chloroplasts
Chloroplasts capture light energy from the sun and use it with water and carbon dioxide to produce sugars for food. Chloroplasts look like flat discs and are usually 2 to 10 micrometers in diameter and 1 micrometer thick. A model of a chloroplast is shown in Figure below . The chloroplast is enclosed by an inner and an outer phospholipid membrane. Between these two layers is the intermembrane space. The fluid within the chloroplast is called the stroma , and it contains one or more molecules of small, circular DNA. The stroma also has ribosomes. Within the stroma are stacks of thylakoids , sub-organelles that are the site of photosynthesis. The thylakoids are arranged in stacks called grana singular: granum . A thylakoid has a flattened disk shape. Inside it is an empty area called the thylakoid space or lumen. Photosynthesis takes place on the thylakoid membrane.