The process of photosynthesis is included in Unit 3: Cellular Energetics of the AP Biology Course and Exam Description (CED). Many teachers use the floating leaf disk assay from “AP Biology Investigative Labs: An Inquiry Based Approach” to teach this biochemical process; but often face procedural difficulties, time requirement challenges, inconsistent data, and student confusion pertaining to the overall learning goals of the lab experience. This alternate procedure streamlines the experimental set up and shifts the data collection goal to measuring the volume of oxygen generated by the light reaction. The protocol provides students opportunities to design their own variations of the experiment to analyze environmental conditions that may influence the rate of oxygen generation during the light reaction.