Chew on This. Investigating the Function of the Digestive System

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1 Chew on This Investigating the Function of the Digestive System OBJECTIVE Students will identify the structure and function of the digestive system. The student will investigate the role of enzymes in the digestive system. LEVEL Middle Grades Life Science NATIONAL STANDARDS UCP.1, UCP.5, C.5 CONNECTIONS TO AP AP Biology: III. Organisms and Populations B. Structure and Function of Plants and Animals TIME FRAME 50 minute class period Chew on This MATERIALS (For a class of 28 working in groups of 2) 42 paper cups (small) 14 graduated cylinders, 25 or 50 ml 56 test tubes 14 test tube racks 14 wax pencils (for labeling test tubes) 14 lactase enzyme tablets soda crackers (2-4 per group) 1 quart whole milk 14 dropper bottles of Benedict s solution 14 amber dropper bottles of Lugol s solution 14 mortar and pestle sets 14 beakers, 500 ml (for water bath) 28 test tube clamps 14 hot plates 14 stopwatches 42 toothpicks (for stirring) T E A C H E R Copyright 2012 Laying the Foundation, Inc., Dallas, TX. All rights reserved. Visit us online at AP, Pre-AP, and Advanced Placement are registered trademarks of the College Entrance Examination Board. The College Board was not involved in the production of this product. 1

2 TEACHER NOTES This lesson is designed to introduce students to the process of digestion and the organs and enzymes involved in digestion. This lab should be incorporated into a unit on the discussion of living systems and the organization, structure, and function of systems. Students will need an understanding of the organization of living systems before beginning this lab (particularly that cells are required to perform the functions of the body but are organized into tissues and organs, then organ systems). Students will need some background on the molecules found in food (protein, carbohydrates and lipids; information on these compounds may be found in the MGLE lesson Biochemistry ) and the function of enzymes. Teacher Prep: Chew on This You will need to prepare the bottles of Lugol s and Benedict s prior to beginning the lab. Both chemicals can be purchased through biological supply houses. The Lugol s should be transferred to amber dropper bottles because exposure to light will degrade the Lugol s. The Benedict s can be transferred to either clear or amber bottles. Teacher Demonstration: Setup a demonstration for the class to show the presence of starch on the cracker. Do this by placing the cracker on a napkin and add 2-3 drops of Lugol s solution to the cracker. Leave this setup in a central location as students will be instructed to refer to it in their procedure. REFERENCES Levine, Joseph S., Miller, Kenneth R., Biology pp T E A C H E R Copyright 2012 Laying the Foundation, Inc., Dallas, TX. All rights reserved. Visit us online at 2

3 DATA AND OBSERVATIONS Data Table 1 Observations of demonstration cracker Molecule present based on demonstration cracker? Taste of chewed cracker after 30 seconds Taste of chewed cracker after 5 minutes cracker was blue/black in presence of Lugol s solution starch salty sweet Data Table 2 Lugol s Test Tube Contents Lugol s Test Color Change Molecule Present Enzyme Present Crackers, saliva, Lugol s solution None, remained brown not starch none Benedict s Test Tube Contents Cracker, saliva Benedict s Test Color Change Blue, then green, then red/orange Data Table 3 Molecule Present Monosaccharides Enzyme Present Yes, amylase T E A C H E R Test Tube no enzyme enzyme present No Yes Glucose Present at End of Test?

4 ANALYSIS Cut along the dotted lines and arrange the following boxes in order of location and steps of digestion. When you have the correct order, glue to a separate sheet of paper and draw arrows to indicate the direction. Finally, add the following information to each box: function of the structure accessory organs and enzymes necessary for that step, as applicable Mouth: beginning of digestion, amylase Esophagus: connects the mouth to the stomach Stomach: mixes and churns food; pepsin to digest proteins Duodenum: Beginning of the small intestine; final digestion and absorption of molecules into cells; (see data table for enzymes) Jejunum: continued absorption of molecules Ileum: final location for absorption of food molecules into cells Ascending colon: beginning of the large intestine; absorption of water from waste Transverse colon: absorption of water from waste Descending colon: absorption of water from waste Sigmoid colon: final portion of large intestine before solid waste enters the rectum T E A C H E R Rectum: holding location for solid waste Anus: exit for solid waste

