How to teach osmosis and diffusion with agar cubes – a free activity

High School

Why did the oxygen molecule cross the cell membrane? To get to the other side, of course! Ok, that's a little corny, but how cells work is one of the many fascinating natural phenomena that your students will begin to understand when they study diffusion and osmosis.

The cell membrane is the world's greatest border guard. Despite being only 6 to 10 nanometers thick and visible only through an electron microscope, the cell membrane keeps a close watch over what goes in and out of the cell. The cell membrane allows nonpolar molecules (those that don't readily bond with water) to flow from an area where they're highly concentrated to an area where they're less concentrated.

Your students will be fascinated by how many other ways diffusion and osmosis can be found throughout nature. The size of elephant ears, flatworm survival, swollen water-soaked raisins, and plant root systems are just a few examples. Once your students complete this activity, they can have fun trying to think of other examples of where diffusion and osmosis play a role in the real world.

Students can use cubes of agar in this activity to model how diffusion occurs in cells and investigate how size impacts diffusion. Then they'll finally be able to answer that nagging question we all have in the back of our minds "why are cells so darn small?" 

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Ward's® Prepared Agar Cubes 

Making agar cubes can be a time-consuming and messy process. Use these prepared agar cubes that make this activity a lot faster and easier! These cubes are exclusive to Ward's Science and are also included in our AP Biology Investigation kit on osmosis and diffusion.

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Prepared Phenolphthalein Agar

Convenient: no mixing or sterilizing needed.

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Ward's® Timer

Ward's® Timer

Great for classroom activity. Three-button operation: start/stop, lap, and reset. Lap button allows you to stop, take a reading, then press again to continue. Includes battery. Includes a storage case.

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