An investigation into environmental sustainability, this unit emphasizes the structures of ecosystems, the cycling of matter and energy within ecosystems, and the ways in which humans affect sustainability of ecosystems. Because this unit involves some outdoor investigations, it should be placed first if taught in the autumn semester, or last, if taught in the winter semester. The unit itself is divided into four sections. 1.The unit begins with a brief consideration of energy and thermodynamics and the limits placed on ecosystems by the first two laws. 2.Recycling matter is the focus of the second part of the unit. Students investigate the water cycle, food webs and other biotic components of ecosystems. 3.Next, students are given the opportunity to investigate abiotic and biotic parameters in a local aquatic ecosystem. 4.The unit concludes with a five-day performance task that will enable students to examine human affects on the sustainability of ecosystems.