I will be teaching 5th grade this year, and decided to design this assignment around the following standard:
Students who demonstrate understanding can: 5-LS2-1. Develop a model to describe the movement of matter among plants, animals, decomposers, and the environment.
Crosscutting Concepts: Systems and System Models: A system can be described in terms of its components and their interactions. I would begin with discussions about different types of systems: circulatory system, solar system, even video game systems. What is it that makes a system, exactly? What makes an “ecosystem”? From this discussion, we could begin to talk about how matter moves through an ecosystem.
Disciplinary Core Ideas: LS2.A: Interdependent Relationships in Ecosystems. I think the key ideas that need to be addressed in this standard relate all to the concept of “interdependence”. Students are familiar with the idea of a food chain or food web, and this would be a good place to start this discussion. Yet still, it would need to be pushed further, more into the idea of what forms an ecosystem.
Science and Engineering Practices: Developing and Using Models Modeling in 3–5 builds on K–2 models and progresses to building and revising simple models and using models to represent events and design solutions. Develop a model to describe phenomena. This one is a little trickier, since I would want to move beyond just having kids recreate a food web on paper. I always think of this particular dimension of the NGSS as “building something to provide a solution”, but here the concept seems a little harder. If anything it might be interesting to design or develop a game where one part of the interdependent web is removed, and see what effect this has on the rest of the ecosystem.