High School Resource
In this activity, you will,
- Test that your glucose test strips work with positive and negative controls. Follow the directions on your brand of strip, and dip strips into:
a) glucose solution positive control), and
b) water (the negative control). Wait for length of time specified by strip directions, then record any color changes of the strip and compare to the key on the bottle to determine glucose concentration of the tested fluid. If the strips determine that the glucose solution has NO glucose in it, or registers far less than 2%, the strips are defective and should be discarded. The experiment cannot be performed until new strips are obtained. Teachers may wish to check the strips prior to introducing this activity to their class. When performed by the class, the results of these controls should be recorded on the board for future reference.
- Pour about one half inch of regular milk (about 3 ml) and Lactaid (lactose free) milk into separate test tubes, one of each for each group, and label “A” and “B” to hide the identity of the fluids from the students.
- Determine the glucose concentration of “A” by following the directions for your brand of glucose test strips. Compare the color of the strip after dipping it in the milk (as per directions on the test strip bottle) with the color-coded key on the side of the bottle to determine the concentration of glucose in the milk.
- Determine the concentration of glucose in “B” by using a fresh test strip, following the directions on the bottle and comparing the color of the test strip after dipping it in the milk with the color-coded key on the side of the bottle.
- Class results should be tabulated on the board so that everyone can see them. Acknowledge that small variations between groups may be due to differences in how the procedure was carried out (for example; most strips require reading at an exact time after dipping; if students do not follow the instructions exactly, small variations in results may be obtained). Do not be overly concerned about small variations, as long as the water is “negative” for glucose and the glucose solution is “positive” for glucose.
- Add one drop of “mystery drops” to one half inch of “A” (the same “A” from step #3). Warm the milk by rolling the tube back and forth in your hands for 2 minutes. Repeat the glucose test with a fresh test strip as indicated in #3 above. Is the glucose concentration now the same or different as compared to the concentration in “A” prior to adding the “mystery drops”?
- Add one drop of mystery fluid to “B” (the same “B” from step #4 above. Warm the milk by rolling the tube back and forth in your hands for 2 minutes. Repeat the glucose test with a fresh test strip as indicated in #4 above. Is the glucose concentration now the same or different as compared to the concentration in “B: prior to adding the “mystery drops”?
- Tabulate class results on the board, as in #5 above.
- Explain your results. Is there a difference in glucose concentration between fluids “A” and “B” before addition of the “mystery drops”? Postulate as to what the difference means. Do the glucose concentrations of “A” and “B” change after the addition of the “mystery drops”? What could account for the change? At this point, students may conclude that somehow the “mystery drops” converted something in the regular milk to glucose. This may be true, but at this point one other possibility cannot be ruled out – see if the class can think of what that is. If they are unable to present an alternate hypothesis, prod them with the following: How do you know that the mystery drops are not glucose? The “mystery drops” are added to a substance which had a negative glucose reaction, and all of a sudden that same substance gives a positive reaction. Unless the mystery drops (I.e. lactase drops) themselves are tested with the glucose strips, no conclusions can be reached! Students should then test the “mystery drops” with the glucose strips. Add the result of this test to the data recorded on the board. Now what sort of conclusions can be drawn from the data?
Related NY State Academic Standards: S.MS.LS.1.1, S.MS.LS.1.2, S.MS.LS.1.3, and more!
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