a flattened sac or vesicle lined with a pigmented membrane that is the site of photosynthesis, in plants and algae occurring in interconnected stacks constituting a granum of the chloroplast, and in other photosynthesizing organisms occurring either singly or as part of the cell membrane or other structure.
Origin: 1965–70; < GermanThylakoid < Greekthȳlakoeidḗs resembling a bag, equivalent to thȳ́lak(os) sack + -oēidēs-oid
thylakoid (thī'lə-koid') Pronunciation Key
A saclike membrane that contains the chlorophyll in cyanobacteria and in the chloroplasts of plant cells and green algae. In chloroplasts, thylakoids are arranged in stacks called grana.