Living things has emerged into three domains called Archaea, bacteria, and eukaryotes. Evident that support the idea that multi cellular that is eukaryotic cell evolved from the prokaryotic cell are the descendents of the separate prokaryotic cells that together form a union which are inter dependent.
For example: The mitochondria which is referred to the energy source of the cell is considered as the great-great-great-granddaughter of a bacterium cell which is free living. This free living bacterium bacterial cell was consumed by an other cell and this remained as the stable guest in the cell. This mitochondria provided chemical energy to the cell and also protected the nutrient rich environment. which surrounds it. This process of one organism residing in the other organism completely is called endosymbiosis.
