This lesson will allow students to observe and identify evidence of an enzyme's activity, lactase, and its function, and action on a substrate found in milk, lactose. They will then relate the absence of lactase to the condition of lactose intolerance, which many students or family members of students experience. Enzymes are a type of protein essential to life and necessary for many of the metabolic reactions that occur in the human body. Since these reactions occur at the molecular level within the body, students do not directly observe enzymes functioning.
Lesson Plan Template: Learning Cycle (5E Model)
Learning Objectives: What will students know and be able to do as a result of this lesson?
- Students will be able to identify an enzyme as belonging to the macromolecule group proteins and name the monomers of a protein, amino acids.
- Students will be able to identify if lactase is present and functioning in a sample of milk.
- Students will be able to describe the results of the enzyme lactase functioning or being absent/inactive regarding human milk digestion.
Prior Knowledge: What prior knowledge should students have for this lesson?
- Students should be able to name the four major macromolecules: carbohydrates, proteins, nucleic acids, and lipids.
- Students should be able to name the monomers, or building blocks, for each macromolecules.
- The macromolecules and the associated monomer are: carbohydrates and monosaccharides; lipids and glycerol plus fatty acid chain; nucleic acids and nucleotides; and proteins and amino acids.
- Students should be able to explain that a macromolecules must be broken down into its monomers to be utilized in physiological processes of the body.
- Lactose intolerance, absence of lactase, is the same as an allergy to milk in which the immune system reacts.
- A lactose intolerant person can never drink any milk products.
- A lactose intolerant person can drink milk and milk products that have been treated with lactase.
Guiding Questions: What are the guiding questions for this lesson?
- How are the structure and function of proteins, especially enzymes, related?
The structure of the protein, especially with enzymes, determines which substrates the enzyme can interact with.
- Why are enzymes necessary for life to exist?
Most chemical reactions involving physiological processes in living organisms require an enzyme. Enzymes are necessary for physiological processes to occur fast enough to maintain life.
- If an organism has a mutation that causes an enzyme to be non-functional or missing, can another enzyme perform the function of the non-functional or missing enzyme?
No. Enzymes are specific for the substrate in the chemical reaction.
- What would be the result for an organism if an enzyme was non-functioning or inactive?
The chemical reaction on which that enzyme worked would not occur at all or not in a time frame rapid enough to support the physiological process. If the chemical reaction and/or the physiological process were necessary for life, the organism would die. An example of a fatal disease resulting from a missing enzyme is Tay-Sachs disease. If the chemical reaction and/or the physiological process were not necessary for life, the organism may experience minor adverse effects but continue living.
- Which foods would a person who is lactose intolerant (non-functioning lactase) need to avoid?
A lactose intolerant person would need to avoid any food containing lactose. Foods to avoid would include: milk, soft not aged cheeses such as cream cheese and cottage cheese, yogurt, butter, and ice cream.
- What are the signs and symptoms of lactose intolerance (non-functioning lactase)?
Symptoms of lactose intolerance include: increased gas production, diarrhea, cramping, and bloating.
Engage: What object, event, or questions will the teacher use to trigger the students' curiosity and engage them in the concepts?
The teacher will display a picture of a glass of milk.
The teacher will ask: "Do you avoid drinking milk because it causes stomach problems?" The teacher may ask students to raise their hands if they answered "yes" to above question.
The teacher can count the number with raised hands and calculate the class percentage that avoids drinking milk due to stomach problems.
The teacher will tell class that the lab will explore the cause of stomach problems in certain individuals when consuming milk or milk products.
Explore: What will the students do to explore the concepts and skills being developed through the lesson?
Students will be given two samples of milk, samples A and B. They will be told that one sample has had lactase, an enzyme, added and one sample is untreated milk with no lactase added.
Students will also be given two pieces of glucose test paper/strips. They will be asked to use one strip or paper to test each sample. They will write the results on the lab worksheet data table. Each sample will be identified as testing positive or negative.
Explain: What will the students and teacher do so students have opportunities to clarify their ideas, reach a conclusion or generalization, and communicate what they know to others?
The teacher will use a PowerPoint Presentation to convey the following content: (see attached PowerPoint)
- Enzymes as part of the macromolecule group of proteins
- Function of enzymes in human physiology
- Mechanism of function of an enzyme including substrate, enzyme, product, and activation energy
- Specific function of lactase in humans
- Products resulting from the action of lactase
- Consequences of lactase becoming inactive
Elaborate: What will the students do to apply their conceptual understanding and skills to solve a problem, make a decision, perform a task, or make sense of new knowledge?
Students will be broken into small collaborative groups of 2-4 and given the following questions written on a handout to discuss. Each group will share their answers in a whole class discussion.
- Discuss what would happen to an organism if there were no functioning enzymes.
metabolic reactions in the body would not occur or occur fast enough to sustain life
- Discuss what would happen if just one enzyme were to be non-functioning.
Results can vary from being problematic but having a workable solution, such as absence of lactase leading to lactose intolerance, to being fatal, such as the absence of enzyme for lipid metabolism in Tay-Sachs disease. Students should be able to identify that the results will vary from problematic but having a solution to fatal. The teacher can supply examples for each end of the spectrum, lactose intolerance to Tay-Sachs.
