Algae, a type of protist, supports life on earth by producing much of the oxygen present in the atmosphere. Some protists, such as diatoms, dinoflagellates and foraminiferans, also play an essential role in marine ecosystems by serving as a source of food and shelter for many organisms.
Algae produces oxygen by performing photosynthesis, which converts sunlight into energy. Microscopic algae gardens directly and indirectly support all higher life forms in aquatic ecosystems. Red algae is rich in vitamins and minerals, and many species of red algae are edible. For example, carageenan, a polysaccharide extracted from red algae, is used as a thickening agent in ice cream and other foods. Seaweed, another type of algae, is a dietary staple in many coastal communities, particularly in East Asia.
Protists are a diverse group of eukaryotic organisms, which means their genetic material is contained inside a nucleus in the cell. They are not plants, fungi or animals, but scientists believe their development paved the way for the evolution of plants, fungi and animals. For instance, the ancestors of green algae likely gave rise to today's more complex multicellular plants. There are four main categories of protists: unicellular algae, protozoa, water molds and slime molds.