Human cells are all eukaryotic cells, which are composed of cell membrane, cytoplasm and nucleus. There are a large number of membrane structures on the cell surface and inside the cell, which are collectively called biofilm and have similar structural characteristics. The membrane existing on the outer surface of cells is called extracellular membrane or cytoplasmic membrane, commonly known as cell membrane; The membranous structure in cells is called intima or intima system. Cytoplasm consists of organelles such as amorphous matrix, ribosome, rough endoplasmic reticulum, smooth endoplasmic reticulum, mitochondria, Golgi complex, lysosome, microsome, centrosome, cytoskeleton, and inclusions such as lipid droplets, glycogen and lipofuscin. The nucleus is the center of cell metabolism and genetic control, and plays a decisive role in cell life activities. A cell usually has only one nucleus, some cells have multiple or even dozens to hundreds of nuclei, and some terminal cells have no nuclei. The size of the nucleus varies greatly, which is related to the volume of cytoplasm.
The nucleus of most cells contains chromatin, which is the material basis of human inheritance. Some characteristics of human body are reduced to deoxyribonucleic acid (DNA) molecules and passed down from generation to generation. Chromosomes can only be seen during cell division, when chromatin spirals into short and thick condensed chromosomes. The human body has 23 pairs of chromosomes, of which 22 pairs are called autosomes, which determine various characteristics of the body. By inheriting the characteristics of both parents, the children born are somewhat like their parents. There is also a couple who decide the sex of the child.