Coloured transmission electron micrograph (TEM) of a section through a chloroplast in a cell from a Coleus blumei plant showing stacks of parallel thylakoids (membranes, green lines) called grana. 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 the grana. The brown area at centre is a nucleoid, the site of DNA (deoxyribonucleic acid) synthesis in a chloroplast. Mag: x80,000 when printed at 10cm wide.