![Food web with plants and animals](/exchange/files/imagecache/large_350/foodweb.png)
To begin this hands-on, minds-on activity, students view a video about ecosystem changes that resulted when wolves were eliminated from Yellowstone National Park and later returned to Yellowstone. Then, students learn about food chains and food webs, and they construct and analyze a food web for Yellowstone. Students use what they have learned to understand a trophic cascade caused by the elimination of wolves from Yellowstone.
Next, students learn that the biosphere requires a continuous inflow of energy, but does not need an inflow of carbon atoms. To understand why, students apply fundamental principles of physics to photosynthesis, biosynthesis, and cellular respiration, the processes which result in carbon cycles and energy flow through ecosystems.
In the final section, students use the concepts they have learned to understand trophic pyramids and phenomena such as the relative population sizes for wolves vs. elk in Yellowstone. Thus, students learn how ecological phenomena result from processes at the molecular, cellular, and organismal levels.