Plant reponses Flashcards

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1
Q

What is a tropism

A

a plant that shows directional growth in response to environmental cues

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2
Q

Key roles of auxins

A
  • cell elongation
  • prevent leaf fall
  • fruit ripening
  • involved in tropisms
  • ethene release
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3
Q

Key roles of gibberelins

A
  • stem elongation
  • trigger mobilisation in of food stores in seed germination
  • stimulate pollen tube growth in fertilisation
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4
Q

Key roles of ethene

A
  • fruit ripening
  • abscission in deciduous trees
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5
Q

Key roles of abscisic acid (ABA)

A
  • stimulate stomatal closing
  • stimulate cold protective responses
  • maintain seed and bud dormancy
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6
Q

What is a cotyledon

A

a food store in a dicot seed

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7
Q

How do gibberellins stimulate seed germination

A
  • gibberellins begin to be produced when a seed absorbs water and the embryo is activated
  • gibberellins stimulate the production of enzymes that break down food stored
  • embryo uses food stores to produce ATP for building materials to break through seed coat
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8
Q

Role of auxins in growth

A

Apical dominance- growth of the main branch only

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9
Q

How do auxins affect cell wall plasticity

A
  • auxin present means the wall stretches more easily
  • auxin molecules bind to receptors in the plant cell membrane, causing the pH to fall to 5
  • pH 5 is the optimum for enzymes to keep the walls stretchy
  • as the cells mature, auxin is destroyed, causing pH to rise so enzymes maintaining plasticity are inactive
  • walls become rigid so cells can no longer grow and expand
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10
Q

What do high concentrations of auxins do

A
  • suppress the growth of lateral shoots (branches)
  • results in apical dominance
  • shoots lower down aren’t affected so that lower lateral shoots grow better
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11
Q

What is an internode

A
  • regions between leaves on a stem
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12
Q

What is synergism

A
  • different hormones work together, complimenting each other
  • give a response greater than they would individually
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13
Q

What is antagonism

A
  • substances have opposite effects, the balance between them determines the plants response
  • give an effect smaller than they would individually
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14
Q

Why do plants lose their leaves as a result of abiotic stress

A
  • glucose required for respiration and to maintain leaves > glucose produced by photosynthesis
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15
Q

What is photoperiodism

A
  • the idea that plants are sensitive to lack of light in their environment
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16
Q

What is phytochrome

A

-a light sensitive pigment, existing in 2 forms, Pr and Pfr
- each of the forms absorbs a different type of light

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17
Q

What is the abscission zone

A
  • made up of 2 layers of cells, sensitive to ethene
  • at the base of the leaf stalk
18
Q

Process of leaf abscission

A
  • falling light levels results in lower auxin concentrations
  • leaves respond to low auxin by producing gaseous hormone ethene
  • ethene initiates gene switching on in the abscission zone
    -gene switching on results in production of new enzymes which digest and weaken cell walls in the separation layer
  • vascular bundles that carry materials in and out the leaf are sealed off
  • fatty material is deposited into the cells on the stem side of the separation layer (forms protective scar later)
  • cells in separation zone respond to hormonal cues by retaining water and swelling, straining the outer layer
  • more abiotic stressors put to much strain on the leaf, it falls off leaving a scar
19
Q

What is the separation zone

A

cells in the outer layer of the abscission zone

20
Q

How do cells prevent freezing

A
  • cytoplasm and sap in the vacuole contain solutes that lower the freezing point
  • some solutes act as antifreeze- stop cytoplasm freezing
  • different genes are suppressed and activated in response to change in daylength
21
Q

Role of ABA in stomatal control

A
  • open and close stomata in response to abiotic stress
  • leaf cells now appear to release ABA when under abiotic stress
22
Q

What is herbivory

A
  • the process by which herbivores eat plants
23
Q

Physical defences against herbivory

A

thorns, spikes, hairy leaves, stings, inedible tissue

24
Q

Chemical defences against herbivory

A
  • Tannins
  • Alkaloids
  • Terpenoids
  • Pheromones
  • VOC’s
    -Fold in response to touch
25
Q

Tannins

A
  • have a bitter taste to animals
  • toxic to insects- bind and deactivate digestive enzymes in saliva
26
Q

Alkaloids

A
  • bitter tasting, nitrogenous compounds
  • e.g. caffeine, nicotine, cocaine, morphine
  • Caffeine toxic to fungi and insects
27
Q

Terpenoids

A
  • act as toxins to insects and fungi
  • e.g. phyrethin interferes with insect nervous system
  • some act as insect repellent
28
Q

Pheromones

A
  • chemicals made by an organism that affect the social behaviours of other members of the same species
  • mainly animals only, e.g. maple trees
29
Q

VOC’s

A
  • volatile organic compounds
  • act as pheromones between plants and other organisms
  • e.g. attract herbivore predators
30
Q

Plants that respond in response to touch

A
  • Venus fly trap
  • Mimosa Pudica= folds and collapses in seconds, removes herbivore, scares others, plants has prickles and toxic alkaloids
31
Q

Phototropism

A
  • plant growth in response to light from 1 direction
32
Q

Geotropism

A
  • plant growth in response to gravity
33
Q

Chemotropism

A
  • plant growth in response to chemicals
34
Q

Thigmotropism

A
  • plant growth in repsonse to touch
35
Q

How are plants phototropic

A
  • results of auxin movement
  • if exposed to light brighter on 1 side (unilateral light), shoots grow towards light, roots grow away
  • shoots= phototropic, roots= negatively phototropic
  • enables maximum photosynthesis
36
Q

Effects of unilateral light on a plant

A
  • causes auxin to move laterally, with a greater concentration on the unilluminated side
  • this stimulates cell elongation and growth towards the light
  • results in bend plant
37
Q

Growth of plants in the dark

A
  • grow more rapidly in the dark- grow upwards to reach light ASAP
  • gibberellins responsible for extreme internode elongation in the dark
38
Q

Shoot and root geotropism

A
  • shoots= negatively geotropic, grow against gravity
  • roots= positively geotropic, grow towards gravitational pull
39
Q

Hormones controlled in plant ripening

A
  • ethene
  • fruit is harvested a long time before it is ripe so it can be transported easier
  • when time for sale, exposed to monitored levels of ethene to ripen
40
Q

Hormones affecting rooting powders and micropropagation

A
  • auxin application to cut shoots stimulates production of new roots
  • cuttings can cause roots to appear
  • dipping the cut stem into hormone rooting powder increases chances of successful propagation occurring
  • easier to develop cuttings for people to sell
41
Q

Hormone weedkillers

A
  • synthetic auxins used as weed killers= plants affected by weeds are often monocot, weeds are dicot
  • if synthetic dicot auxins are used, destroys weeds without harming plant
42
Q

Uses on plant hormones commercially

A
  • fruit ripening
  • rooting powder/ micropropagation
  • weed killers
  • auxin involved in seedless food production
  • ethene promotes fruit dropping
  • cytokinin prevent aging of ripened fruit
  • gibberellins also delay ripening and aging, improve fruit shape and size