Demonstrate the ratio of surface area to volume in your high school class by using phenolphthalein, gelatin, and an onion. Intrigue the class by leading a discussion on osmosis and diffusion, then making "scientific jello." Participants note the changes before and after the addition of sodium hydroxide.

Concepts

surface area, volume, cell membranes

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Additional Tags

science

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Instructional Ideas

• Relate the activity to an organ system in the body, such as the urinary system and kidney function

Classroom Considerations

• Phenolphthalein is flammable and may explode; take proper care and ensure participants follow all safety measures
• Class members should complete "The Parts of an Experiment: Introduction to Inquiry and the Scientific Process" prior to this activity

Pros

• Multiple parts of this activity allow time in between to discuss results and answer any questions before moving to the next phase
• Participants can design an experiment, as an extension to this activity, to demonstrate the effect of surface area on diffusion using starch and iodine

Cons

• None