BIOLOGY 102-001L What’s In Your Food? (Biological Macromolecules) A Scientific Investigation – What types of food contain starch and lipids?1 In this activity you will learn about starch and lipids and investigate which types of food contain starch and which types contain lipids. Part 1 – Introduction Organic Compounds including Starch and Lipids What are organic compounds? Almost all of the food we eat comes from plants and animals. Plants and animals contain mainly water and organic compounds, which are molecules made by living organisms such as plants or animals. 1. The table below lists the most common types of organic compounds found in living organisms. For each type of organic compound, give one or two examples and describe one characteristic, e.g. whether it is greasy, whether it contains genetic material, composition, etc. (2 points) Type of Organic Compound Examples Characteristic of This Type of Organic Compound Carbohydrates Lipids Nucleic acids Proteins 1 By Lara Mabry, School of Biological Sciences, University of Missouri – Kansas City, © 2017. 1 BIOLOGY 102-001L What’s In Your Food? (Biological Macromolecules) Starch is a polymer of glucose molecules. A polymer is a large molecule made up of many repeated subunits, called monomers. Starch molecules store glucose for later use. For example, the starch in a seed provides glucose for the growing embryo after the seed sprouts. 2. Which monomers are joined together to form a starch molecule? (1 point) Unlike starch, lipids are not polymers of a repeating monomer. Lipids are a diverse group of molecules, composed predominately of hydrocarbon (C-H) bonds. They have one common characteristic in that they are insoluble in water. The most familiar lipids are the fats and oils we consume in the foods we eat. One important function of lipids is the storage of energy in the form of hydrocarbon bonds. Fatty acids, triglycerides, and phospholipids are all types of lipids. A fatty acid is a long, unbranched chain of hydrocarbons. Fatty acids without double bonds are referred to as saturated fatty acids and are linear molecules. Fatty acids with double bonds are referred to as unsaturated fatty acids and have a kink due to their double bonds. 3. The image on the below left is fatty acids while the image on the below right is 2 BIOLOGY 102-001L What’s In Your Food? (Biological Macromolecules) fatty acids. (fill in the blank) (2 points) Part 2 – Testing for Lipids and Starch What are indicators? An indicator is a substance that changes color in the presence of a particular type of molecule. In this lab, you will learn how to use an indicator to test for the presence of starch. You will also use a different type of test for lipids. Testing for lipids 1. If a food that contains lipids is put on brown paper, it will leave a spot that lets light through. To test for lipids, divide a piece of a brown paper bag into 5 sections. Label the sections "vegetable oil", "glucose", "starch", "powdered egg whites", and “water”. 2. In each section, rub a small amount of the substance onto the brown paper. With a paper towel, rub off any excess that may stick to the paper. 3. Set the paper aside until the spots appear dry—about 10 to 15 minutes. While you are waiting, answer questions 4-6 and then continue with the tests on page 3. 4. Which substance or substances do you expect to test positive for lipids? (2 points) 5. What is the purpose of testing water for lipids? (2 points) 3 BIOLOGY 102-001L What’s In Your Food? (Biological Macromolecules) 6. Why should you test all of the substances for lipids even though you believe that some of them do not contain lipids? (2 points) 7. Continue on with the test below detecting carbohydrates. After all the sections of the brown paper are dry, hold the paper up to a bright light or window. You will notice that at least one sample has left a spot on the brown paper that lets light through. This type of spot indicates the presence of lipids. 8. Complete the last column of the data table below. Put a plus for any samples that tested positive for lipids and a minus for the samples that did not. (10 points) Lipid Carbohydrate Tests Test Sample Iodine test Lipid Starch present color present Vegetable oil Sugar (mix with ¼ tsp water) Starch from potatoes Egg white Tap Water Testing for Carbohydrates 9. You will be using a chemical as an indicator. You must wear gloves to protect yourself. 10. You will use an indicator to test for a common type of carbohydrates - starch. Obtain 5 containers and use masking tape to make labels for each container. Label the containers "vegetable oil", "sugar", "starch", “egg white,” and “water”. 11. For each container, add a small amount of the substance indicated on the masking-tape label. Next, add about 1/2 teaspoonful of water to each container. Stir the contents of each container to mix the substance with the water. 12. To test for starch you will use iodine as an indicator. In the presence of starch, iodine will change color from yellow-brown to blue-black. Add 5 drops of iodine solution to each container. Stir the contents of each container. CAUTION: Be careful when handling iodine; it can stain hands and clothing. 4 BIOLOGY 102-001L What’s In Your Food? (Biological Macromolecules) 13. In the data table above, record the color of the iodine solutions. Put a plus next to those samples testing positive for starch and a minus for those testing negative. 5 BIOLOGY 102-001L What’s In Your Food? (Biological Macromolecules) Part 3 – What types of food contain starch? What types of food contain lipids? 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 14. Begin by summarizing the results from question 8 in this table. (4 points) Food derived Did this food Did this food from animals have starch? have lipids? Food derived Did this food Did this food from plants have starch? have lipids? 15. Use the results summarized in question 14 to write a hypothesis about which types of food contain starch (all or some foods from animals and/or plants). (1 point) 16. Use the results to write a hypothesis about which types of food contain lipids. (1 point) 17. Choose four (4) foods to test your hypotheses. Be wise about your choices to test your hypothesis List them in column 1. Complete columns 2-4 in this table to predict the expected results. (10 points) Food (with instructions to prepare sample for testing) Does this food come from plants or animals? Based on your hypotheses, do After testing, indicate you expect this food to contain: whether the food contains: starch? lipids? starch? lipids? TO RECEIVE CREDIT FOR THIS LAB, MAKE SURE YOU SNAP A PHOTO OF YOUR RESULTS! UPLOAD THIS PHOTO WITH THIS COMPLETED LAB REPORT. **FAILURE TO UPLOAD YOUR PHOTO WITH YOUR LAB REPORT WILL RESULT IN A ZERO (0) FOR THE LAB** 6 BIOLOGY 102-001L What’s In Your Food? (Biological Macromolecules) 18. Use the cautions on page 2-3 and the instructions to guide your testing. Record your data in columns 5-6. 19a. Is your hypothesis about which types of food contain starch (question 15) supported by the new data (in question 17)? Explain how the evidence does or does not support your hypothesis. (3 points) 19b. If your hypothesis was not supported, write a new hypothesis that takes account of all of the data you have. 20a. Is your hypothesis about which types of food contain lipids supported by the new data? Explain how the evidence does or does not support your hypothesis. (3 points) 20b. If your hypothesis was not supported, write a new hypothesis that takes account of all of the data you have. 21. Indicate any limitations of the evidence and any uncertainty in your conclusions. What additional evidence would be useful to evaluate your hypothesis? (2 points) 7 
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