Lab Activity: Milk Makes Me Sick Investigation (Part 2 of 2)

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SWBAT complete the laboratory investigation, construct an explanation of the enzyme activity , and hypothesize how this chemical reaction occurs in human physiology.

Big Idea

Uh oh - you just ate that bowl of ice cream, now what are you going to do? Is there enough lactase in your body to digest your lactose-rich dessert? Students will experience first-hand the chemical process of enzymes with this real-world experiment.

Lesson Introduction: Bring Biology to Life

1 minutes

This video clip serves as an introduction to today's lesson focusing on the effects of enzymes speeding up chemical reactions in an effort to maintain homestasis in our bodies.  The lab activity demonstrates the ability of enzymes (lactase) to break down the lactose (disaccahride sugar in milk) in our digestive system.  Students are able to make real-world connections between our Biology curriculum and their health conditions.  

Hook - Enzymes In Action

5 minutes

The students will arrive in class with prior knowledge of yesterday's lesson and the introduction of the Milk Makes Me Sick Pre-lab Sheet.  Although students have reviewed enzymes in prior lessons, it is good pedagogy to begin class with a brief review to make sure all students are focused and ready to work.  The Enzyme Anticipatory Activity is a reading passage that discusses the chemical activity of enzymes followed by a set of  comprehension questions.  Students will work with their neighbor to quickly complete the questions.  The teacher will review any questions that proved difficult for the student-pairs in a whole-class review.  This anticipatory activity should be quick since the lab is time sensitive and students may struggle to complete during the allotted class period.


Lab Preparation - Milk Makes Me Sick

20 minutes

Students will organize into their lab groups of four students each.  The lab can be completed with as few as two students and as many as five students depending on the class size and availability of lab resources.  

Lab Supplies for Each Lab Group:

  • 100 mL Beaker filled only half way with nonfat milk
  • 100 mL Beaker filled only half way with water
  • 100 mL Beaker filled only half way with a solution of Lactase (Lactase pills ground up and dissolved to make saturated solution)
  • 3 medicine droppers - place one for each beaker 
  • 4 test tubes - labeled #1,#2,#3,#4 (label with a permanent marker)
  • A test tube rack
  • A hot plate for 2-4 student groups to share - plugged in at the side counter for student safety!
  • A 250 mL beaker half filled with water - used to make a warm water bath 
  • Marking pen to label test tubes
  • 4 strips of glucose test stripes (Diastix)

Have the students prepare the test tubes as described on the Student Lab Procedure Sheet.  The procedure is a super simple procedure that only requires students to count the number of drops of each solution as they prepare each of the four test tubes.

Experimental and Control Groups: Students will be testing how the activity of the enzyme (lactase) is affected by a change in temperature.  Students will be comparing the outcomes of Test Tube 2 at room temperature (the temperature control group) and Test Tube 4 in the warm water bath at 37C to mimic the human body's internal environment (the temperature's experimental group)

Students will also be comparing the differences observed in Test Tubes 1 (room temp) and Test Tubes 3 (warm water bath) which are used as the control groups since neither test tube has the lactase enzyme added to its contents.  

Time Sensitivity: It is really important to have your students prepare their test tubes in a timely manner since test tubes 3 and 4 need to be placed in the warm water bath for 15 minutes to allow for the decomposition of lactose into glucose and galactose.






Lab Investigation - Milk Makes Me Sick

25 minutes

Preparing The Test Tubes

Test Tube #1: 30 drops nonfat milk and 15 drops of water

Test Tube #2: 30 drops nonfat milk, 10 drops of lactase solution, and 5 drops of water

Test Tube #3: 30 drops nonfat milk and 15 drops of water

Test Tube #4: 30 drops nonfat milk, 10 drops of lactase solution, and 5 drops of water

Waiting for The Chemical Reaction - Once the students have prepared the test tubes according to the student lab sheet. Test Tubes 1 and 2 will be placed in the test tube rack for the remainder of the lab while Test Tubes 3 and 4 will be placed into the warm water bath for 15 minutes to allow the chemical reaction to occur.  In the past, I have reduced this time as low as 8 minutes due to shortage of time in the class period, but the outcome is not as dramatic for the students to observe.  

