Eukaryotic cells have a nuclear membrane, which is of great significance in the history of evolution. As the boundary membrane between the cytoplasm and the nucleus, the nuclear membrane plays a very important role in stabilizing the morphology and chemical composition of the nucleus. The main functions of the nuclear membrane are as follows. 1． Barrier effect. The nuclear envelope is part of the "membrane system" found throughout cells. One of its special functions is to concentrate nucleic acids, especially DNA, in the nucleus. 2. Controls the exchange of information and materials between the nucleus and cytoplasm. The main points are as follows. (1) Ions and water molecules can pass through the nuclear membrane freely. However, it has a certain barrier effect on certain ions (such as Na+), but it is not an active transport process. (2) Small molecular substances such as monosaccharides, disaccharides, amino acids, dyes, nucleosides, nucleotides, protamine, histones, RNase and DNase can freely pass through the nuclear membrane. (3) Exchange of macromolecules and small particles: Macromolecules such as gamma globulin, albumin, etc. must pass through the nuclear pore when entering and exiting the nucleus. 3． The role of the nuclear envelope in chromatin (body) positioning and cell division. (1) Chromatin terminal filaments are often connected to nuclear pores. This could help explain why very complex chromatin does not become disordered in hyperactive cell nuclei. (2) When cell division begins, chromosome aggregation may begin at the nuclear membrane and then develop from the outside inward. During prophase or early metaphase, the nuclear membrane is fragmented. These fragments may join the microtubule components attached to the nuclear membrane and promote their growth, thereby positioning and separating the attached chromatids. When cell division is completed, the nucleus of the daughter cell is rebuilt, and the nuclear membrane is regenerated or restored, it may have the effect of centering the nucleolus and tending to the central position. 4. The role of the nuclear envelope in nuclear fusion. When the egg cell is fertilized, the nuclear membranes of the sperm and egg cells can recognize and contact each other, connect to each other at more than one location, and then fuse with each other to form a nucleus. 5. The nuclear envelope has certain biosynthetic functions. Ribosomes are attached to the surface of the outer nuclear membrane so that protein synthesis can proceed. A variety of structural proteins and enzymes are present in the perinuclear cavity, which also synthesizes small amounts of membrane proteins, lipids, and histones. Some people also reported that the nuclear membrane has sugar synthesis