Cell Membrane Permeability – a Teaching Tidbit from SERSI12

This summer I was privileged to be the facilitator for the Cell/Development group at the Southeast Regional Summer Institute (SERSI), one of 7 replicate progeny of the National Academies/HHMI Summer Institute for advancing undergraduate biology teaching in the nation’s research universities. In an intense, week-long workshop, participants from universities around the Southeast learn the principles and practices of Scientific Teaching (Handelsman et al. 2004). They then apply these principles by developing a Teachable Tidbit, that aligns learning goals and learning objectives, formative and summative assessments, learning activities, and issues of classroom diversity.

My group chose the concept of semi-permeability of cell membranes, for a large-enrollment (>250 students) freshman biology for majors lecture course. This is the tidbit they came up with, with suggestions to how to implement this in the lecture hall.

Cell Membrane Permeability
Group 2- Cell Development
Gladys Alexandre (1), Cristina Calestani (2), John Koontz (1), Silvia Moreno (3), Brian Ring (2), William Said (3)

(1) University of Tennessee; (2) Valdosta State University; (3) University of Georgia

Learning objectives: Students should be able to:

  • Explain the concept of selective permeability.
  • Predict the movement of molecules across the phospholipid membrane based on their structure.
  • Interpret and graph kinetics of molecule transport across a phospholipid membrane.

Learning activities:

It begins with a short demonstrative play – 4 student volunteers are recruited to the front of the lecture hall, in a central location visible to all students. Two students join hands to form a barrier. One student simulating random movement runs into the barrier and bounces off. A second student is allowed passage through the barrier (the students that form the barrier unlink their hands and allow passage). The previous student tries again, and is rejected again by the barrier. The selectivity should be based on any easily distinguishable characteristic, such as gender, color of clothing, etc.

Clicker Question #1 follows the demonstration. This question assesses whether students have read the assigned chapter and can define the concept of selective permeability of phospholipid membranes (Learning Objective #1).

CQ#1: A semi-permeable membrane allows…

  1. Only small molecules to cross.
  2. Only charged molecules to cross.
  3. Certain molecules to enter the membrane but not cross to the other side.
  4. Molecules to cross the membrane until they reach equal concentration on both sides.
  5. Molecules to cross dependent upon their chemical characteristics.

After addressing any student misconceptions revealed by student responses, the students are given the following scenario:

Sally went to the doctor for a fever and she was prescribed a sulfa-drug antibiotic. The doctor and her pharmacist insisted that she took her medication with food.
Sally wonders why.

Why does she have to take the drug with meals?

Let’s find out…

In this group project, students discuss in groups how to categorize the 6 molecules shown in the figure. The instructor should explain that this is a pure phospholipid bilayer (no proteins are shown), the molecules are added to the side at the top, and students should not only decide which molecules cross the membrane fast, slow, or not at all, and write their reasoning. After the allotted time, different groups are called upon to answer which molecules they placed in each category. The discussion should lead to the conclusion that lipids molecules (like estrogen) and small, non-polar molecules (like oxygen) will cross the lipid bilayer rapidly; that small polar molecules (like glycerol and acetic acid at pH 1.5) will cross slowly; and that large polar molecules (like sucrose) or charged molecules (like acetic acid at pH 7) will not cross at all.

Next, students are asked to consider real cell membranes, where 50% of the weight consists of membrane proteins.

In the next slide, students are asked to discuss the question with a neighbor, then answer the question using their clickers. In the table, “+” indicates the compound enters the cell from the outside, and “-” indicates that the compound cannot enter the cell.

Another think-pair-share clicker question asks students to identify which molecule crosses the membrane by simple diffusion, based on the same table.

After discussion of the differences between active transport and diffusion, and the role of transport proteins and channels, students then consider kinetics. How does the mode of transport (active transport, facilitated diffusion, or simple diffusion) affect the kinetics (rate of transport as a function of the concentration difference across the membrane)? This presumes that students have already learned about enzyme kinetics.

In groups, students are asked to plot the kinetics of the transport of each of the molecules from the same table above:

In the presentation to the SERSI participants, observers thought the X-axis would be difficult for students to conceptualize, and would require further explanation. Perhaps the instructor should explain that this is the concentration of the compound added to the outside the cell, when the concentration of the compound inside the cell is zero. The ultimate goal is to get the students to describe and draw saturation kinetics for compound B.

The teachable tidbit then returns to the original question Sally posed:

These figures are all from the attached Powerpoint file, provided with permission from members of the group. The file also contains the test questions (summative assessment) that students should be able to answer as a result of these learning activities and formative assessments.

So this is an example of what one group of faculty produced in the form of a teachable tidbit after 4 days of hard work. They all learned a lot about backwards design, active learning, and scientific teaching. We all agreed that, given how much work it takes to produce even one tidbit, it would be wonderful to be able to share them with each other, and with other instructors. Although all the tidbits, packaged into a Powerpoint, are shared among all the Regional Summer Institute participants in a Dropbox folder, we want a forum where people can comment on tidbits after they try them out, and upload revisions and additions.

So consider this a trial run, with one tidbit. Please feel free to download the materials, try them out in your classes, and provide feedback. If other groups want to share their tidbits on this site, please let me know and I’ll post them, or better yet, allow you to post them as a guest author.

Tidbit-Group 2 Cell Development v7


About jchoigt

I'm an Associate Professor in the School of Biology at Georgia Tech, and Faculty Coordinator of the Professional MS Bioinformatics degree program.
This entry was posted in Teaching and learning biology, Teaching Tidbit and tagged , , , , . Bookmark the permalink.

1 Response to Cell Membrane Permeability – a Teaching Tidbit from SERSI12

  1. Brian Ring says:

    Fantastic! I’m going to use this tidbit this summer. As one of the members of the team, I learned a lot and plan to use Scientific Teaching in my courses. What an enlightening experience! Thanks Jung.

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