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Figure 1. Lactase digestion of lactose into galactose and glucose. Formulating a hypothesis You are asked to develop an experiment to answer the following question: Does lactose content vary by milk type?D1.What would you propose as an answer to the above questions? What is your hypothesis? D2.What is your independent variable for testing this hypothesis?
42 D3.What could your dependent variable(s) be? D4.What are some of the controlled variables? Experimental Procedure Materials Milk-based types of milk – whole, 2%, 1%, non-fat and lactose-free Plant-based types of milk – soy, almond, coconut 20% sucrose solution Lactase solution (Lactaid tablets; 300mg/200 mL) Glucose strips P1000 micropipette Tubes in a rack Small beakers Forceps Timer 1. Choose 2 milk samples for your experiment (for example a whole milk and almond milk). 2. Each group will need 4 tubes for each replicate. A total of 3 replicates will be performed per milk sample. Clearly label tubes for all of your milk samples (for example A1 – A4, B1 – B4) for each of the three replicates (R1, R2). [2 types of milk x 4 tubes x 3 replicates = 24 tubes total] 3. Add reagents to each tube as described in Table 2 for each of your milk samples. Set up one set of tubes at a time, without adding the enzyme. When all your tubes are set up, then add the enzyme and start the time. After 10 min of digestion measure the presence/absence of glucose using a glucose strip. Table 2.Experimental set-up for various milk samples. Tube Milk Enzyme solution Sucrose solution Water 1 1 ml 1 ml - - 2 1 ml - - 1 ml 3 - 1 ml 1 ml - 4 - - 1 ml 1 ml 4. Insert the glucose strip into the sample and leave it in for 1-2 sec. Gently shake the glucose strip to remove any excess milk.
43 5. Place the glucose strip on a piece of paper towel to dry and after 3 min read the results. Make sure to label everything so you don’t get your milk samples and replicates mixed up. 6. Observe the color change of the glucose strip and compare it to the glucose concentration label on the packaging. Write down the glucose concentration for each condition in Table 3. Data Analysis