Transcript Plant Responses

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.