Food Allergies BACKGROUND SCENARIO BIOTECHNOLOGY LAB. Name Period Date

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1 BIOTECHNOLOGY LAB Food Allergies BACKGROUND Sometimes Jamie's younger brother Andrew complains that his stomach hurts and he might vomit his food. Other times he breaks out in hives all over his body. Jamie learned about antigens, antibodies, and allergies in his biology class. Antigens are proteins on the surface of pathogens that can make a person sick. Some antigens are structures on the surfaces of bacteria, viruses, or pollen. When the immune system encounters an antigen, the immune system produces antibodies. The antibodies bind to specific antigens. When antibodies bind to antigens, the antigens become inactive. In the case of bacteria and viruses, you want your immune system to make antibodies so that you will fight off infection. Sometimes the immune system makes antibodies for harmless antigens such as pollen, animal dander, and some foods such as nuts, fish, and eggs. The result is an allergic reaction. The antibodies cause white blood cells to release histamines. Normally, histamines help fight infection by increasing blood flow to the infected area of the body. In the case of allergic reactions, however, there is no infection, and blood is needlessly taken away from other areas of the body. Blood flow can decrease to the muscles in the respiratory system, particularly the bronchi in the lungs. Muscles can contract, making breathing difficult. When people with an allergy to eggs, peanuts, milk, soy, fish, or wheat come into contact with that food, they might get hives or have swelling of the mouth, throat, and eyes, stomach cramps, nausea, diarrhea or vomiting. In some cases, the allergic reaction can be more severe. Jamie wondered if his brother could have a food allergy, so he and his parents kept a food journal for a week and noticed that Andrew had a reaction after he ate certain foods. Jamie's parents took Andrew to the doctor and explained the situation. The doctor drew some of Andrew's blood and performed a test. SCENARIO In the following experiment, your class will perform a model of the test performed by Andrew's doctor. The real test checks for the presence of certain antibodies in a person's blood. Blood is put into the center hole of an agar plate and different foods are dropped into the surrounding holes. The blood sample and the food samples diffuse through the agar. If the blood sample contains antibodies for any of the antigens on the food, the antibodies and food molecules clump and proteins will precipitate out. If clumping occurs, a doctor can conclude that the patient is allergic to that type of food. In the model of the test, your class will use a nonblood containing reagent that mimics the antibodies in a person's blood. Holt McDougal Biology 1 Immune System and Disease

2 PROBLEM What food group is Andrew allergic to? MATERIALS agar plate plastic straw toothpick marker eye droppers Food Sample A Food Sample B Food Sample C Food Sample D Food Sample E Food Sample F Reagent A PROCESS SKILLS Observing Analyzing Data Drawing Conclusion PROCEDURE 1. Use the straw to punch out holes in the agar plate in the following arrangement. Holt McDougal Biology 2 Immune System and Disease

3 2. Use a toothpick to remove the small pieces of agar punched out by the straw. 3. On the bottom of the plate, use the marker to label the six holes that make a ring around the center hole A, B, C, D, E, and F respectively. 4. Drop 1 2 drops of Food Sample A into the hole in the agar plate labeled A as shown. 5. Repeat Step 4 for the remaining food samples, dropping 1 2 drops of each sample into the corresponding hole in the agar. Use a new dropper for each sample. 6. Drop 1 2 drops of Reagent A into the center hole of the agar plate. Cover the plate and store overnight at room temperature. 7. After 24 hours, examine your plate. Hold the plate up to the light or a window as shown. Look for white lines that may have formed between the center hole and the holes containing the food samples. These lines are called precipitin lines. The presence of these lines indicates an allergy to the food sample. Record your observations in the data table. Holt McDougal Biology 3 Immune System and Disease

4 TABLE 1. FOOD SAMPLE RESULTS Food Sample Observation/Precipitin Line A B C D E F ANALYZE AND CONCLUDE 1. Analyze Which sample foods caused the precipitin line to form? 2. Evaluate Obtain from your teacher the identities of the food samples. Which ingredient do all of these foods have in common? 3. Apply If these were the results of Andrew's allergy test, what would you conclude about his food allergies? Why? Holt McDougal Biology 4 Immune System and Disease

5 4. Apply A doctor suspects his patient may be allergic to peanuts. He is going to perform the same test done in this experiment to identify the food allergy. Make a list of six sample foods the doctor should use in the test. Holt McDougal Biology 5 Immune System and Disease