LESSON 4 Digestion in the Mouth INTRODUCTION Now that you know how to perform chemical tests for starch and sugar, it’s time to use those skills to begin your investigation of the digestive processes. In this lesson, you will see what hap- pens to food while it is in the mouth. Is there a good reason to chew your food well before you swallow it? Do your teeth get any help as they tear and grind a bite of food before you swallow it? Once you’ve explored these questions, you’ll be prepared to move on to investigate what happens in the stomach, where the process of digestion continues. All these activities have one goal: to get food into a form that can be absorbed into your bloodstream and used by the cells to maintain life. OBJECTIVES FOR THIS LESSON INTYRE/PHOTO RESEARCHERS, INC. C Explore mechanical digestion in the mouth. © WILL/DENI M Explore chemical digestion in the mouth. That pizza looks great! But take it easy—it’s important Begin to construct a definition of the to chew your food carefully before you swallow it. word “enzyme.” 24 STC/MS™ H UMAN B ODY S YSTEMS MATERIALS FOR Getting Started LESSON 4 1. Your teacher will give you a cracker. Put it For you in your mouth. Chew it very slowly. Pay 1 copy of Student close attention to everything that happens Sheet 4.1: in your mouth. When you are ready to Chemical Testing swallow it, put your thumb and index finger for Sugar and gently around your Adam’s apple. Swallow Starch the cracker. In your science notebook, 1 sheet of four describe exactly what happened while you summary boxes were chewing and swallowing the cracker. (for homework assignments) A. Why do you think that chewing the 1 pair of safety cracker was important? goggles B. What happened to your Adam’s apple For your group as you swallowed? 1 plastic box 2 dropper bottles of 2. Share your ideas with the class. Benedict’s solution 2 dropper bottles of Lugol solution 2 dropper bottles of Inquiry 4.1 salivary amylase 2 dropper bottles of Exploring Chemical distilled water (DW) Digestion in the Mouth 2 dispensing bottles of starch solution PROCEDURE 2 medium test tubes 1 test tube rack 1. Pick up your materials. You will work in 2 test tube clamps pairs in this lesson. You will perform 2 6-cup lab trays chemical tests for sugar and starch using 2 plastic pipettes Benedict’s solution and Lugol solution. 8 toothpicks Take turns so that each of you gets equal 2 black markers experience with both tests. STC/MS™ H UMAN B ODY S YSTEMS 25 LESSON 4 D IGESTION IN THE M OUTH Read along as your teacher reviews the SAFETY TIPS 2. Safety Tips. Always wear safety goggles Number the cups in your lab tray from when using 3. 1 to 6. Use Figure 4.1 as a guide. chemicals and hot pots. 4. Using Figure 4.1 and your teacher’s Lugol solution guidance, complete the design of the data contains a small collection table on Student Sheet 4.1. amount of Give the table a name. iodine, which is considered poi- sonous. Do not place any of the chemicals in or near your mouth. Do not get the chemicals on your skin or clothing. Lugol solution will leave a stain. If Benedict’s solu- tion comes in contact with your eyes or skin, thoroughly flush Figure 4.1 Designing the data collection table the affected area with a generous Add 30 drops of starch solution to cups amount of water. 5. 1, 2, 5, and 6. Wipe up acciden- tal spills of Lugol 6. Add 30 drops of distilled water to cups and Benedict’s 3 and 4. solution with paper towels, which you can dispose of in the trash. 26 STC/MS™ H UMAN B ODY S YSTEMS LESSON 4 D IGESTION IN THE M OUTH 7. Add 2 drops of amylase to cups 3, 4, 5, 10. Using the technique you learned in and 6, as shown in Figure 4.2. Lesson 3, perform a chemical test for starch for the substances in the cups on the bottom row (cups 2, 4, and 6). Refer to the Procedure in Inquiry 3.1 on pages 17–19 if necessary. 11. Record the results of your tests in your data table on Student Sheet 4.1. 12. Follow your teacher’s directions for cleanup. REFLECTING ON WHAT YOU’VE DONE Figure 4.2 Add amylase to cups 3 through 6. 1. Discuss your answers to the questions that appear in Step 8 of the Procedure. 