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

In the chloroplasts, there are stacks of flattened membranous discs known as thylakoids. They appear as similar stacks of coins. Inside the chloroplast, and they trap the energy from sunlight to carry out photosynthesis. These stacks of thylakoids are known as grana. A system of tubules connects them.