Based on the recommendation of the AAAS and the NRC, middle level science is the rightful introduction for a systems approach, including the study of its parts, subsystems, interconnections, and interrelationships. Dr. Seuss's "The Lorax" provides an excellent opportunity to combine ecological consequences within a systems approach (Sweeney 2001). The inquiry-based lesson described here is designed using the 5E instructional model and develops students' critical-thinking skills as they create concept maps to depict the relationships among components of a larger system. (Contains 2 figures.)