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Biology > Plant responses- Module 5 > Flashcards

Plant responses- Module 5 Flashcards

1
Q

what do Hormones in plants control

A

Anything relating to growth:

-roots and shoots
-seed germination
-leaf fall
-disease resistance
-fruit formation and ripening
-flowering time
-Bud formation

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2
Q

Tropism

A

Directional growth response
-plants grow in a certain direction in a response to a stimulus

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3
Q

Roots growing downwards into dark soil =

A

Negative phototropism

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4
Q

Shoots growing upwards towards light =

A

positive phototropism

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5
Q

Negative Geotropism =

basic

A

Shoots growing upwards against gravity

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6
Q

Positive geotropism =

A

Shoots growing downwards in direction of gravity

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7
Q

Auxins in the roots causes cells to _____ elongating ….

A

auxin causes cells to STOP elongating

and this causes positive gravitropism/geotropism

helps the plant roots to anchor the plant in place and to reach moisture underground

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8
Q

Hormones _____ growth in shoot

Hormones _____ growth in Roots

A

Stimulate

Retard

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9
Q

Positive Phototropism in shoot

Process

A

when light hits a plant shoot from one side (unilateral light), the auxin moves laterally to the shaded side of the shoot
-higher auxin conc. on shaded side
-Higher auxin conc promotes cell elongation on shaded side -> grows faster
The shoot ends up bending towards the light.

*Once the light is hitting the shoot more evenly, the amount of auxin will be even out on both sides of the shoot and the shoot will start to grow straight again

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10
Q

Geotropism process

A

In roots and shoots underground, the auxin is pulled by gravity to the lower side of the roots and shoots

The auxin makes the lower side of the shoot grow more so the shoot grows up towards the light. (negative geotropism)

In the root, the opposite happens (as higher auxin conc in roots inhibits growth), the Top grows faster, so the root grows downwards to anchor itself in the soil (positive geotropism)

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11
Q

Effect of auxin on Lateral shoots

A

-high auxin concentration inhibit lateral shoots
-produces apical dominance
-Growth in the main shoot is stimulated by the auxin in teh tip, so is rapid
-as you descend the stem, auxin concentration is lower
-Later shoot growth is more rapid​

Lots of experimental evidence​

Remove the apical shoot and no auxin is produced​

Lateral shoots then grow faster​

Auxins can be reapplied artificially​

Apical dominance is reasserted​

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12
Q

auxin functions in plants

A

-control cell elongation
-prevent leaf fall (Abscission)
-maintain apical dominance
-involved in tropisms
-stimulate the release of ethene
-Prevent fruit ripening

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13
Q

Gibberellin

A

-cause stem elongation (increase internode length)
-trigger mobilisation of food stores in food germination
-stimulate pollen tube growth in fertilisation (aids fertilisation)
-

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14
Q

ethene

A

-causes fruit ripening
-promotes abscission in deciduous trees

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15
Q

ABA (abscisic acid)

A

-maintains dormancy of seeds and buds
-stimulates cold protective responses e.g: antifreeze production, stimulates stomatal closing

(antagonist to gibberellins)

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16
Q

experimental evidence for gibberellins

A

-mutant varieties of seeds have been bred which lack the gene that enables them to make gibberellins these seeds do not germinate. If gibberellins are applied to the seed externally, the seed will germinate normally

-if gibberellin biosynthesis inhibitors are applied to seeds, they do not germinate as they cannot make the gibberellins needed to break dormancy. If the inhibition is removed or gibberellins added, the seed breaks dormancy/ germinates

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17
Q

what are indoleacetic acid

where are they made

where can the travel

what do their effects depend upon

A

Auxins

growth stimulants in plants. small quantities can have powerful effects

made in cells at tips of roots and shoots, and in the meristems

can move down the stem and up the root both in transport tissue and cell to cell

the effect of the auxin depends on its concentration and any interaction it has with another hormone

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18
Q

process of the effects of auxin (IAA) on Cell Elongation

A

-auxins synthesised + released from meristem cells
-auxins diffuse down the concentration gradient, away from tip towards zone of elongation
-auxins bind to receptor sites in plant cell membrane. Opens protein channels on plasma membrane that specifically allow Hydrogen ions to enter the cell. H+ Move in.
-vacuoles form and low PH (around 5) develops
-low pH of cell walls keeps them flexible (optimum pH for enzymes maintaining plasticity of wall), allowing cells to expand as they absorb water (without bursting). Vacuoles get bigger + cell walls stretch
-Large central vacuole formed. Auxins leave and destroyed by enzymes.
-Protein channels close to prevent further entry of hydrogen ions.
-pH rises so enzymes maintaining plasticity denature. Cell wall becomes rigid. no further cell elongation is possible

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19
Q

what do high concentrations of auxins do to lateral shoots

explain apical dominance

A

suppress the growth of lateral shoots

Growth in main (apical) shoot is stimulated by auxin in tip, so is rapid.

