In the given diagram of chloroplast, the parts marked as $A, B, C$ and $D$ are respectively granum, thylakoid, stromal lamella and stroma. Granum is a stacked membranous structure that contains the chlorophyll and is the site of the light reactions of photosynthesis. Thylakoids are saclike membranes that make up grana. Stromal lamella are the extensions that run from one granum, through the stroma, into a neighbouring granum.The space between the inner membrane and the thylakoid membrane is filled with stroma, a matrix containing dissolved enzymes, starch granules, and copies of the chloroplast genome.