A multicellular organism is comprised of many cells which have varying degrees of specialization and individualization as the life forms reach higher levels of complexity. Some cells become efficient at one particular task. Multicellular animals require organs to carry out vital functions, such as digestion, communication between cells and relating to the environment. The point of various organ systems is to ensure the survival of cells within a body.
BBC Science explains that all animal and plant life starts as a unicellular organism, such as a fertilized egg, seed or spore. This one-celled object multiplies repeatedly until the life form has all of its cells necessary for life. A life form's genetic material, or genome, determines what pattern the cells take.
A multicellular organism is formed by proliferation, specialization, interaction and movement among cells. Proliferation refers to producing many cells from one source. Specialization creates cells with different characteristics to perform certain jobs. Interaction coordinates the behavior of one cell to another. Movement among cells rearranges these biological parts to form tissues and organs.
According to the National Center for Biotechnology Information, a study published in the Journal of Evolutionary Biology explains that larger life forms create specialized cells more readily than life forms with fewer cells. Therefore, evolutionary steps and mutations are more easily accomplished in life forms with more cells; and, the survival of the species is more likely when specialized cells are created.