-As you descend the stem, auxin concentration is lower
-Lateral shoot growth is more strong

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20
Q

what experimental evidence is there for the role apical dominance

A

-remove apical shoot and no auxin produced
-Lateral shoots then grow faster
-Auxins can be reapplied artificially
apical dominance is reasserted

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21
Q

Auxins in root growth

low to high conc

A

-low concentrations of auxins promote root growth
-up to a given concentration, the more auxin that reaches the root, the more they grow
-High concentrations of auxin inhibit growth

-auxin is produced by the root tips
-some makes it way from the shoot to the roots

22
Q

expertimental evidence for effect of auxins on the roots

A

if apical shoot is removed, less auxin reaches root
Growth slows
-replacing auxins artificially at the cut apical shoot restores growth of roots

23
Q

hormonal process of germination

A

-Seeds absorb water
-produces gibberellins
-stimulates production of enzymes
-break down food stores: starch>Maltose>glucose
-glucose used to grow plant
-Energy released for seedling growth

*evidence suggests gibberellins turn on genes for amylases and proteases
some evidence that ABA acts as an antagonist
Relative levels of both hormones determine germination

24
Q

Ethene and _____ have an antagonistic relationship

A

Auxin

25
Q

ABA and _______ have an antagonistic relationship

A

Gibberellins

26
Q

Synergism

A

hormones working together

27
Q

Antagonism

A

hormones opposing each other

28
Q

Should you refer to the presence or the concentration of hormones in plants

A

Concentration

refers to Hormonal Balance

29
Q

Generally, how do scientists find evidence of plant hormones

A

-Mutate genes that make the hormone
-Disrupt production pathway
-Cut shoot tip (remove auxins)

Then
-See changes
-Apply hormones externally
-Further changes?

30
Q

How does apical dominance benefit a plant

A

Allows it to better compete for light.

e.g: Lateral shoots higher up are shorter so they don’t block the light for shoots below

31
Q

Benefit of stem elongation

A

higher conc. of gibberellins = larger internodes

larger internodes = Taller plants

Taller plants = better compete for light

=more photosynthesis

32
Q

Why would farmers want to reduce stem elongation?

A
  • Decrease waste
    -prevent crop damage by bad weather
33
Q

p

A

p

34
Q

Abscission process

A

1) Phytochromes Detect falling light levels
2) Decreases auxin production
3) Increase Ethene levels
4)Ethene activates genes in cells in abscission zone to produce digestive enzymes
5) Enzymes digest cell wall in the Separation zone (e.g: Cellulase)

6)Vascular bundles are sealed in the protective layer.

factors such as wind will then remove the leaf

35
Q

Why is Abscission important

A

1)Reduce energy needed to maintain leaves in winter
2)Fallen leaves insulate roots
3)Rotten leave provide minerals to plants

36
Q

Plant response to lack of water Summary process

Why does this happen

A

1) root hair cells detect lack of water and Produce ABA
2) ABA transported up the stem to leaves and binds to receptors on guard cells
3)Causes a change in ion channels. Ions move out of guard cells. Affects WP gradient
4)Water leaves by osmosis
5)Guard cells become flaccid/plasmolysed and close stomata

occurs to reduce transpiration

37
Q

Physical plant defences to herbivory

A

-Thorns, hairy leaves, Spikes

38
Q

Chemical plant defences to herbivory

A

-Tannins
-Alkaloids
-Terpenoids
-Pheromones
-Volatile organic compounds

39
Q

Tannins in plants

A

Bitter taste, toxic to insects

40
Q

Alkaloids in plants

A

bitter taste, poisonous to animals (affect metabolism)

41
Q

Terpenoids in plants

A

Toxic to insects and fungi (neurotoxin, repellent)

42
Q

Examples of alkaloids that humans use

A

Caffeine - increase metabolic rate

Nicotine- Addictive, increases heart rate

Morphine- painkiller

cocaine-

43
Q

use of pheromones in plant

A

Affect social behaviour of other members of the same species
e.g: signal to produce callose

44
Q

use of Volatile organic compounds in plants

A

Affect social behaviour of other species

e.g: VOCs can attract predators of the pest insect

45
Q

Folding response in _____ ______ does..

A

Mimosa pudica

Scares herbivores away

make insects slide off

46
Q

Advantages of phototropism

A

(positive) ensure max rate of photosynthesis due to more light exposure
(Negative phttrphsm) Roots grow away from light to get water and minerals in soil

47
Q

Negative phototropism

A

1) auxins move away from light to shaded side of root
2) Roots like LESS auxins to grow quicker (more auxins = grow less)
3)Lit up side that has less auxins grows quicker than shaded side
4) So roots bends downwards away from the light

48
Q

Key points with auxins and Their interactions with light, roots, shoots

A

Auxins- Hate light, Obey gravity

-Promote shoot growth

-retard root growth

49
Q

Scientists originally thought auxin was ____ by light but was disproved by plants growing in the dark and in unilateral light had ____ auxin levels

A

Destroyed

Similar

50
Q

Wbu is gibberellin classed as a hormone

A

-chemical messenger
-produced in one part of plant, has effects in another part.
-affects activity of target cells
-Long lasting
-wide-spread effect

Biology (45 decks)

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