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Plant Tropisms

Plant Tropisms. What are we talking about?. Tropism - directional growth of a plant, or part of a plant, in response to an external stimulus. What are we talking about?. Stimulus – an action or condition that causes a response

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Plant Tropisms

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  1. Plant Tropisms

  2. What are we talking about? • Tropism - directional growth of a plant, or part of a plant, in response to an external stimulus

  3. 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

  4. Types of Tropism • We are going to be studying 6 Tropisms: Thermotropism Hydrotropism Thigmotropism Gravitropism Heliotropism Phototropism

  5. Hydrotropism • Stimulus: Water • Response: A plant’s roots grow towards the source of water • Is this a positive or negative response?

  6. 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.

  7. Gravitropism • Stimulus: Gravity • Reaction: • Positive – the roots grow downward, with gravity • Negative – the stalk grows upward, against gravity

  8. 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.

  9. Photropism • 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?

  10. 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?

  11. References • Pictures: • http://virtualastronaut.tietronix.com/textonly/act25/images/hydrotropism.gif • http://k53.pbase.com/u48/roving_rube/large/30489110.a.c.birch.jpg • http://www2.brevard.edu/jefrick/rhod.htm • http://www.xtec.cat/~mherna23/summer03/amspot/picture/gravitropism.gif • http://img1.photographersdirect.com/img/17231/wm/pd1198793.jpg • http://wpcontent.answers.com/wikipedia/commons/9/9d/Dionaea_muscipula_closing_trap_animation.gif • http://img1.photographersdirect.com/img/17231/wm/pd1198796.jpg • http://farm2.static.flickr.com/1423/1402179998_4e1712d584.jpg • Information: • http://www.hasc.qld.edu.au/csnotes06/biowedGG/Notes%20for%20Sandra/Plant%20Tropisms.doc • www.wikipedia.org

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