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

3.  External Stimulus  Stimulus occurring on the outside  Example: sun causes you to squint your eyes  Internal Stimulus  Stimulus occurring on the inside  Example: you get goose bumps because you are cold

4.  a reaction to a stimulus

5.  A plant’s response to a stimulus Three types of Tropisms are:  Geotropism  Phototropism  Thigmotropism

6.  the way a plant grows or bend in response to the Earth (or gravity).

7.  the way a plant grows or bend in response to light.

8. Thigmotropism  the way a plant grows or bend in response to touch

9.  A plant’s response to water

10. 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

11.  Roots respond positively to gravity by growing down into the soil  Trunk and branches respond positively to light by growing toward the light

12.  Trunk and branches respond negatively to gravity by growing up toward the sky

13.  The pressure of the cell contents against the cell wall  A force is exerted on the cell wall that keeps the plant rigid

14. NO TURGOR PRESSURETURGOR PRESSURE