We focus on a particular class of human actions: Our actions as consumers of essential goods and services, including food, clothing, shelter, air, water, and transportation.  Goods and services in each of these categories pass through a number of environmental systems on their way to us (the supply chain) and go through additional systems after we are done with them (waste disposal).  The human systems that supply all of our essential goods and services - food, clothing, shelter, water, transportation - begin and end in the earth’s natural systems. Our goal is to find out more about student understanding of the connection between human engineered systems and natural systems.  This is essential in order to help them develop model-based reasoning about supply and waste disposal chains, which requires that students be able to trace matter and energy through these chains and make connections between them.  Through understanding supply and waste disposal chains, students can begin to examine human ecological footprints, how they can have a greater or lesser impact on the environment based on decisions that they make with regards to supply and waste disposal chains, and realize that individual and societal decisions make a difference.