Cell differentiation refers to the normal process by which a less specialized cell goes through development and maturation in order to become more distinct in terms of form and function. It is the process in which a cell changes into another cell type. During cell differentiation, the changes may include cell shape, cell size, membrane potential, metabolic activities, and responsiveness. These changes are brought about by modifications in gene expressions. An example of cell differentiation is the development of a single-celled zygote into a multicellular embryo that further develops into a more complex multisystem of distinct cell types of a fetus. The cell size, shape, polarity, metabolism and responsiveness to signals change dramatically such that a less specialized cell becomes more specialized and acquires a more specific role. A cell that underwent differentiation is described as differentiated. A differentiated cell means a cell that has changed in form and matured from being generalized into being more specific in terms of function. The term undifferentiated is used to describe a cell (or a tissue) that has not yet acquired a special structure and function. An undifferentiated cell therefore would be a primitive cell or a progenitor cell that is yet to undergo cellular differentiation.