what is a stimulus? stimulus: any change in an organism’s environment that causes the organism to...
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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.
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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.
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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.
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Write a stimulus and response that you have experienced
recently. Underline the stimulus and circle the response.
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2 Types of Stimuli
External Stimuli
Or
Internal Stimuli
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External Stimulus
External stimulus: a stimulus that comes from outside an organism.
Examples:
1. You feel cold so you put on a jacket.
2. A snake lunges at a rabbit so it runs away.
3. A dog feels hot so it gets water.
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Internal Stimulus
Internal Stimulus: a stimulus that comes from inside an organism.
Examples:
1. You feel hungry so you eat.
2. A cat feels thirsty so it drinks water.
3. You sweat because you are hot.
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Internal Stimulus – Wilting in plantsWilting refers to the loss of rigidity of non-
woody parts of plants (leaves). Plants wilt because of 1. Over watering: Most common in indoor
plants.2. Lack of water: Plants need water.3. Root bound plants: move the growing
plant to another container.4. Too much sun5. Not enough sun6. Too much fertilizer7. Disease
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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:
1. Drugs 2. Pain and Stress 3. Motion sickness 4. Food poisoning 5. Excessive consumption of alcohol 6. Eating disorders (eg: bulimia)
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Make a T-Chart on your paper and label the columns internal and external. Put the
letter of each stimulus in the proper column
A. You have a stomach ache and decide to lay
down.
B. A bird is thirsty and drink some water.
C. A squirrel sees a cat and runs up a tree.
D. A lion gets hungry and eats a gazelle.
E. You see a spider and scream.
internal
internal
external
internal
external
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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.
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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?
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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.
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Phototropism
Positive: Leaves and Stem
because it is going toward the
light source.
Negative: Roots because it
is going away from light
source.
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Hydrotropism
What is positive hydrotropism?
Roots
What is negative hydrotropism?
Leaves and stem
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GeotropismWhat is the
positive geotropism?
What is the negative geotropism?
Roots
Stem and leaves
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Assessment
1. Identify the external response from the following.
A. Your muscle sores when you run a mile
B. You drink water when you are thirsty
C. You run away when you see a tiger
D. After school you eat when you are hungry
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2. Which part of the plant shows positive geotropism?
A. Leaves
B. Stems
C. Flower
D. Roots
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3. Which of the following is not an external stimulus dealing with plants?
A. Light
B. Touch
C. Gravity
D. None of the above
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4. In the word phototropism, what is the stimulus?
A. Touch
B. Light
C. Water
D. None of the above
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5. If the plants is placed upside down and allowed to grown, in what direction would the roots grow?
A. Up
B. Down
C. Sideways
D. Not grow
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6. If the plants were tilted and allowed to grow sideways, in what directions would the leaves and stem grow?
A. Up
B. Down
C. Sideways
D. None of the above
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Assessment
7. Write an example of a stimulus and response.
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8. Give an example of positive phototropism.
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9. Give an example of positive geotropism.
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10. What is thigmotropism?