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Tropism in plants
A stimulus is anything in the environment
that causes a response in an organism.
The response often involves movement
either toward the stimulus or away from
the stimulus.
Plants respond to stimuli such as touch,
light, water, and gravity.
Some responses of a plant to an external
stimuli are called tropisms
Geo = gravity.
Response in plants to
gravity.
The stem/shoots
show negative
tropism. (Against
gravity.)
The roots show
Positive tropism
(towards gravity.)
provide firm
anchorage for
roots.
ensure the plant
can get adequate
supply of water
Picture from http://cbse.myindialist.com/biology-x-control-andcoordination-coordination-in-plants-movement-due-to-growth/
Response to light.
When a plant
grows toward light
it is called a
positive response
enables leaves to
be in a position to
receive as much
sunlight as possible
for photosynthesis
Picture from
http://herbarium.desu.edu/pfk/page11/page
12/page13/page13.html
Response to water.
Example: plants
moving to a higher
humidity, roots
moving to a
greater
concentration of
water.
ensures that a
plant gets enough
water for
photosynthesis
Picture from http://www.tutorvista.com/content/biology/biologyiv/plant-growth-movements/paratonic-movements.php
Response to touch.
The stem bends and
twists around any object it
touches.
Gives the plant additional
support.
Picture from http://wikipedia.com
Picture from http://www.sunnysidescience.com/plant_responses.htm
Picture from http://cdnwrite.demandstudios.com/upl
oad/1000/600/10/8/391618.jp
g
Rapid response of rapid
movements of plant
organs in response to a
stimulus
Used as a defense.
Used to trap its prey in
carnivorous plants.