Plant Responses How plants move

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.