Short answers, pulled from the story.
A chloroplast is a type of plastid organelle found in plant and algal cells that conducts photosynthesis, converting light energy into chemical energy stored as sugar. Beyond photosynthesis, chloroplasts also carry out fatty acid synthesis, amino acid synthesis, and participate in the plant immune response.
Chloroplasts evolved from a free-living cyanobacterium that was engulfed by an early eukaryotic cell approximately two billion years ago in a process called endosymbiosis. With one exception, the amoeboid Paulinella chromatophora, all chloroplasts on Earth trace back to that single ancient event. The closest living relative of the original engulfed cyanobacterium is thought to be Gloeomargarita lithophora.
Hugo von Mohl gave the first definitive description of a chloroplast in 1837, calling it a Chlorophyllkorn or grain of chlorophyll. Andreas Franz Wilhelm Schimper named these bodies chloroplastids in 1883, and Eduard Strasburger adopted the modern term chloroplasts in 1884.
Yes, chloroplasts contain their own genome separate from the cell nucleus, a consequence of their endosymbiotic origin. Chloroplast DNA was identified biochemically in 1959 and first sequenced in 1986. Most chloroplast genomes are circular molecules of 120,000 to 170,000 base pairs, far smaller than the cyanobacterial ancestor's genome of over 3,000 genes.
Paulinella chromatophora is an amoeboid organism with the only known independently evolved chloroplast, called a chromatophore, which was acquired from a cyanobacterium in the genus Synechococcus between 90 and 140 million years ago. Its chromatophore genome is about one million base pairs, roughly one third the size of Synechococcus genomes. Because this event happened so much more recently than the original chloroplast acquisition, Paulinella is studied to understand how early chloroplast evolution unfolds.
Secondary endosymbiosis occurs when an organism engulfs an alga that already contains a primary chloroplast, gaining a chloroplast indirectly. This process typically adds membranes to the chloroplast structure, producing organelles with three or four surrounding membranes rather than two. Groups such as euglenophytes, chlorarachniophytes, haptophytes, and dinoflagellates acquired their chloroplasts this way.