activity 1 the upper end of the alimentary...

Active Chemistry

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What Do You Think?About 65 million Americans (25%) have digestive problems and must take medications.

• Where in your body does the digestion of your food first take place?

• What chemical and physical changes occur there?

The What Do You Think? questions are provided to get you engaged in the activity. They are meant to grab your attention. They are also used to find out what you already know or think you know. Don’t worry about being right or wrong. Discussing what you think you know is an important step in learning.

Record your ideas about these questions in your Active Chemistry log. Be prepared to discuss your responses with your small group and the class.

InvestigatePart A: Past the Teeth and into the Mouth

1. Imagine that you’ve just been given either a piece of pizza, a potato chip, or a chocolate-chip cookie.

a) Describe what happens when you put the food in your mouth. Be as detailed as possible. How many bites do you take? How long do you chew before swallowing? Which teeth do you use to chew? What is happening in your mouth?

Activity 1 The Upper End of the Alimentary Canal

GOALSIn this activity you will:

• Experience both the mechanical and chemical digestions of a cracker.

• Test for the presence of starch and its hydrolysis products.

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Active Chemistry It’s Alimentary

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b) Which of the changes are physical changes of the food?

c) Which of the changes are chemical changes of the food?

2. In the classroom area (not the lab), place a piece of unseasoned cracker on your tongue. No chewing is allowed.

a) Record any taste changes in two minutes.

3. Take another piece of cracker and chew it for 30 seconds. Do not swallow. Time how long it takes from when you start to chew until the cracker starts to change taste.

a) Record the time and describe the taste change.

b) Write an explanation on why you think the two times were different.

4. In the lab, break off a small piece of a cracker. Put a drop of the Lugol’s (iodine/iodide) solution on it.

a) What do you observe happening?

b) Lugol’s solution is a positive test for starch. Describe your observation in terms of starch presence.

Part B: What Does Saliva Do?

1. You saw a positive test for starch in Part A when you applied a drop of Lugol’s solution to the cracker. You will now see if you can gather evidence of what type of chemical digestion started in your mouth as you chewed the cracker.

2. Your teacher will show you a demonstration by setting a warm water bath at 37ºC, which is body temperature (equal to 98.6°F).

3. Your teacher will deposit about 1.0 mL of saliva in one test tube. Then your teacher will add 1.0 mL water to a second test tube.

4. Your teacher will add two drops of starch solution to each test tube. Both are then placed in the 37°C water bath.

a) What is the importance of the test tube containing water?

b) Record your observations in your Active Chemistry log.

5. Wait at least three minutes after the starch has been added.

a) During this time, predict what will be observed when Lugol’s solution is added to each test tube.

b) You teacher will now add one drop of Lugol’s solution. What do you observe? Record your observations and possible explanations for the results of this investigation in your Active Chemistry log.

Part C: What Chemical Digestion Takes Place in the Mouth?

1. The substance in saliva that is responsible for digestion is an enzyme called salivary amylase. You will look at the beginning of digestion in the mouth in more detail. Use five test tubes, each to represent a set of conditions in the mouth. Label them A, B, C, D, E.

2. Begin heating water in a large beaker on a hot plate. You will need this for a boiling water bath later.

Be sure the food is not contaminated by anything in the lab before you eat it.

Safety goggles and a lab apron must be worn at all times in a chemistry lab.

Be sure to carefully dispose of the cracker that has been tested with iodine. Clean up any iodine spills immediately.


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3. Put a second beaker of water on another hot plate. Hang a thermometer from a ringstand so that the tip of the thermometer remains submerged in the water. Adjust the hot plate to maintain a temperature of 55°C.

4. Add 5 mL of distilled water only to tube A.

5. Place 5 mL of 1% fungal amylase solution into test tubes B, C, D, E.

6. Place all five tubes in the 55˚C water bath.

7. Get four pieces of cracker that are about the same size.

8. Crumble a piece of cracker in tube B. After five minutes, crumble another piece in tube C. After another five minutes, crumble a piece of cracker in tube D. After four more minutes, crumble the last piece in tube E. Make sure that the entire cracker is covered by the solution in each test tube. You may need to push it down with a glass stirring rod.

9. When the piece of cracker has been in tube E for one minute, remove all five test tubes from the 55˚C water.

10. Place 10 drops of Benedict’s solution into test tubes A to E. Benedict’s solution is used to check for the presence of sugar in a substance. The darker the red, the more sugar there is. Since there is no sugar in the distilled water, you would expect that the Benedict’s solution does not indicate the presence of sugar in tube A.

