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Lactose and Lactase: Exploring Enzymes as Catalysts

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Author: Beth Touchette

Digestive enzymes help your body break down your food.  It’s hard to obtain many human digestive system enzymes (without vomiting, that is!), but luckily, one of them is sold as a tablet in many drug stores: lactase. Lactase breaks down a milk sugar called lactose that’s found in milk. Many people in the world don’t drink milk because their bodies don’t make any lactase. If they try to drink milk, the undigested lactose can lead to bloating, gas, and diarrhea. No fun! Lactase pills can help. Get your hands on some lactase pills so you can see how digestive enzymes work and perhaps find out ways to make them work even better.

Glucose is produced when milk sugar (lactose) is broken down by the digestive enzyme lactase. It's pretty easy to mix up lactose and lactase. Here’s a tip to help you remember the difference: sugar names end in -ose, while enzyme names end in -ase.  

Problem:

Does more lactase create more glucose when mixed with the lactose in milk?

Materials

  • Milk (it can be fat free, 2%, skim, or whole)
  • 6 or more small, clean glasses
  • 6 or more clean spoons
  • ½ cup measuring spoon or measuring cup
  • 6 or more dairy digestive aid tablets, which contain fast-acting lactase
  • Spatula
  • Glucose test strips (available at some drug stores in the diabetes section, or online)
  • Teaspoon
  • Baking soda
  • White vinegar

Procedure 1

How does the amount of enzyme effect the digestion of milk sugar?

  1. Go online with an adult to conduct some research about enzymes. What can you find out about how enzymes work? Make a hypothesis as to how much glucose will be produced in glasses of milk mixed with 0, 1, or 2 lactase tablets. Make sure to explain your reasoning!
  2. Measure a half cup of milk into three glasses. Place a spoon inside each.
  3. Use the spatula handle to crush three of the lactase tablets while they’re still encased in their foil packaging. Why do you think it’s important to crush up the tablets?
  4. Open the foil and pour the crushed contents of one tablet in your second glass.
  5. Place the contents of two more crushed tablets in your third glass.
  6. Stir each glass once a minute for ten minutes. Enzymes need time to work.
  7. Use your glucose test strips according to the directions on the packaging to find the amounts of glucose present in each of the three glasses of milk. Make sure you record your results. Do your results confirm your hypothesis?

Procedure 2:

Can other chemicals affect how well a digestive enzyme works?

  1. Make another hypothesis about how you think adding baking soda or vinegar might affect glucose production. Do some research first: What other chemicals are normally present in the human digestive system? How can we describe those chemicals?
  2. Fill each of three glasses with ½ cup milk. Place a spoon inside each.
  3. Add 1 teaspoon baking soda to the first glass. Stir.
  4. Add 1 teaspoon vinegar to the second glass. Stir.
  5. Don’t add any vinegar or baking soda to your third glass.
  6. Use the spatula handle to crush three lactase tablets while they’re still encased in their foil packaging.
  7. Peel back the foil packaging of one crushed pill and pour the contents into your first glass. Stir the contents of the glass.
  8. Peel back the foil packing of another crushed pill and pour the contents into your second glass. Stir the contents of the glass.
  9. Peel back the foil packing of your third crushed pill and pour the contents into your third glass. Stir the contents of the glass.
  10. Stir each glass once a minute for ten minutes.
  11. Use your glucose test strips according to the directions on the packaging to find the amounts of glucose present in each of your two glasses of milk. Make sure you record your results.
  12. Do your results confirm your hypothesis?
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