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.