Computer Simulation Modeling Using STELLA
to Enhance Investigative Learning in a Biology Curriculum

Steven K. Rice, Grant E. Brown and R. Paul Willing
Department of Biological Sciences
Union College
Schenectady, NY 12308

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RECOMMENDATIONS FOR USING STELLA IN BIOLOGY COURSES

combining modeling with experiments enhances investigative labs. Students report that the modeling helps them understand complex processes like photosynthesis by helping them visualize and explore how the various parts of the process interact. In addition to recognizing the value of the modeling, the majority of students find the exercises enjoyable. However, the perceived value is related to the difficulty the students had in constructing and parameterizing the models. We suggest the following guidelines for educators seeking to incorporate such modeling exercises into their laboratory courses.  Following the guidelines, we present an example of how we have implemented this in a laboratory experience in photosynthesis (link).

1. Use simple models that relate clearly to the laboratory in terms of either content or process.

2. Have students work in groups of 2-3. In larger groups, some students fail to engage in the modeling process.

3. Restrict modeling exercises to less than two hours.

4. Structure the experiences to begin with an individual component of a larger model. Introduce modeling techniques by demonstrating how a model of the component can be constructed, parameterized, and its dynamics explored. Present a modeling problem that students can solve using this component as a starting point. Relate the results to the experiment.

EXAMPLE: LIMITATIONS ON PHTOSYNTHESIS

Students are introduced to STELLA modeling by generating a simple model of diffusion of carbon dioxide from the atmosphere (the cloud) to the chloroplast (Ci).   In this example, model inputs are: Ca = ambient [CO2] which starts at 360 ppm; Ci = internal [CO2] which can begin at 50 ppm; g = conductance; diffusivity = 1.56 m2 s-1; diffusion = 1.56 * g * (360 - Ci).   Students explore dynamics with 0 < g < 1 mol m-2 s-1.

Students add complexity and realism to their simple model.  This can be done as an open-ended exercise that is later parameterized using published data, or as a structured one that assists students with the model complexity.  Ths model shown is taken from Collatz et al. 1991. Agric. For. Meteorol. 54: 107-136.

Students explore the model dynamics under conditions of light and carbon dioxide limitation.  These results are then compared with light response curves for C3 and C4 plants which are generated in the laboratory using gas exchange equipment.