The structures that are formed by stacking of organised flattened membranous sacs in the chloroplasts are

The structures that are formed by stacking of organised flattened membranous sacs in the chloroplasts are grana. The flattened membranous structure is called thylakoids. 

Flat membranous tubules called the stroma lamellae connecting the thylakoids of the different grana.

The space limited by the inner membrane of the chloroplast is called the stroma.       

The inner membrane of mitochondria forms a number of infoldings called the cristae towards the matrix. The cristae increase the surface area.