Any green algae of the genus Chlorella , found in fresh or salt water and in soil.
They have a cup-shaped chloroplast . Chlorellas are used often in studies of photosynthesis , in mass cultivation experiments, and for purifying sewage wastes. Because they multiply rapidly and are rich in proteins and in B-complex vitamins, they have been studied as a potential food product for humans both on Earth and in outer space. Chlorella farms, closed systems that provide humans with food, water, and oxygen, have been established in the U.S., Japan, The Netherlands, Germany, and Israel.