Phytoplankton are microscopic organisms that live in the ocean. There are three main types of phytoplankton: Cyanobacteria, also known as blue green algae; Chysophyta, a protist family that includes diatoms and golden brown algae; and Dinophyta, which are single celled organisms with two flagella.
Phytoplankton are important to the earth's ecology as they produce most of the oxygen that humans and other animals breathe. These organisms are also at the very foundation of the oceanic food chain. They are primary producers, organisms that can convert inorganic substances into organic ones.
Phytoplankton can be found in both fresh and salt water areas. They require sunlight to survive, so they cannot live in deep ocean areas that do not receive sunlight.