A thylakoid is a membrane-bound structure found in the chloroplasts of plant cells. It plays a crucial role in the process of photosynthesis, where it helps convert light energy into chemical energy. Thylakoids are organized into stacks called grana, which increase the surface area for light absorption. Each thylakoid contains chlorophyll, the green pigment that captures sunlight. The light-dependent reactions of photosynthesis occur in the thylakoid membranes, producing energy-rich molecules like ATP and NADPH. These molecules are then used in the light-independent reactions, also known as the Calvin cycle, to synthesize glucose.