Today, Atticus and I completed a lab activity which illustrated how the cell membrane is semipermeable. Our lab activity consisted of placing a wire mesh segment over a bowl, and pouring nuts/seeds of various sizes over the mesh to see how size and shape affect the nuts'/seeds' ability to penetrate the "membrane". This principle applies to the cell membrane being semipermeable. Only materials (proteins/ions/minerals) of certain sizes and shapes may penetrate the cell membrane. He recorded his observations and inferences in his workbook.