Chloroplast, light micrograph. Chloroplasts are organelles found in green plants and some algae. They are the site 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) called grana (black). Large starch grains (oval), one of the products of photosynthesis, are also seen. Chloroplasts measure between 1 micron and 10 microns in length.