As the students are waiting for the time to pass, they should be working in their collaborative lab groups to respond to the Discussion Questions on their Got Milk - Student Answer Sheet.

Testing for Glucose - After 15 minutes, students will remove Test Tubes 3 and 4 from the warm water bath using test tube tongs and add them to Test Tubes 1 and 2 in the test tube rack.  Students will then use the Image - Glucose Indicator Strips to determine if there is glucose present in any of the solutions in the four test tubes.  The glucose test strips can be read using the color scale on the package to determine the amount of glucose present.  If the enzyme (lactase) effectively decomposed lactose the color on the indicator strip will be green to represent a large amount of glucose present.  If the test strip is yellow, there is only a small amount of glucose present which means the enzyme broke down the lactose but the chemical reaction did not occur at the same rapid pace as the "green" sample.  If no color change was observed on the indicator strip,  the lactose (disaccaharide) molecule remained unchanged and did not break down into glucose and galactose (both monosaccaharides).

Recording the Data - Students will record the results of the glucose test in the data table on their student lab handout and continue their collaborative efforts respond to the remaining Discussion Questions on their Got Milk - Student Answer Sheets.

Sample of Student Work: Lab Answer Sheets- As expected the student work shows a varied level of mastery of the concept of enzyme influence on chemical reaction speed, specifically with the lactose/lactase reaction.  Students seemed to comprehend the concept of a disaccharide being decomposed to two monosaccharides, but struggled to convey their understanding through a model and provide an accurate narrative.  These topics will be reviewed in a follow-up class discussion to improve student understanding of the model of the chemical reaction and the real-world application of lactose intolerance.  The samples demonstrate near mastery all the way to needs review and needs work!

Image - Student Checking The Solutions:  The students need to check their solutions to determine if a color change was observed.  

Image - Lab Group Collaboration: Students needed to work together to prepare the four test tubes by following the detailed directions provided in the lab procedure.

Close - The Meaning of Glucose

5 minutes

Once all student groups have cleaned up the supplies, the teacher will lead a whole-class discussion to determine the significance of glucose in the test tubes.  What does the presence of glucose represent in terms of the chemical reaction that has occurred in the test tube?  Each lab group will select a group spokesperson to share their lab experience and offer a detailed analysis of what has occurred in terms of enzyme function.  

After a lively discussion, the teacher will summarize that the presence of glucose in the solution represents the decomposition of lactose into glucose and galactose.

  • Test Tube 2 at room temperature should have a small presence of glucose to show that the lactase has started to break down lactose, but only in a small volume due to the cooler temperature.  
  • Test Tube 4 in the warm water bath should have the most glucose present to demonstrate that the heat has sped up the enzymatic activity and mimicked the conditions of the lactase enzyme in the human digestive system.
  • Test Tubes 1 and 3 did not contain the enzyme, thus did not experience any changes.  

Students will use the Enzyme Lecture Notes and Enzyme Flow Chart from the previous lesson's homework assignment as a guide, to design a flow chart that models the chemical reaction that was observed in today's laboratory investigation.  Students will also create a written narrative to describe each event.

Sample of Student Work: Milk Makes Me Sick Flow Chart Model - Both of these student models show a basic understanding of how the disaccharide molecule, lactose, was broken down into the two monosaccharides, glucose and galactose, using the enzyme to lower the activation energy and speed up the chemical reaction.

Sample of Student Work: Student Narrative Enzyme Action- Students struggled transferring their understanding the model of enzyme action into words.  This difficulty further exemplifies the need for writing across content areas that are emphasized in the Common Core Standards and NGSS.