From lactose to glucose

This exercise is a part of Educator Guide: Built for Speed / View Guide

Class time: 30-50 minutes

Purpose: Testing the effects of different conditions on lactase, an enzyme that catalyzes the conversion of lactose (milk sugar) to glucose (simple sugar).

Notes to the teacher: You can adapt this activity depending on the number and the level of the students, as well as the amount of available class time.  


  • URS-1G-100 Teco glucose assay strips from (currently $9.95 for
    100 strips)
  • Scissors (to cut glucose strips in half lengthwise, so one strip will become two)
  • Lactaid or similar generic chewable lactase tablets (available at drug stores and in the pharmacy section of grocery stores, Walmart and Target)
  • Pliers (to crunch lactase tablets to powder) or a mortar and pestle
  • Milk (any type except Lactaid milk that has already been treated with lactase)
  • Test tubes
  • Test tube racks
  • Beakers or cups
  • Thermometers
  • Balances
  • Weigh paper
  • Crackers (if time permits for this part of the experiment)
  • Stop watches or timers
  • Gloves


  1. Assign students to lab groups, each with a rack of test tubes, a bottle of glucose test strips and the other supplies.
  2. Have milk and water available for the whole class. Milk should ideally be in a beaker so it can be easily poured into test tubes.
  3. Let the students conduct the lactase reactions with different conditions. Hand out the student activity guide and have students record their results.
  4. Have the students graph their results.
  5. If you have the time, allow your students to experiment with their own saliva (and make sure that they dispose of it properly when finished). Saliva contains amylase, an enzyme that breaks down starch into glucose. Have them crumble a cracker in water in a cup. Then they should chew another cracker for 30 seconds, spit it into a second cup and test both cups for glucose.  Even the test strips rely on the enzymes glucose oxidase and peroxidase.