chloroplast - (n.)

The central, light-utilizing organelles of all eukaryotic phototrophs : Evolutionarily derived from endosymbiotic cyanobacteria, chloroplasts are dense, oblong particles, about one ten-thousandth of an inch in size, surrounded by two membranes and filled with stacks (grana) of flat, membranous pouches (thylakoids) bearing membrane embedded photosystems I and II, together with associated electron-transfer chains. ~ See Also: Chlorophyll, Cyanobacteria, Electron-transfer chain, Endosymbiont.