This lab is fantastic after teaching students about the organic molecules found in our foods. It is also great to use if you want students to practice writing formal lab reports.
It opens with the description of a crime scene of the murder of a high profile lawyer. A sample of vomit found at the crime scene needs to be tested to determine if it belongs to any of the suspects. The lab handout details the foods eaten the night of the murder by the victim and each of the suspects. At this point, I will have already done simple tests for starch, simple sugars, lipids, and proteins with the students so they will already be familiar with the procedures. Page 10 of the handout includes basic instructions for running the tests for each organic molecule.
Once the testing is done, students are asked to write up their results in a formal lab report that includes 5 sections: introduction, materials and procedure, data, analysis, and conclusion. Directions and tips for completing each section can be found in the handout. The lab requires that students include internal citations within the introduction and conclusion section, as well as a Works Cited in MLA format at the end of the report. A rubric is included on page 9 of the handout that gives a detailed list of each requirement and its point value.
As for timing - You'll want to introduce it the day before actually testing the vomit samples (about 20 minutes). If this is your first time doing these tests with them, show them what a positive/negative test looks like for each molecule. Students will need 40-50 minutes to run the tests and organize their thoughts the next day. You may also want to spend a 3rd day giving them time to work on their rough drafts in class. If you don't have the time or feel that they can finish independently, the rest of the report can be written outside of class and turned in at a later date. I have also used a day for peer editing in the past where students are asked to critique at least 2 of their classmates' lab reports. They can use the rubric as a guide.This works great usually because they can catch their own silly mistakes.
Supplies needed ahead of time are: test tubes, droppers, hot water bath, Biuret reagent, Benedict reagent, Lugol's solution, Sudan III solution (or brown paper bags), and distilled water. For the vomit samples - I usually prepare 2-4 different samples so that not all of the student groups are getting the same results. For meals containing protein - I use raw eggs or gelatin, for meals containing starch - I use potato flakes or corn starch, for meals containing simple sugars, I use mashed up bananas or applesauce, and for lipids - I use vegetable oil. You want to make sure that your vomit samples only test positive for ONE of the suspects' meals, so I suggest trying each test on your sample before the students do, especially if you are going to try items that are different than those listed above.
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