The cell is the basic unit of living organisms; while some organisms are made up of a single cell (bacteria, protozoa) others are made up of many cells, organised into tissues and organs that perform specific functions. Individuals cells in human and other eukaryotic organisms are organized into functional areas-organelles-that perform a specific function. Cells usually divide by mitosis to produce identical daughter cells to allow the development of issues or the replacement of dying cells. However, for the purpose of reproduction, they divide by meiosis in which the daughter cells each possess half a full set of chromosomes. In developed tissues, mitosis occurs to replace those cells that have become damaged; if such cell division occurs in an unregulated fashion, cancer may result.
The cytology or cell biology is a biological science which deals with study of cells from morphological, biochemical, physiological, development, genarical, pathological and evolutionary poin of views. Recently, it has shown rapid progress and has become fundamental in the study of structure and function of living organism and the anatomic and physiologic substract of biologic phenomena. In its morphological aspect, modern cell biology has gone beyond simple description of structures visible to the light microscope; by the application of new methods, an analysis has been started of sub-microscopic organizations-the architectural arrangements of the molecules and miscalls comprising living matter.
In the functional aspect, it has transacted the stage of pure description of Physiologic changes and seeks an explanation of them in the intimate physic-chemical and metabolic processes of protoplasm.