What are grana in chloroplasts primarily composed of?

Grana are primarily composed of stacked structures called thylakoids. These thylakoids are membrane-bound sacs that contain the chlorophyll and other pigments necessary for photosynthesis. The stacking of thylakoids in the grana increases the surface area available for light absorption, making the process of converting light energy into chemical energy more efficient. In this way, grana play a crucial role in the light-dependent reactions of photosynthesis, where the energy absorbed by chlorophyll is used to generate ATP and NADPH, which are essential for the subsequent stages of photosynthesis. The structure of grana, therefore, is fundamental to the functionality of chloroplasts and the overall process of photosynthesis in plants.