Helping students develop principle-based accounts of ecosystem functioning: A study of the effectiveness of an instructional intervention

Background/Question/Methods

Understanding the importance of preserving our ecosystems cannot be fully realized if students’ explanations of ecological phenomena are not constrained by scientific principles (i.e. conservation of matter and energy). Studies show that college level students have limited understanding that atoms, although rearranged and reorganized into different molecules, are fundamentally conserved within ecosystems. The purpose of this exploratory study was to determine if a set of previously developed research-based activities promote the development of principle-based accounts of ecosystem functioning. The instructional module included a series of data-rich problem tasks (designed to create cognitive disequilibrium) and several discussion-based scenarios all focused on helping students trace matter and energy through ecosystems. The module was implemented in two different contexts:  an introductory undergraduate Ecology and Evolution course, and a high school AP Environmental Science course. Validated and published diagnostic question clusters (DQCs, see www.ThinkingLikeABiologist.com) were used as pre- and post-tests to assess changes in students’ knowledge and reasoning about ecosystem carbon transformations (e.g., photosynthesis, decomposition, cellular respiration, and biosynthesis), conservation of matter, and ability to make connections between biological levels of organization. Prior research shows that with traditional instruction, we see little to no gain in DQC results.

Results/Conclusions

The data from this study reveal that the instructional module promoted the development of more sophisticated accounts of the transformation of matter in ecosystems. The pre- and post-test comparison for the high school group showed a mean growth of 11.0 points, or 25%, (t₍₁₆₎ = 4.85, p < 0.05) with an average normalized gain (g) of 0.27. The undergraduate data show a mean growth of 9 points (t₍₁₄₎ = 8.19, p < 0.001), with an average normalized gain (g) of 0.24. Qualitative analyses of the written responses show that both groups of students began integrating multiple scales (organismal, cellular, & molecular) when explaining ecological phenomena. Of equal importance, however, is the insight the data provide about concepts that were particularly difficult for students to learn (e.g. that matter does not turn into energy, or that cellular respiration occurs in all living organisms). Further, students grappled, often unsuccessfully, with how to connect macroscopic processes like photosynthesis with small-scale cellular changes that involved the rearrangement of atoms and molecules during various types of transformation. These findings provided insight into next steps for instruction; we need to continue to find ways to help students use atomic-molecular accounts to explain macro-level phenomena.