Diagnostic question clusters (DQC's) improve teaching about decomposition and transformations of nutrients and energy

Background/Question/Methods   At all academic levels, ecology students struggle with misconceptions about transformations of matter and energy. Ecology teachers may be more effective if we recognize these barriers to learning before we teach, then design activities to address them, and finally assess whether student understanding has improved. This study examines students' change in comprehension of the role of decomposers in the cycling of nutrients (matter) and the flow of energy through organisms and ecosystems. I assessed student understanding with diagnostic question clusters (DQC's) in pre- and post-tests. DQC's are groups of questions designed to reveal problems with reasoning due to hidden misunderstandings. Pre-tests indicated that over 80% of students were making basic mistakes in questions about respiration and/or most were thinking of matter and energy interchangeably. For example, over 98% of students believed that “decomposers release energy that is cycled back to plants.” To teach these concepts better, in 2009 I added two active-learning strategies to complement traditional lectures. First, students created a diagram depicting energy flow and carbon cycling among trophic levels, and their diagram synthesized simple images typically found in textbooks. Second, we used a “carousel brainstorm” activity to discuss four posters dealing with energy flow, metabolic heat and carbon cycling.

Results/Conclusions   Post-test scores indicated that the course improved understanding and reasoning, with 50-70% more students correct in post-test questions compared to pre-tests. More importantly, in 2009 the increases in post-tests were 20-50% higher than increases seen in previous courses – courses that lacked the learning strategies developed in response to pre-tests. Despite these gains, however, 20-40% of students still retained important misconceptions, such as the idea that plants get their “energy” from CO2 or from soil nutrients released by decomposers. One source of confusion may be that ecologists typically use the term “nutrients” to include only mineral nutrients and elements that are cycled (i.e., matter), while outside of ecology the same term refers to sources of both matter and energy. In sum, DQC's are valuable tools that can 1) reveal content that needs special attention during a course, and 2) assess effectiveness of learning and teaching strategies.