https://learn.concord.org/resources/760/diffusion-across-a-semipermeable-membrane
( http://lab.concord.org/embeddable.html#interactives/sam/diffusion/4-semipermeable.json )
Explore the role of pore size in the diffusion of a substance across a membrane. Diffusion is the process of a substance spreading out from its origin. Molecules diffuse through random molecular motion. Diffusion is always happening, even when a system appears to have reached equilibrium, because molecules are always moving. Cells are selectively permeable, meaning that their membranes allow some substances to cross easily while others are unable to cross without assistance. Cell membranes are selectively permeable, in part because its pores are small, allowing the cell to prevent larger molecules from moving across the membrane.
This activity runs entirely in a Web browser. Preferred browsers are: Google Chrome (versions 30 and above) Safari (versions 7 and above), Firefox (version 30 and above), Internet Explorer (version 10 or higher), and Microsoft Edge.
Performance Expectations
From Molecules to Organisms: Structures and Processes. Students who demonstrate understanding can: Develop and use a model to describe the function of a cell as a whole and ways parts of cells contribute to the function.
From Molecules to Organisms: Structures and Processes.