5 Conclusion Questions 1. Based on your data, what would you expect a test using Lugol s on food that has reached the small intestine to indicate? There should be no starch in the small intestine. The Lugol s test should show this by indicating a brown/yellow color only, confirming the absence of starch. 2. Based on your data, what disaccharide was being broken down by the enzyme lactase? Would you expect this enzyme to work on any other disaccharide? Why or why not? The enzyme that would have been broken down is lactose. It would not be expected to work on any other disaccharide. The enzyme s specific purpose is to break down the disaccharide lactose. Other enzymes exist to work on other disaccharides. 3. Where does digestion of protein begin? What enzyme(s) is/are involved in the digestion of protein in this location? What test could be used to identify the presence of protein in food? The stomach Pepsin Biuret s test could be used to test for the presence of protein in food. 4. Rachel has a slice of ham, mashed potatoes and a honey-butter roll for dinner. Describe the location that will be involved in the digestion of each of her foods. Include a discussion of the enzymes that will be used. Digestion will begin in the mouth on the starches in the roll and mashed potatoes. In addition, digestion on the honey will begin. Amylase will be the enzyme involved in this digestion. Digestion of the ham will begin in the stomach digestion of the starches will stop here. Digestion of all molecules will occur in the small intestine including the fat in the ham and roll. Lipase will digest the fat after bile has emulsified it. Trypsin will continue the breakdown of protein into dipeptides. Amylase will continue the breakdown of starches into disaccharides. Lactase, sucrase and maltase will continue the breakdown of disaccharides into simple sugars. Peptidase will break the dipeptides down into amino acids. T E A C H E R

6 5. Lactose-intolerance involves a person s inability to digest the sugar, lactose. This can lead to problems such as upset stomach. Describe the cause of lactose-intolerance in terms of digestion where does the problem begin? What enzyme is involved? What food is most likely to lead to the problems caused by lactose-intolerance? Why? The enzyme necessary to digest lactose is not present. The problem begins in the small intestine The enzyme necessary is lactase. Milk and other dairy products contain lactose and will lead to the problems caused by being lactose-intolerant. 6. Assume that the enzyme amylase is absent from a person s saliva. Will there be negative effects on digestion from this? Why or why not? There should be no negative effects. Since amylase is also released into the small intestine, the starches that pass through the stomach into the small intestine will undergo digestion in this location. T E A C H E R

7 Chew on This Investigating the Function of the Digestive System The human digestive system functions to convert food into smaller molecules that can be used by the body. It is built around a continuous, one-way tube, called the alimentary canal. This tube passes through the body and along the way, digestion occurs. Digestion may be either chemical, requiring chemical reactions to break down the food, or mechanical, requiring movement to break, chop, stir, mix and churn the food. Chew on This Digestion begins in the mouth. As you chew, which is a form of mechanical digestion, food is broken down into smaller pieces. The tongue, which aides in mechanical digestion, helps to mix the food with saliva to begin chemical digestion. Saliva contains enzymes, which are molecules that speed up the breakdown of certain substances. Amylase, an enzyme found in saliva, is responsible for the breakdown of starch, a complex carbohydrate. Starch is a long chain of simple sugars, such as glucose, fructose and galactose. The amylase begins to assist in breaking the bonds between these sugars so that they may be divided into smaller sugar molecules, usually consisting of only two sugars, called disaccharides. The resulting formation of the chewed, partially digested ball of food is called a bolus. When you swallow, the bolus is pushed into the esophagus. The esophagus is a long, muscular tube that moves in wave-like contractions, called peristalsis. Peristalsis moves the food bolus down towards the stomach. A thick ring of muscle, called the cardiac sphincter, closes as food moves out of the esophagus and into the stomach. This prevents the backflow of the stomach contents into the esophagus. However, instances may occur when acid from the stomach will travel back up into the esophagus. The result is a burning sensation, called heartburn. Although it has nothing to do with the heart, it gets that name due to the region in which the burning sensation is occurring. Once the bolus enters the stomach, which is a large, muscular sac, it undergoes further mechanical and chemical digestion. Mechanical digestion continues through muscle contractions of the stomach that mix and churn the bolus. Chemical digestion continues as enzymes and acid are released into the stomach. The stomach is lined with mucous to prevent the acid from damaging the lining. The hydrochloric acid produced by cells in the stomach Copyright 2012 Laying the Foundation, Inc., Dallas, TX. All rights reserved. Visit us online at 3

