Body is made up of numerous cells. The cell are smaller in size according to their function and location. Division of labour may be at cellular, tissue, organ and organ system level. It gives high degree of operational efficiency. The cell sizzes ranges from 5um to 100mm. The cell have capacity to regeneration. Growth is the result of the cell division of cell multiplication. Different cells are specialized to perform different functions.
Only outer cells are specialized to face the environment. Inner cells are devoted to other functions. Lifespan is long due to limited load of work for each cell type. Certain specialized cells lose power of division. The capacity of regeneration decreases with increasing specialization. Cells have a double role. One for themselves and other for the organism.