8. Stir the contents of cups 3, 4, 5, and 6 with separate toothpicks. Let the cups rest for 2. Using the observations you have made in at least 5 minutes. While you are waiting, this inquiry, along with the information in think about the following questions and “Spies: Into the System,” which appears discuss them with your lab partner. at the end of this lesson in the Student Guide, finish answering the questions on A. What do you think amylase is? Student Sheet 4.1. B. What do you think amylase will do when 3. Do you think that anything other than you mix it with the starch solution? eating might cause saliva to form? Your teacher will tell you about a discovery C. Why do you need to wait 5 minutes made by a Russian scientist named Ivan before you perform the tests on the Pavlov. Discuss Pavlov’s ideas with starch solution and amylase mixture? the class. 9. Using the technique you learned in Lesson 3, perform a chemical test for sugar for the substances in the cups in the top row (cups 1, 3, and 5). If you don’t remember how to perform this test, reread the Procedure for Inquiry 3.1 on pages 17–19. STC/MS™ H UMAN B ODY S YSTEMS 27 LESSON 4 D IGESTION IN THE M OUTH 4. Think about what happened when you swallowed the cracker at the beginning of the lesson. What route did it take to get to your stomach? Study Figure 4.3 while your teacher discusses what happens during swallowing. Bolus Entrance to the trachea is open so that air can pass through. Epiglottis Esophagus Trachea Entrance to the trachea is covered by the epiglottis Epiglottis during swallowing. Bolus Esophagus Trachea Figure 4.3 Action of the epiglottis during swallowing 28 STC/MS™ H UMAN B ODY S YSTEMS LESSON 4 D IGESTION IN THE M OUTH Making It Simple Why does your body Starches are made together break apart. need to break down up of chains of simple The result is simple starch into sugar? sugar particles that sugar particles. The reason is that are held together by These particles are the body cannot use chemical bonds. small enough to move carbohydrates until But once the starch through the body and they are in a form is chewed and acted enter the cells. They that is simple enough on by digestive provide cells with to dissolve in water enzymes in the nutrients they need and pass through cell mouth and small to do their jobs. membranes into the intestine, the bonds Simple sugars. A blood and, ultimately, that hold the links of simple story. Do you to the body’s cells. the starch chain agree? After the chemical bonds of the starch chains are broken, the smaller sugar particles can pass through the cell membrane. STC/MS™ H UMAN B ODY S YSTEMS 29 LESSON 4 D IGESTION IN THE M OUTH INTO THE SYSTEM Peppi and Bollo are ready for their first investigation. It’s noon. Time for lunch. They hop aboard a slice of pizza (topped with mushrooms, sausage, and green pepper) and enter a human mouth. “Who’s our host?” says Bollo. “Her name is Joanne. She’s 18— an adult as far as human digestive systems are con- Watch out, Joanne! You are about to be cerned. She’s healthy, invaded by aliens! too. No digestive problems. If we can discover what’s going name is ‘saliva.’ Saliva handle. The salivary to work first. These on in Joanne’s diges- is produced by three glands produce about sharp teeth act like tive tract, we’ll have pairs of glands in the 1.5 liters of saliva scissors. The canine a good idea about sides and the back of each day. teeth, at the sides of human digestive the human mouth. “And those ‘blades,’” the mouth, are pointy. activity,” replies Peppi. The salivary glands go Peppi goes on, “are They cut up the food “Wow, it’s dark,” to work whenever a teeth. Adult humans some more. says Bollo. “And wet human smells, sees, usually have 32 of The tongue is mus- and slippery, too. or even thinks about them.” cular. It helps move Watch out for those food. Once food is in Peppi and Bollo take food around. It moves huge white blades!” the mouth, the saliva a look around. It’s a the pizza to the back “The liquid is spit,” moistens it and busy scene. The front of the mouth, where says Peppi. “Its formal makes it easier to teeth, or incisors, go the heavy-duty work 30 STC/MS™ H UMAN B ODY S YSTEMS LESSON 4 D IGESTION IN THE M OUTH of chewing goes on. human body is spe- The broad, flat bicus- cialized,” says Bollo. pids and molars grind “You’re right,” says the food and make it Peppi.