Cells in tumors mutate very quickly as they grow and divide, creating a tumor with multiple populations of different cells. In this 50-minute lesson students will learn how these mutations can result in tumor heterogeneity and make tumors more sensitive or resistant to chemotherapy treatment. Students participating should have a basic understanding of cellular division (mitosis) and DNA structure and replication. Using this knowledge, students will run a tumor growth and treatment simulation to model how a tumor’s heterogeneous composition can change the efficacy of chemotherapy treatment. We’ve included an optional statistics segment where students can apply basic statistical techniques to analyze data generated in the experiment.  Students participating in this optional activity should have an understanding of basic statistics. In order to complete this lesson, you’ll need paper bags, beads/beans/similar materials of five different colors, cups, and one timer. For each group of three students, you will need 1 paper bag, 6 cups (or other bead-holding vessels), and 25 beads of each color.