This student-led project is used to meet the Ecosystems: Interactions, Energy, and Dynamics HS-LS2-5 standard. Students develop a model to illustrate the role of photosynthesis and cellular respiration in the cycling of carbon among the biosphere, atmosphere, hydrosphere, and geosphere. Students choose what type of model to make (physical model, computer modeling, presentation, project, etc.) to convey understanding. Grading rubric is included.