Plants Respond to External Stimuli

Plants Respond to External Stimuli - We now know, from the...

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Plants Respond to External Stimuli One plant response to environmental stimulus involves plant parts moving toward or away from the stimulus, a movement known as a tropism . Nastic movements are plant movements independent of the direction of the stimulus. Alterations in Growth Patterns Generate Tropisms Charles Darwin and his son Francis studied the familiar reaction of plants growing toward light: phototropism . The Darwins discovered that the tips of the plant curved first, and that the curve extended gradually down the stem. By covering the tips with foil, they prevented the plant from curving. They concluded that some factor was transmitted from the tip of the plant to the lower regions, causing the plant to bend.
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Unformatted text preview: We now know, from the 1926 experiments of Frits Went, that auxin, a plant hormone produced in the stem tip (auxins promote cell elongation), moves to the darker side of the plant, causing the cells there to grow larger than corresponding cells on the lighter side of the plant. This produces a curving of the plant stem tip toward the light, a plant movement known as phototropism. Geotropism is plant response to gravity. Roots of plants show positive geotropism, shoots show negative geotropism. Geotropism was once thought a result of gravity influencing auxin concentration. Several new hypotheses are currently under investigation....
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This note was uploaded on 11/29/2011 for the course BIO BSC1010 taught by Professor Gwenhauner during the Fall '10 term at Broward College.

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Plants Respond to External Stimuli - We now know, from the...

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