-ve shoot grows away from water

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16
Q

chemotropism

A

+ve roots growing towards region of mineral store in soil
-ve roots growing away from acidic region of soil

17
Q

Darwin’s experiment into phototropism - removing tip of coleoptile

A
  • removed top of coleoptile and shoot didn’t grow towards light source
  • to show it wasn’t due to plant damage, he covered the tip with an opaque cap which also stopped it growing towards light
  • he also covered it with a transparent cap which didn’t stop the phototropic response occurring
18
Q

Boysen Jenson’s experiment into phototropism - gelatin and mica sheet

A
  • cut off tip of coleoptile and replaced it with thin layer of gelatin (permeable) between tip and stem
  • this didn’t stop the shoot bending towards light because auxin could diffuse through the gelatin to elongate one side of the stem
  • then he put a thin mica sheet (impermeable) below tip of coleoptiles on non-shaded side
  • this didn’t prevent curvature because the auxin goes to the shaded side so the shoot can bend towards light
  • when mica sheet on shaded side - no curvature
  • concluded that chemical is produced at tip then travels down shaded side - opposite side to stimulus causing growth on shaded side
19
Q

Paal’s experiment into phototropism - tip of coleoptile placed off centre

A
  • side of coleoptile that tip placed on grew more causing it to curve
  • this shows in the light, the phototropic response is caused by a hormone diffusing through the plant tissue stimulating growth
20
Q

Went’s experiment into phototropism - gelatin block

A
  • cut tip of coleoptile placed on block of gelatin allowing the hormone to diffuse into it
  • block placed on coleoptile off centre in the dark - stem grew on side that gelatin block placed on
  • concluded that substance in gelatin block diffused in coleoptile causing cell elongation in that side
21
Q

geotropism in context of auxin

A
  • shoots grow away from gravity - negative geotropism
  • gravity causes auxin to accumulate on lower side of shoot, increasing rate of growth on lower side, causing shoot to grow upwards
  • roots grow towards gravity (positive geotropism)
  • in roots high auxin conc causes lower rate of cell elongation
22
Q

physical defences in plants

A
  • spikes
  • bark
  • cell wall
23
Q

chemical defences in plants

A
  • alkaloids - nitrogenous bitter tasting compound, many act as drugs eg. nicotine, caffeine, morphine, cocaine - usually interfere with metabolism
  • tannins - very bitter tasting compounds to animals, toxic to insects - digestive enzyme inhibitors eg. in red wine
  • terpenoids - can form essesntial oils and are toxic to insects eg. citronella as insect repellent
24
Q

pheromone

A
  • chemical released that affects behaviour of other members of the same species
  • eg. maple tree can release pheromones when being eaten to signal to other maple trees to release defence chemicals
25
Q

volatile organic chemicals

A
  • chemicals released that allow plants to communicate with other species
  • eg. parasitic wasp and white cabbage
26
Q

leaf abscission

A
  • deciduous plants drop their leaves seasonally
  • cost of energy required to maintain anti-freeze chemicals in the leaves is greater than the glucose produced by photosynthesis in the winter (less light)
  • light levels drop, auxin levels drop
  • ethene levels rise, switching on genes for enzymes that digest cell walls
  • cell walls in separation of abscission layer get weaker
  • vascular bundles sealed off by deposited fatty material forming protective layer
  • cells in separation zone retain water causing strain on the outer layer and the leaf falls off the plant
27
Q

abscisic acid (ABA) on stomata

A
  • controls opening and closing of stomata in response to abiotic stress
  • roots produce ABA and it’s transported to the leaves
  • ABA binds to receptors on membrane of guard cells causing change in ionic conc and reducing water pot of guard cell
  • guard cells become less turgid and stomata close
28
Q

commercial use of ethene

A
  • controlled ripening - stimulates fruit to ripen
  • climacteric fruit - requires ethene to ripen eg. banana, apple, avocado
  • easier to transport when unripened as they don’t bruise as easily
  • when ready for sale, ethene gas is released - prevents wastage
  • as ethene conc increases, CO2 conc increases as respiration rate increases
29
Q

commercial use of auxin (rooting powder)

A
  • at low doses, auxin powder can stimulate growth of new roots in cuttings
  • used in micropropogation - producing clones from a plant with desirable traits
30
Q

commercial use of auxin (selective weed killer)

A
  • synthetic auxin in v high conc can be sprayed onto unwanted plants, causing increased metabolism and rapid growth - susceptible to pathogens and unstable - unsustainable so plant dies
  • cost effective, low toxicity to animals
31
Q

cytokines commercial use

A
  • prevent ripe fruit from ageing eg. lettuce

Biology (17 decks)

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