What is the name for the flattened membrane sacs within chloroplasts that convert light energy into chemical energy?

The flattened membrane sacs within chloroplasts, which are essential for converting light energy into chemical energy during photosynthesis, are known as thylakoids. These structures contain chlorophyll and other pigments that capture light energy, initiating the light-dependent reactions of photosynthesis. Within the thylakoids, light energy is used to create ATP and NADPH, which are then utilized in the Calvin cycle to synthesize glucose.

Granum refers to a stack of thylakoids, which enhances the surface area for light absorption but does not denote the individual sacs themselves. The stroma is the fluid matrix surrounding the thylakoids, where the light-independent reactions occur. The chloroplast membrane encompasses the entire chloroplast structure but is not involved in the conversion of light energy into chemical energy, making thylakoid the most precise term for the structures responsible for this process.