N1966, american biologist lynn margulis proposed the theory of endosymbiosis, or the idea that mitochondria are the descendants of symbiotic, aerobic eubacteria. what does the theory of endosymbiosis explain?

Endosymbiosis theory claims that aerobic bacteria were taken to the inner side of aerobic cells through the endophagocytosis. Half-digested food molecules are what aerobic bacteria feeds on in the cells of cytoplasm and it receives a high amount of energy and in turn, it benefits the host cell.
Now that both organisms have benefited, they form an endosymbiotic relationship together with the bacteria which evolves into organelles. For example chloroplasts and mitochondria and aerobic cells which are evolved in the eukaryotic cells. Endosymbiosis in important in the life of earth. For example, through endosymbiosis, we have a development of chloroplasts which leads to oxygenation of earth's atmosphere and allows evolution for more complex oxygen for organisms which are breathing, for example, human organisms which are being classified in the same genus, order with DNA sequence and family.
Some observation makes scientist conclude that prokaryotic organisms which are living in the cell of other organisms which are which are evolved from plastids and mitochondria.

Fungi is were it belongs