A Scientific Investigation What types of food contain starch and protein? by Dr. Ingrid Waldron, Department of Biology, University of Pennsylvania, 2013, http://serendip.brynmawr.edu/sci_edu/waldron/#starch In this activity you will investigate which types of food contain starch and which types contain protein. First, you will need to have some way to test for starch and for protein. Part 1 Which indicator solutions can be used to test for starch and for protein? An indicator solution is a good test for starch if it changes color in the presence of starch, but does not show the same color change in the presence of other molecules such as proteins, lipids or sugars. You will be given two indicator solutions, and you will evaluate whether either of these indicator solutions can be used to test for starch. You will also evaluate whether either of these indicator solutions can be used to test for proteins. The supplies you will have available to test the indicator solutions are: Indicator Solution 1 Indicator Solution 2 Containers for testing, plus marker and masking tape for labeling these containers Stirrers; gloves Samples you can use for testing the indicator solutions: - Corn starch - Sucrose = table sugar - Gelatin (protein from bones, skin, etc. of farm animals) - Vegetable oil - Potato starch - Water - Powdered egg whites (high in protein) 1. Complete this table. An indicator solution that is a good test for protein will change color when added to these samples from the above list: An indicator solution that is a good test for protein will not change color when added to these samples from the above list: To design procedures for testing whether each indicator solution is a good test for starch or for protein, answer questions 2 and 3. Be specific. 2. Which of the samples listed above will you use to test each indicator solution? Explain your reasons for including or excluding each sample in the above list. 3. How will you evaluate each test? What will you look for? 1
4. Suppose that two groups are assigned to test the same indicator with the same sample, but the first group reports a color change and the second group does not. How could this happen? To be confident of your results, you will need to carry out each test carefully and have replicate tests (i.e. have two groups carry out each test). A large number of tests will be required to evaluate whether either indicator solution can be used to test for starch or for protein. Your teacher will lead a discussion to agree on a class procedure and then assign specific tests to each student group. Before you begin your tests, read the cautions and instructions below. Cautions: Do not add both indicator solutions to the same sample; use each indicator solution on a different sample in a separate container. Be careful when handling indicator solution 1; it can stain hands and clothing. Indicator solution 2 contains sodium hydroxide, a strong base. Be very careful not to splash or spill any. If you splash any indicator solution on yourself, wash it off immediately with water. Call your teacher for assistance. Wear gloves to protect yourself. 5. Complete the following table to record the data for the tests assigned for your group. Sample* Indicator Solution 1 or 2 # Color of Indicator Solution after Added to Sample Did the indicator solution change color? Yes or No * For either type of starch, powdered egg whites, or sucrose, dissolve about 1/2 ml of the sample in about 2 ml of water. For gelatin, dissolve up to 1/4 ml in about 2 ml of water. For oil and water, use about 1 ml as your sample. # To use indicator solution 1, add up to 5 drops to the sample and stir. To use indicator solution 2, add up to 20 drops to the sample and stir. With either indicator solution, you can stop as soon as you observe a color change in the indicator solution. With indicator solution 2, the color change may take up to a minute. 2
6. Use the data from all of the student groups to complete the following table. Sample Corn Starch Potato starch Powdered egg whites Gelatin Sucrose Vegetable oil Water Did indicator solution 1 Did indicator solution 2 change color? change color? Replicate 1 Replicate 2 Replicate 1 Replicate 2 If there are any differences between the replicates of any test, your class will discuss the possible reasons for these differences. To get a definitive result, you will probably need an additional replicate test using the best methodology. 7. Is either indicator solution a good test for starch? If yes, which one? Briefly summarize the evidence that supports your conclusion. What additional evidence would help you to be more certain of your conclusion? 8. Is either indicator solution a good test for protein? If yes, which one? Briefly summarize the evidence that supports your conclusion. What additional evidence would help you to be more certain of your conclusion? 3
Part 2 What types of food contain starch? What types of food contain protein? In this part of the activity, you will evaluate whether starch and protein are found in - all foods derived from animals - some foods derived from animals - all foods derived from plants - some foods derived from plants - all foods derived from animals or plants - some foods derived from animals or plants 9. Begin by categorizing the results from Part 1 in the table below. Food derived from animals have starch? have protein? Food derived from plants have starch? have protein? 10. Use the results summarized in question 9 to write a hypothesis about which types of food contain starch (all or some foods from animals and/or plants). Use the results to write a hypothesis about which types of food contain protein. 11. You will be given the foods listed below to test your hypotheses. Complete columns 2-4 in this table to predict the expected results; if your hypotheses do not predict a specific result, put a?. Food Does this Based on your hypotheses, do Based on the class results, (with instructions food come you expect this food to contain: does this food contain: to prepare from plants sample for testing) or animals? starch? protein? starch? protein? Beans (mash 2 beans into a paste) Butter (~1 ml) Jelly (mix ~1 ml with ~½ ml water) Bread (crumble ~1 ml; add ~½ ml water) Yogurt (~1 ml) 4
12. To evaluate your hypotheses (question 10), you will need to test your predictions (question 11). Briefly describe how your class will test these predictions. A large number of tests will be needed, so your teacher will assign specific tests to each student group. Record the data as instructed by your teacher. Then, record the class data in the last two columns of the table in question 11 and answer questions 13 and 14. 13. Is your hypothesis about which types of food contain starch supported by the new data? Explain how the evidence does or does not support your hypothesis. If your hypothesis was not supported, write a new hypothesis that takes account of all of the data you have. Indicate any limitations of the evidence and any uncertainty in your conclusions. What additional evidence would be useful to evaluate your hypothesis? 14. Is your hypothesis about which types of food contain protein supported by the new data? Explain how the evidence does or does not support your hypothesis. If your hypothesis was not supported, write a new hypothesis that takes account of all of the data you have. Indicate any limitations of the evidence and any uncertainty in your conclusions. What additional evidence would be useful to evaluate your hypothesis? 5