1. Stimulus & Response
TEKS 7.13B describe and relate responses in organisms that may result from internal stimuli such as wilting in plants and fever or vomiting in animals that allow them to maintain balance
TEKS 7.13A investigate how organisms respond to external stimuli found in the environment such as phototropism and flight or fight

2. Stimulus
A change in organism’s environment

3. Types of Stimuli A stimulus can either be external or internal.
External stimuli- come from factors found in the environment.
Examples- temperature, predators, presence of water or food, etc
Internal stimuli- come from factors within an organism
Examples- germs, dehydration, lack of energy, pain

4. Stimulus
Is this stimulus external or internal?

5. Response
An organisms reaction to change.

6. Response

7. Homeostasis Homeo- same Stasis- state of balance
The purpose of response to stimuli in organisms is to maintain homeostasis, a balance within it’s internal systems.

8. Examples Stimulus = Lack of water Is this internal or external?
Response =
Lack of water
Wilting
Bacteria or Virus
Fever

9. Examples Stomach virus Stimulus = Is this internal or external?
Response =
Stomach virus
vomiting
Saber-tooth Tiger
Fight or flight

10. Just as animals respond to the environment, plants do as well.

11. Tropisms
Tropism = plant’s growth response toward or away from a stimulus

12. Tropisms
Tropism = plant’s growth response toward or away from a stimulus
Positive tropism
Negative tropism

13. Tropisms
Tropism = plant’s growth response toward or away from a stimulus
Positive tropism = plant grows toward a stimulus
Negative tropism

14. Tropisms
Tropism = plant’s growth response toward or away from a stimulus
Positive tropism = plant grows toward a stimulus
Negative tropism = plant grows away from a stimulus

15. Hydrotropism Hydrotropism = a plant’s roots grow toward water
Is this positive or negative?

16. Phototropism Plants grow toward a source of light Animation:

17. Examples

18. Thigmotropism A plant grows toward or away from pressure
Positive turns toward pressure
Negative turns away from pressure

19. Geotropism A plant grows with or against gravity
Also called Gravitropism
Positive- A plant’s roots grow down, with the pull of gravity
Negative- A plant’s stems or trunk grow up, against the pull of gravity.
Animation:

20. Regardless of the position a seed is planted in, the roots grow down with gravity and the stem up against gravity.
Regardless of the slope of the land, the tree grows up against gravity.

21. Working Together + phototropism + geotropism - geotropism
Plant tropisms work together to maintain homeostasis within the plant
Plants in Motion Video
+ phototropism
+ geotropism
- geotropism
+ hydrotropism