Practice question

Secondary endosymbiosis occurs when a eukaryotic cell that already possesses primary plastid, such as red alga or green alga, is engulfed by another non-photosynthetic eukaryote, which then retains algal plastid as secondary plastid often enclosed by three or four membranes reflecting additional engulfment steps. This process explains plastid diversity outside Archaeplastida, including euglenids bearing green algal secondary plastids and stramenopiles, alveolates, haptophytes containing red algal plastids. Nucleomorph remnants and periplastidial compartments provide evidence distinguishing secondary from primary endosymbiotic acquisition of photosynthesis.