This was the first Investigation of the LabLearner CELL Examining Nutrition. In it, students learned the difference between mechanical digestion and chemical digestion.

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A. Begin the analysis of the Lab by helping students remember the experiments they conducted. The following questions may be helpful in prompting student discussion:

1. Ask students: Can anyone explain what you investigated in the Lab? Students should indicate that they investigated the two types of digestion: mechanical and chemical. They also investigated the digestive system and the function of each of its parts.

2. Ask students: Can you describe the experiments you performed when investigating the digestive system? Students should indicate that a stick of chalk was used to model a piece of food and the two types of digestion. In the first part of the experiment, they broke the chalk into smaller pieces. In the second part, they placed the pieces of chalk into vinegar. For the last part of the Lab, they used resource materials to identify the parts of the digestive system, then explored the human torso to answer several questions.

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B. Review the modeled experiments and what each represented in order to help students understand the process of digestion. Use the following questions to aid in initiating student discussion:

1. Ask students: What did the chalk represent? Students should indicate that the chalk represented a piece of food that had been eaten.

2. Ask students: What did breaking the stick of chalk represent, mechanical or chemical digestion? Why? What observations from your experiments support your conclusion? Students should indicate that when they broke the stick of chalk, the chalk changed in size and shape. This indicated a change in the physical form of the chalk. In addition, students did not observe any signs of a chemical change such as an unexpected color change, a release of a gas or a change in temperature. Together these observations suggest that the breaking of chalk represented mechanical digestion.

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1. Affirm that the breaking of the chalk into smaller pieces represented mechanical digestion. Explain that during mechanical digestion, food is broken down into smaller pieces but that the smaller pieces are not changed into different substances.

2. To help students understand that the smaller pieces are the same chemical substance in a different physical form, explain that substances that undergo physical changes can be put back together into their original form.

3. Ask students: Could the pieces of chalk be put back together? Yes. The pieces of chalk could be glued or taped back together.

4. Ask students: What did placing the pieces of chalk into the vinegar represent mechanical or chemical digestion? Why? What observations from your experiment support your conclusion? Students should indicate that putting the chalk into the vinegar represented chemical digestion. During the digestion of the chalk in vinegar, students observed two signs of chemical change, the release of gas (bubbles) and an unexpected color change in the chalk. The observance of these two signs indicated that the reaction of the chalk with the vinegar was a model of chemical digestion that broke down larger molecules, which cannot be absorbed, into smaller pieces that are needed by the body.

5. Affirm that the experiment with chalk and vinegar was a model of chemical digestion. To help students understand that substances released in the bubbles were different than the chalk, ask students: Could the substances in the bubbles that were in the vinegar be put back together with the chalk? Students should indicate that the substances in the bubbles that were released in the chalk could not be put back together with the chalk.

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C. Ask students: Did you see any similarities and/or differences between mechanical and chemical digestion? How could you organize the data from your experiment to describe these similarities and differences? Student answers may vary. Guide students to realize that a Venn diagram would help show this information.

1. Permit students time to discuss the possibilities. After listening to their ideas, suggest that students use a Venn diagram to show this information.

2. Explain that they will make a Venn diagram to show the similarities and differences between the two types of digestion they modeled in the Lab. If necessary, review how a Venn diagram is created.

3. Direct students to create their diagram of it in Problem 6 in their Student Data Record. Encourage students to think about the following questions as they create their Venn diagram:

a. Did the size of the “food” change during the different types of digestion?

b. How do mechanical and chemical digestion relate to chemical and physical changes?

c. Can the “food” be put back together following each type of digestion?

d. Are different substances formed as a result of each type of digestion?

4. When students have completed this task, discuss the results as a class. Use the following questions to prompt student discussion:

a. Ask students: What are some of the differences between the two types of digestion? Students should suggest that mechanical digestion breaks food into smaller pieces using physical means, while chemical digestion breaks food into smaller pieces through the use of chemicals. In mechanical digestion, the food remains the original substance, but chemical digestion changes the food into a new substance or substances.

b. Ask students: How did you see these differences in the Lab? Mechanical digestion was observed in the Lab when the chalk was physically broken into smaller pieces, which could be put back together to form the original piece of chalk. Chemical digestion was observed in the Lab when the chalk was placed into the vinegar and smaller pieces and bubbles were released from the chalk. The chemical process was observed when gas was released (bubbles rising) and when there was an unexpected color change.

c. Ask students: What are some similarities between mechanical and chemical digestion? Both mechanical and chemical digestion are similar in that they both break food into smaller and smaller pieces.

d. Ask students: How did you see these similarities in the Lab? The process of mechanical digestion was observed when the piece of chalk was broken into smaller pieces. The process of chemical digestion was observed when the pieces of chalk broke into even small pieces or became smaller is shape as they dissolved in the vinegar.

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Remind students that during the PreLab they were asked to associate the terms mechanical and chemical with three other descriptive words. 

Ask students: What words would you use now to associate with these terms? Record the students’ new suggestions on a piece of chart paper or transparency beneath the students’ first suggestions.

