Give your students a hands-on investigation of the cell cycle, mitosis, and the effects of environmental signals with this AP Biology lab. In this lab, students compare an "unknown" prepared onion root tip slide to a control sample to determine if the cells were exposed to a growth compound (IAA, a plant hormone/auxin). This lab emphasizes quantitative analysis, cell observation, and data interpretation. Students observe cells and count cells in each phase of mitosis, calculate percentages, crea