Endosymbiosis is a relationship where one organism lives inside the other and both are benefited. It is thought that ancestral eukaryotic cells consumed aerobic bacteria and photosynthetic bacteria leading them to evolve into mitochondria and chloroplast respectively. Endosymbiotic theory stats that, the modern eukaryotic cells (mitochondria ) evolved in steps through inter-cooperation into cells from a nuclear line of descendants of chemoorganotrophic and phototrophic symbionts. It states that Mitochondria and Chloroplast were free-living bacteria that established residency in the primitive eukaryotic cells, eventually yielding the modern eukaryotic cell. Symbiosis is a specific type of relationship in which organisms from two different species live in a close, dependent relationship take advantages from each other.