Cells require a constant supply of glucose and oxygen to produce energy. As a result of this process, large quantities of waste carbon dioxide must be expelled from the cell. All materials involved in this reaction are either imported or exported through the cell membrane by diffusion.
In this demonstration, students soak agar “cells” containing phenolphthalein indicator in a solution of sodium hydroxide, NaOH(aq). Students observe the effect of cell volume and surface area on the extent of diffusion of the sodium hydroxide solution through the “cell”.