What are the flattened membranes in chloraplast called?

The flattened membranes in chloroplasts are called thylakoids. These structures are organized into stacks known as grana, which are crucial for the photosynthesis process as they contain chlorophyll and other pigments that capture light energy. The thylakoid membranes are where the light-dependent reactions of photosynthesis occur, converting light energy into chemical energy.