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Responsive Growth Movements

Responsive Growth Movements - Responsive Growth Movements...

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Responsive Growth Movements: Tropisms Responsive growth movements toward or away from an external stimulus are called  tropisms . If the  plant movement is  toward  the stimulus, it is a  positive tropism;   away from  the stimulus, a  negative  tropism Phototropism The tropic response to unidirectional light is called  phototropism . In general, shoots grow toward  light and hence are positively phototropic; roots grow away from light and are negatively phototropic.  Well-known and often-repeated experiments with oat seedlings have shown that the auxin IAA,  which causes elongation of cells, migrates to the shaded side of oat coleoptiles. The subsequent  differential growth on the two sides causes the coleoptiles to bend toward the light. Although green  stems also bend and grow toward the light, in this case an IAA inhibitor prevents cells from 
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