<Dd> 3.2 Thylakoid membrane </Dd> <P> 4 Stromal thylakoid 5 Stroma 6 Nucleoid (DNA ring) 7 Ribosome 8 Plastoglobulus 9 Starch granule </P> <P> A thylakoid is a membrane - bound compartment inside chloroplasts and cyanobacteria . They are the site of the light - dependent reactions of photosynthesis . Thylakoids consist of a thylakoid membrane surrounding a thylakoid lumen . Chloroplast thylakoids frequently form stacks of disks referred to as grana (singular: granum). Grana are connected by intergranal or stroma thylakoids, which join granum stacks together as a single functional compartment . </P> <P> The word thylakoid comes from the Greek word thylakos meaning "sac" or "pouch". Thus, thylakoid means "sac - like" or "pouch - like". </P>

Little stacks of disks that make up the thylakoid membrane system