Explanation

A multicellular organism is composed of numerous cells. The cells are of three main types (i) Undifferentiated or Stem Cells They are unspecialised cells which usually possess the power of division, e.g., stem apical meristem, root apical meristem, vascular cambium, cork cambium, stratum germinativum of skin, germina epithelium, bone marrow, etc. Zygote is also an undifferentiated cell (ii) Differentiated or Post-mitotic Cells The cell are specialised to perform specific functions. Differentiation occurs in shape, size, structure and function through an orderly switching on and off of some particular genes of the cells by means of chemicals named as inducers and repressors. It leads to better organisation, division of labour and higher efficiency. Duplication of work is avoided (iii) Dedifferentiated cells They are differentiated cells which revert to undifferentiated state to take over the function of division. The process by which they lose their specialisation is called dedifferentiation. It involves reactivation of certain genes that prevent differentiation, allow limited growth and induce division. Cork cambium of plants is always produced through dedifferentiation. Dedifferentiation helps in healing of wounds, regeneration in animals, or vegetative propagation in plants. Cell culture experiments are based on this dedifferentiation of cells