17 Digestion - Student.pdf - haspi

Digestion & Enzyme Activity 

HASPI Medical Biology Lab 17 

Background 

The Digestive System 

The digestive system is made up of the digestive tract 

—a series of hollow organs joined in a long, twisting 

tube from the mouth to the anus—and other organs 

that help the body break down and absorb food. 

Organs that make up the digestive tract are the 

mouth, esophagus, stomach, small intestine, large 

intestine—also called the colon—rectum, and anus. 

Inside these hollow organs is a lining called the 

mucosa. In the mouth, stomach, and small intestine, 

the mucosa contains tiny glands that produce juices to 

help digest food. The digestive tract also contains a 

layer of smooth muscle that helps break down food 

and move it along the tract. 

Name: ____________________________ 

Period: ___________ Date: ___________ 

Two “solid” digestive organs, the liver and the 

pancreas, produce digestive juices that reach the 

intestines through small tubes called ducts. The 

gallbladder stores the liver’s digestive juices until they 

are needed in the intestine. 

The Digestive Enzymes 

The digestive glands that act first are in the mouth—the salivary glands. Saliva produced by these 

glands contains an enzyme called amylase that begins to digest the starch from food into smaller 

molecules. An enzyme is a substance that speeds up chemical reactions in the body. 

http://www.pc.maricopa.edu/Biology/rcotter/BIO%20205/LessonBuilders 

/Chapter%207%20LB/activesite.jpg 

http://2.bp.blogspot.com/_i0dNvDsh49w/SwrJRirbBJI/AAAAAAAAAC8/v 

kLKiseJgCo/s1600/digestive%252525252525252525252Bsystem.gif 

The next set of digestive glands is in the stomach 

lining. These produce hydrochloric acid and an 

enzyme called pepsin that digests protein. A thick 

mucus layer coats the mucosa and helps keep the 

acidic digestive juice from dissolving the tissue of the 

stomach itself. After the stomach empties the food 

and juice mixture into the small intestine, the juices of 

two other digestive organs mix with the food. One of 

these organs, the pancreas, produces a juice that 

contains a wide array of enzymes such as amylase to 

break down the carbohydrate, lipase to break down 

fat, and trypsin to break down protein. 

The second organ, the liver, produces yet another digestive juice—bile. Bile is stored between meals 

in the gallbladder. At mealtime, it is squeezed out of the gallbladder, through the bile ducts, and into 

the intestine to mix with the fat in food. The bile acids dissolve fat into the watery contents of the 

intestine, much like detergents that dissolve grease from a frying pan. 

235

Name: __________________________________________ Date: ___________ Period: _________ 

The 3 Major Digestible Macromolecules 

Protein Carbohydrate Lipids 

Polypeptide 

Polysaccharide 

Fat Molecule 

Polymer 

http://users.rcn.com/jkimball.ma.ultra 

net/BiologyPages/P/Peptide.gif 

Amino Acid 

http://bioweb.wku.edu/courses/biol115/ 

wyatt/biochem/Carbos/Carb_poly.gif 

Monosaccharide 

http://www.foodmuseum.com/images 

/exfatMoleculeandCells.jpg 

Fatty Acid or Cholesterol 

Monomer 

Build and repair body 

tissues 

Glucose 

http://kentsimmons.uwinnipeg.ca/cm150 

4/Image69.gif 

Energy 

http://www.protocolsupplements.com/Sports- 

Performance-Supplements/wpcontent/uploads/2009/06/amino-acid-mcat1.png 

http://www.clker.com/clipart- 

10765.html 

Stored energy 

Use in the 

Body 

http://content.contentthatworks.com/image 

s_articles/2006/health/health_20060724_car 

egiver_flexedarm.jpg 

Meat, eggs, beans 

http://pullenl.wonecks.net/files/2010/09/ 

Children-Running-Outside.jpg 

Breads, pasta, fruits, 

vegetables 

http://photos.demandstudios.com/ge 

tty/article/103/163/82370075_XS.jpg 

Oils, butter, meat, dairy, 

fast food 

Foods 

Sources 

http://www.gethenchnow.com/wpcontent/uploads/2011/01/high_protein 

_foods.jpg 

http://www.magazine.ayurvediccure.com/wpcontent/uploads/2009/02/carbohydrate.jpg 

http://cdn2- 

b.examiner.com/sites/default/files/styles/i 

mage_full_width/hash/af/13/af1309885ddd 

ea6427ea13af260f4ca4.jpg 

NIH. 2008. Your Digestive System and How it Works. National Digestive Diseases Information 

Clearinghouse, NIH Publication No. 08-2681. www.digestive.niddk.nih.gov 

Adapted from Neo/Sci Food Digestion Lab Activity 2011 236


Materials 

Spot plate 2% Albumin (protein) 1% Hydrochloric acid 

20 pH strips 3% Pepsin Biuret 

10 stirring sticks 1% Starch solution 2% Amylase 

Forceps Potassium iodine Corn oil 

Paper towels Water Liquid soap 

Procedure 

Purpose: The goal of this lab will be to observe how digestive enzymes are able to break down 

macromolecules. All data tables are located in the analysis portion of the lab. 

