This is a great introductory project for the environmental science classroom. The student must design, and create a ecosystem in a bottle. Make observations and connections (trophic levels and carbon/nitrogen/water cycles). Then they will explore human impact on their environment by selecting a manipulated variable to simulate (fertilizer runoff, acid rain, saltwater intrusion). You can take this project to so many levels! My students said, "I feel like I'm really doing science!" Needless to say, they love it!