This activity has two parts: the first is meant to get students focused on bacterial cell structure; the second involves analytical thinking and data interpretation. In the first part, students are given diagrams of three cell envelopes (from a gram positive, gram negative, and archaeal cell) to label. In the second part, students are given some information about two antibiotics (polymyxin and vancomycin) and the results from two experiments. Based on the data and their knowledge of cell envelope structure, they predict which experiment reflects data from which antibiotic.