thylakoidy

Thylakoids are membrane-bound compartments found inside chloroplasts and cyanobacteria. They are the site of the light-dependent reactions of photosynthesis. Within the thylakoid membranes, pigments like chlorophyll absorb light energy, which is then used to split water molecules, releasing oxygen, and generating ATP and NADPH. These energy-carrying molecules are subsequently used in the light-independent reactions (Calvin cycle) that occur in the stroma of the chloroplast. Thylakoids are typically arranged in stacks called grana, although they can also exist as single, unstacked lamellae that connect different grana. The internal space of a thylakoid is called the lumen. The structure of thylakoids, with their extensive internal surface area and precisely organized protein complexes, is crucial for efficient light capture and energy conversion during photosynthesis.