Chlorella is a general unicellular green algae belonging to the phylum Chlorella. It is a spherical single-celled freshwater algae with a diameter of 3 to 8 microns. It is one of the earliest life on earth and appeared more than 2 billion years ago. It is a highly efficient photosynthetic plant, which grows and reproduces with photosynthetic autotrophy, and has a wide distribution.