Because of that they're barriers, they separate the inside of the cell from the outside of a cell, and only certain kinds of molecules can pass through a cell membrane.

因为它们的屏障作用,将细胞内外区隔开来,只有特定的,某些分子才能穿过细胞膜

耶鲁公开课 - 生物医学工程探索课程节选