It does so because there are some molecules in the surface of the membrane that allow glucose to move in and out.

而这个过程的完成依赖于,膜表面存在的一些分子,这些分子能够将葡萄糖运进或者运出细胞

耶鲁公开课 - 生物医学工程探索课程节选

Well, the way that your immune system recognizes it is that all the cells of our body express a molecule on their surface, a membrane protein called the MHC1 complex.

而免疫系统识别的方法是,身体内所有细胞在其表面表达一种分子,一种叫做MHC1复合体的膜蛋白

耶鲁公开课 - 生物医学工程探索课程节选