In this activity (app. 25 min), a case-study style problem is presented to students (“The Roundup Story") that describes the use of roundup (herbicide) in agriculture, and the development of “roundup ready” crop strains. The case study approach incorporates a great number of questions, which are designed to guide the students to a clear understanding of how genetically modified organisms (GMOs) are developed, particularly in terms of the molecular modifications necessary for the successful use of this biotechnology. Students are then asked to apply this new knowledge. The primary activity component challenges students to develop a lemon that tastes and looks like pink lemonade, using molecular techniques. Groups work together to construct a plasmid that could be introduced to the typical lemon genome, in a manner that would result in the desired product. Homework is also described which prepares students for a subsequent discussion/debate on GMOs. The activity is appropriate for both undergraduate majors and non-majors in biology.