To begin the lesson, I review with students the way that they could identify a positive test result when testing for the presence of starch. Students are familiar with this process because of their work in the previous lesson.
I then model for my students how they will conduct the day's tests. I display all of the materials for the lab under the document camera. The students will use eight food samples, eight numbered spoons, a ten-section test tray, iodine, and water in the day's lab. Modeling correct lab procedures is an important step in this lab as it is the first time students will be testing food samples for a nutrient. As in the previous lesson, students will add a food sample to a section of the test tray. The students then need to add a few drops of water to the test sample. The water softens the food sample and allows the iodine used for testing to change colors when starch is present. After modeling the test process, I allow students to ask questions to clarify their understanding of the lab procedures.
Next, I distribute a copy of the starch in foods lab worksheet to each student. I review the guiding question with students so that they better understand the purpose of the lab. I ask students to use their prior knowledge to make a hypothesis about which foods contain starch. After each student has made their predictions, I provide time for the student groups to complete the lab. During this time, I circulate around the classroom clarifying expectations, answering questions, and monitoring student lab work.
At the end of the lab time, I ask students to share their test results so that I can record them on the class' food test chart. To help quickly obtain results from each student group, I use a thumbs up, thumbs down strategy. I say the name of each food and ask students to give thumbs up if their test showed the presence of starch and thumbs down if they got a negative test result. This allows me to take a brief visual survey of each student's results and to arrive at a general consensus to apply to the class chart.
In this lab, there is little controversy over the test results as the only food that gives questionable results is coconut. Coconut contains a small amount of starch and the iodine usually changes the water's color to orange or pink. The sweetened coconut I use contains more starch than the natural fruit, so usually gives a clear, positive result.
After the completion of the lab, I assign a reading assignment to each student. The reading assignment is designed to help students learn more about how starch helps the human body and which foods contain starch. The article I assign to students comes from the STC curriculum, however, there are many articles online which can serve to provide the same information. After students have completed their independent reading, I ask them to complete the starch questions. This serves as a quick formative assessment of student understanding about starch.
A sample of a student's complete questions can be found here.