PART A: Protein Digestion 

In part A the albumin represents a polypeptide protein. Pepsin is the enzyme needed to break down 

the albumin into amino acids, but can only work within a certain pH range. The Biuret will turn pink 

with smaller protein chains and will turn purple in the presence of large proteins. 

1. Using a pencil, label the wells on your spot plate 1-5. 

2. Place 5 drops of 2% Albumin in wells 1-4. 

3. Add 5 drops of 1% HCl to wellS 2, 4, and 5. 

4. Add 5 drops of 3% Pepsin to wells 3 and 4. 

5. Use separate stirring sticks to mix each well, and allow them to sit for 5-7 minutes. 

6. Use the forceps to dip a separate pH strip into each of the wells 1-5. Compare the color 

change of each strip to the pH strip chart to determine the pH of the mixture in each well. 

Record your results in Data Table 1. 

7. Add 2 drops of Biuret to wells 1-5. A positive test for protein breakdown will turn pink. If the 

well is positive, put a + in Data Table 1. If the well is negative put a -. 

8. Record your observations of each of the mixtures in Data Table 1. 

9. Rinse out your spot plate and dry it off with a paper towel. 

PART B: Carbohydrate Digestion 

In part B starch is a polysaccharide, and amylase is the enzyme responsible for breaking starch down 

into monosaccharides. Since the potassium iodine tests for starch, you will be looking for a negative 

test to determine whether amylase actually broke down the starch. 

1. Using a pencil, label wells 1 and 2 on the spot plate. 

2. Add 15 drops of 1% Starch solution to wells 1 and 2. 

3. Add 5 drops of 2% Amylase solution to well 2. 

4. Use separate stirring sticks to mix each well, and allow them to sit for 5-7 minutes. 

5. Add 1 drop of Potassium iodine to wells 1 and 2. A positive test for starch will turn dark blueblack. 

If a well is positive for starch, put a + in the Data Table 2. If the test is negative for 

starch put a –. 





PART C: Fat Digestion 

In part C the corn oil represents the lipid polymer, and lipase is the enzyme responsible for breaking 

the lipid down. A change in pH will demonstrate that the enzyme is active. The soap works similarly 

to bile, and will break up the oil so lipase can work more easily. 

1. Using a pencil, label wells 1-3 on the spot plate. 

2. Add 10 drops of water to wells 1-3. 

3. Add 3 drops of Corn oil to wells 1-3. 

4. Use separate stirring sticks to mix each well thoroughly. 

5. Use the forceps to dip a separate pH strip into each of the wells 1-3. Compare the color 

change of each strip to the pH strip chart to determine the pH of the mixture in each well. 

Record your results in Data Table 3. 

6. Add 5 drops of lipase to well 2 and 3. 

7. Add 2 drops of liquid soap to well 3. 

8. Re-stir the mixture in each well, and allow them to sit for 20 minutes. 

9. Retest the pH and record your results in Data Table 3. 



PART D: Testing for Macromolecules in Food 

In part D you will be performing portions of the tests from parts A-C to determine whether your food 

sample contains proteins, carbohydrates, and/or lipids. 

1. Choose a food item that is easily mixed with water. 

2. In a beaker, mix a small amount of your food sample in 10 ml of water. If the food sample is 

solid it will need to be thoroughly smashed. 

3. Using a pencil, label wells 1-5 on the spot plate. 

4. Add 5 drops of your food sample mixture to wells 1-5. Well 1 will act as the control. 

5. Use the forceps to dip a separate pH strip into each of the wells. Compare the color change of 

each strip to the pH strip chart to determine the pH of the mixture in each well. Record your 

results in Data Table 4. 

6. Test your food sample for protein by adding 5 drops of pepsin and 5 drops of HCl to well 2. 

7. Allow well 2 to sit for 5-7 minutes, then add 2 drops of Biuret. The mixture will turn pink if 

protein is present. Retest the pH of well 2. Record the results in Data Table 4. 

8. Test your food sample for carbohydrates by adding 5 drops of amylase to well 4. 

9. Allow well 3 and 4 to sit for 5-7 minutes then retest the pH of wells 3 and 4. 

10. Add 1 drop of potassium iodine to well 3 and 4. The mixture will turn blue-black in the 

presence of starch. Record the results in Data Table 4. 

11. Test your food sample for lipids by adding 5 drops of lipase and 2 drops of soap to well 5. 

12. Allow well 5 to sit for 20 minutes, then retest the pH of well 5, and record the results in Data 

Table 4. 



