1. How plants respond to stimuli

2. What’s a stimulus?
Things in the environment that can cause change or a reaction
Ex. Change in temperature, a loud noise, the presence of a predator
Extra: The Plural form of stimulus is Stimuli
The reaction to a stimulus is called a response

3. Can Plants respond to stimuli?
YES!
Plants respond to:
Sunlight
Water
Gravity
Touch
We call these responses Tropisms

4. What’s a tropism?
A tropism is a plant’s movement in response to its environment.

5. Tropisms can be positive or negative
movement TOWARD the stimulus
Movement AWAY from the stimulus

6. Phototropism Movement of plants toward light
Plant response: Stems and leaves turn toward light
Why?
Maximize amount of sun for photosynthesis to make their food.
Phototropism

7. Geotropism Movement of plants in response to gravity plant response:
1. roots grow down toward gravity
2. shoot, stems, and leaves grow up away from gravity
Why?
Allows plants to grow properly and get nutrients and sunlight

8. Hydrotropism Movement of plant toward water.
Plant response: roots will move toward water
Why?
Water is needed for photosynthesis, to transport nutrients, and turgor pressure

10. Thigmotropism Plants moving in response to touch. Plant response:
1. Positive is toward touch (vines wrap around structures)
2. Negative is away from touch (some plants close up when touched)
Why?
to reach sunlight (positive)
or to protect itself (it’s movement may scare away a predator)

11. Review

12. Geotropism Gravity causes a response in plant growth
In the picture above, which part of the plant exhibits positive tropism, and which exhibits negative tropism?

13. Hydrotropism The way a plant grows or bends in response to water
Why would it be important for some parts of a plant to be pulled toward water?

14. Thigmotropism Plants bend and grow because of touch.
What are some other ways a plant can be “touched”?

15. Phototropism The way a plant grows or bends in response to light.
Why do you think sunflowers were given their nickname?

16. Draw the pictures

17. Hydroptropism

18. Geotropism

19. Phototropism

20. Geotropism

21. Phototropism

22. Thigmotropism

23. TROPISM QUIZ
Identify the type of tropism in the following pictures

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