Human body is a combination of various organs, each performing specific functions in sync with other organs to keep the entire system functional properly. The organs are formed due to arrangement of various tissues which in turn are composed of a group of similar cells. The cell is the smallest structural and functional unit of life which carries out all the metabolic functions. All the life processes like respiration, growth, energy production occuring in the body are a manifestation of the cellular metabolism. The cells are themselves invisible to naked eyes (about 100-10000 times smaller than the width of hair) but the association of the cells constitute the body of all organisms including humans. Cells require nutrition for producing energy which in turn drives all the metabolic processes of the body. The cells obtain nutrients from the digested food, which is sent to each and every individual cells. A very remarkable property of cells is their ability of self-replication i.e., they divide themselves to produce new cells of their kind; which is undertaken to replace dead or worn-out cells for tissue regeneration.