If a cell membrane was indeed just a lipid bilayer, then glucose could never enter the cell because it can't permeate through cell membranes.

如果细胞膜只是一个脂质双分子层的话,葡萄糖就不可能进入细胞,因为它不能渗透过细胞膜

耶鲁公开课 - 生物医学工程探索课程节选

Now, sodium and potassium don't ordinarily move across membranes, they're charged molecules, they can't dissolve, they can't permeate through a cell membrane, but they go through because there are channels that allow them to pass through in the membrane.

钠和钾通常是不能跨过细胞膜的,它们都是带电粒子,它们不能溶解在细胞膜中,不能渗透通过细胞膜,但它们之所以能通过细胞膜,全赖膜上离子通道的作用

耶鲁公开课 - 生物医学工程探索课程节选