The structural and functional characteristics of the cell membrane are, respectively, a certain fluidity and selective permeability. The phospholipid molecules and protein molecules that make up the cell membrane are not static, but can move relatively, so the cell membrane has a certain fluidity in structure. The cell membrane allows water molecules to pass freely, and the ions and small molecules that the cell wants to selectively absorb can also pass through, while other ions, small molecules and macromolecules can not pass through, so functionally the cell membrane is a selective permeability membrane. And the function of the cell membrane is to maintain a certain form of the cell, the cell plays a protective role, the living cells continue to carry out the metabolism, not only from the surrounding environment in the intake of essential nutrients as well as oxygen, but also can be discharged metabolites, the exchange of substances inside and outside the cell must be through the cell membrane.