Breakdown ACTIVITY OVERVIEW SUMMARY KEY CONCEPTS AND PROCESS SKILLS. Teacher s Guide B-37 L A B O R ATO R Y

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1 Breakdown to 2 50-minute sessions ACTIVITY OVERVIEW L A B O R ATO R Y SUMMARY Students use antacid tablets and vinegar to model the processes of chemical and mechanical breakdown of food. After a preliminary investigation of the interaction between an antacid tablet and vinegar, students design and perform an investigation to determine the effect of mechanical breakdown on the speed of chemical breakdown. KEY CONCEPTS AND PROCESS SKILLS 1. Graphing data can reveal patterns that are not apparent from data tables. 2. Elements of good experimental design include a completely described procedure, variables (except for the one being tested) kept constant, the use of a control, appropriate use of quantitative and qualitative data, and a large sample size. These elements result in reproducible investigations. 3. Each system within the human body is defined by the functions that it performs. For example, the digestive system is a group of organs, each of which contributes to the process of breaking down food into smaller particles. 4. Creating models is one way to understand and communicate scientific information. 5. Both mechanical and chemical processes contribute to the breakdown of food. 6. Chemical reactions occur at surfaces. The greater the surface area available for contact, the faster the reaction. This is why mechanical breakdown facilitates chemical breakdown. Teacher s Guide B-37

2 Activity 14 Breakdown KEY VOCABULARY chemical breakdown control digestive system function hypothesis model organ qualitative/ quantitative data surface area (optional) variable mechanical breakdown MATERIALS AND ADVANCE PREPARATION For the teacher 1 Transparency 7.1, Elements of Good Experimental Design 1 Transparency 14.1, Human Digestive System * 1 non-effervescent antacid tablet containing calcium carbonate (optional) * 1 overhead projector For the class * access to watch or wall clock with a second hand * balances (optional) For each group of four students 4 effervescent antacid tablets containing sodium bicarbonate mL bottle of vinegar 2 SEPUP trays 2 30-mL graduated cups For each student * 1 2 hard candies (optional) *Not supplied in kit If you plan to allow all of your classes to complete Step 11 of the Procedure, you may need to purchase additional effervescent antacid tablets containing sodium bicarbonate. Teacher s Note: You may want to provide plastic knives to cut the tablets. Making the pieces the same size is difficult when the tablets are broken by hand. You may also want to have extra tablets on hand for students who end up with quarter tablets of very inconsistent sizes. B-38 Science and Life Issues

3 Breakdown Activity 14 TEACHING SUMMARY Getting Started 1. Briefly discuss elements of the digestive process. Doing the Activity 2. Introduce the model and have students explore its use to investigate breakdown (Part One). 3. Students design and perform their investigations (Part Two). Follow-Up 4. Discuss conclusions and the relevance of the investigation. 5. Introduce the importance of surface area in chemical and other interactions. Teacher s Guide B-39

