Tropisms- Response to Change

Stimuli – A change in an organism’s surroundings that causes the organism to react.

External Stimulus – stimuli occurring on the outside

Internal Stimulus – stimuli occurring from the inside.

Response – a reaction of a living thing to a stimulus.

Interesting Characteristic of plants They can change their growth in response to their environment.

These changes are called Tropisms

Tropism- an automatic movement by an organism (especially by a plant) that involves a turning or growing toward or away from a stimulus.

Four types of Tropisms are: Geotropism Phototropism Thigmotropism Hydrotropism

Geotropism – the way a plant grows or bends in response to the Earth (or gravity).

Phototropism – the way a plant grows or bends in response to light.                

Thigmotropism – the way a plant grows or bends in response to touch

Hydrotropism – the way a plant grows or bends in response to water.

Responses can be positive or negative. A Positive response is when the plant moves toward the stimulus A Negative response is when a plant moves away from the stimulus

Examples of a positive response – Roots respond positively to gravity by growing down into the soil Trunk and branches respond positively to light by growing toward the light Example of a negative response: Trunk and branches respond negatively to gravity by growing up toward the sky