In the engaging unit described here, imaginary organisms are used to teach a variety of topics related to ecosystems—food chains and energy flow, food webs, limiting factors, carrying capacity, and the effects of natural and human-made events on ecosystems. By inventing organisms, the teacher is able to control the level of complexity, and the number of organisms can be modified to meet each student’s level. Because the organisms are figments of the imagination, the assignment is not complicated by students’ prior knowledge. Once the unit is finished, the class can discuss the ecosystem and how it is similar to and different from real ecosystems.