Analysis 

Data Table 1 

Well Contents pH Protein Test Observations 

1 Albumin 

2 Albumin + HCl 

3 Albumin + 

Pepsin 

4 Albumin + 

Pepsin + HCl 

5 HCl 

PART A Analysis Questions - on a separate sheet of paper complete the following 

1. Explain what may have happened to the protein in well #2 after the addition of hydrochloric 

acid? After the addition of pepsin in well #3? After the addition of pepsin and hydrochloric 

acid in well #4? 

2. What are the subunits that make up a protein? 

3. How could you tell that protein digestion took place? 

4. Which of the wells showed the greatest degree of protein digestion? Why? 

5. What is the purpose of well #1? 

6. What is the role of pepsin in human digestion? In what parts of the digestive system does 

protein digestion take place? 

7. Does the effectiveness of pepsin depend on pH? Explain. 

8. What can you conclude about the optimal pH for pepsin? 

Data Table 2 

Well Contents Starch Test Observations 

1 Starch 

2 Starch + Amylase 

PART B Analysis Questions - on a separate sheet of paper complete the following 

1. Explain what happened to the starch in well #2 after the addition of amylase? 

2. What are the subunits that make up carbohydrates? 

3. How could you tell that carbohydrate digestion had taken place? 

4. What is the purpose of well #1? 

5. What is the role of amylase in human digestion? Where is it produced? 

6. Where does carbohydrate digestion take place? 

7. What do you think may happen if HCl was added to the starch + amylase mixture? Explain 

your answer. 



Data Table 3 

Well Contents Initial pH Final pH Observations 

1 Oil + Water 

2 Oil + Water + 

Lipase 

3 Oil + Water + 

Lipase + Soap 

PART C Analysis Questions - on a separate sheet of paper complete the following 

1. How does the pH of each solution show that fat digestion has occurred? 

2. Which well showed the greatest degree of fat digestion? Explain. 

3. Where does fat digestion take place in the human digestive system? 

4. Describe the effects of bile on fat. 

5. Why is emulsification necessary for efficient digestion of fats, but not for proteins or 

carbohydrates? 

6. What effect would fat digestion have on the pH of the surrounding solution? Explain. 

7. Predict the effect of a blocked bile duct on the composition of a patient’s stool. 

Data Table 4 

Well Contents Initial pH Final pH Observations 

1 Food sample 

2 Food sample + 

Pepsin + HCl 

3 Food sample 


Amylase 


Lipase + Soap 

PART D Analysis Questions - on a separate sheet of paper complete the following 

1. Summarize the pH changes in each well. 

2. What macromolecules were present in your food sample? Was this what you expected? 

Explain your answer. 

3. What macromolecules do you think you might find in the following foods: bread, eggs, 

broccoli, apple, steak, potato chips. 

4. CONCLUSION: In 1-2 paragraphs summarize the procedure and results of this lab. 



Review Questions - on a separate sheet of paper complete the following 

1. What is the function of the digestive system? 

2. What is the role of the liver and pancreas? 

3. What is the responsibility of the gallbladder? How 

do you think having the gallbladder removed will 

affect digestion? 

4. What is an enzyme? 

5. Explain the function and location of the following 

enzymes: amylase, pepsin, trypsin, and lipase. 

6. Diagram A shows the rate of enzyme activity of 

digestive enzymes – amylase, pepsin, and trypsin – 

in a variety of pH. Using the knowledge of what you 

learned during this lab, identify which enzyme is most 

like A, B, and C in the graph. Explain your answer. 

7. What effect does cooking have on enzyme activity? Why? 

8. Why does freezing food preserve it? 

9. What is the role of bile in digestion? 

10. The polymer of protein is _______, and the monomer is ________. 

Diagram A 

http://mshuda.files.wordpress.com/2010/04/digestiv 

e-enzymes-ph.jpg 

11. Why does the body need proteins, and from what food sources can they be obtained? 

12. The polymer of carbohydrates is _______, and the monomer is _________. 

13. Why does the body need carbohydrates, and from what food sources can they be obtained? 

14. The polymer of lipids is _______, and the monomer is ________. 

15. Why does the body need lipids, and from what food sources can they be obtained? 

16. Based on what you learned about digestion, explain why it is important to eat a variety of foods 

to nourish your cells. 

On the attached digestive system diagram, label the following: 

17. Mouth, pharynx, esophagus, stomach, small intestine, large intestine, rectum, liver, 

gallbladder, pancreas. 

18. Areas where the following occur; carbohydrate digestion, protein digestion, lipid digestion. 

19. Area where absorption of nutrients occurs. 

20. Area where water is reabsorbed.

17 Digestion - Student.pdf - haspi

Create successful ePaper yourself

Delete template?

Save as template?