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Plant Responses How plants move www.wou.edu/~bledsoek/103materials/.../Plant_responses.ppt Early Inquiry The houseplant observation • For years, people noticed that houseplants tended to lean toward a source of light. • Charles Darwin and his son Francis, wondered why. How does a plant “know” where to lean? Tropisms • Tropisms are the growth of a plant toward or away from a stimulus, including: • Phototropism: in response to light • Gravitropism: in response to gravity • Thigmotropism: in response to touch Tropisms: cell elongation • In general, tropisms involve cell elongation or suppression of cell elongation on one side of a plant, causing the plant to grow in a particular direction. Phototropism • Look at the sprouts in the bottom picture and the explanatory diagram at the top. Explain why the sprouts are all leaning in the same direction. Gravitropism • In this Impatiens plant, shoots grow upwards and roots grow downwards in response to gravity. • On which side of the shoot and root do you think auxins are more concentrated? Thigmotropism • In some plants, vining stems or tendrils will grow in response to touch. • Which side of the tendril is elongating? Where might the auxin be? (Remember, this is the shoot system.) Nastic movement in the sensitive plant (Mimosa pudica) Other examples • Sunflowers follow the sun during the day. • Leaves of many plants turn to follow the sun.