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Plastids are vesicle-type organelles that perform a variety of functions in plants. Amylopasts store starch, and chromoplasts store pigment molecules that give some plants their vibrant orange and yellow colors.

Chloroplasts are plastids that carry out photosynthesis, a process in which water and carbon dioxide are transformed into sugars. The interior of chloroplasts contains an elaborate membrane system. Thylakoids bisect the chloroplasts, and attached to these platforms are stacks of membranous sacs called grana. Each granum contains the enzymes necessary for photosynthesis. The membrane system within the chloroplasts is bathed in a fluid called stroma, which also contains enzymes.

Like mitochondria, chloroplasts resemble some ancient single-celled prokaryotes and also contain their own DNA sequences. Their origin within eukaryotes is thought to have arisen from the endosymbiotic relationship between a photosynthetic single-celled prokaryote that was engulfed and remained within another prokaryotic cell.

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Science EncyclopediaScience & Philosophy: Categorical judgement to ChimaeraCell - Types Of Cells, Prokaryotes And Eukaryotes, Cell Size And Numbers, The Structure And Function Of Cells - The structure of eukaryotes, Plant organelles, Vacuoles, Cell wall