Chlorella is a genus of single-celled green algae belonging to the division Chlorophyta. It is spherical in shape, about 2 to 10 μm in diameter, and is without flagella. It contains the green photosynthetic pigments chlorophyll-a and -b in its chloroplast. In ideal conditions it multiplies rapidly, requiring only carbon dioxide, water, sunlight, and a small amount of minerals to reproduce.
The name Chlorella is taken from the Greek χλÏŽρος, chlÅros/ khlÅros, meaning green, and the Latin diminutive suffix ella, meaning small. German biochemist and cell physiologist Otto Heinrich Warburg, awarded with the Nobel Prize in Physiology or Medicine in 1931 for his research on cell respiration, also studied photosynthesis in Chlorella. In 1961, Melvin Calvin of the University of California received the Nobel Prize in Chemistry for his research on the pathways of carbon dioxide assimilation in plants using Chlorella.