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INTRODUCTIONNow that you know how to perform chemicaltests for starch and sugar, it’s time to use thoseskills to begin your investigation of the digestiveprocesses. 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 wellbefore you swallow it? Do your teeth get anyhelp as they tear and grind a bite of food beforeyou swallow it?

Once you’ve explored these questions, you’ll beprepared to move on to investigate what happensin the stomach, where the process of digestioncontinues. All these activities have one goal: toget food into a form that can be absorbed intoyour bloodstream and used by the cells to maintain life.

4Digestion in the Mouth

LESSON

OBJECTIVES FOR THIS LESSON

Explore mechanical digestion in the mouth.

Explore chemical digestion in the mouth.

Begin to construct a definition of theword “enzyme.”

That pizza looks great! But take it easy—it’s important

to chew your food carefully before you swallow it.

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STC/MS™ HU M A N BO D Y SY S T E M S 25

Getting Started

1. Your teacher will give you a cracker. Put itin your mouth. Chew it very slowly. Payclose attention to everything that happensin your mouth. When you are ready toswallow it, put your thumb and index fingergently around your Adam’s apple. Swallowthe cracker. In your science notebook,describe exactly what happened while youwere chewing and swallowing the cracker.

A. Why do you think that chewing thecracker was important?

B. What happened to your Adam’s apple as you swallowed?

2. Share your ideas with the class.

Inquiry 4.1 Exploring ChemicalDigestion in the Mouth

PROCEDURE

1. Pick up your materials. You will work inpairs in this lesson. You will performchemical tests for sugar and starch usingBenedict’s solution and Lugol solution.Take turns so that each of you gets equalexperience with both tests.

MATERIALS FOR LESSON 4

For you1 copy of Student

Sheet 4.1:Chemical Testingfor Sugar andStarch

1 sheet of foursummary boxes(for homeworkassignments)

1 pair of safetygoggles

For your group1 plastic box2 dropper bottles of

Benedict’s solution2 dropper bottles of

Lugol solution2 dropper bottles of

salivary amylase2 dropper bottles of

distilled water (DW)2 dispensing bottles

of starch solution2 medium test tubes1 test tube rack2 test tube clamps2 6-cup lab trays2 plastic pipettes8 toothpicks2 black markers

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LESSON 4 DI G E S T I O N I N T H E MO U T H

2. Read along as your teacher reviews theSafety Tips.

3. Number the cups in your lab tray from 1 to 6. Use Figure 4.1 as a guide.

4. Using Figure 4.1 and your teacher’s guidance, complete the design of the datacollection table on Student Sheet 4.1.Give the table a name.

5. Add 30 drops of starch solution to cups 1, 2, 5, and 6.

6. Add 30 drops of distilled water to cups 3 and 4.

Figure 4.1 Designing the data collection table

SAFETY TIPS

Always wear safety goggleswhen usingchemicals andhot pots.

Lugol solutioncontains a smallamount ofiodine, which isconsidered poi-sonous. Do notplace any of thechemicals in ornear your mouth.

Do not get thechemicals on yourskin or clothing.Lugol solution willleave a stain. IfBenedict’s solu-tion comes incontact with youreyes or skin, thoroughly flushthe affected areawith a generousamount of water.

Wipe up acciden-tal spills of Lugoland Benedict’ssolution withpaper towels,which you candispose of in the trash.

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LESSON 4 DI G E S T I O N I N T H E MO U T H

7. Add 2 drops of amylase to cups 3, 4, 5,and 6, as shown in Figure 4.2.

Figure 4.2 Add amylase to cups 3 through 6.

10. Using the technique you learned inLesson 3, perform a chemical test forstarch for the substances in the cups onthe bottom row (cups 2, 4, and 6). Referto the Procedure in Inquiry 3.1 on pages 17–19 if necessary.

11. Record the results of your tests in yourdata table on Student Sheet 4.1.

12. Follow your teacher’s directions forcleanup.

REFLECTING ON WHAT YOU’VE DONE

1. Discuss your answers to the questionsthat appear in Step 8 of the Procedure.

2. Using the observations you have made inthis inquiry, along with the information in“Spies: Into the System,” which appearsat the end of this lesson in the StudentGuide, finish answering the questions onStudent Sheet 4.1.

3. Do you think that anything other thaneating might cause saliva to form? Yourteacher will tell you about a discoverymade by a Russian scientist named IvanPavlov. Discuss Pavlov’s ideas with the class.

8. Stir the contents of cups 3, 4, 5, and 6 withseparate toothpicks. Let the cups rest forat least 5 minutes. While you are waiting,think about the following questions anddiscuss them with your lab partner.

A. What do you think amylase is?

B. What do you think amylase will do whenyou mix it with the starch solution?

C. Why do you need to wait 5 minutesbefore you perform the tests on thestarch solution and amylase mixture?

9. Using the technique you learned inLesson 3, perform a chemical test forsugar for the substances in the cups in the top row (cups 1, 3, and 5). If youdon’t remember how to perform this test,reread the Procedure for Inquiry 3.1 onpages 17–19.

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LESSON 4 DI G E S T I O N I N T H E MO U T H

4. Think about what happened when youswallowed the cracker at the beginning ofthe lesson. What route did it take to get to your stomach? Study Figure 4.3 whileyour teacher discusses what happens during swallowing.

