Students are introduced to an engineering challenge in which they are given a job assignment to separate three types of apples. However, they are unable to see the color differences between the apples, and as a result, they must think as engineers to design devices that can be used to help them distinguish the apples from one another. Solving the challenge depends on an understanding of wave properties and the biology of sight. After being introduced to the challenge, students form ideas and brainstorm about what background knowledge is required to solve the challenge. A class discussion produces student ideas that can be grouped into broad subject categories: waves and wave properties, light and the electromagnetic spectrum, and the structure of the eye.