Cell membranes are mainly elastic, translucent membranes composed of phospholipids and are 8-10 nm thick. For animal cells, the outer side of the membrane is in contact with the external environment and its main functions are selective exchange of substances, absorption of nutrients, excretion of metabolic wastes, and secretion and transport of proteins. The main functions are the following six aspects: i. separation, formation of cells and organelles, providing a relatively stable internal environment for cellular life activities, the area of the membrane is greatly increased, improving the biological functions that occur on the membrane; ii. barrier effect, water-soluble substances on both sides of the membrane cannot pass freely; iii. selective material transport, accompanied by energy transfer; iv. biological functions, the main hormone action, enzymatic reactions , cell recognition, electron transfer, etc.; v. Identification and information transfer functions, mainly dependent on glycoproteins; vi. Material transport functions, material exchange between the cell and the surrounding environment, achieved through the transport function of the cell membrane.