Diffusion across a Selectively Permeable Membrane

Students investigate the effects of molecule size on diffusion across a synthetic selectively permeable membrane. This investigation includes observation and analysis of osmosis (diffusion of water across a selectively permeable membrane). Additional questions guide students in analyzing the relative advantages of different types of model of the cell membrane.

Download Student Handout: PDF format or Word format

Download Teacher Preparation Notes: PDF format or Word format

The Teacher Preparation Notes provide instructional suggestions and background information and explain how this activity is aligned with the Next Generation Science Standards.

We invite comments on this Hands-On Activity and the accompanying Teacher Preparation Notes, including suggestions for other teachers who are planning to use the activity, useful preparatory or follow-up activities, additional resources or any questions you have related to the activity, or a brief description of any problem you might have encountered. If you would prefer to send your comments or questions in a private message, please write Ingrid Waldron at iwaldron@sas.upenn.edu.

See also a complete list of activities:
Hands-on Activities for Teaching Biology to High School and Middle School Students


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2014 revisions

The revised Student Handout includes clarified instructions for the experimental procedure and improved explanations and questions concerning membrane structure, osmosis, and the use of models to improve understanding of transport across cell membranes. The revised Teacher Preparation Notes clarify the instructions for the experimental procedure.

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2011 revision

The Student Handout has been streamlined and the questions have been focused on the topic of diffusion across a selectively permeable membrane.

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2009 revision


The major change is the addition to the Teacher Preparation Notes of two ways to modify the activity: (1) to focus on osmosis specifically or (2) to help students develop a more sophisticated understanding of how molecules move across biological membranes.


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