1. Lesson 3: Stimuli
Foundation
Science
SC 22101

2. Review Questions
1. What is an external stimulus?
2. Copy the word “PHOTOTROPIC” in your notebook.
Underline the prefix, put a box around the suffix.
3. What does phototropic mean?
4. You see a bird dive down into the ocean. Guess what the
external stimulus was to make the bird dive into the water
like this.

3. Internal Stimulus
Stimuli that are present inside of an organism
are called internal stimuli.
Stimulus - ?
Response - ?

4. Internal Stimulus
Stimuli that are present inside of an organism
are called internal stimuli.
Stimulus - hunger
Response – look for food
Body then back more
toward homeostasis

5. Internal Stimulus
We don’t see, hear, smell, touch or taste
internal stimuli.
Examples of internal stimuli:
-Headache
-Being thirsty
-Being hungry

6. Internal or External?
A fever is usually a reaction to an internal
stimulus.
Stimulus = too many bacteria in your body
Response = body makes itself hot to kill bacteria
(most bacteria die if they get too hot)

7. Questions
1. Label internal or external stimulus:
-You see a spider and scream.
-You have a stomach ache and decide to lay down.
-A bird is thirsty and drinks some water.
-A squirrel sees a cat and runs up a tree.
-A lion gets hungry and eats a gazelle.
2. If an organism is not in homeostasis, it will probably be motivated to find
food or water by ____________ stimuli.
3. True or False: bacteria respond to internal and external stimuli.
4. Sea anemones catch fish by using their sticky tentacles. What stimuli do the
sea anemones respond to in order to catch the fish? External or internal?