During the germinal period of prenatal development, some cells become part of the brain, some become part of the leg, some become part of the stomach, and so on. the term for this process is

Multicellular organisms accomplish this by designating particular functions to particular cells. This allows different cells to work together to maintain homeostasis within a larger organism. Unicellular organisms do not need cell specialization to maintain homeostasis because they are only made up of ONE type of cell.