1. What is a stimulus?
Stimulus: any change in an organism’s environment that causes the organism to react. It is a fancy way of saying “cause”.
Stimulus – singular
Stimuli – plural
Example: An animal is cold so it moves into the light.

2. What is a response?
Response: how the organism reacts to a stimulus and results in a change in behavior. It is a fancy way of saying “effect”
Example: Getting a drink when you are thirsty.

3. Examples of stimuli and their responses.
You are hungry so you eat.
A rabbit gets scared so it runs away.
You are cold so you put on a jacket.
A dog is hot so he lies in the shade.
It starts raining so you take an umbrella.

4. Write a stimulus and response that you have experienced recently
Write a stimulus and response that you have experienced recently. Underline the stimulus and circle the response.

5. 2 Types of Stimuli
External Stimuli Or
Internal Stimuli

6. External Stimulus
External stimulus: a stimulus that comes from outside an organism.
Examples:
You feel cold so you put on a jacket.
A snake lunges at a rabbit so it runs away.
A dog feels hot so it gets water.

7. Internal Stimulus
Internal Stimulus: a stimulus that comes from inside an organism.
Examples:
You feel hungry so you eat.
A cat feels thirsty so it drinks water.
You sweat because you are hot.

8. Internal Stimulus – Wilting in plants
Wilting refers to the loss of rigidity of non-woody parts of plants (leaves).
Plants wilt because of
Over watering: Most common in indoor plants.
Lack of water: Plants need water.
Root bound plants: move the growing plant to another container.
Too much sun
Not enough sun
Too much fertilizer
Disease

9. Internal Stimulus: Vomiting in humans
Vomiting is
the forceful expulsion of the contents of one's stomach through the mouth and sometimes the nose.
It is a response to internal stimuli such as:
Drugs
Pain and Stress
Motion sickness
Food poisoning
Excessive consumption of alcohol
Eating disorders (eg: bulimia)

10. Make a T-Chart on your paper and label the columns internal and external. Put the letter of each stimulus in the proper column
You have a stomach ache and decide to lay down.
A bird is thirsty and drink some water.
A squirrel sees a cat and runs up a tree.
A lion gets hungry and eats a gazelle.
You see a spider and scream.
internal
internal
external
internal
external

11. Tropism – The growth response of a plant toward or away from a stimulus
Phototropism – the way a plant grows or bends in response to light.
Geotropism – the way a plant grows or bends in response to gravity.
Hydrotropism – the way a plant grows or bends in response to water.
Thigmotropism – the way a plant grows or bends in response to touch.

12. Assessment
1. What is the difference between a stimulus and a response?
2. Vomiting is what type of stimulus?
3. Wilting in plants is what type of stimulus?

13. Positive vs Negative Tropism
Positive Tropism: Going toward the stimulus.
Example: If a plant grows toward the stimulus (light, earth, water, etc.) it shows a positive tropism.
Negative Tropism: Going away from a stimulus.
Example: Roots grow downwards showing negative tropism to light.

16. Phototropism Positive: Leaves and Stem because it is going toward the
light source.
Negative: Roots because it
is going away from light
source.

17. Hydrotropism Roots What is negative hydrotropism? Leaves and stem
What is positive hydrotropism?
Roots
What is negative hydrotropism?
Leaves and stem

18. What is the positive geotropism?
Roots
What is the negative geotropism?
Stem and leaves

19. Assessment Identify the external response from the following.
Your muscle sores when you run a mile
You drink water when you are thirsty
You run away when you see a tiger
After school you eat when you are hungry

20. 2. Which part of the plant shows positive geotropism?
Leaves
Stems
Flower
Roots

21. 3. Which of the following is not an external stimulus dealing with plants?
Light
Touch
Gravity
None of the above

22. 4. In the word phototropism, what is the stimulus?
Touch
Light
Water
None of the above

23. 5. If the plants is placed upside down and allowed to grown, in what direction would the roots grow?
Sideways
Not grow

24. 6. If the plants were tilted and allowed to grow sideways, in what directions would the leaves and stem grow? Up
Down
Sideways
None of the above

25. Assessment
7. Write an example of a stimulus and response.

26. 8. Give an example of positive phototropism.

27. 9. Give an example of positive geotropism.

28. 10. What is thigmotropism?