6. Compare the two lists of words. Ask students: Why did you think of different words to describe the same terms? Students should suggest that they have a better understanding of the terms after performing their Lab experiments.

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D. Remind students that during the PreLab they were asked to think about how food would look after each type of digestion. Explain that students will have a chance to answer this question again, but this time you would like them to associate the different types of digestion with the different organs in the digestive tract. Students can then predict how the food will look as it moves from one organ to another.

1. Ask students: What might be a good way to organize the information about the digestive system and mechanical and chemical digestion? Student answers will vary.

2. Work with students to develop a Table that will organize their data. Remind students that Completion of a Data Table is a tool from the Procedural Toolbox. If necessary, help students review the steps they should consider as they complete a data table.

• Are there questions I need to answer?

• What type of results or information did I obtain?

• How could I combine the data I recorded for each Trial I conducted in the Lab?

3. Refer to the Table in the slide. Direct students to locate Problem 7 in their Student Data Record and enter the headings for each column.

4. Ask students: What are the parts of the digestive system? They are listed in the first column of the Table. Students should also list them in the Table in Problem 7.

5. As a class, discuss the information for the second column as it is entered in the Table. Ask students the following questions, and refer to the Table as you discuss the responses with the class. Students should refer to the information from Trial 3 in order to enter the data into Column Two of their Table.

a. Ask students: What happens to the food you place in your mouth? Student answers may vary. The teeth break the food into smaller pieces by chewing and grinding the food.

b. Ask students: What function does the tongue perform in digestion? Student answers may vary.

c. Explain that along with the mouth and teeth, the tongue mixes food with saliva. Ask students: What do you think is the saliva’s function? Student answers may vary. Saliva mixes with the food to make swallowing easier. There are also special chemicals in the saliva called enzymes that begin to chemically digest the food.

d. Ask students: What happens to your food after it is swallowed? Students should indicate that the food is pushed through the throat and into the esophagus. The muscles of the esophagus contract to move it down to the stomach. 

e. Ask students: Does mechanical or chemical digestion occur as food travels through the throat and esophagus? Student answers will vary.

f. Explain that when food travels through the esophagus, it does not undergo chemical or mechanical digestion. These organs function as a means of transportation to the stomach.

g. Ask students: What happens to your food when it reaches the stomach? Student answers will vary.

h. Explain that in the stomach food continues to mix and break into smaller pieces. When the food particles are small enough, chemicals called acids and enzymes break the food particles down further through chemical digestion, causing the food to change into different substances.

j. Ask students: What happens to your food when it reaches the small intestine? Students should indicate that food continues to be broken down by enzymes when it reaches the small intestines.

k. Ask students: What function does the large intestine perform? Students should indicate that water and some vitamins are absorbed and any remaining undigested food that reaches the large intestine is passed through this organ and out of the body as waste.

Continued on Next Slide ➡

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Continued from Previous Slide ➡

7. Use the questions that follow to complete the last column of the table. Encourage students to refer to their Scientist’s Glossary and to look at the data in the table as they complete the information in this column.

a. Ask students: While in your mouth, is your food changed physically or chemically before you swallow it? How do you know? Remind students to think about Trial 1.  Students should indicate that the food is mixed and broken into smaller pieces by the teeth and tongue before it is swallowed. During this time it is also mixed with saliva which contains enzymes, or special chemicals that help break down food. Both physical and chemical changes occur to the food. The mixing and grinding is mechanical digestion. As saliva combines with the food, chemical digestion begins to occur. 

b. Ask students: What type of digestion occurs in the stomach? Why?  Student answers may vary. Both mechanical and chemical digestion occurs in the stomach. Food is mechanically digested into smaller pieces by mixing, then chemically digested by acids and enzymes even smaller into different (new) substances, including nutrients.

c. Ask students: Does digestion occur in the small and large intestines? Why? Student answers may vary. Chemical digestion occurs in the small intestines because food is chemically digested by enzymes. In the large intestines, water and some vitamins are absorbed and undigested food is carried out of the body. More of the function of the large intestine lies with the absorption of nutrients rather than with the breakdown of food.

d. Ask students: How do the nutrients from food get to the cells of the body? Students should indicate that most of the nutrients from food are absorbed through the walls of the small intestine into blood vessels that carry the nutrients to where it is needed in the body’s organs and cells. Some nutrients, like water and some vitamins, are also absorbed in the large intestine.

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E. Help students to associate the process of digestion with the change in the size of the food they consume as it moves through their bodies.

1. Ask students to think about how the size of their food changes as it moves through their digestive system. Remind students that during the PreLab they were asked what food looks like after it is mechanically and chemically digested. Encourage them to create a representation that shows how their food changes and record their representation in Problem 8 of their Student Data Record.

2. After students have completed their task, have students present their new ideas to the class. Ask students to compare this representation to what they recorded during the PreLab. Students may simply hold up their representation for the class to view, briefly describe the concept, and compare the new representation to what was recorded in the PreLab.

F. To complete this Investigation, tell students they will continue to study the process of digestion and how this process applies to having a healthier body throughout this CELL.