Plant TropismsPlant Tropisms

What are we talking about?What are we talking about?

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

What are we talking about?What are we talking about?

Stimulus – Stimulus – an action or condition that an action or condition that causes a responsecauses a response

Response – Response – an action or condition that is a an action or condition that is a reaction to a stimulusreaction to a stimulus Negative responseNegative response – when the growth of a – when the growth of a

plant is away from the stimulusplant is away from the stimulus Positive responsePositive response – when the growth of the – when the growth of the

plant is towards the stimulusplant is towards the stimulus

Types of TropismTypes of Tropism

We are going to be studying 6 Tropisms:We are going to be studying 6 Tropisms:

HydrotropismThermotropism

Gravitropism

Thigmotropism

Phototropism Heliotropism

HydrotropismHydrotropism

Stimulus: Stimulus: WaterWater

Response: Response: A plant’s roots grow towards A plant’s roots grow towards the source of waterthe source of water Is this a positive or negative response? Is this a positive or negative response?

ThermotropismThermotropismStimulus: Stimulus: TemperatureTemperatureResponse: Response: a plant grows in the direction of/away from a a plant grows in the direction of/away from a source of heat or coldsource of heat or cold Example: In the first picture, this tree has a Example: In the first picture, this tree has a positivepositive response to response to

the coldthe cold.. Example: A plant called a Rhododendron curls its leaves Example: A plant called a Rhododendron curls its leaves awayaway

when it experiences when it experiences cold weathercold weather..

GravitropismGravitropism

Stimulus: Stimulus: GravityGravity

Reaction:Reaction: Positive – Positive – the roots the roots

grow downward, with grow downward, with gravitygravity

Negative – Negative – the stalk the stalk grows upward, against grows upward, against gravitygravity

ThigmotropismThigmotropism

Stimulus: Stimulus: TouchTouchResponse – Response – the leaves the leaves (or part of the plant that (or part of the plant that is touched) move or coil is touched) move or coil away from the touch, or away from the touch, or trigger some other actiontrigger some other action Example: The Venus Fly Example: The Venus Fly

Trap is a plant that shows Trap is a plant that shows thigmotropism. thigmotropism. It closes It closes when a bug or some other when a bug or some other object touches it. object touches it.

PhototropismPhototropism

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

HeliotropismHeliotropismStimulus: Stimulus: SunlightSunlightResponse – Response – a plant grows or turns to face the direction of a plant grows or turns to face the direction of the sunthe sun Example: Example: Young Sunflowers face the sun all day long. As the sun Young Sunflowers face the sun all day long. As the sun

goes across the sky, the sunflower turns so that it is always facing goes across the sky, the sunflower turns so that it is always facing it. it.

Is a Sunflower growing towards the sun an example of Is a Sunflower growing towards the sun an example of Phototropism or Heliotropism? Phototropism or Heliotropism?

ReferencesReferencesPictures: 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_musci

pula_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