Systems Modeling with Bottle Biology
Hedi Baxter Lauffer
Director, Wisconsin Fast Plants® Program
University of Wisconsin, Madison
COO, Wisconsin Energy Institute
Systems thinking and the science and engineering practice of modeling are now in the foreground of learning expectations as defined by the Next Generation Science Standards (NGSS). For many of us, supporting students to understand what a system is and integrating systems thinking explicitly into our learning outcomes will require some adjustments. Similarly, many of us will need to make some revisions to or adopt new lessons to prepare students to engage in the modeling practices that are described in the NGSS Performance Expectations. In this article, we describe and give specific examples of how tried-and-true Bottle Biology ecosystems investigations can effectively support both systems thinking and modeling practices.
Bottle Biology is an inventive program with ideas and instructions for using recycled plastic bottles to construct various systems—modeling some aspect of nature—that came out of the Wisconsin Fast Plants® Program at the University of Wisconsin, Madison. How a bottle system is constructed depends on what portion of an ecosystem is to be modeled, and the decisions that need to be made when deciding what kind of bottle system to construct hold important lessons about systems thinking.
Construction of a model system
Consider the following Bottle Biology example in which a bottle system is constructed to model a forest ecosystem. Modeling parts of a forest ecosystem can be a useful way to learn about the cycling of matter and flow of energy among living and non-living parts of an ecosystem, a middle school life science NGSS Performance Expectation. Before beginning to construct a 3-D model with bottles, it must be decided what aspects of the forest ecosystem will be included (and what will not). This is true for the construction of any model system—theoretical, mathematical, or graphical. Defining the boundaries of the system is a foundational step in systems thinking. For example, an investigation could focus on the cycling of matter and flow of energy that occurs on the forest floor, in which case the system model could be a Decomposition Column that defines the system to include only the leaf litter layer of the forest floor plus the atmosphere in the 4 inches above ground level. Alternatively, the system could be defined to include the herbaceous plants that grow beneath the forest's trees, in which case the bottle system would need to include both the leaf litter layer and growing plants. In both of these examples, additional decision making follows to define the system. For example, will the system include soil microbes, earthworms, etc., and why or why not? Each decision depends on the question(s) driving the investigation and the constraints that define the system model.
Once the physical model system is constructed, it can then support the more abstract conceptual modeling work that needs to be done to explain the relationships among the system's elements. For example, middle school students learning about the carbon cycle need to explain the relationships that involve the transfer of carbon in their model systems. This conceptual modeling will require that students go beyond explaining what is directly observable at the macroscopic scale; an accurate model of the carbon cycle will need to account for matter movement and transformations that take place at the molecular and atomic scale. However, using the physical model system as a starting point affords all students a common experience with and frame of reference for the conceptual modeling that includes matter and processes that cannot be seen. In this way, a Bottle Biology growing system can support students to think across scales (a Crosscutting Concept in the NGSS) while engaging in the practice of modeling.
Another important consideration in system modeling involves recognizing how the model is like and unlike the natural system being modeled. Back to the example of modeling a forest ecosystem to learn about the cycling of matter and flow of energy: a closed bottle system could be constructed by adding a bottle top on the decomposition column or it could be left open. A closed system would make it possible to observe condensation that would result from the water generated by decomposers respiring; however, the limited flow of oxygen into the system would also limit how well the system models decomposition in nature. In this way, every decision about how to construct and bound the system effects how the model is useful. This is an important lesson to be learned about scientific models. George Box, a famous statistician, summarized this aspect of modeling by saying, "Essentially all models are wrong, but some are useful." Understanding this about models is a learning target that is described in the Framework for the NGSS, with the most sophisticated goal being for students by 12th grade to "Discuss the limitations and precision of a model as the representation of a system . . . " (page 50). In working towards that learning goal—even during elementary years—we need to find ways for students to identify the trade-offs and affordances associated with different ways of modeling natural systems.
The TerrAqua Column is a good example of a bottle growing system that can be customized by teachers and/or students to model different aspects of a natural ecosystem. A TerrAqua Column can be constructed to have a variety of different boundaries with input/output variables selected according to different investigation questions. Interconnected bottles can be assembled into an open or closed system, optionally including:
- Aquatic components (modeling surface or ground water or rain)
- Various soil types and layers
- Plant and other biotic components
- Abiotic environmental variables (temperature, light, contaminants, etc.)
Wisconsin Fast Plants® are particularly well suited for use as a model photosynthetic organism in a TerrAqua Column system. Such a model system could be used by students at the middle school level to investigate the Disciplinary Core Idea that "Organisms, and populations of organisms, are dependent on their environmental interactions both with other living things and non-living factors" (MS-LS2-1). At the same time, students can be learning Science and Engineering Practices that include developing and using models to describe phenomena (MS-LS2-3) and engaging with multiple Crosscutting Concepts. Similar clusters of modeling Practices, Disciplinary Core Ideas, and Crosscutting Concepts at the elementary and high school levels can be supported with lessons that include constructing model systems using Bottle Biology basics.
The possibilities for system modeling with recycled bottles are virtually endless. You and your students can unleash your curiosities and creativity, building on the bottle basics that are explained on the Bottle Biology Web site and in the Bottle Biology book. In addition to supporting system-modeling-related learning, Bottle Biology's reliance on readily available, recycled materials opens the door for creating lessons in which students engage in engineering practices, inventing and developing new growing system solutions. Though the NGSS are new and Bottle Biology has been in classrooms for over 25 years, the alignment is tight between the foundational ideas on which Bottle Biology was built and the learning goals that are described in our new standards.