Animation of the internal structure of a plant cell, showing the structure and function of a chloroplast. Chloroplasts are the site of photosynthesis in the cell. Each contains discs of thylakoid (yellow) arranged in stacks called grana. The thylakoid contains a pigment (chlorophyll) that absorbs sunlight and uses its energy to convert water and carbon dioxide into sugars. Water is oxidised, contributing electrons to the reaction and releasing oxygen gas as a waste product.