Plants: Essential Processes Responses to Stimuli Terrestrial plants, anchored, by necessity, to their substrate, have limited mobility and few ways in which they can respond to environmental stimuli. The primary way in which plants do respond is through changes in growth. As we have seen in Essential Processes, Plant Hormones , hormones are often responsible for changing the growth patterns of plants. This section will explore tropisms and turgor movements, two forms of plant movement that allow the plant to react to stimuli. Tropisms Tropisms are responses to stimuli that result in the long-term growth of the plant toward or away from the stimulus. This growth results from cell elongation occurring at different rates on different sides of the plant, so that the plant bends in one direction. Phototropism, a reaction to light, causes the plant to bend toward the light source (see Essential Processes, Auxins). Thigmotropism, a reaction to touch, causes parts of the plant to thicken or coil as they touch or
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