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Three Cases from the Membrane Files

The Exploding Fish, the Pleasurable Poison, and the Dangerous Diet


Eric Ribbens
Department of Biological Sciences
Western Illinois University


This PowerPoint-driven case study presents three different stories, each of which explores an aspect of membranes. The first (The Exploding Fish) covers diffusion, specifically addressing the question of why animal cells explode in freshwater but fish do not, and differences between saltwater and freshwater fish. The second case (The Pleasurable Poison) is designed to show that alcohol can slip across membranes and also highlights some of the problems of ingesting this toxin. The third case (The Dangerous Diet) explores a weight-loss drug, DNP, and how it operates in mitochondrial membranes. The first of these case studies also includes a number of "clicker" questions. These cases were originally designed for a semester-long, introductory biology course for non-majors, and instructors can choose to use one or all of the cases to suit their course.

  • Explain the concept of diffusion, both generally and across a semi-permeable membrane.
  • Describe at a basic conceptual level how the mitochondria generate ATP.
  • Apply these principles to the case scenarios to indicate why water balance management is important, why drinking alcohol has such devastating effects on our bodies, and how DNP can disrupt mitochondrial activity.
Keywords: Membranes; mitochondria; semi-permeable; kidneys; alcohol; dinotrophenol; DNP; ATP; diffusion; osmosis
Topical Area: N/A
Educational Level: High school, Undergraduate upper division
Formats: PDF, PowerPoint
Type/Method: Clicker, Interrupted
Language: English
Subject Headings: Biology (General)   Cell Biology  
Date Posted: 7/30/2015
Date Modified: N/A
Copyright: Copyright held by the National Center for Case Study Teaching in Science, University at Buffalo, State University of New York. Please see our usage guidelines, which outline our policy concerning permissible reproduction of this work.

Teaching Notes

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Supplemental Materials

Optional PowerPoint presentation that can be used as preparatory material.

  Optional Pre-class Presentation


The following video(s) are recommended for use in association with this case study.

  Diffusion Across Membranes hhmi/
This four-second animation discusses two types of transport across cell membranes: active and passive transport. Running time: 0.04 min. Produced by HHMI BioInteractive.

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