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Glossary of BIO 1510: Lecture Exam 3-6: 40

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Tropism
Positive or negative growth responses to external stimuli
Phototropism
bending of growing stems toward light (+)
Gravitropism
growth of roots (+) and shoots / stems (-) in response to gravity
Thigmotropism
growth in response to touch
Dormancy:
Adaptation to unfavorable environ-mental conditions
Dormancy: Deciduous Trees
leaves are shed; meristems become inactive & are protected by “scales”
Dormancy: Annuals
spend winter as seeds

Some seeds can germinate after thousands of years of dormancy
Dormancy: Perrenials
spend winter underground as stems or roots with stored food
Auxin
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
Cytokinins
stimulate cell division & differentiation

Synthesized in root apical meristems

Bacterial infections can cause overproduction of cytokinins
Ethylene
stimulates the ripening of fruit; and inhibits root & stem elongation
Abscisic Acid
promotes adaptation to environmental stress

Produced in mature leaves & fruits

Counteracts auxin, suppresses elongation, promotes leaf senescence, controls opening/closing of stomata
Why do trees enter dormancy in winter?
there is a lack of water

by loosing their leaves trees prevent evaporation and therefore conserve water

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