Practice question

Primary endosymbiosis leading to photosynthetic eukaryotes involved stable incorporation of cyanobacterium capable of oxygenic photosynthesis into non-photosynthetic eukaryotic host already bearing mitochondria. This ancient event around 1.5 billion years ago generated Archaeplastida ancestor containing plastids surrounded by two membranes corresponding to cyanobacterial inner and outer membranes with peptidoglycan remnant in glaucophytes. Gene transfer to nucleus and establishment of translocon complexes integrated plastid metabolism. Descendants diversify into glaucophytes with phycobilisomes, red algae with phycoerythrin, and green algae plus land plants with chlorophyll b, all sharing cyanobacterial 16S rRNA ancestry.