Figure 4.3 Action of the epiglottis during swallowing

Entrance to thetrachea is coveredby the epiglottisduring swallowing.

Entrance to the trachea is openso that air can pass through.

Epiglottis

Trachea

Esophagus

Bolus

Epiglottis

Bolus

TracheaEsophagus

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LESSON 4 DI G E S T I O N I N T H E MO U T H

Why does your bodyneed to break downstarch into sugar?

The reason is thatthe body cannot usecarbohydrates untilthey are in a formthat is simple enoughto dissolve in waterand pass through cellmembranes into theblood and, ultimately,to the body’s cells.

Starches are madeup of chains of simplesugar particles thatare held together bychemical bonds.

But once the starchis chewed and actedon by digestiveenzymes in themouth and smallintestine, the bondsthat hold the links ofthe starch chain

together break apart.The result is simplesugar particles.

These particles aresmall enough to movethrough the body andenter the cells. Theyprovide cells withnutrients they needto do their jobs.

Simple sugars. Asimple story. Do youagree? �

Making It Simple

After the chemical bonds of the starch chains are broken, the smaller sugar particles

can pass through the cell membrane.

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name is ‘saliva.’ Salivais produced by threepairs of glands in thesides and the back ofthe human mouth.The salivary glands goto work whenever ahuman smells, sees,or even thinks aboutfood. Once food is inthe mouth, the salivamoistens it and makes it easier to

handle. The salivaryglands produce about1.5 liters of salivaeach day.

“And those ‘blades,’”Peppi goes on, “areteeth. Adult humansusually have 32 ofthem.”

Peppi and Bollo takea look around. It’s abusy scene. The frontteeth, or incisors, go

to work first. Thesesharp teeth act likescissors. The canineteeth, at the sides ofthe mouth, are pointy.They cut up the foodsome more.

The tongue is mus-cular. It helps movefood around. It movesthe pizza to the backof the mouth, wherethe heavy-duty work

INTO THESYSTEM

Peppi and Bollo areready for their firstinvestigation. It’snoon. Time for lunch.They hop aboard aslice of pizza (toppedwith mushrooms,sausage, and greenpepper) and enter ahuman mouth.

“Who’s our host?”says Bollo.

“Her name isJoanne. She’s 18—an adult as far ashuman digestive systems are con-cerned. She’s healthy,too. No digestive problems. If we candiscover what’s goingon in Joanne’s diges-tive tract, we’ll have a good idea abouthuman digestive activity,” replies Peppi.

“Wow, it’s dark,”says Bollo. “And wetand slippery, too.Watch out for thosehuge white blades!”

“The liquid is spit,”says Peppi. “Its formal

Watch out, Joanne! You are about to be

invaded by aliens!

Then they start mov-ing backward. Thebolus has triggered aswallowing reflex.Goodbye, mouth!

Looking down, theysee something closeover one of the twotubes below them.

“The epiglottis,” saysPeppi. “Each time ahuman swallows, itcloses over the wind-pipe to make sure thatfood goes to the stom-ach. The windpipeleads to the lungs, andyou don’t want anyfood in there!”

“One tube for air,one for food. The

human body is spe-cialized,” says Bollo.

“You’re right,” saysPeppi. “You’re alsogoing to find out thatthese specializedorgans and systemsneed each other.They work togetherto help keep the bodyin balance. Now keepyour eyes open. We’retraveling through thesecond organ of thedigestive system, theesophagus.”

Down and down theygo, squeezed by mus-cular contractions ofthe walls of this dark-pink tube. Then all of asudden, another tightsqueeze, and pop!

The spies arrive inthe stomach. Theyhave passed throughthe last gatepost on theroad to the stomach,the lower esophagealsphincter. The sphinc-ter is a ring of musclethat helps keep foodthat has been swal-lowed where it shouldbe—in the stomach.

“What happensnow?” asks Bollo.

“I like your curios-ity, Bollo. Stay posted.Our journey will sooncontinue,” Peppireplies. �

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that bite of pizza. Itlooks like a big, soggy ball.”

“You’re right. Thatball of food is called abolus,” says Peppi.“And if I took out mytesting equipment, Icould show you thatthe pizza crust isalready starting to bedigested—because ofthe action of amylase.”

Down the Tubes“Eeeeeeee!” shrieksBollo. Before he cansay more, he and Peppiare pushed up againstthe roof of the mouth.It’s a tight squeeze.

of chewing goes on.The broad, flat bicus-pids and molars grindthe food and make itsoft. Meanwhile, thesaliva is doing itsthing. It moistens thefood and makes it easier to chew.

“This tearing, grinding, and mixing,”Peppi says, “is calledmechanical digestion.And although we can’t see it, it’s impor-tant to know that sali-va contains an enzymecalled amylase. Theenzyme activity marksthe beginning of chemical digestion.”

“Hold on a minute.You’re going too fast,”says Bollo. “What’s an enzyme?”

“An enzyme is aspecial protein pro-duced by the body.Digestive enzymeshelp the body breakdown nutrients intoforms that the bodycan use. Amylase, forexample, helps breakdown the starch inpizza to simple sugar.As we continue, we’llsee other enzymes thathelp digest other types of nutrients.”

“The human mouthis efficient,” notesBollo. “It’s only been afew seconds, and Ican’t even recognize

Peppi and Bollo are off to a scary start.