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Five known classes of hormones control plant growth and development
Auxin – promotes fruit growth
Cytokinins – stimulate cell division
Gibberellins – stimulate growth in leaves and stems
Abscisic Acid – slows plant growth
Ethylene – inhibits root growth

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Phototropism –bends shoot towards light; enhances photosynthesis
Gravitropism – uses specialized plastids
(statoliths).
Roots display positive gravitropism
(grows down towards the earth) and the shoot displays negative gravitropism
(grows up out of the earth)

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Thigmotropism:
Developmental response to mechanical stimulation
 Example: thicker stemmed plants are found in locations where the winds are strong

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Turgor movements are relatively rapid, reversible plant responses

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Biological clocks control circadian rhythms in plants and other eukaryotes

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Photoperiodism synchronizes many plant responses to changes of season

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Phytochrome functions as a photoreceptor in many plant responses to light and photoperiod

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Control systems enable plants to cope with environmental stress

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The study of plants began when early humans began to distinguish edible plants from poisonous ones.
Then began to make things from wood and other plant products.

 Today scientists aim for increasing crop productivity, but the fun of discovery is what motivates most plant scientists.

 Plant biology, one of the oldest branches of science, is driven by curiosity and need – curiosity about how plants work and a need to feed, clothe, and house an increasing human population. Plant biology is in the midst of a renaissance, in which new methods, coupled with clever choices of experimental organisms, have catalyzed a research explosion.