The main role of the thylakoids in chloroplasts is to facilitate photosynthesis. These membrane-bound structures contain chlorophyll, which captures light energy. This energy is used to convert carbon dioxide and water into glucose and oxygen during the light-dependent reactions of photosynthesis. Thylakoids are arranged in stacks called granum, optimizing the surface area for light absorption. They play a vital role in producing energy-rich molecules like ATP and NADPH, which are essential for the synthesis of carbohydrates in the light-independent reactions.