Plant hormones and growth in plants

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Auxin roles
Cell elongation, leaf fall (abscission), maintain apical dominance, involved in tropisms, stimulates release of ethene, fruit ripening
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Gibberellin
Stem elongation, mobilisation of food stores in seed at germination, pollen tube growth in fertilisation
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Ethene (hormone)
Causes fruit ripening, promotes abscission in deciduous trees
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Abscisic Acid (ABA)
Maintains dormancy of seeds and buds, stimulates cold protective responses eg stomatal closing
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What food store is in dicot seeds?
Cotyledons
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What food store is in monocot seeds?
Endosperm
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Describe seed germination
The seed absorbs water which activates the embryo & produces gibberellins, this stimulates production of enzymes which break down food stores, providing ATP for building materials
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What does evidence suggest about gibberellins role in seed germination?
That gibberellins switch on genes that code for amylase and protease, both digestive enzymes needed in germination to break down food stores
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What does evidence suggest about the hormone ABA in germination?
That ABA is an antagonist to gibberellins and will interfere with the action of the gibberellins and also that relative levels of both gibberellins and ABA will determine when the seed will germinate
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Give 2 examples of experimental evidence supporting the role of gibberellins in seed germination
Mutant seeds which lack the gene to produce gibberellins do not germinate but when gibberellins are applied externally they will, when gibberellin biosynthesis inhibitors are added to a seed they will not germinate, when taken away they will
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Where are auxins made?
Shoots and tips of the plant and also in the meristems
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What is the apical shoot?
The main central shoot of a plant
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How does auxin effect the apical shoot growth?
Auxin synthesised in meristem, auxin diffuse away from tip & bind to receptor sites on cells which lowers PH inside cell to 5 (optimum for enzymes to keep cell wall flexible), cell absorbs more water & grows & auxin is destroyed when cell is mature
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Describe apical dominance
Growth in apical shoot stimulated by auxins in tip and lateral shoots are inhibited by auxin so dont grow near the tip of the apical shoot, however lower down the stem there are less auxins present so the lateral shoots grow more strongly
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Describe the effect of auxins on root growth
The presence of auxin in low concentrations stimulate root growth, auxin is produced by tips of roots which cause them to grow, up to a given concentration the more auxin at the roots, the more they will grow
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What else do gibberellins effect?
The growth of internode- these are the regions between leaves and can make the plant very tall
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Why have scientists bred plants where gibberellin pathways are interrupted?
Because with out gibberellin, the plants are a lot shorter meaning they produce less waste and also are less susceptible to weather damage
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What is synergism?
When hormones compliment each other which in turn creates a greater response
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What is antagonism?
When hormones have opposite effects so they inhibit one another, the balance between them determines the effect given out
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Other cards in this set

Card 2

Front

Gibberellin

Back

Stem elongation, mobilisation of food stores in seed at germination, pollen tube growth in fertilisation

Card 3

Front

Ethene (hormone)

Back

Preview of the front of card 3

Card 4

Front

Abscisic Acid (ABA)

Back

Preview of the front of card 4

Card 5

Front

What food store is in dicot seeds?

Back

Preview of the front of card 5
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