NCIt definition : Photosynthetic organelle containing chlorophyll, the photosynthetic pigment, in cells
of leaves and young stems of higher plants. Lens-shaped and rather variable in size
but approximately 5 m long. Surrounded by a double membrane and contains circular
DNA (though not enough to code for all proteins in the chloroplast). Like the mitochondrion,
it is semi-autonomous. It resembles a cyanobacterium from which, on the endosymbiont
hypothesis, it might be derived. Chlorophyll is associated with the membrane of vesicles
(thylakoids) that are stacked to form grana.;