Light microscopy of the unicellular green algae Chlamydomonas reinhardtii. Each alga is some 10 micrometres in diameter. It swims with two flagellae. It has a cell wall made of hydroxyproline-rich glycoproteins, a large cup-shaped chloroplast, a large pyrenoid, and an eyespot that senses light. Although widely distributed worldwide in soil and fresh water, C. reinhardtii is used primarily as a model organism in biology. C. reinhardtii is also of interest in the biopharmaceuticals industry and the biofuel field, as a source of hydrogen.