Have students go outside, or think about outside, and make a list of all of the interdependent (i.e., mutually dependent) kinds of systems that they can identify. Ideally, each separate (or related) example they list should be represented by three or more specific sub-systems or parts: a water tower/a fire hydrant/a drinking fountain/a lawn sprinkler; a TV broadcasting tower/a TV antenna/a portable TV set; an electric pole or wires/a fuse box or transformer/an electric light/a computer terminal a mailbox/a postal person or postal truck/an airmail plane From their lists, which "systems" are interdependent with two or more other "systems"? Which use the most energy? The least? Which ones require regulation? Who regulates each one? Who pays for each one? Which of these "systems" do no exist in , e.g., in an African rainforest? The Atacam desert? The tundra region of northern Asia? The interior of Australia? Note: This exercise provides an ideal opportunity to involve someone from students' homes to help them develop their list of systems.