4 Breakdown Activity 14 TEACHING SUGGESTIONS GETTING STARTED 1. Briefly discuss elements of the digestive process. Project Transparency 14.1, Human Digestive System. Use the transparency to identify some of the major organs/structures of the digestive system (mouth, stomach, small intestine, large intestine). You do not need to stress the other digestive organs, since they are presented in depth in the next activity. You may, however, want to point out the location of the liver. Ask students, What are the major functions of the digestive system? Students may recall from Activity 12, What s Happening Inside? that the stomach stores and breaks down food. They may mention the role of the digestive system in food breakdown and absorption. Ask, Where does this breakdown happen? Some students may suggest that it happens in the stomach, small intestine, and large intestine. Inform the class that there are two types of breakdown: mechanical breakdown, in which food is physically broken into smaller pieces, and chemical breakdown, in which particles of food are broken down by chemicals. Use Transparency 14.1 to indicate the major locations of mechanical breakdown (mouth, stomach) and chemical breakdown (mouth, stomach, small intestine). Ask, Why is breakdown important? Establish the idea that food must be broken down in order to be absorbed by the body. Teacher s Note: As mentioned in the Safety Note in the Student Book, vinegar has a strong odor. Certain students may be extremely sensitive to pungent smells. Decide in advance how you will address any complaints or problems that may arise. DOING THE ACTIVITY 2. Introduce the model and have students explore its use to investigate breakdown (Part One). Students may be unfamiliar with the idea of a chemical reaction. You can demonstrate the greater reactivity of vinegar compared to water and reinforce the concept of chemical breakdown by placing an antacid tablet containing calcium carbonate in both liquids. (Calcium carbonate tablets do not dissolve quickly in water. The student activity uses effervescent antacid tablets, which quickly dissolve in both water and vinegar.) In water, nothing will happen immediately to the non-effervescent tablet. In vinegar, small bubbles will begin to form around the tablet. Note, however, that these are not speedy reactions. As minutes pass by, tablets in both liquids will appear to break down; however, the tablet in the vinegar breaks down more quickly. The vinegar causes a chemical reaction, while the water merely dissolves the tablet (a physical change). Point out that vinegar, like chemicals in the stomach that contribute to chemical breakdown, is an acid. Steps 1 4 of the Student Procedure allow students to explore the breakdown model before they design their experiments. The table on the next page shows the essential parts of the model. Pause briefly after students complete Step 4 to discuss the model before continuing. Ask, How did you decide when the chemical breakdown was over? Did Teacher s Guide B-41

5 Activity 14 Breakdown The Model Material/Process Represents antacid tablet food breaking or mechancial breakdown crushing tablet (chewing) adding vinegar chemical breakdown you observe or record how long it took before the tablet piece completely dissolved? Use these questions to help students design their experiments. 3. Students design and perform their investigations (Part Two). This activity provides an opportunity to assess students on the Recording Design or Procedure element of the DESIGNING AND CONDUCTING INVESTIGA- TIONS (DCI) variable. If you are planning on DCI using this assessment with your students, inform them in advance and provide them with enough time to develop and conduct complete experiments (as described in Steps 5 7 of the Student Procedure). You can use Transparency 7.1, Elements of Good Experimental Design, to review important ideas. You can also encourage on-task behavior by assessing students with the Task Management and/or Shared Opportunity element(s) of the GROUP INTERACTION variable. GI Students may need help getting started. However, encourage students to perform Part Two of the Student Procedure as independently as possible. Remind them to focus on the experimental question, How does the size of your food affect the speed at which chemical breakdown occurs? If necessary, rephrase the question as, Does the amount you chew your food affect your ability to digest it chemically? You may need to discuss ways in which they can answer their experimental question. For example, students could use an intact quarter tablet to represent food that had not been chewed, quarter tablets broken into smaller pieces to represent partially chewed food, and completely crushed tablets to represent completely chewed food. They could then add identical amounts of vinegar and time the reactions. Some students may focus on varying the amount of vinegar, but this does not address the experimental question. Guide students by asking, Can you change the amount of acid in your stomach? What do you control directly in the digestion process? Help students think about mechanical breakdown as the process directly under conscious control. Step 10 of the Student Procedure instructs students to construct a bar graph of their data. Students may need assistance in creating a graph. You may want to refer to bar graphs already produced in this course: students completed bar graphs in Activities 3 and 7, and also had the opportunity to construct a bar graph in Activity 9. A bar graph of sample student data is shown below. Graph 1: Sample Student Data Time (in seconds) Whole Pieces Powder 1/4 Tablet Piece B-42 Science and Life Issues

