Algae are protists that range in size from the very small nanoplankton to the giant kelp. This image shows algae in a lake. Like plants and bacteria, algae are autotrophs. They are capable of self nourishing or generating their own types of seaweed, typically from sunlight.
Regina Bailey is a board-certified registered nurse, science writer and educator. Her work has been featured in “Kaplan AP Biology” and “The Internet for Cellular and Molecular Biologists. Pond scum, seaweed, and giant kelp are all examples of algae. Algae can reproduce sexually, asexually or by a combination of both processes through alternation of generations. Algae can be categorized into seven major types, each with distinct sizes, functions, and color. Euglena are fresh and salt water protists. Like plant cells, some euglenoids are autotrophic.
They contain chloroplasts and are capable of photosynthesis. Due to their photosynthetic capabilities, Euglena were classified along with algae in the phylum Euglenophyta. Scientists now believe that these organisms have acquired this ability due to endosymbiotic relationships with photosynthetic green algae. As such, some scientists contend that Euglena should not be classified as algae and be classified in the phylum Euglenozoa. Golden-brown algae and diatoms are the most abundant types of unicellular algae, accounting for around 100,000 different species. Both are found in fresh and salt water environments. Diatoms are much more common than golden-brown algae and consist of many types of plankton found in the ocean.
Fire algae are unicellular algae commonly found in oceans and in some fresh water sources that use flagella for motion. They are separated into two classes: dinoflagellates and cryptomonads. Dinoflagellates can cause a phenomenon known as a red tide, in which the ocean appears red due to their large abundance. These are Netrium desmid, an order of unicellular green algae that grow in long, filamentous colonies.
They are mostly found in freshwater, but they can also grow in saltwater and even snow. Green algae mostly abide in freshwater environments, although a few species can be found in the ocean. Like fire algae, green algae also have cell walls made of cellulose, and some species have one or two flagella. This is a light micrograph of part of the finely branched thallus of the red algae Plumaria elegans. Red algae are commonly found in tropical marine locations. Unlike other algae, these eukaryotic cells lack flagella and centrioles.