8 upon the arrival of the bolus, activates the enzyme pepsin. This enzyme is responsible for beginning the breakdown of protein into chains of amino acids. Amylase from the saliva is deactivated in the stomach due to the highly acidic environment, which breaks down that enzyme. The mixture created in the stomach is called chyme. Chew on This Chyme leaves the stomach through another ring of muscle called the pyloric sphincter, which again, prevents backflow. The chyme moves from the stomach into the small intestine where many enzymes are introduced to further aid in chemical digestion. The small intestine consists of series of tubes, called the duodenum, jejunum and ileum. The small intestine s inner lining is folded with small, fingerlike projections called villi. This is helpful because the extra folds and projections increase the amount of surface area available for the absorption of molecules into cells. Accessory organs, such as the pancreas and liver, provide enzymes to complete the mechanical digestion of the chyme as it enters the duodenum. These enzymes are listed below: Enzyme Amylase Trypsin Lipase Maltase Sucrase Lactase Peptidase Effect on Chyme Continues breakdown of starch into disaccharides (a molecule of two sugars) Continues breakdown of protein into dipeptides (a molecule of two amino acids) Breakdown of fat Breakdown of the disaccharide, maltose Breakdown of the disaccharide, sucrose Breakdown of the disaccharide, lactose Breakdown of the protein into amino acids In addition to these enzymes, a substance called bile is released into the duodenum. Bile is produced in the liver and stored in the gall bladder. It serves to help emulsify, or dissolve, fat molecules into smaller units to be digested by the lipase. Much of the chemical digestion is finished in the shorter region, or duodenum. After the chyme has undergone this further digestion, it moves into the longer areas of the small intestine known as the jejunum and ileum, where absorption of the individual molecules into cells continues. The remaining waste from the small intestine begins to move into the large intestine. The large intestine is recognized in three segments the ascending colon, which moves upward in the abdomen, the transverse colon, which moves across the abdomen and the descending colon, which moves back down the abdomen. From here the colon narrows into the sigmoid colon and ends in a region called the rectum. Water is absorbed by cells that line the colon, leaving behind solid waste. There are also bacteria that reside here that are responsible for producing compounds that are beneficial to the body, such as Vitamin K. When the solid waste reaches the final portion of the large intestine, the rectum, it is stored until removal as waste, which exits the body through the anus. Copyright 2012 Laying the Foundation, Inc., Dallas, TX. All rights reserved. Visit us online at 4

9 Chew on This PURPOSE In this lab, you will investigate the process of digestion. You will determine when digestion has occurred and identify the original and final molecules of the foods being digested. MATERIALS 2 test tubes test tube rack wax pencil lactase enzyme tablet soda crackers (2-4 per group) 40 ml whole milk Benedict s solution Lugol s solution mortar and pestle 500 ml beaker 2 test tube clamps hot plate 2 paper cups 25 or 50 ml graduated cylinder stopwatch 3 toothpicks SAFETY ALERT When heating water for water bath, do not let water boil over onto hot plate. When working with test tubes, keep the test tube pointed away from those working around you. Take caution when using hot plate. Take caution when handling solutions. The following chart will assist you in interpreting your results: Reagent Molecule Tested Color if Molecule is Not Present Color if Molecule is Present Lugol s solution starch brownish yellow blue/black Benedict s solution carbohydrate blue green, then orange/red Biuret s solution protein blue purple Copyright 2012 Laying the Foundation, Inc., Dallas, TX. All rights reserved. Visit us online at 5

10 PROCEDURE Before beginning this lab, you will need to create a hot water bath to do this, obtain a 500 ml beaker and fill it to the 300 ml mark with water. Place the beaker on a hot plate, turn the hot plate on a medium setting, and allow the water to heat. Be careful not to let the water boil. If water begins to boil, reduce the heat on the hot plate. Keep an eye on the hot water bath as you work. You will be using this for steps later in your procedure. PART I: TESTING FOR THE DIGESTION OF STARCHES IN THE MOUTH 1. Observe the demonstration cracker that your teacher has prepared and record your observations in Data Table 1 of your student answer pages. 2. Obtain, for each group member, 1 soda cracker and a paper cup. 3. Put the cracker into your mouth and begin chewing. 4. After 30 seconds do not swallow the cracker, but record the taste of the cracker in Data Table 1. Continue to chew, for 5 minutes. 5. After 5 minutes, record the taste of the cracker in Data Table Spit the cracker into your paper cup. 7. Add 10 ml of distilled water to your paper cup and stir using the toothpick. 8. Obtain a test tube rack and two test tubes. 9. Label one test tube with the word Lugol s, and the other test tube with the word Benedict s. Add half of the cracker mixture that you prepared in #7 to the Lugol s test tube and half of the mixture to the Benedict s test tube. 10. Record the contents of each tube in the space provided in Data Table 2 of your student answer pages. 11. Add 10 drops of Lugol s solution to the test tube labeled Lugol s. Record any color change in the space provided in Data Table Add 10 drops of Benedict s solution to the test tube labeled Benedict s. 13. Using your test tube holder, place, and hold the test tube in the hot water bath for 3-5 minutes. 14. Record any color change in the space provided in Data Table Use the chart provided to determine what molecules were present in the test tubes based on your color change. Use your knowledge of digestion to determine what enzymes may have been present, based on any color change (if no enzyme is present write none ). 16. Record this information in Data Table 2. Chew on This Copyright 2012 Laying the Foundation, Inc., Dallas, TX. All rights reserved. Visit us online at 6