6 Breakdown Activity 14 Note that Step 11 gives students a chance to revise their design and possibly repeat the experiment. After they have fully completed their experiment and recorded their results, have them continue to work together in their groups to discuss Questions 1 and 2. They can then write their conclusions using Analysis Question 3 as a guide. This activity can also be used to teach elements of a complete lab report (see Teacher s Guide to Activity 1, Solving Problems: Save Fred! ). FOLLOW UP 4. Discuss conclusions and the relevance of the investigation. Have students share their results with the class. You may want to review the use of concepts such as variables, quantitative and qualitative data, multiple trials, and reproducibility in the design of their experiments. Explain that chemical experiments like the one they have done are conducted to gain a better understanding of biochemical processes in the body. Emphasize the main concepts of the activity: Food must be broken down in order to be absorbed by the body. Both mechanical and chemical processes contribute to the breakdown of food. Food breaks down faster if both chemical and mechanical breakdown occur. 5. Introduce the importance of surface area in chemical and other interactions. You may wish to give each student a piece of hard candy to eat to explore the importance of surface area. Instruct half of the students to chew their candy and the other half to not chew. Measure the amount of time it takes for the candies to completely dissolve. (Tell students not to swallow any undissolved pieces.) Some students may notice the role of the tongue in mechanical breakdown, since the friction of the tongue against the candy can greatly speed its dissolving. Have students think about why the candy that was chewed dissolved more quickly. Use their responses to build the idea that the surfaces of the candy are the key to this process. For the candy to dissolve, its surface has to be in contact with the saliva. Ask, How does chewing affect how much candy surface there is? Chewing creates new surfaces for interaction between the candy and the saliva. Chemical interactions occur at the surfaces, so the more surface available, the faster the interactions can occur. The dissolving antacid and the dissolving candy both illustrate this important chemical and biological concept. Similarly, the smaller the pieces of swallowed food, the faster they can interact with stomach acid and other substances and be digested. The concept of surface area will be further explored in Unit C, Micro-Life of Science and Life Issues, when students investigate why cells are so small. Safety Note: If you use candy that contains sugar for the following part of the activity, it should not be eaten by any students who must restrict sugar intake. Teacher s Guide B-43

7 Breakdown Activity 14 SUGGESTED ANSWERS TO ANALYSIS QUESTIONS 1. a. In your experiment, what variables did you keep the same? The amount of tablet and the amount of vinegar were kept the same. In addition, students could have made sure that tablets that were mechanically broken down were crushed uniformly. If they added tablets to vinegar (instead of the reverse), they would have had to make sure that all of the powder was added simultaneously. b. Were there any variables (except for the one being tested) that you could not keep the same? There was some unavoidable variation in the amount of tablet used. c. How could you or did you improve the design of your experiment? Explain. Most experiments could have been improved by using a balance to weigh out identical amounts of tablet. 2. a. What part of digestion was modeled by breaking the tablet? Mechanical breakdown b. What part of digestion was modeled by adding vinegar? Chemical breakdown 3. How does the size of your food affect the speed at which chemical breakdown occurs? Explain how your conclusions are based on the data collected during your experiment, and whether your hypothesis was supported or disproved. The more the food is broken down mechanically, the faster it can be broken down chemically. Students should support this general conclusion by using their quantitative data (such as how many seconds longer the unbroken piece took to dissolve), by determining a ratio, or by making any other statement that directly uses their group s or the class s experimental data. Student data will vary depending on the amount of vinegar added (adding more vinegar speeds the process) and the size of the tablet used (smaller pieces dissolve faster). 4. Were your conclusions based on qualitative or quantitative data? Explain. While students collected both qualitative data (in Step 3) and quantitative data (in Step 9), their conclusions are more likely to be based on quantitative data, such as time, ratios, or any other statement that directly uses their group s or the class s experimental data. You may wish to review the use of qualitative and quantitative data in this activity and the different purposes served by each. Teacher s Guide B-45

8 Activity 14 Breakdown 5. Besides preventing choking, why is it important to chew your food? If your students are having difficulty with this question, rephrase it as: Why is it important to mechanically break down your food before it reaches your stomach? Chewing your food is one method of mechanical breakdown, which speeds the process of chemical breakdown. Students are likely to have observed that the tablets that were broken into smaller pieces reacted more quickly with the vinegar. In like manner, food that is broken down more quickly can be absorbed by the body sooner. (You may also want to mention that chewing also enables your food to move more smoothly through your esophagus and prevents choking because smaller pieces of food are more easily lubricated by the saliva.) B-46 Science and Life Issues

9 Human Digestive System salivary glands esophagus liver bile duct gall bladder stomach pancreas small intestine large intestine 2006 The Regents of the University of California rectum anus Science and Life Issues Transparency 14.1 B-47