Algae are a diverse group of photosynthetic, eukaryotic organisms that range from single cells to massive kelp/05%3A_The_Eukaryotes_of_Microbiology/5.04%3A_Algae). They are found in both aquatic and terrestrial environments, and their photosynthetic pigments are more varied than those of plants. Algae lack true roots, stems, and leaves, and a vascular system to circulate water and nutrients throughout their bodies. They can be unicellular or multicellular, and they may also form colonies/05%3A_The_Eukaryotes_of_Microbiology/5.04%3A_Algae). Algae are important ecologically and environmentally because they are responsible for the production of approximately 70% of the oxygen and organic matter in aquatic environments/05%3A_The_Eukaryotes_of_Microbiology/5.04%3A_Algae). Algae can be used as indicator organisms to monitor pollution in various aquatic systems, and they are also economically important as a source of crude oil and as sources of food and a number of pharmaceutical and industrial products for humans. The study of algae is called phycology, and a person who studies algae is a phycologist.