11 Chew on This PART II: TESTING FOR THE DIGESTION OF DISACCHARIDES IN THE SMALL INTESTINES 1. Obtain two paper cups. Label one cup no enzyme and label the other enzyme present. 2. Add 20 ml of whole milk to each cup. 3. Obtain one enzyme tablet and a mortar and pestle. 4. Crush the tablet to a powder, using your mortar and pestle. 5. Add the powder to the cup labeled enzyme present and stir using a clean toothpick. 6. Obtain two test tubes. Label one test tube, no enzyme, and the other, enzyme present. 7. Add the milk from the no enzyme cup to the test tube labeled no enzyme 8. Add the milk from the enzyme present cup to the test tube labeled enzyme present. 9. Add 10 drops of Benedict s solution to each test tube and place the test tubes in your hot water bath for 5 minutes. 10. Record your results in Data Table 3. Copyright 2012 Laying the Foundation, Inc., Dallas, TX. All rights reserved. Visit us online at 7

12 Chew on This Investigating the Function of the Digestive System DATA AND OBSERVATIONS Observations of demonstration cracker Molecule present based on demonstration cracker? Taste of chewed cracker after 30 seconds Taste of chewed cracker after 5 minutes Data Table 1 Chew on This Lugol s Test Tube Contents Lugol s Test Color Change Data Table 2 Molecule Present Enzyme Present Benedict s Test Tube Contents Benedict s Test Color Change Molecule Present Enzyme Present Test Tube Data Table 3 Glucose Present at End of Test? No enzyme Enzyme present Copyright 2012 Laying the Foundation, Inc., Dallas, TX. All rights reserved. Visit us online at 8

13 Chew on This ANALYSIS Cut along the dotted lines and arrange the following boxes in order of location and steps of digestion. When you have the correct order, glue to a separate sheet of paper and draw arrows to indicate the direction. Finally, add the following information to each box: function of the structure accessory organs and enzymes necessary for that step, as applicable Anus Esophagus Ileum Rectum Transverse Colon Stomach Descending Colon Jejunum Duodenum Sigmoid Colon Ascending Colon Mouth Copyright 2012 Laying the Foundation, Inc., Dallas, TX. All rights reserved. Visit us online at 9

14 CONCLUSION QUESTIONS Chew on This 1. Based on your data, what would you expect a test using Lugol s on food that has reached the small intestine to indicate? 2. Based on your data, what disaccharide was being broken down by the enzyme lactase? Would you expect this enzyme to work on any other disaccharide? Why or why not? 3. Where does digestion of protein begin? What enzyme(s) is/are involved in the digestion of protein in this location? What test could be used to identify the presence of protein in food?. 4. Rachel has a slice of ham, mashed potatoes and a honey-butter roll for dinner. Describe the location that will be involved in the digestion of each of her foods. Include a discussion of the enzymes that will be used. Copyright 2012 Laying the Foundation, Inc., Dallas, TX. All rights reserved. Visit us online at 10

15 Chew on This 5. Lactose-intolerance involves a person s inability to digest the sugar, lactose. This can lead to problems such as upset stomach. Describe the cause of lactose-intolerance in terms of digestion where does the problem begin? What enzyme is involved? What food is most likely to lead to the problems caused by lactose-intolerance? Why? 6. Assume that the enzyme amylase is absent from a person s saliva. Will there be negative effects on digestion from this? Why or why not? Copyright 2012 Laying the Foundation, Inc., Dallas, TX. All rights reserved. Visit us online at 11