Multicellular organisms are made up of many cells, ranging from hundreds to trillions, depending upon the complexity of the organism structure. All these cells perform specific functions. All the cells specialised for performing similar functions are grouped together as tissues in the body. Hence, a particular function is carried out by a group of cells at a definite site and by definite tissues in the body. Similarly, each type of tissues are differentiated to perform specialised functions. This phenomenon is known as division of labour in multicellular organisms.