11. Using a test-tube clamp, place the five test tubes (A to E) in the boiling water bath for 10 minutes.

12. After 10 minutes, remove the test tubes with a test-tube clamp. Place them in a test-tube rack.

a) Prepare a table similar to the one below, in your Active Chemistry log. Enter your observations. (Reminder: Benedict’s solution is used to check for the presence of sugar in a substance. The darker the red, the more sugar there is.)

b) In addition to the observations, you can also make inferences explaining what has happened. How can you explain these results? Where did the sugar come from? Why aren’t all the tubes the same color?

13. Dispose of the materials as directed by your teacher. Clean up your workstation.

Tube A no cracker

Tube B 15 min

Tube C 10 min

Tube D 5 min

Tube E 1 min

color before boiling

color after boiling

place in order according to sugar content


Wash your hands and arms thoroughly after the activity.



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THE BEGINNING OF DIGESTION

Parts of the Digestive System

The alimentary canal (digestive tract) is essentially a long hollow tube that extends from the mouth to the anus. You can think of it as a chemical factory located inside a 7.6 m long tube. Its purpose is to store and break down the organic molecules of the food you eat into smaller particles. The tissues of the body can then absorb these smaller particles. A smooth-running operation can process its food in anywhere between 24 and 72 hours (depending upon what you eat). This process is called digestion. It starts in the mouth, as you found in this activity.

You eat and digest food every day. You probably rarely think about the process of digestion unless something goes wrong. For example, you can get a stomach ache, vomit, or develop diarrhea.

Hydrolysis of Starch

When you first let the cracker dissolve in your mouth, you probably noticed that the starchy taste became a sweet taste. Starch molecules, after interaction with the saliva or the amylase solution, become sugar molecules.

The process of digestion begins in the mouth. Because food is in the mouth for such a short time, only partial digestion takes place there. Essentially, the digestion that occurs in the mouth is a chemical process called hydrolysis.

You can understand this better by looking at both starch and sugar at the molecular level. Starch is made of a string of glucose (sugar) molecules. By adding water, hydrolysis takes place. This means that the bonds connecting subunits of complex foods are broken down through the reaction with water (hydro means water). The long string of glucose molecules are broken into pairs of glucose molecules which are a sugar called maltose. In the activity,

the Lugol’s (iodine/iodide) solution showed the presence of starch in the cracker. It reacted and formed a dark blue/black product, indicating that starch is present. The Benedict’s solution then showed the presence of the maltose. Many, but not all, sugars react with Benedict’s solution to form a brick-red precipitate of copper (I) oxide, Cu2O.

Chem Wordsdigestion: the physical and chemical breakdown of food into smaller nutrient particles.

starch: a complex molecule (polymer) made up of thousands of glucose units linked together.

hydrolysis: the breaking down of a larger molecule into smaller ones through a reaction with water.


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The diagram above shows starch and maltose molecules. At first, the diagram appears to be quite overwhelming, but it simply shows that starch combines with water to produce sugar through a process called hydrolysis. You can decipher this complex picture by noticing the following:

• The starch molecule is composed of a string of glucose molecules. In the starch molecule shown, you can see four of the many, many glucose molecules. Some starches have as many as 6000 glucose molecules.

• Water is added to the starch as shown with the H2O arrows pointing toward the bonds holding the glucose molecules together.

• The arrow pointing down indicates that hydrolysis is taking place.

• The bottom part of the diagram shows that maltose is created. Maltose is two glucose molecules bound together and is a simple sugar. If there were four glucose molecules in the starch, there would be two maltose sugars created. The diagram just shows one of the maltose molecules.

