Plant Tropisms

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Plant Tropisms
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What are we talking about?

• Tropism - directional growth of a plant, or part
  of a plant, in response to an external stimulus

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Stimulus

• Stimuli an action or condition that causes a
  response
• Stimuli can be either internal or external

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Types of Stimuli

• External stimuli- come from factors found in the
  environment.
• Examples- temperature, presence of water or
  nutrients, light etc
• Internal stimuli- come from factors within an
  organism
• Examples- germs, dehydration, lack of nutrients,
  etc.

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Stimulus
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Response

• An organisms reaction to change.

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Response
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What are we talking about?

• Stimulus an action or condition that causes a
  response
• Response an action or condition that is a
  reaction to a stimulus
• Negative response when the growth of a plant is
  away from the stimulus
• Positive response when the growth of the plant
  is towards the stimulus

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Example

• Stimulus Lack of water.
• Is this internal or external?
• Response wilting
• Is it positive or negative?

Examples
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Homeostasis

• Homeo- same
• Stasis- state of balance
• The purpose of response to stimuli in organisms
  is to maintain homeostasis, a balance within its
  internal systems.

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What are we talking about?

• Tropism - directional growth of a plant, or part
  of a plant, in response to an external stimulus
• Usually named for the stimulus involved

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Types of Tropism

• Today we are going to be studying the types
  tropisms

Heliotropism
Hydrotropism
Thigmotropism
Geotropism
Thermotropism
Phototropism
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Hydrotropism

• Stimulus Water
• Response A plants roots grow towards the source
  of water
• Is this a positive or negative response?

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Thermotropism

• Stimulus Temperature
• Response a plant grows in the direction of/away
  from a source of heat or cold
• Example In the first picture, this tree has a
  positive response to the cold.
• Example A plant called a Rhododendron curls its
  leaves away when it experiences cold weather.

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Geotropism/Gravitropism

• Stimulus Gravity
• Reaction
• Positive the roots grow downward, with gravity
• Negative the stalk grows upward, against gravity

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Thigmotropism

• Stimulus Touch
• Response the leaves (or part of the plant that
  is touched) move or coil away from the touch, or
  trigger some other action
• Example The Venus Fly Trap is a plant that shows
  thigmotropism. It closes when a bug or some other
  object touches it.

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Phototropism

• Stimulus Light
• Response the plant grows in the direction of a
  unidirectional light (it only comes from one
  direction)
• What type of response is this?

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Heliotropism

• Stimulus Sunlight
• Response a plant grows or turns to face the
  direction of the sun
• Example Young Sunflowers face the sun all day
  long. As the sun goes across the sky, the
  sunflower turns so that it is always facing it.
• Is a Sunflower growing towards the sun an example
  of Phototropism or Heliotropism?

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Working Together

• Plant tropisms work together to maintain
  homeostasis within the plant
• Heliotropism
• Geotropism
• -Geotropism
• Hydrotropism

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References

• Pictures
• http//virtualastronaut.tietronix.com/textonly/act
  25/images/hydrotropism.gif
• http//k53.pbase.com/u48/roving_rube/large/3048911
  0.a.c.birch.jpg
• http//www2.brevard.edu/jefrick/rhod.htm
• http//www.xtec.cat/mherna23/summer03/amspot/pict
  ure/gravitropism.gif
• http//img1.photographersdirect.com/img/17231/wm/p
  d1198793.jpg
• http//wpcontent.answers.com/wikipedia/commons/9/9
  d/Dionaea_muscipula_closing_trap_animation.gif
• http//img1.photographersdirect.com/img/17231/wm/p
  d1198796.jpg
• http//farm2.static.flickr.com/1423/1402179998_4e1
  712d584.jpg
• Information
• http//www.hasc.qld.edu.au/csnotes06/biowedGG/Note
  s20for20Sandra/Plant20Tropisms.doc
• www.wikipedia.org