Goal 4 - Tropism and Taxis Notes
Tropisms
Tropisms are directional movement responses in plants that occur in response to a directional stimulus. Tropisms are controlled by a plant hormone called auxin.
Tropisms are named based upon the stimulus.
Types of tropisms:
Tropisms are directional movement responses in plants that occur in response to a directional stimulus. Tropisms are controlled by a plant hormone called auxin.
Tropisms are named based upon the stimulus.
Types of tropisms:
- Phototropism – The way a plant grows or bends in response to light. (Plant stems grow towards light – A plant will lean towards a window where the light is stronger than inside a room).
- Graviotropism or geotropism – The way a plant grows or bends in response to gravity or earth. (Plant roots grow downward into the earth because of gravity).
- Chemotropism – The way a plant grows or bends in response to a chemical.
- Hydrotropism – The way a plant grows or bends in response to water.
- Thigmotropism – The way a plant grows or bends in response to touch. (Some people notice that their houseplants grow better when they touch them and pay attention to them. A mimosa plat will curl its leaves when touched. A venus fly traps closes its leaves when a fly enters.)
Taxis
A taxis is the directional movement of animals in response to a stimulus.
Taxis are named based upon the type of stimulus.
Types of taxis:
Taxis are named based upon the type of stimulus.
Types of taxis:
- Chemotaxis – The directional movement of an animal in response to a chemical such as pH wrong in a fish tank. A female dog in heat attracting a male (pheromones)).
- Phototaxis – The directional movement of animals in response to light. (A snake laying on a rock on a sunny day)
- Thigmotaxis – The directional movement of an animal in response to touch (A cat purring while you pet it).
Positive vs Negative
Tropisms and taxis may be positive or negative.
- If an animal/plant moved toward the stimulus, then the response was POSTIVE. A plant bending toward a window would be a positive phototropism.
- If an animal/plant moves away from a stimulus, the response is NEGATIVE. An owl coming out at night to hunt would be a negative phototaxis.