1. Tropisms- Response to Change

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

3. External Stimulus
– stimuli occurring on the outside

4. Internal Stimulus
– stimuli occurring from the inside.

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

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

7. These changes are called Tropisms

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

9. Four types of Tropisms are:
Geotropism
Phototropism
Thigmotropism
Hydrotropism

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

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

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

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

14. 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

15. 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