Primary endosymbiosis

Primary endosymbiosis is the evolutionary incorporation of a cyanobacterium into a eukaryotic cell, producing a plastid enclosed by two membranes and the descendants of that plastid.

Cyanobacteria: A phylum of bacteria that performs oxygen-producing photosynthesis using chlorophyll a. A cyanobacterium supplied the photosynthetic machinery that became the primary plastid.
Archaeplastida: A eukaryotic supergroup comprising glaucophytes, red algae, green algae, and land plants. Its members share plastids generally traced to primary endosymbiosis.
Endosymbiosis: A close association in which one organism lives inside another organism. Primary endosymbiosis is a particular evolutionary outcome of an internal partnership.
Photosynthesis: The process by which organisms use light energy to convert carbon dioxide and water into organic compounds, releasing oxygen in oxygenic forms. Primary plastids enabled photosynthesis in major eukaryotic lineages.
Phagocytosis: A cellular process in which a cell engulfs particles or other cells into membrane-bound compartments. Engulfment offers a route by which an ancestral eukaryote could take up a cyanobacterium.
Glaucophytes: A small group of freshwater algae whose plastids retain peptidoglycan between their two envelope membranes. Their unusual plastid envelope preserves a clue to bacterial ancestry.
Mitochondrion: A eukaryotic organelle that generates much of a cell’s ATP through aerobic respiration and descends from bacteria. Mitochondria provide a parallel example of bacterial ancestry within eukaryotic cells.
Secondary endosymbiosis: The incorporation of a photosynthetic eukaryote by another eukaryote, transferring an already established plastid. Primary plastids later spread to additional lineages through engulfment of algae.
Plastid: A plant or algal organelle descended from an endosymbiotic bacterium, with roles including photosynthesis and storage. The plastid is the organelle produced by the incorporation event.
Red algae: A diverse lineage of photosynthetic eukaryotes with plastids containing chlorophyll a and phycobilin pigments. Red algae represent one major branch carrying primary plastids.

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