- List causes of inactivation of an enzyme in the human body.
A genetic mutation in Tay-Sachs causes the enzyme for lipid metabolism to function inefficiently. A change in pH, such as changes from an acidic environment of the stomach to the alkaline environment of the small intestine, in activates pepsin, a stomach enzyme used to digest proteins. A change in temperature, such as the normal functioning of enzymes at 37 degrees C to a decreased or non functioning enzyme activity as the body temperature rises with a fever. Students should be able to identify three causes of inactivation of enzyme activity: genetic, pH, and temperature. The teacher may need to assist with specific examples for each.
The lab report includes an extra credit question about how the absence of lactase can result in diarrhea and gas.
Lab Report (a key is included in the document)
The report will include:
- Correct identification of which of the two samples of milk were treated with lactase.
- Diagramming and labeling the formation of a protein from amino acid monomers.
- Diagramming and labeling how lactase reacts with lactose by identifying the substrate, enzyme, and resulting products.
- An analysis, outlining how the student was able to identify the milk sample treated with lactase using a glucose paper/test strip.
- When students complete the testing of the milk samples, the teacher will check their results. Students will need to identify each sample as either being positive or negative and record results on the lab report.
- The teacher will have students compare and correct their drawings of a protein showing amino acids bonded together with peptide bonds to correspond with completed drawing shown on whiteboard.
- The teacher will have students compare and correct their drawings of the lactase (enzyme) and milk (substrate) reaction and resulting products (glucose and galactose) to correspond with completed drawing shown on whiteboard.
Feedback to Students
Student will be given feedback:
- About correctly identifying sample A and sample B as positive or negative based on results of the glucose test paper. When the entire class has recorded their results from testing each sample, the teacher will show a slide with the results. Students compare their results to the correct answer on the slide. If results do not match the answer given on the slide, students will retest the sample and correct the lab report.
- About the correctness and completeness of their drawings of the structure of proteins including the monomers, amino acids, and peptide bonds, and drawings of enzyme-substrate reaction and resulting products. The teacher will show slide with the reaction between lactase and milk. Students will compare and adjust their drawings on the lab report.
- About identifying the product produced by the reaction and tested for by the glucose paper/test strip and explain the how they were able to identify the treated sample using the glucose paper/test strip. The teacher will grade the analysis section of the lab report.
- About applying knowledge of lactase's role in milk digestion to make a list of 5 foods that would be excluded from the diet of a person who is lactase deficient, also called lactose intolerant. The teacher will grade the answer on the lab report.
Accommodations & Recommendations
A handout of the PowerPoint slides from the Explain portion of lesson can be given to ESE and ESOL students to assist in note taking.
The lab report can be modified to include pictures to accompany the procedural part of the lab.
An unlabeled diagram of the enzyme substrate reaction and resulting products can be provided for question #2. Students would then label the diagram provided.
This lesson can be extended into a discussion of evolution. The continued production of lactase beyond infancy and weaning is a mutation. The environmental and cultural selective pressures that gave our lactose tolerant ancestors an adaptive advantage resulted in natural selection and ultimately the evolution of lactose tolerance throughout life. Students can trace the evolution through natural selection of the mutation allowing lactose tolerance across time, geographic regions, and cultures.
Suggested Technology: Computer for Presenter, Interactive Whiteboard
Special Materials Needed:
- Print out one copy of the lab report per student.
- Note that the lab report is the first three pages of the document; the answer key begins on page 4.
- Test tubes labeled A and B to hold milk samples; one set of sample tubes per group
- Milk (fat content does not affect results) to provide two sample tubes of milk per group of students
- Lactase tablets to treat one sample, A or B, one tablet per group
- Generic tablets can be purchased from the pharmacy department of local store. Variety and pricing is usually better through an online vendor.
- Glucose test paper/strips for urine (usually sold in the form of test strips to be dipped into urine specimens to determine presence of glucose in urine), two strips per group.
- Note: do not purchase test strips meant to measure blood glucose levels that are used with a machine to measure blood glucose levels. The test strip or paper must be type used for glucose in the urine.
- Variety and pricing is usually better through an online vendor.
- Key to compare glucose test strip to determine presence or absence of glucose in sample.
- May need to make copy of key on glucose test paper/strip package for each student group or have station with key for students to compare results.
If glucose test paper/strips are not available, this lesson can still be use. Using two index cards, the teacher will label the front of each card "Sample A" or "Sample B." On the back of the card, the teacher can have a picture of what the glucose test paper/strip would look like after testing. The teacher can color a square with the color corresponding to the test strip key. One card should show a "positive" result; the other card should show a "negative" result. Students then compare the picture to the glucose test paper/strip key to determine the results.
To minimize costs, test strips can be cut in half prior to testing. This will not affect the results but will decrease cost and increase the amount of testing material.
Source and Access Information
Name of Author/Source: Marie Blackwell
District/Organization of Contributor(s): Orange
Access Privileges: Public
* Please note that examples of resources are not intended as complete curriculum.