Plant Tropisms

What are we talking about? Emergence - An outgrowth, as a projection, on the surface of a plant Force – A push or a pull Turgor Pressure - pressure exerted on the plant cell wall by water passing into the cell by osmosis Tropism – an involuntary response of an organism to a stimulus (in plants)

Tropisms 101 Stimulus – something that causes a action from an organism. 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

Types of Tropism We are going to be studying 3 Tropisms: Hydrotropism Gravitropism AKA “Geo”tropism Phototropism

Hydrotropism: “water” Stimulus: Water Response: A plant’s roots grow toward the source of water IIIIs this a positive or negative response?

Gravitropism: “Geo” Stimulus: Gravity Response: 2. Positive – the roots grow downward, towards gravity 1. Negative – the stalk grows upward, against gravity N P

Phototropism- “light” Stimulus: Light Response – the plant grows in the direction of a the light (it only comes from one direction)  What type of response is this?

Other types of Tropisms

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.

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

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?

References Pictures:   gif gif       gif gif     pula_closing_trap_animation.gif pula_closing_trap_animation.gif     Information:   dra/Plant%20Tropisms.doc dra/Plant%20Tropisms.doc  