Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
14 2 0- m inu te s e ss i ACTIVITY OVERVIEW LA O RY o5 on 40 -t s Breakdown BO RA T 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 Activity 14 • Breakdown KEY VOCABULARY chemical breakdown model control organ digestive system qualitative/ quantitative data function surface area (optional) hypothesis 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 1 120-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. n 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 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 Breakdown • Activity 14 TEACHING SUGGESTIONS n 1. GETTING STARTED 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. gent smells. Decide in advance how you will address any complaints or problems that may arise. n 2. DOING THE ACTIVIT Y 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 Ask students, What are the major functions of the both liquids. (Calcium carbonate tablets do not dis- digestive system? Students may recall from Activity solve quickly in water. The student activity uses 12, “What’s Happening Inside?” that the stomach effervescent antacid tablets, which quickly dissolve stores and breaks down food. They may mention the in both water and vinegar.) In water, nothing will role of the digestive system in food breakdown and happen immediately to the non-effervescent tablet. absorption. Ask, Where does this breakdown happen? In vinegar, small bubbles will begin to form around Some students may suggest that it happens in the the tablet. Note, however, that these are not speedy stomach, small intestine, and large intestine. reactions. As minutes pass by, tablets in both liquids 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 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. (mouth, stomach) and chemical breakdown (mouth, Steps 1–4 of the Student Procedure allow students to stomach, small intestine). Ask, Why is breakdown explore the breakdown model before they design important? Establish the idea that food must be bro- their experiments. The table on the next page shows ken down in order to be absorbed by the body. the essential parts of the model. n Teacher’s Note: As mentioned in the Safety Note Pause briefly after students complete Step 4 to dis- in the Student Book, vinegar has a strong odor. Cer- cuss the model before continuing. Ask, How did you tain students may be extremely sensitive to pun- decide when the chemical breakdown was over? Did Teacher’s Guide B-41 Activity 14 • Breakdown You may need to discuss ways in which they can The Model Material/Process Represents antacid tablet food breaking or crushing tablet mechancial breakdown (chewing) adding vinegar chemical breakdown 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. you observe or record how long it took before the tablet piece completely dissolved? Use these ques- Some students may focus on varying the amount of tions to help students design their experiments. vinegar, but this does not address the experimental question. Guide students by asking, Can you change 3. Students design and perform their investi- the amount of acid in your stomach? What do you gations (Part Two). control directly in the digestion process? Help stu- This activity provides an opportunity to assess stu- dents think about mechanical breakdown as the dents on the “Recording Design or Procedure” ele- process directly under conscious control. ment of the DESIGNING DCI TIONS AND CONDUCTING INVESTIGA- (DCI) variable. If you are planning on 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 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. important ideas. You can also encourage on-task behavior by assessing students with the “Task ManGI Graph 1: Sample Student Data agement” and/or “Shared Opportunity” ele- 100 90 ment(s) of the GROUP INTERACTION variable. 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 Time (in seconds) 80 Students may need help getting started. However, 70 60 50 40 30 at which chemical breakdown occurs? If necessary, 20 rephrase the question as, Does the amount you chew 10 your food affect your ability to digest it chemically? B-42 Science and Life Issues 0 Whole Pieces 1/4 Tablet Piece Powder Breakdown • Activity 14 Note that Step 11 gives students a chance to revise You may wish to give each student a piece of hard their design and possibly repeat the experiment. After candy to eat to explore the importance of surface they have fully completed their experiment and area. Instruct half of the students to chew their recorded their results, have them continue to work candy and the other half to not chew. Measure the together in their groups to discuss Questions 1 and 2. amount of time it takes for the candies to com- They can then write their conclusions using Analysis pletely dissolve. (Tell students not to swallow any Question 3 as a guide. This activity can also be used to undissolved pieces.) Some students may notice the teach elements of a complete lab report (see Teacher’s role of the tongue in mechanical breakdown, since Guide to Activity 1, “Solving Problems: Save Fred!”). the friction of the tongue against the candy can n 4. greatly speed its dissolving. FOLLOW–UP Have students think about why the candy that was Discuss conclusions and the relevance of chewed dissolved more quickly. Use their respons- the investigation. es to build the idea that the surfaces of the candy Have students share their results with the class. You are the key to this process. For the candy to dis- may want to review the use of concepts such as vari- solve, its surface has to be in contact with the sali- ables, quantitative and qualitative data, multiple tri- va. Ask, How does chewing affect how much candy als, and reproducibility in the design of their exper- surface there is? Chewing creates new surfaces for iments. Explain that chemical experiments like the interaction between the candy and the saliva. one they have done are conducted to gain a better Chemical interactions occur at the surfaces, so the understanding of biochemical processes in the body. more surface available, the faster the interactions can occur. The dissolving antacid and the dissolv- 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. ing 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 Breakdown • Activity 14 SUGGESTED ANSWERS TO ANALYSIS QUESTIONS 1. a. In your experiment, what variables 3. How does the size of your food affect the did you keep the same? speed at which chemical breakdown occurs? The amount of tablet and the amount of vine- Explain how your conclusions are based on the data gar were kept the same. In addition, students collected during your experiment, and whether your could have made sure that tablets that were hypothesis was supported or disproved. mechanically broken down were crushed uni- The more the food is broken down mechani- formly. If they added tablets to vinegar (instead cally, the faster it can be broken down chemi- of the reverse), they would have had to make cally. Students should support this general con- sure that all of the powder was added simulta- clusion by using their quantitative data (such as neously. how many seconds longer the unbroken piece b. Were there any variables (except for the one took to dissolve), by determining a ratio, or by being tested) that you could not keep the same? making any other statement that directly uses their group’s or the class’s experimental data. There was some unavoidable variation in the Student data will vary depending on the amount of tablet used. c. How could you or did you improve the design of speeds the process) and the size of the tablet your experiment? Explain. used (smaller pieces dissolve faster). 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. amount of vinegar added (adding more vinegar 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 What part of digestion was modeled by adding or the class’s experimental data. You may wish vinegar? to review the use of qualitative and quantitative Chemical breakdown data in this activity and the different purposes served by each. Teacher’s Guide B-45 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 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