Many plants are pollinated by insects and vertebrates e. Margulis' original hypothesis proposed that aerobic bacteria that require oxygen were ingested by anaerobic bacteria poisoned by oxygenand may each have had a survival advantage as long as they continued their partnership.
Oxygen, released as a byproduct, began to accumulate in the atmosphere. Despite their many similarities, mitochondria and chloroplasts aren't free-living bacteria anymore.
A compelling case for an endosymbiotic origin has always been easier to make for the plastid than for the mitochondrion. But P. The fossil record indicates that the first flowering plants had primitive flowers.
Abbreviations used:. In addition, it is unlikely trnE could be replaced by a cytosolic tRNA-Glu as trnE is highly conserved; single base changes in trnE have resulted in the loss of haem synthesis.
Secondary Endosymbiosis Primary endosymbiosis involves the engulfment of a bacterium by another free living organism.