1. Stimulus & Response

2. Stimulus Achange in organism’s environment 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 = Is this internal or external? Is this internal or external?  Response =  Stimulus = Is this internal or external? Is this internal or external?  Response = Lack of water Wilting Bacteria or Virus Fever

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

10. Tropisms  Positive tropism  Negative tropism

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

12. 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

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

14. Phototropism Plants grow toward a source of light Animation: http://botanical-online.com/animation8.htm

15. Examples

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

17. Geotropism  A plant grows with or against gravity  Also called Gravitropism Negative- A plant’s stems or trunk grow up, against the pull of gravity. Positive- A plant’s roots grow down, with the pull of gravity Animation: http://botanical-online.com/animation4.htm

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

19. Working Together   Plant tropisms work together to maintain homeostasis within the plant - geotropism + phototropism + geotropism + hydrotropism