An ordinary chicken egg allows you to explore the movement of materials into and out of a cell. Instructions explain how to dissolve the shell of an egg. The membrane that surrounds the de-shelled egg is selectively permeable, allowing some substances to pass easily through and blocking the passage of others. By soaking de-shelled eggs in various solutions, you discover what substances pass through the membrane.

The de-shelled egg is a good model of a human cell. This activity introduces diffusion (the movement of particles from an area of higher concentration to an area of lower concentration because of random molecular motion) and osmosis (the diffusion of water across a selectively permeable membrane).