plant hormones Flashcards

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1
Q

what is the advantage of apical dominance to plants

A
  • prevents side shoots from growing which saves energy, and prevents side shoots from the same plant competing with the shoot tip and lower leaves for light.

This allows plants to grow tall very fast

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1
Q

what is the role of the plant hormone auxin

A

stimulates growth of the apical bud, inhibits growth of side shoots from lateral buds, therefore promotes apical dominance

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2
Q

how does the concentration of auxin differ down the plant

A

auxin becomes less concentrated further away from the apical bud, therefore side shoots grow at the bottom

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3
Q

what is the role of giberellins (2)

A

stimulates the stems of plants to grow via stem elongation in the internodal regions.

stimulates seed germination and flowering.

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4
Q

outline how giberellin stimulates seed germination

A

seed germination is activated by water, radical and pineal cells produce giberellin which activates genes to produce amylose which breaks down starch in the endosperm to glucose, which is used for respiration

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5
Q

explain the 2 terms that can describe how auxins and giberellins work together

A

they are synergistic - work together to have a large effect, larger than they would have working independantly eg. help plants grow very tall

they are antagonistic - oppose each others actions eg. giberellins stimulates growth of side shoots, auxin inhibits the growth of side shoots.

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6
Q

why is leaf loss in deciduous plants an advantage

A

losing leaves in winter helps conserve water which may be difficult to absorb from the soil.

reduces energy needed to maintain leaves in the winter, fallen leaves insulate roots, rotten leaves provide minerals in the soil

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7
Q

outline and explain the 2 hormones involved in leaf loss

A

leaf loss is triggered by shortening day lengths which is detected by receptors called phytochromes.

auxins inhibits leaf loss
ethene stimulates leaf loss, a layer of cells called the abscission layer develops at bottom of leaf stalk. Ethene stimulates the cells in the abscission layer to exapnd and activates genes to produce digestive enzymes which break down the cell wall, causing the leaf to fall off

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8
Q

what plant hormone is involved in stomatal closure

A

abscisic acid (ABA)

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9
Q

outline how the hormone ABA triggers stomatal closure

A
  • ABA binds to receptors on guard cell membrane
  • ion channels open, Ca 2+ ions enter the cytosol from the vacuhole
  • increased conc. of Ca2+ ions causes more ion channels to open, which allows ions to leave the guard cell.
  • water potential increases
  • water leaves the guard cell via osmosis.
  • cell becomes flaccid and stomata closes
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10
Q

give an example of how a plant may respond to abiotic stress

A

carrots produce antifreeze proteins, these bind to ice crystals and lower the temp that water freezes at, preventing more icecrystals from forming.

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11
Q

what are alkaloids, give an example

A

chemicals with a bitter taste, noxious smell or poisonous characteristics that deter or kill herbivors.

Tobacco plants produce the alkaloid nicotine, which is highly poisonous to insects.

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12
Q

what are tannins

A

plants produce tannins in response to herbivory, they have a bitter taste, and in some herbivors can bind to proteins in the gut making them hard to digest.

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13
Q

what are pheremones

A

signalling chemicals - plants can release alarm pheremones in the air in response to herbivore grazing, this causes nearby plants to start maming chemical defences.

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14
Q

give an example of how pheremones deter herbivores

A

corn plants are eaten by catepillars, they release pheremones which causes parasitic wasps to kill the catepillars

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15
Q

what is something some plants can physically do to deter herbivores

A

some plants can fold up in response to touch for example, the mimosa pudica, this helps to knock of small insects.

16
Q

how do plants respond to external stimuli

A

by regulating growth

17
Q

what is. the definition of a tropism

A

response of a plant to a directional stimulus.

18
Q

what is phototropism

A

growth of a plant in response to light

  • shoots are positvely phototropic - grow towards
  • roots are negatively phototropic - grow away
19
Q

what is geotropism

A

growth in response to gravity

  • shoots are negatively geotrophic - grow upwards
  • roots are positively geotrophic - grow downwards
20
Q

apart from geotropism and phototropism, what are other types of tropisms

A

hydrotropism- growth in response to water
thermotropism - temperature
thigmotropism - growth in response to touch

21
Q

outline and explain how auxin causes growth of shoots and what its effect is on roots.

A

auxin is produced in the tips of shoots (meristems) in response to light, and diffuses backwards into the zone of elongation.

Auxin binds to receptors on plant cell, pH inside the cell lowers as H+ ions are actively transported into the cell, creating optimum conditions for expansion enzymes.

Expansins break bonds in the cell wall, increasing the flexibility and allowing the vacuhole to absorb more water.

central vacuhole forms, auxins are destroyed and cell wall becomes rigid. no more elongation is possible.

high concentrations of auxin inhibits growth of roots.

22
Q

what is Indoleacetic acid, how is it transported around the plant

A

IAA is a type of auxin.

moves via the phloem for long distances and diffusion + active transport for short.

this results in uneven distribution of IAA and therefore uneven growth of plant.

23
Q

outline how IAA responds to directional light

A

IAA diffuses to the shaded side of the shoot, causing uneven growth and the shoot to bend towards the light.

IAA diffuses to the underside/more shaded side of the root, growth here is inhibited to root bends away from the light.

24
Q

outline how IAA controls geotropism

A

IAA also regulates geotropism by accumulating on the underside of shoots and roots. In shoots, IAA causes cell elongation on the underside of the shoot, causing it to bend upwards, away from the force of gravity. In roots, IAA inhibits cell growth, causing roots to grow downwards, towards the force of gravity

25
Q

what are cytokinins

A

stimulate cell division and cell differentiation.

26
Q

outline how IAA actually causes cell elongation and growth

A

It works by entering the nucleus of plant cells and binds to the promoter regions of DNA. It then acts as a transcription factor, activating or inhibiting the transcription of genes which code for proteins involved in cell elongation and growth.

27
Q

describe and explain the commercial use of ethene

A

stimulates enzymes that breaks down cell walls and converts starch into sugar. This makes fruit soft, ripe and ready to eat.

28
Q

describe and explain the different commercial uses of the plant hormone auxins.

A

used in selective weedkillers - make them produce long stems, this means the weed grows too qucikly so can’t get enough water or nutrients causing them to die.

  • used as a rooting hormone to make a cutting grow roots. Means clones can be grown quickly.
29
Q

outline the commercial use of giberellin

A

produces seedless fruit, can be used to make unpollinated flowers develop fruit.

can delay ripening and aging of fruit.

30
Q

what is the experimental evidence for the role of giberellin in seed germination

A

Seeds of mutant varieties of the Arabidopsis plant that do not produce gibberellins can be induced to germinate if gibberellins are applied

Seeds of certain lettuce varieties that require light in order to germinate can be made to germinate in the dark if gibberellins are applied