Ecosystems Lesson 4 Background Information

Three-dimensional Learning Progression

In Lesson 4, students explain carbon movement in ecosystems in terms of pools and fluxes. A pool size is constant when the fluxes into and out of it are the same or balanced – i.e., when the net flux is zero. Pool sizes change when in and out fluxes are not balanced. High school students explain how photosynthesis limits the maximum, steady state amount of organic matter an ecosystem can support. When an ecosystem reaches its photosynthesis limit, the rate of photosynthesis and cellular respiration are essentially the same. Students explain how different types of disturbances affect pool sizes and flux rates.