Cell biology was developed from Cytology, which is a study of cell structure and function (especially chromosomes). Modern-day Cell biology studies the structure, function, and life activities of cells from different levels, such as the micro level, ultra micro level, and molecular level. Cells can be devided into two fundamental classifications, prokaryotic and eukaryotic cells. They are different from cell nucleus and other organelles. Study of the componment and working mechanism of cells is important for us to know better of organic organism.