Chloroplasts
Plastids are cytoplasmic organelles of photosynthetic protists and plants.
They often possess pigments such as chlorophylls and carotenoids, and are the sites of synthesis and storage of food reserves.
The most important type of plastid is the chloro plast.
Chloroplasts contain chlorophyll and use light energy to convert C02 and water to carbohydrates and 0 that is, they are the site of photosynthesis.
Two major types of chloroplasts have been identified: those that evolved from a primary endosymbiotic event and those that evolved from a secondary or tertiary event .
The chloroplasts of plants and some photosynthetic protists are primary plastids and are the focus of this discussion.
Chloroplasts are quite variable in size and shape, but they share many structural features.
Most are oval with dimen sions of 2 to 4 flm by 5 to 10 flm, but some photosynthetic protists possess one huge chloroplast that fills much of the cell.
Like mitochondria, chloroplasts are encompassed by two membranes .
A matrix called the stroma is en closed by the inner membrane.
The stroma contains DNA, ribosomes, lipid droplets, starch granules, and a complex internal membrane system whose most prominent components are flattened, membrane delimited sacs called thylakoids.
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