algae
Algae are photosynthetic eukaryotic organisms. Some are classifi ed as Protista and others as plants according to their morphology, which is varied. Some exist as single-celled organisms, and some are multicellular. Usually, algae are aquatic, occu- pying both marine and freshwater environments. The dinofl agellates and the diatoms are free fl oating, and the red and brown algae require a solid substrate to which they attach. They are further classifi ed by their photosynthetic pigments, thus the names brown, red, green, and blue-green algae. Many are of industrial importance providing thickeners for foods and bacterial culture media. See agar.