tylakoid

The thylakoid is a membrane-bound compartment found within chloroplasts and cyanobacteria. These flattened sacs are the site of the light-dependent reactions of photosynthesis. Thylakoids are typically arranged in stacks called grana, though they can also exist as single, unstacked lamellae. The thylakoid membrane contains chlorophyll and other pigments that capture light energy. This energy is then used to drive the synthesis of ATP and NADPH, crucial energy-carrying molecules. The internal space of the thylakoid is called the lumen. Within the lumen, protons accumulate during the light reactions, creating a proton gradient that powers ATP synthase. The structure of the thylakoid system is highly efficient, maximizing the surface area available for light absorption and electron transport. This intricate arrangement is fundamental to the process by which light energy is converted into chemical energy.