Student learning about tracing matter and energy in ecosystems
Vision and Change describes one of their six core concepts as pathways and transformations of energy and matter. College-level biology courses for majors and non-majors commonly use pool and flux models to describe matter cycling and energy flow in ecosystems, with processes such as photosynthesis and cellular respiration moving carbon and other elements from one reservoir to another in biological communities and the non-living environment. Our previous research has shown that most biology students have significant difficulties understanding these processes on the atomic-molecular and organismal scales. We are exploring the additional challenges students have when explaining carbon-transforming processes at an ecosystem scale. Our research question is to describe different levels of sophistication of student explanations of matter and energy at the ecosystem scale.
We interviewed undergraduates in a non-majors general science course post instruction (n=16). The course focused on the principles of matter and energy but primarily taught photosynthesis, biosynthesis, cellular respiration and decomposition at an organismal scale with at least one class period about the above processes at an ecosystem scale. This course is effective at helping students give explanations of carbon transforming processes at an organismal level based on previous research. The interviews were analyzed using multiple iterations of emergent coding to describe patterns in student responses.
We found that student difficulties in tracing matter and energy in ecosystems commonly included omitting cellular respiration in plants and fungi, confusing types of molecules, describing thermal energy from the sun as a primary story (rather than chemical energy movement) in ecosystems, and omitting thermal energy release from ecosystems. Few students traced matter in the context of a complex problem like explaining a biomass pyramid. Students’ descriptions of the biomass pyramid were primarily focused on the “need” of higher trophic levels to have food to eat, rather than cellular respiration or of inefficiency of transfer of organic materials between trophic levels, similarly to force-dynamic reasoning at the organismal scale. We conclude that learning about carbon-transforming processes at an organismal scale is not sufficient for student achievement at the ecosystem scale. Students may need highly scaffolded activities to connect the atomic-molecular and landscape scales while explaining carbon-transforming processes.