Demonstrating and modeling changes in ecosystem processes in the laboratory classroom can be logistically difficult and expensive. This complexity often leaves little time for students to generate and test hypotheses. Yet, we must foster student understanding of how matter and energy move through ecosystems to develop an appreciation of how current ecosystems function and how human-mediated global change may alter ecosystem processes. In this lesson, we describe an adaptation of the Tea Bag Index (TBI) that provides students with an inexpensive, adaptable, and easily replicated method for testing how an ecosystem function (i.e., decomposition by microorganisms) alters carbon flow between two carbon pools (i.e., dead organic matter and the atmosphere). We outline the steps that small student research groups can take to develop testable research questions with an emphasis on how abiotic factors (e.g., temperature, moisture availability) can influence the rate of biomass loss. We outline the equipment and methods that can be used for conceptual add-ons (e.g., CO₂ gas analysis) and include exercises that work on teaching students principles of tidy data organizing and data analysis. Finally, we include rubrics for written and graph-based assignments and an example dataset to assist instructors in implementing the lab in their own courses. In post-lab evaluations, students reflected positively on this lab exercise in open-ended course evaluation prompts and we observed better quality data collection and analysis in subsequent experimental labs, likely motivated by the practice and guidelines provided in this lab module.

Primary Image: The biomass of dead plants as an energy source for multiple decomposers. Dead organic matter is a rich energy source for those fungi and bacteria that can break down cellulose. In this picture, multiple species of fungal decomposers work to break down a fallen log in Mt. Spokane State Park (Washington, USA). One species of Xeromphalina fungi (Division: Basidiomycota; Class: Agaricomycetes) has derived enough energy from decomposition to produce a fruiting body (dusky orange caps and stems) that this fungus will use to spread its spores. Photo Credit: Brian Connolly.

Using analogies is a standard practice for both teaching and communicating ideas in science. Here we upend the traditional lesson, where the instructor provides a fully constructed analogy and explains it, by having the students develop a complex analogy themselves. This high engagement, peer learning activity engages students in critical thinking and analogical reasoning to foster deeper understanding of molecular processes and their interconnection. In this lesson, groups of students are asked to relate given items to DNA and to decide which level it best represents (nucleotide, gene, chromosome, or genome). Next they are tasked with extending the analogy to include other actors in the central dogma of molecular biology (RNA, protein, polymerases, ribosomes, etc.), and then to extend it even further (introns/exons, mutations, evolution, etc.). Finally, each group presents their analogy to the class, and they evaluate each other. We provide multiple examples of items that can be used in the activity, but others can be identified with some creativity. This exercise is also an excellent tool for instructors to discover where their students have gaps and need help making connections to bridge their understanding of processes in molecular biology.

Primary Image: Items to compare to DNA. Is each most similar to a gene, a chromosome, or a genome?