Chloroplast. Coloured transmission electron micrograph (TEM) of chloroplast from the leaf of a Coleus blumei plant. Chloroplasts are the sites of photosynthesis, the process that synthesises carbohydrates from carbon dioxide and water using sunlight. The pigment responsible for photosynthesis, chlorophyll, is found on stacks of parallel thylakoids (membranes, brown lines) called grana. A starch grain (round, pale) is seen towards the left of the chloroplast. Grana is visible as the threadlike structures running the length of the chloroplast. These are thin, membranous layers which contain photosynthetic pigments (chlorophyll). Magnification: x15,300 when printed at 10 centimetres wide.