Downtown Campus Biology > Biology 181 > Lesson 1 Activities > Scientific Method- Page 2

4. Testing

Most people associate science with testing or experimentation only. However, scientists have to go through the first three steps before they even begin to experiment. (In fact, scientists often spend more time designing an experiment on paper than they do actually doing the experiment. A well thought-out experiment saves time and resources in the long run.)

Materials and Methods

We can set up a simple experiment to see if Lacteez really breaks down lactose, releasing glucose and galactose. We will use milk, Lacteez and Clinistix in our experiment. Clinistix detect the presence or absence of glucose. (They are usually used to test for glucose in urine - an important monitoring tool for diabetes.)

• If the lactase in Lacteez breaks down lactose into glucose and galactose, then we should be able to detect the presence of glucose in milk.
• If lacteez does not work, we will NOT be able to detect the presence of glucose in milk.

Let's set up the experiment.

In the kit, you will find:

• two identical beakers
• a wax pencil to mark the beakers
• a bottle of Lacteez
• a bottle of Clinistix

PLEASE KEEP THE BOTTLE OF CLINISTIX CLOSED UNTIL YOU ARE READY TO USE THEM, AND THEN REPLACE THE LID AS QUICKLY AS POSSIBLE! ALSO, PLEASE DO NOT TOUCH THE PAD ON THE STICK - HOLD THE STICK BY THE OPPOSITE END FROM THE PAD! Keeping the sticks in the sealed container and not touching the pad will keep the Clinistix fresh and ensure accurate testing.

Step 1: Find the two beakers in your kit, and thoroughly wash and rinse them at the sink. If the beakers are still contaminated from the last experiment, you may get misleading results. Then mark the beakers with the wax pencil (ie, “T” for “test” and “C” for “control”) so that you know which beaker is which.

Why do we need two beakers, one labeled “test” and one labeled “control”? Remember, in a controlled and well-designed scientific experiment, we need to have all possible variables kept constant, except for the single variable that is the focus of our experiment. Therefore, we need identical beakers, each with an identical amount of milk, with both beakers in the same place at the same temperature. The only variable will be the presence or absence of Lacteez.

Step 2. In the student refrigerator, you will find a container of milk, labeled R24. Fill each beaker with milk to about the 20 ml mark, then bring the beakers back to your workstation. (Please measure out the milk you need, and return the bottle of milk to the refrigerator as soon as possible -- it lasts longer that way!)

Step 3. Add 2 drops of Lacteez to the “test” beaker. Please don't add more, since Lacteez is not exactly cheap!

Step 4. To speed up the reaction a little more, you can do two things, both of which increase the rate at which the lactose molecules come into contact with the Lacteez.

• You can gently swirl the beakers a little. This is a controlled experiment, so we need to gently swirl both beakers the same amount. (Remember, we want to make sure that the only difference between the beakers of milk is the presence of lacteez in the “test” beaker.)
• You can warm up the beakers a little. Hold them in your hands, and let your hands warm the beakers.

Step 5. After about 5 minutes, carefully take out 2 test strips from the Clinistix bottle. Be sure to handle the strips on the opposite end from the pad.

• Dip a strip in the “control” beaker (the one without Lacteez), keeping the strip in the milk for only about 1 second, then take it out. Wait 10 seconds, then compare the color on the pad to the color chart on the bottle. Is glucose present? (The strips will darken over time. Be sure to read the color at exactly 10 seconds to determine if glucose is present or not.)
• Now repeat using the other strip, and dipping it in the “test” beaker that contains Lacteez. Again, compare the color on the pad to the color chart on the bottle. Is glucose present?

DON'T PUT ANYTHING AWAY YET! On your worksheet, summarize your results, and address the following:

• Briefly describe how Lacteez is supposed to work.
• Briefly describe the design of your experiment, and tell why you used two beakers rather than one.
• Describe the results of your experiment, and explain whether the results of your experiment support the claim made by Lacteez.

You're almost done, but not yet!

Lab points: Please show your work to someone at the front desk in the Biology Learning Center. You MUST leave your equipment out until you receive lab points.

Cleanup: After you receive lab points, please clean up the lab supplies and put the kit away. Be sure to clean the beakers carefully at the sink, to make sure that no residue of either milk or Lacteez remains in the beakers. Please make sure the lids are on tightly on both the Lacteez and Clinistix bottles. Then put the kit back in the refrigerator.

OK, now you're done!

Lacteez (which is a Canadian product) is similar to Lactaid, which is found in US drugstores in pill form. For more information on Lactaid, visit their website at: http://www.lactaid.com

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