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In some groups of [[mixotrophic]] [[protist]]s such as the [[dinoflagellate]]s, chloroplasts are separated from a captured alga or diatom and used temporarily. These [[kleptoplasty|klepto chloroplasts]] may only have a lifetime of a few days and are then replaced.<ref name=Skovgaard>Skovgaard, A (1998) Role of chloroplast retention in a marine dinoflagellate. ''Aquatic Microbial Ecology'' 15, 293-301</ref>

 

 

Chloroplasts are observable morphologically as flat discs usually 2 to 10 micrometer in diameter and 1 micrometer thick. In land plants they are generally 5 μm in diameter and 2.3 μm thick. The chloroplast is contained by an envelope that consists of an inner and an outer phospholipid membrane. Between these two layers is the intermembrane space. A typical [[parenchyma]] cell contains about 10 to 100 chloroplasts.

The material within the chloroplast is called the stroma, corresponding to the [[cytosol]] of the original bacterium, and contains one or more molecules of small circular DNA. It also contains [[ribosome]]s, although most of its proteins are encoded by genes contained in the host cell nucleus, with the protein products transported to the chloroplast.

[[Image:Chloroplast.svg|thumb|275px|right|Chloroplast ultrastructure:<br />

 

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