Begin by discussing the main question posed at the beginning of the section. Why don't natural systems run out of the materials they need? Use this idea to compare the flow of energy in a community to the flow of nutrients (abiotic factors) in a community. Emphasize that nutrients cycle but energy does not.
Brainstorm with students all the forms of water they have observed-oceans, lakes, rivers, streams, puddles, rain, snow, ice, sleet, hail, etc.
Discuss the terms evaporation, precipitation, condensation, and transpiration as components of the water cycle.
Activity 4-1: A Day in the Life of a Water Molecule can be used to introduce how water cycles through the environment. Activity 4-1 can be used as an introductory activity. Enrichment 4-1: What Goes Up Must Come Down: Water Cycle Simulation can be used to reinforce how water cycles through the environment.
Assign Mini Activity: A Day in the Life of a Carbon Atom for students to examine the path of a carbon atom, which will demonstrate how carbon cycles through the environment.
To explore how other nutrients such as oxygen, nitrogen, and phosphorus cycle through a natural community assign Mini Activity: Create a “Cycle Poster.” Display the finished posters around the classroom throughout the study of Ecology.