Chloroplasts are organelles that carry out photosynthesis in eukaryotic cells. As are other types of organelles, a chloroplast is enclosed in a lipid bilayer that forms a limiting membrane. Within is the stroma, a cytoplasm-like fluid.
These green organelles are thought to be the descendants of endosymbiotic cyanobacteria, and have circular chromosomes like those of prokaryotes. This circular genome, termed the plastome, codes mostly for redox proteins involved in electron transport during photosynthesis.
Within the stroma are the thylakoids, the hollow, nummiform bodies where photosynthesis takes place, which are arranged in a network composed of stacks called grana (sing. granum).
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Chlorplasts within the cells of Plagiomnium affine
Many-fruited
Thyme-moss (click to enlarge). Image: Kristian Peters
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