INSTRUCTOR GUIDE

IMPLEMENTATION

Duration:  2 sessions of 2 hours per session.

Equipment required:  Computers / software

Specific equipment needed:  The labs described in the next section take place in this unit cameras, light box (can be a laptop screen), microscopes, petri dishes, pipettes, agarose gel, dye, running buffer for electrophoresis, micron-size polystyrene beads. Optional, bacteria from spoiled milk.

Basic implementation tips & tricks:  This material challenges the students in a number of ways. 1) Probability has been operationally introduced in high school, but not as a model-building tool. 2) diffusion of a gas and Brownian motion of individual particles are the same thing. 3) Understanding requires flexible and facile movement between mathematical, graphical, and descriptive representations. 4) Predictions are made from statistical principles - this is counter-intuitive. 5) These ideas are important building blocks for thermal physics and biophysics.

How does this resource fit into the flow of your course?  Presentation immediately follows the discussion of the mathematical formalism and foundations for probability. Students are challenged to relate ideas and models based on coin flips, for example, to molecules diffusing through cells. The unit on diffusion is followed by entropy and thermodynamics. The statistical ideas bridge from a single particle dynamics driven by deterministic forces to stochastic motion of large numbers of particles.

PEDAGOGY

Pedagogical approach:  Peer Instruction / Think-Pair-Share; Collaborative problem-solving; Conceptually-oriented activities; Context-rich problems; Ranking tasks; SCALE-UP / studio / workshop physics; Mathematically-focused activities; Experimentally-focused activities

Skills / Competencies:  Dimensional analysis; Functional dependence; Multiple representations; Estimation; Intuition building; Building models; Evaluating models; Error and uncertainty; Designing experiments; Performing experiments; Analyzing experimental data; Applying physical principles; Interdisciplinarity; Metacognitive skills

What insights or realizations do you hope students gain from this resource?  That motion at the molecular motion is random, driven by forces between colliding molecules. Diffusion is slow, scales with the square root of time and is not directed. Even so this mechanism is efficient and leads to Brownian motion and diffusion. These are very different looking manifestations of the same phenomena. The sublinear time dependence means that diffusion is impractically slow at even moderate distance (larger than 10 microns, the diameter of a cell). These are important aspect buried in the mathematical representation, so they need to be emphasized.

Why is this resource useful to life sciences students?  Diffusion is biologically important because it harnesses the the thermal energy that is inherent to deliver nutrients, oxygen, and biochemical messengers to cells. In situations where directed motion is needed, other transport mechanism (molecular motors) are invoked. However, in the limiting cases where directionality is not important or distances are short enough that the sublinear time dependence is not an impediment.

DISCUSSION

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SUBMISSION DETAILS

Copyright:   2021 Mark Reeves, Phoebe Sharp, Pi Nuessle, Rachael Stewart, IBET RAMIREZ-URREA

License:   CC: BY-NC-SA - Attribution, No Commercial uses and Share Alike. Derivative works must have the same license

Last Edit Date:  June 29, 2021

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