Introduce the section by using the metaphor of the conveyor belt in reverse as the digestive system breaks down a bacon, lettuce, and tomato sandwich.
Before students begin the journey through the gastrointestinal tract in the inner space capsule, direct them to the illustration (Figure 3.5).
Assign Mini Activity: Can You Tell the Types of Teeth?
Introduce and assign Activity 3 -1: Digestive Enzyme in Action.
Continue to follow the journey of the inner space capsule until it leaves the stomach and enters the small intestine. Point out that in the next section students will investigate peristalsis.
Assign and discuss the Journal Writing relating to stress.
Draw students' attention to the key ideas using means such as posters and overhead transparencies.
Select appropriate Projects to complete if time permits.
You may want to do Enrichment 4-1: Transport of Materials-Exploring Diffusion as a demonstration when beginning the section. Students can do this activity again themselves at the end of Section 4.
Use the Apply Your Knowledge and Review Questions in reviewing the section.
What Do You Think?
Why do you think some birds need to swallow stones to help them digest their food? Describe how you think their digestive systems work, considering the kinds of food they eat.
What Do You Think?
Have you ever watched a TV commercial for a hot, steaming pizza that made you hungry even though you weren't hungry a moment before? A Russian scientist named Dr. Pavlov did an experiment on salivation. Dr. Pavlov rang a bell whenever a dog was fed. The dog salivated because it smelled and tasted the food. After many feedings, the dog would begin salivating when the bell rang, even if there wasn't any food. What do you think this shows about how the brain connects to our digestive systems? Why do we sometimes convince ourselves we are hungry when our bodies don't agree, or that we aren't hungry when we really are? Is this healthy behavior? Why or why not?
Can You Tell the Types of Teeth? Students look at their teeth in a mirror and identify the incisors, canines, bicuspids, and molars.
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Can you tell what kinds of foods different animals eat by looking at their teeth? Describe some differences between animal teeth and how they match the diets of those animals.
The sight or smell of good food can make you salivate. Another condition that causes you to salivate is nausea, for example, when you get seasick. What role do you think saliva can play when you are nauseated?