1. Stimulus & Response

2. Stimulus
A change in organism’s environment

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

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, or protection.

8. Examples Stimulus = Is this internal or external? Response =
Lack of water
Wilting (to conserve water)
Bacteria or Virus
Fever (to kill germs)

9. Fight or Flight Response
An organisms biological response to extreme stress.
Can include-
Increased heart and breath rate
Shaking
Adrenaline rush- extreme strength
Freezing in place (cannot move)

10. Examples of Fight or Flight

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. Phototropism Plants grow toward a source of light Animation:

16. Examples

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

18. Gravitropism A plant grows with or against gravity
Also called Geotropism
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:

19. 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.

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

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

22. Turgor Pressure
The pressure exerted by water inside the cell against the cell wall.
This celery stalk has the least amount of turgor pressure because of water pressure in the cells
This celery stalk has more turgor pressure than the 1st
This celery stalk has the most turgor pressure of all because it has the greatest water pressure in the cells of the plant