To gain expertise in a field is to recognize, understand, and effectively use underlying disciplinary principles. Too often students rely on rote memorization rather than principle-based reasoning to solve problems. These students list the steps in water transport or stomatal opening but cannot reason to a correct prediction when changes are introduced in the system, e.g. when drought or fusicoccin toxicity occur. A learning progression helps us understand how students’ mental models of key principles are refined and strengthened over a curriculum. Our goal is to develop a learning progression to describe how students reason about the fundamental physiological principle of flux (movement of a substance is directly proportional to the size of the gradient and inversely proportional to the resistance).
To develop our learning progression, we used interviews and short-answer questions to solicit explanations and predictions in six contexts: plant tropisms, plant transport, neuromuscular, renal, cardiovascular, and respiratory physiology. We interviewed 90 students and collected short-answers from 2500 students ranging from freshman to seniors. We used a constant comparative approach to uncover emerging patterns of reasoning.
Results/Conclusions
We propose the following learning progression: Lowest level, L1: Provide explanations that tell stories in a non-mechanistic way that often contain teleological, anthropomorphic, or “these things move like this naturally” ideas. L2: Begin using principle-based reasoning but with errors. When explaining or predicting movement of a substance, students include gradients or resistance ideas inappropriately, incompletely and/or with errors. L3: Use principle-based reasoning with non-interacting components. Students constrain their explanations or predictions of material movement by using gradients (e.g., electrical & chemical) and variation in resistance independently without integrating them. L4: Use principle-based reasoning that considers interacting components. Students constrain their explanations or predictions of material movement by identifying and qualitatively integrating the impact of all gradients (e.g., electrical & chemical) and all variation in resistance. Upper level, L5: Use principle-based reasoning that fully considers the interacting components and threshold values. In addition to the impact of all gradients (e.g., electrical & chemical) and all variations in resistance, students quantitatively reason about threshold values when determining changes in flux (e.g., students use equilibrium potential to make predictions about the direction of ion movement). This learning progression will afford faculty insight into how students physiology reasoning develops. This insight can inform their ecophysiology course design to better support students’ learning.