The purpose of this activity is to help students understand passive transport in cells (i.e., diffusion and osmosis) and how the size of a cell can impact the time it takes for important molecules to diffuse through a cell. This activity also helps students learn how to engage in practices such as using planning and carrying out investigations, arguing from evidence, and communicating information. This activity, in addition, is designed to give students an opportunity to learn how to write in science and develop their speaking and listening skills.