1. Tropisms

2. Stimulus Change in an organism’s surroundings that causes a response
Internal (chemicals and hormones)
External (light, touch, water, gravity)
All living organisms, including plants, respond to stimuli

3. Response
Reaction of a living thing to a stimulus

4. Stimulus/Response
Response
Stimulus

5. Internal Stimulus/Response
Stimulus or response happens inside the organism
Chemicals and hormones

6. External Stimulus/Response
Stimulus or response occurs outside the organism
Light, touch, water, gravity, electricity, temperature, darkness etc…

7. Tropism
Automatic movement by an organism toward or away from a stimulus
Positive (toward)
Negative (away)

8. Phototropism When a plant or animal moves toward or away from light
Positive – toward light
Negative – away from light

9. Phototropism

10. Phototropism

11. Geotropism Also called gravitropism
Plants or animals response to gravity
Positive - roots growing down
Negative - stems growing up

12. Geotropism

13. Geotropism

14. Hydrotropism Directional movement toward water
Usually occurs only in the roots

15. Hydrotropism

16. Thigmotropism
When an organism responds to touch
Vines
Venus flytrap

17. Thigmotropism

18. Thigmotropism

19. Emergence of Seedlings
Unbalanced forces allow seedlings to push their way through the soil and sometimes rock

20. Turgor Pressure Force in the form of pressure
helps some plants stand upright.
In animals, it also helps blood move around the body

21. Turgor Pressure

22. Turgor Pressure

23. emergence of seedlings
thigmotropism
phototropism
geotropism
organism’s response to light
organism’s response to gravity
organism’s response to touch
hydrotropism
turgor pressure
emergence of seedlings
organism’s response to water
pressure inside the plant that allows it to stand up.
seedling pushing up through the ground