Student-constructed models reveal biogeochemical understanding

Background/Question/Methods

Pedagogical approaches that engage students in the active construction and evaluation of conceptual models may support students’ acquisition of deep content knowledge and systems thinking skills, both critical skills in contemporary ecology. The process of creating conceptual models of biogeochemical cycling, for example, requires that students actively select specific pools and describe how matter moves between pools, thus revealing content understanding. We used an iterative, model‐based pedagogy to help students build systems thinking skills while gaining content understanding in an introductory undergraduate biology course. Specifically, this research focuses on student understanding of biogeochemical cycling as evidenced by their ability to model carbon and nitrogen movement. We ask (1) how accurate are student-generated models of nitrogen and carbon movement and (2) what errors in understanding emerge through an analysis of the relationships students articulate. Using a comprehensive final exam, we randomly assigned students to construct a model of either carbon or nitrogen movement through a specified ecosystem. Following completion of the individual task, students worked collaboratively to develop a composite model of nitrogen and carbon movement through the same ecosystem. We coded both individually- and group-generated models for overall correctness and for presence, absence, and correctness of key pools and fluxes.

Results/Conclusions

Student-constructed models of carbon cycling were generally more correct than those of nitrogen cycling (mean scores of 92% and 85%, respectively). Student-constructed models of carbon and nitrogen cycling revealed students’ propensity to identify macroscopic pools (e.g., plants, consumers) and difficulty in representing microscopic pools (e.g., decomposers). Students were proficient identifying visible fluxes (e.g., consumption) yet often omitted respiration and photosynthesis from carbon cycling. In nitrogen cycle models, students often used biologically vague terminology, using ‘absorbs’ or ‘used by’ in place of assimilation, for example. Collaborative models decreased in correctness (mean score of 83%). In these models, students tended to conflate or merge fluxes across cycles, suggesting that students were challenged to integrate their knowledge of two seemingly distinct biogeochemical cycles. These results provide insight into students’ ecological content understanding and confirm prior research documenting student difficulty with reasoning about the microscopic level in the context of carbon cycling. Further, this work underscores the utility of a model-based pedagogy in supporting student learning in introductory biology and in refocusing the introductory biology classroom away from rote memorization to relationships between and among biological concepts.