The Role of Amylase Enzymes

Hydrolysis is one of the most important reactions occurring in the digestive process. But it cannot take place with water alone, as you observed in the activity. Water alone cannot change the starch to sugar. Saliva in the mouth contains a substance called salivary amylase. It makes the hydrolysis of starch in the mouth possible. As you learned, starch is a natural polymer made up of many smaller subunits that are bonded

H

H

H

H H H

HH H H

H H H

H

H

H HH

HH

O

OO

O

O

O

O

O

O

OHOH

Glucose

hydrolysis

OHOH

OHOH

OHOH

C

CH2OH

CH2OH

CH2OH

CH2OH

CH2OH

H2O

H2O

H2O

C

CC C C C

C C C

H H

OC C

C

C

C

HH

H

O

OHOHC

C

CH

OHC

C C C

C

C CC

H

HH

H

O

OHHOOH

CH2OH

C CC

C

Maltose

Hydrolysis of Starch



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together. These smaller units are molecules of a simple sugar called glucose. Sugars are molecules made up of C, H, and O, and starch is a set of glucose molecules hooked together in a special way. The amylase enzyme in your saliva enables the hydrolysis of some of the bonds hooking the glucose subunits together to occur.

Other Changes That Occur in the Mouth

Physical digestion also takes place in the mouth. The teeth are an important part of digestion. They bite, tear, and grind the food into a bolus (a ball). Saliva contains amylase. However, saliva is a watery fluid that also dissolves food particles. You can only detect flavor if the food is in solution, and you know how important tasting your food is!

Just the sight and smell of food can activate the salivary glands, which produce saliva.

What Do You Think Now?At the beginning of this activity you were asked:

• Where in your body does the digestion of your food first take place?

• What chemical and physical changes occur there?

How does digestion begin before food gets to the stomach? What kind of chemical do you have in your mouth that starts the digestion process?

Checking Up1. What does hydrolysis

have to do with digestion?

2. What are the chemical subunits that make up starch?

3. What are you testing for when you use the Benedict’s test?

4. What are you testing for when you use the iodine test?

5. What physical changes take place in the mouth?


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What does it mean?

Chemistry explains a macroscopic phenomenon (what you observe) with a description of what happens at the nanoscopic level (atoms and molecules) using symbolic structures as a way to communicate. Complete the chart below in your Active Chemistry log.

How do you know?

What evidence do you have to support the idea that amylase will hydrolyze starch into sugars?

Why do you believe?

Recently our nation has experienced a nutritional trend that stresses a “low-carb” diet. “High-carb” foods like pasta, breads, potatoes, etc., are full of starch. How can you use the information you gained in this activity to explain the benefits of a low-carbohydrate diet?

Why should you care?

Your theme park ride might include the concept that digestion actually begins in the mouth. How will your vehicle simulate the effects of amylase on your particle of food?

MACRO NANO SYMBOLICIn Part A, why did the cracker become sweet as it sat in your mouth? In Part B, which test tube tested positive for starch? In Part C, what does the time have to do with the variation in color for the different test tubes?

What is meant by hydrolysis? What enzyme is needed and how does time play a role in this process?

Make a simple sketch to describe what happens to the starch when it comes in contact with saliva and water, and becomes the sugar maltose. In this simple sketch, glucose can be drawn as a small shape.

Reflecting on the Activity and the ChallengeIn creating your portion of the ride down the alimentary canal, you must remember that you and your vehicle have become microscopic. You have become the size of a molecule and not the size of food you normally see. In this activity, you observed the result of physical and chemical changes that food undergoes in the mouth. The saliva in the mouth contains the enzyme amylase, which broke down starch into the sugar maltose. There are two tests that can help you to identify two important substances in food: the iodine test for starch, and Benedict’s test for sugar. You should begin thinking of ways in which your skit might show how food is changed inside the mouth. You can now use the concepts of chemistry to describe what is occurring at the beginning of the alimentary canal.




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1. Digestion consists of physical and chemical changes in food.

a) What physical changes go on in the mouth as food starts its trip down the alimentary canal?

b) What chemical changes go on in the mouth as food starts its trip down the alimentary canal?

2. What are the products of the hydrolysis of starch?

3. What is the color change that takes place when iodine is added to a starch?

4. What is the color change that takes place when iodine is added to maltose or glucose?

5. Why did you not get the same color in each of the test tubes containing the cracker when Benedict’s solution was added?

6. Suppose you added the Lugol’s solution to the test tubes containing the crackers instead of Benedict’s solution. What would you predict that you would see? How would you explain these observations?

7. Why did you set your water bath temperature to 37ºC in Part B?

8. Preparing for the Chapter Challenge

You can begin designing your ride. You can begin your ride by depicting chewing as a physical change. Then, show the chemical changes that occur as the starch molecules become sugar molecules.

Inquiring Further

Other uses for starch

What are some uses of starch other than being in foods? Research this question and present your findings to the class.

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activity 1 the upper end of the alimentary...

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