thylakoid

noun Cell Biology.

1. 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.

1. 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.