This biological division contains the diatoms, golden-brown algae, and yellow-green algae. Scientists estimate that there are about 12,000 species in this division. These organisms are all single-celled and are mainly found in marine environments. They conduct photosynthesis and contain chlorophylls a and c; diatoms and golden-brown algae also contain the acessory pigment fucoxanthin. They store their food as large droplets of oil or in the form of the carbohydrate leucosin. These organisms usually reproduce by cell division. There are about 10,000 living species of diatoms, 1500 species of golden-brown algae, and 600 species of yellow-green algae.