Contemporary biologists study complex systems, from cells to ecosystems. By extension, current undergraduate education reform recognizes complex systems as a core concept underpinning biological literacy. However, the skills and content knowledge comprising systems thinking are largely undefined. We believe an essential component of systems thinking is the ability to delineate the system of interest, that is, to articulate what is – and is not – part of the system. A second component of systems thinking may be the ability to reason dynamically, to describe how the system changes or responds to perturbations. Using a model-based pedagogy, we explore students’ systems thinking abilities within the core concept of matter movement and transformation (e.g., carbon cycling). Before and after relevant instruction, introductory biology students constructed a concept model of carbon movement in a given ecosystem and were then asked to use that model to reason about a perturbation to the carbon cycle in that system. We coded student models for the presence and correctness of key carbon pools and fluxes as a measure of their ability to delineate the focal system. Students’ extended responses were coded to understand whether and to what extent students were able to reason dynamically about an ecosystem.
Results/Conclusions
Prior to instruction, introductory biology students struggled to completely and correctly delineate the focal ecosystem. For example, less that 2% of students include decomposers in their carbon cycle models. Students also rarely included fluxes that moved carbon dioxide to/from the atmosphere: 4% of students included plant respiration and none included respiration by decomposers. Following instruction, students more completely and correctly delineated the ecosystem, with over 75% including decomposers and over 60% correctly including respiration by decomposers. Further, prior to instruction, student reasoning about system perturbations focused mostly on visible pools (e.g., 76% mentioned primary consumers), and only discussed changes to pool size for primary consumers (35%). Flux discussions included consumption (26%) and heterotrophic respiration by visible system pools (5%). After instruction, students’ reasoning about ecosystem perturbations included substantially more pools (mean range 2.54-5.72) and fluxes (1.16-4.62), with gains made in discussing plants (photosynthesis & respiration) and decomposers. Overall, we found student understanding of non-visible components of ecosystems was initially limited but improved following instruction. Further, responses to the ecosystem perturbation prompt revealed students exploring multiple ways that systems can respond, evidence of their ability to reason dynamically. Together, these results provide preliminary evidence of systems thinking in undergraduate biology.