What is a stimulus?

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 hungryso you eat. • A rabbit gets scaredso 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. 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 What is positive hydrotropism? Roots What is negative hydrotropism? Leaves and stem

18. Geotropism 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? • Up • Down • 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?