Students often find it challenging to learn about complex and abstract biological processes. Using the engineering design process, which involves designing, building, and testing prototypes, can help students visualize the processes and anchor ideas from lab activities. We describe an engineering-design-integrated biology unit designed for high school students in which they learn about the properties of slime molds, the difference between eukaryotes and prokaryotes, and the iterative nature of the engineering design process. Using the engineering design process, students were successful in quarantining the slime mold from the non-inoculated oats. A t-test revealed statistically significant differences in students' understanding of slime mold characteristics, the difference between eukaryotes and prokaryotes, and the engineering design process before and after the unit. Overall, students demonstrated sound understanding of the biology core ideas and engineering design skills inherent in this unit.