tropisms and turgor responses

Plant MovementsTropisms 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

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The type of the stimulus is shown by prefixes:

Photo Geo or Gravi Hydro Chemo Thigmo

Light Gravity Water Chemicals Touch

Plant Physiology Video

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http://www.youtube.com/watch?v=zctM_TWg5Ik&feature=fvw

This video shows how Tropisms work

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

Plants such as runner beans are positively thigmotropic – they grow towards a supporting structure such as another plant.

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Some roots grow away from copper pipes – they are negatively chemotropic

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=PRo4rg07_gg&feature=fvw

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•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.

Examples of Turgor Responses

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.

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