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13 Cards in this Set
- Front
- Back
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Tropism
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Positive or negative growth responses to external stimuli
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Phototropism
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bending of growing stems toward light (+)
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Gravitropism
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growth of roots (+) and shoots / stems (-) in response to gravity
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Thigmotropism
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growth in response to touch
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Dormancy:
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Adaptation to unfavorable environ-mental conditions
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Dormancy: Deciduous Trees
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leaves are shed; meristems become inactive & are protected by “scales”
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Dormancy: Annuals
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spend winter as seeds
Some seeds can germinate after thousands of years of dormancy |
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Dormancy: Perrenials
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spend winter underground as stems or roots with stored food
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Auxin
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increases plasticity of cell walls and promotes cell elongation
Synthesized in shoot apical meristems Light causes auxin molecules to migrate into the shaded portion of the root |
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Cytokinins
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stimulate cell division & differentiation
Synthesized in root apical meristems Bacterial infections can cause overproduction of cytokinins |
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Ethylene
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stimulates the ripening of fruit; and inhibits root & stem elongation
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Abscisic Acid
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promotes adaptation to environmental stress
Produced in mature leaves & fruits Counteracts auxin, suppresses elongation, promotes leaf senescence, controls opening/closing of stomata |
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Why do trees enter dormancy in winter?
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there is a lack of water
by loosing their leaves trees prevent evaporation and therefore conserve water |
