plant responses
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Plant ResponsesHow 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.
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