In this lesson, students learn the chemistry and composition of milk, identify the difference between a monosaccharide and disaccharide, and carry out a laboratory activity testing the effect of the enzyme lactase on various milks. Grades 9-12

• Lactose Lab Answer Key
• Lactose Lab Sheet

disaccharide: a sugar made of two molecules (e.g., sucrose, maltose)

enzyme: protein catalyst, which speeds up a specific chemical reaction

lactase: an enzyme produced by the large intestine which breaks down lactose

lactose: a disaccharide sugar present in milk which contains glucose and galactose units

monosaccharide: a simple sugar molecule that cannot be broken down further into smaller molecules

1. Introduce the lesson and assess your student's prior knowledge by asking them the questions below.  Questions can be asked in a simple question and answer format with your entire class or you may vary your instruction by dividing the class into groups. Print the questions and give each group a single question and a short amount of time to research the answer.  For your reference, the answers can be found in the Background Agricultural Connections section of this lesson plan.
   • "Where does milk come from? When do animals begin producing milk?"
   • "After milk is produced on a farm, it is sent to a processing plant to prepare it to be sold. What takes place at the milk processing plant?"
   • "What nutritional benefits do milk and other dairy products such as cheese and yogurt provide?"
   • "What is the name of the carbohydrate found in milk?"
   • "What is lactose intolerance and how can it be managed so people can still consume dairy products?"
2. After discussing these questions, inform your students that they will:
   • review basic facts about the nutritional benefits of milk and dairy products;
   • learn about the physical and chemical properties of milk as it relates to monosaccharides, disaccharides and enzymes;
   • perform a laboratory experiment to determine levels of glucose found in various milk samples; and
   • identify how milk processing methods can provide digestible milk for individuals with lactose intolerance.

Activity 1: Chemistry and Composition of Milk

1. Open the Chemistry and Composition of Milk PowerPoint.  Provide a method for your students to answer multiple choice questions.  Options include:
   • Use a classroom response or "clicker" system if you have one.
   • If mobile devices, tablets, or iPads are available, use a free app or website to allow your students to answer each question. Poll Everywhere and Socrative are examples, but many programs exist.
   • If digital devices are not available or time does not permit, have students answer using hand signals. A=hold up 1 finger, B= hold up 2 fingers, C=hold up 3 fingers, D=hold up 4 fingers, E=hold up 5 fingers.
2. Use slides 2-4 to establish some basic facts about milk.  Use the questions to help students understand that all female mammals produce milk after giving birth and that in the United States cattle provide the majority of our milk supply. Though all mammals can produce milk, cows produce the most milk when you consider the cost to produce each gallon (labor, feed, housing, healthcare, etc.).
3. Using slide 5, ask your students, "What is milk?"  We have established that the milk in our food supply typically comes from cows.  Your students know it is white and they pour it on their cereal in the morning, but what is it? Explain to your students that milk contains water, lactose, fat, protein, and minerals.
4. Use Slide #6 to review the nutritional benefits of consuming milk and dairy products.
5. Use slide #7 to break down the typical percentages of each milk component.  These percentages represent cow's milk.  Milk from other species will vary in it's content.  For example, goat milk has less lactose than cow's milk.
6. Using slides 8-11 teach or review basic chemistry principles about enzymes, monosaccharides, disaccharides, and lactose. Use the same formative assessment method used in step 1.
7. Using slides 12-14, teach students about lactose and it's enzyme, lactase.
8. Summarize and apply what students have learned by teaching them about lactose intolerance. Use the information found in the "Background Agricultural Connections" section to prepare them for the next laboratory activity.

Activity 2: Lactose Lab

1. To introduce the lab, show your students a commercial for lactose-free milk.  Ask your students to use what they now know about enzymes, lactose, and lactase to guess how milk can be made lactose-free. 
2. Divide students into lab groups.
3. Provide the laboratory supplies for each group and 1 copy of the Lactose Lab handout to each student.
4. Give students adequate time to complete the laboratory procedures and answer the questions on their handout.
5. Once students have completed the laboratory activity, return to your question from step 1. How can milk be processed so that it is lactose-free?  Have students use what they have learned in this lesson to answer the question.

After conducting these activities, review and summarize the following key concepts:

• Milk and milk products provide important nutrition to our diet.
• Milk contains the disaccharide, lactose.
• Food production systems are influenced by consumer's choices. As lactose intolerance has become more prevalent, the agriculture and food processing industries use science to find solutions such as lactose free milk.

• Laboratory idea in Activity 2 from Massachusetts Agriculture in the Classroom.
• Special thanks to Audrey Harmon and Oklahoma Agriculture in the Classroom for pilot testing this lesson.

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