Talk in general about thylakoids.

Inner membrane system has disk-shaped sacks called thylakoids, bounded by a lipid bilayer and arranged in orderly piles called grana (granum means sack) Each pile is about 40 60 grana, having 2 to 100 thylakoids. Certain thylakoids called stroma thylakoids extend laterally and interconnect grana to one another. Role is photosynthesis (reduction of NADP) and photophosphorylation