User:Opisthokonte/sandbox

Relationship to chloroplasts
Primary chloroplasts are cell organelles found in some eukaryotic lineages, where they are specialized in performing the photosynthesis. They are known to have evolved from cyanobacteria through endosymbiosis, i.e. after the engulfment of a cell by another - in this case, a photosynthesizing cyanobacteria that was engulfed in some ancient eukaryotic cell. After some years of debate, it is now generally accepted that the three major groups of primary endosymbiotic eukaryotes (i.e. green plants, red algae and glaucophytes) form one large monophyletic group called Archaeplastida, which evolved after one unique endosymbiotic event. The morphological similarity between chloroplasts and cyanobacteria was first reported by German botanist Andreas Schimper in the XIX th century, thus paving the way for Russian biologist Konstantin Mereschkowski to suggest the symbiogenic origin of the plastid in 1905. Lynn Margulis brought this hypothesis back to attention more than 60 years later but it was not until supplementary data started to accumulate than the idea became fully accepted. The cyanobacterial origin of plastids is now supported by various pieces of phylogenetic , genomic , biochemical  and structural evidence. The fact that another independent and more recent primary endosymbiosis event has been described between a cyanobacterium and a separate eukaryote lineage (the rhizarian Paulinella chromatophora) also gives credibility to the endosymbiotic origin of the plastid. In addition to this primary endosymbiosis, many eukaryotic lineages have been subject to secondary or even tertiary endosymbiotic events, that is the "Matryoshka-like" engulfment by a eukaryote of another plastid-bearing eukaryote. Within this evolutionary context, it is noteworthy that, as far as we can tell, oxygenic photosynthesis only evolved once (in cyanobacteria), and all other photosynthetic eukaryotes (including all plants and algae) have acquired this ability from them. In other words, all the oxygen that makes the atmosphere breathable for aerobic organisms originally comes from cyanobacteria or their later descendants.