Definition of Endosymbiosis Theory

Endosymbiosis theory states that a few organelles i.e. mitochondrion and chloroplast which are present in today’s eukaryotic cell once belonged to the prokaryotic microbes. According to this theory, the first-ever eukaryotic cell was like an amoebic cell which used to get its nutrients by the process of phagocytosis. Its nucleus was formed as a result of pinching off of the cytoplasmic membrane.


These cells ingested some prokaryotes that had the ability to survive within and develop a symbiotic relationship. When the bacteria having the capability of respiring aerobically was ingested by the amoebic cell, a mitochondrion was formed. On the other hand, when the photosynthetic bacteria were taken up by the cell, the chloroplasts were formed. Gradually, both the organelles lost much of their genetic material as well as their cell walls.


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