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Activity 3-1: Digestive Enzyme in Action

PLAN

Summary Students test milk for the presence of glucose both before and after the enzyme lactase has been added. They lest regular milk and lactose-free milk.

Objectives

Students:

\checkmark define the term enzyme.

\checkmark demonstrate a test for the presence of the glucose using lactase with regular and lactose-free milk samples.

\checkmark explain the action of the digestive enzyme lactase on milk.

Student Materials

Per team

  • Activity Report
  • Milk, regular and lactose-free; Glucose test strips (4); Lactase tablets (2); Two small beakers; Masking tape

Teacher Materials

  • Activity Report Answer Key
  • Model or chart of the digestive system; Glucose solution; Extra student supplies

Advance Preparation

Purchase glucose test strips and lactase enzyme tablets (Lactaid) from drugstore. Cut test strips into two strips lengthwise so each student team will receive four slender strips. Purchase milk and lactose-free milk from the grocery store. Prepare glucose solution by adding a small amount of glucose (dextrose) to approximately 100 \ ml of water.

Estimated Time \frac{1}{2} class period

Interdisciplinary Connections

Social Studies Conduct research to find out which ethnic groups have a prevalence of lactose intolerance. Is there an advantage to this intolerance?

Home Arts Survey grocery stores to see what other lactose-free products are available.

Prerequisites and Background Information

Students need to know the function of enzymes as catalysts for chemical reactions. Enzymes play an integral role in the digestive process. It would be helpful for students to know that lactose is a complex sugar that breaks down into two monosaccaride molecules, glucose and galactose.

Chapter 5, “Cultural Mediation: The Evolution of Adult Lactose Absorption” in the book CoEvolution by William Durham (Stanford University Press, 1991) is an excellent resource for background information on lactose intolerance.

IMPLEMENT

You can do this activity as a demonstration or have students conduct the activity in lab teams.

Introduce Activity 3-1 by reviewing the role of enzymes in reactions. Share with students that the enzyme lactase is produced in the small intestine. Lactase breaks down lactose in the small intestine.

Steps 1-3 Demonstrate the positive test for glucose using a glucose solution and a glucose strip. If students are conducting this activity in teams, you might want to introduce a control. Discuss the use of controls in experiments. Then have students use water as a control in this procedure.

Helpful Hints

Lactase is also available in liquid form.

Steps 1-5 Review the importance of maintaining clean test equipment. If the beakers have residue from the other milk being tested, the test results may be contaminated.

Conclude Activity 3-1 by discussing the effect the enzyme lactase had on lactose.

ASSESS

Use the completion of the experiment and written responses on the Activity Report to assess if students can

\checkmark explain the function of enzymes in digestion.

\checkmark interpret the results of the glucose test on regular and lactose-free milk.

\checkmark explain the action of the digestive enzyme lactase on milk.

Activity 3-1: Digestive Enzyme in Action – Activity Report Answer Key

  • Sample answers to these questions will be provided upon request. Please send an email to teachers-requests@ck12.org to request sample answers.
  1. What happens to the glucose test strip in the presence of glucose?
  2. Describe the results of the glucose strip test with
    1. regular milk.
    2. lactose-free milk.
  3. Describe the results of the glucose test with the regular milk after the lactase tablet has been added. Explain.
  4. Describe the digestive action of lactase.
  5. Why do some individuals substitute lactose-free milk for regular milk in their diets?

Think about how you feel when you are under stress. How does your stomach feel? Explain how you think an ulcer can be caused by a person being under a lot of stress. Describe several ways you could deal with the stress in your life to leave you feeling calm instead of upset.

Review Questions/Answers

  • Sample answers to these questions will be provided upon request. Please send an email to teachers-requests@ck12.org to request sample answers.
  1. The three major components in food that require digestion are carbohydrates, fats, and proteins. How is digestion of these three components similar and/or different, until the time they reach the pylorus?
  2. Why is it important to chew food thoroughly?
  3. What role do enzymes play in digestion? Include two examples of enzymes. Explain where each enzyme is produced, where each does its work, and what it does.
  4. What moves food along the food tube? Explain what keeps food moving in the right direction.

Activity 3-1 Report: Digestive Enzyme in Action (Student Reproducible)

1. What happens to the glucose test strip in the presence of glucose?

2. Describe the results of the glucose strip test with

a. regular milk.

b. lactose-free milk.

3. Describe the results of the glucose test with the regular milk after the lactase tablet has been added. Explain.

4. Describe the digestive action of lactase.

5. Why do some individuals substitute lactose-free milk for regular milk in their diets?

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