Final answer:
Thylakoids are the site of light-dependent reactions in photosynthesis, located within chloroplasts and cyanobacteria.
Step-by-step explanation:
The membrane-bound compartment inside chloroplasts and cyanobacteria that serves as the site of the light-dependent reactions of photosynthesis is known as a thylakoid. Thylakoids are disc-shaped structures that contain photosystems I and II, as well as the enzyme NAD+ reductase, necessary for the conversion of light energy into chemical energy. The stacks of thylakoids are called grana, and they are essential to the plant cell's ability to harness sunlight during photosynthesis.