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By Jane Crumlish

Modified by Jane Crumlish from the instructions on LACTAID®. Updated: April 20, 2008

Type of Entry:

  • Lesson/class activity

Type of activity:

  • Hands-on activity
  • Group/cooperative learning

Target audience:

  • Biology students

Notes to the teacher:

Hands-on activities for the study of enzymes usually involve spit or liver; the use of spit is not a good health practice and the students find liver gross. The concept of the enzyme action gets lost in the students' aversion to these enzyme sources. Lactaid-lactose has been successful due to its simplicity. My favorite way to use it is as a student demonstration. Several students do the activity and report to the class on what is happening. We discuss as we progress and students suggest various things to do; they make sure that each section has a control. This activity has been conducted as a lab using paper models of lactose and lactase. It has also been used successfully as a cooperative learning exercise. The reaction rate is very fast when using small amounts. Lactaid® does not denature. Changing the rate of reaction and specificity are the properties best illustrated by Lactaid®.

Required of students

Students should have some knowledge of test papers and indicators. They should also have some knowledge of carbohydrates.

Preparation time needed

Time is needed for shopping and the gathering of the materials. The liquid Lactaid® can be stored in the refrigerator and will last for several years for use in this laboratory. Glucose and sucrose solutions can come from any source.

Class time needed

The minimum is approximately 20 minutes. More time is necessary if paper models are used.


Students use a drop of milk, test it with glucose test paper and establish that there is no glucose in milk. Student also test glucose solutions to discover the color range of the glucose test paper readings. Students test Lactaid® to establish that it contains no glucose. Students mix Lactaid® and milk, use the glucose test paper and discover the presence of glucose.

Paper models can be used to help students visualize enzyme action. A disaccharide is used for lactose; a rectangle with a piece fitting into the junction can be used for the enzyme.



  • Spot plate or glass slide
  • Marker
  • Toothpick for mixing
  • Forceps for handling the glucose test paper
  • Milk-whole, skim or 1%
  • Droppers
  • Lactaid® (lactase source) the liquid form works best
  • Glucose test strips (available from laboratory suppliers such as Carolina Biological, Wards Scientific and others)
  • Any glucose solution
  • Any sucrose solution
  • Paper models of enzyme, HOH, galactose, glucose, lactose.
    Download ready to print paper models. You can tailor models to resemble your text visuals.


Most foods that are ingested are composed of large, complex molecules. These molecules are not useful to the body unless they are first broken down into small, simple molecules. The act of breaking down large molecules into smaller ones is called digestion. Digestion is dependent on various enzymes produced by the organs of the digestive system to make the chemical activity of hydrolysis occur in a reasonable amount of time. The puropse of this activity is to work with models of substrates and enzymes; to test the digestion of lactose with lactase; and to determine if digestion of lactose has or has not occurred.

  1. Define:
    • hydrolysis
    • substrate
    • active site

  2. How many sugar rings are there in lactose? Based on this classify lactose.

  3. Complete the following:
    Lactose or milk sugar      C12H22O11
    Add water   +     ____________
    Subtract Glucose formula   –   _____________________
    Galactose formula   =   _____________________
  4. What would be the enzyme that activates this reaction?

  5. Where does this enzyme act in your body?

  6. Where is this enzyme produced in your body?

  7. Name the substrate.

PUT A STAR * ON THE ACTIVE SITE OF THE LACTOSE MODEL. LABEL THE ENZYME MODEL BY NAME. Cut out all the models along the exterior solid lines. Tape lactose, water and enzyme models in the appropriate spaces (to be determined by teacher). Cut along the dotted lines of the other two models; reverse the procedure that you did for the dehydration synthesis to complete the equation.


  1. Use the marker to draw and number 4 circles on glass plate or slide. Use different droppers for each solution and add the following:

    Circle 1: add 2 drops of glucose solution
    Circle 2: add 2 drops of milk
    Circle 3: add 1 drop of lactase
    Circle 4: add 1 drop of lactase plus 2 drops of milk (mix with toothpick)

  2. After 3 minutes, test each of the above for the presence of glucose by dipping a piece of glucose test paper to each.

  3. After 2 minutes, note any color change in the glucose test paper.

  4. Record the data in table 1 and complete the table.


    Circle Contents Glucose test paper color Interpretation
    1 Glucose      
    2 Milk      
    3 Lactase      
    4 Lactase + Milk      

  5. In which circle would you expect the hydrolysis of the milk sugar, lactose?

  6. What products would result after this hydrolysis?
    How did you know this?

  7. Why did you test the glucose with the glucose test paper?
    Why did you test the lactase with the glucose test paper?

  8. Does milk contain glucose?
    What is your proof?

  9. Does milk combined with lactase contain glucose?
    What is your proof?

  10. Some people cannot drink milk because their digestive systems do not produce lactase. If milk is ingested, it cannot be digested. This results in cramping, bloating, gas, and diarrhea. Suggest a treatment that would allow a person such as this to ingest milk.

Method of Evaluation/ Assessment

Students will answer the above questions as they proceed through the activity

Extension/ Reinforcement/ Additional Ideas

After students have done the initial activity, have them design and execute labs to illustrate that enzymes are specific and that enzymes are reusable.

  • Enzymes are specific. Sucrose solutions can be used to show that the lactase in the Lactaid will not break down sucrose.

  • Enzymes are reusable. Students take a little of the Lactaid- milk and add it to a new drop of milk. Some glucose test papers will turn more intense shades with greater amounts of glucose.

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