A cell with chloroplasts that have four membranes (not counting the thylakoid membranes) likely arose by _____ endosymbiotic event(s).

Question

Quizplus · Accepted Answer

A eukaryotic cell engulfed a photosynthetic cyanobacterium, forming a symbiotic relationship. Over time, the engulfed cyanobacterium evolved into a chloroplast with two membranes. However, some organisms, such as the diatom Phaeodactylum tricornutum, have chloroplasts with four membranes, indicating a secondary endosymbiotic event where the eukaryotic host cell engulfed a photosynthetic eukaryote that had already undergone primary endosymbiosis with a cyanobacterium. This would result in a chloroplast with two membranes from the original cyanobacterium, plus two additional membranes from the engulfed eukaryotic cell. Therefore, the formation of a chloroplast with four membranes would require two endosymbiotic events.

A Cell with Chloroplasts That Have Four Membranes (Not Counting