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Plant
Movements
Tropisms and Turgor
Responses
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Tropisms
 The
growth of part of a plant towards or
away from an environmental stimulus.
 If the growth is towards the stimulus, the
tropism is said to be positive, if it is away
from the stimulus it is said to be negative.
 Tropisms are a directional response – the
environmental stimulus comes from one
direction.
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Types of Tropisms
The type of the
stimulus is shown by
prefixes:
 Photo
 Light
 Geo
 Gravity
or Gravi
 Hydro
 Chemo
 Thigmo
 Water
 Chemicals
 Touch
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Plant Physiology Video
 http://www.youtub
e.com/watch?v=z
ctM_TWg5Ik&featur
e=fvw
 This
video shows
how Tropisms work
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Examples of Tropisms
 The
shoot of a plant is positively
phototropic - it grows towards light.
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Examples of Tropisms
 Roots
of plants are positively geotropic –
they grow down, and shoots are
negatively geotropic – they grow up
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More Examples of Tropisms
Some roots grow away from copper
pipes – they are negatively
chemotropic
Plants such as runner beans
are positively thigmotropic –
they grow towards a supporting
structure such as another
plant.
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Turgor Responses
 These
are responses of plants to stimuli from the
environment that do not come from a particular
direction. These include responses to changes in
temperature, light intensity, humidity and touch.
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Videos of Mimosa Plant and
Venus Fly Trap
 http://www.youtube.com/watch?v=BLTc
VNyOhUc
 http://www.youtube.com/watch?v=PRo4r
g07_gg&feature=fvw
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Examples of Turgor Responses
•The leaves of the Venus Fly
Trap and the Mimosa plants
both close up in response to
touch. The closure is not in
one particular direction.
•The flowers and leaves of
many plants close up when
the light intensity decreases
(it gets dark), regardless of
where light is or isn’t.
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Differences between Tropisms
and Turgor Responses:
 Tropisms
are a directional response, the
stimulus (eg. sunlight through a window)
determines the direction the plant grows.
 Turgor Responses are not the result of a
stimulus from a certain direction.
 Turgor Responses can be fast and do not
result from cell growth, whereas Tropisms
are generally slow growth changes.