Grades 9-12

Cell biology, physiology, macromolecules

Teacher Resources

Looking into Lactase is an activity developed by Learning Undefeated for the exploration of enzymatic activity by investigating the mechanism behind lactose intolerance.

Lactase d eficiency, also known as lactose intolerance, is a condition caused by an absence of the enzyme lactase, a digestive enzyme found in the human body. Since the human body can’t absorb lactose it needs to be broken down by lactase into its two monosaccharide products, glucose and galactose. Like most other enzymes, lactase is specific to just one substrate, in this case, the sugar lactose. Those who are lactose intolerant seek treatment through medications that contain lactase as an active ingredient.

Enzymes are proteins that catalyze chemical reactions by lowering the reaction’s activation energy. Every enzyme has an active site that binds to another molecule called the substrate. Once bound to the substrate, an enzyme can catalyze a reaction up to 10 billion times faster than the comparable, non-catalyzed reaction. Enzymes are not consumed in the reaction and can bind to an infinite amount of substrates.

Learning Objectives

Students will be able to

  • Illustrate how amino acids interact to create a protein
  • Identify an enzyme’s specific substrate
  • Differentiate between three different milk types based upon their sugar content
  • Explain how pH effects enzyme activity
  • Infer how enzyme activity relates to human physiology
Standards Alignments + Connections

Next Generation Science Standards Connections

HS-LS1-1: Construct an explanation based on evidence for how the structure of DNA determines the structure of proteins, which carry out the essential functions of life through systems of specialized cells.

Texas Essential Knowledge and Skills for Science Connections

BIOL.9C: identify and investigate the role of enzymes

Virginia Science Standards of Learning Connections

BIO.2C: enzymes have a role in biochemical processes

Activities to Gather Evidence

Background Information

Follow these links for more information:

Pre-Laboratory Engagement

Pre-Lab Questions

  • What does an enzyme do to reaction speed and how?
  • What causes symptoms of lactose intolerance?
  • How does pH impact enzyme activity?
  • What pH levels do you predict are found in the human body?

Laboratory Activity

You are working in the quality control department of a local bioscience company that produces a lactase enzyme product used to treat lactose intolerance. It is your job to determine the optimal pH of the lactase product by testing the enzyme’s activity in cow’s milk at different pH levels. Unfortunately, due to a mistake in shipping, the labels were removed from the research lab’s milk supply. You know that the lab carries cow, rice, and soy milk, but you don’t know which is which. Before you can test the lactase activity at different pH levels, you must first identify which sample is cow’s milk, by using a special property of enzymes called “specificity.” Lactase specificity describes the fact that the lactase enzyme will break down lactose but no other disaccharide substrate.

Post-Laboratory Extension

For further information on enzymatic activity and lactase deficiency, visit:

Additional Resources

Read about the causes of lactose intolerance and how it is diagnosed

Enzyme Resources
Learn about how enzymes work, how they are named, how they are affected by temperature and pH, and more

What is an enzyme?