This lesson plan teaches students that the earth is a complex sphere composed of a variety of interdependent systems which can be placed in the following order of increasing complexity: organism, species, population, community, ecosystem, biome, and biosphere. The lesson plan provides objectives, skills, time needed, a content outline, materials, significant terms, a glossary, resources, questions for the class, and an activity where students create a poster depicting one level of ecological complexity. The site is part of a group of lesson plans whose main goal is to develop in students an understanding of the interdependence of all organisms and the need for conserving natural resources.