Chlamydomonas is a genus of green algae

Green algae

The green algae are the large group of algae from which the embryophytes emerged. As such, they form a paraphyletic group, although the group including both green algae and embryophytes is monophyletic...

. They are unicellular flagellate

Flagellate

Flagellates are organisms with one or more whip-like organelles called flagella. Some cells in animals may be flagellate, for instance the spermatozoa of most phyla. Flowering plants do not produce flagellate cells, but ferns, mosses, green algae, some gymnosperms and other closely related plants...

s. Chlamydomonas is used as a model organism

Model organism

A model organism is a non-human species that is extensively studied to understand particular biological phenomena, with the expectation that discoveries made in the organism model will provide insight into the workings of other organisms. Model organisms are in vivo models and are widely used to...

 for molecular biology

Molecular biology

Molecular biology is the branch of biology that deals with the molecular basis of biological activity. This field overlaps with other areas of biology and chemistry, particularly genetics and biochemistry...

, especially studies of flagellar

Flagellum

A flagellum is a tail-like projection that protrudes from the cell body of certain prokaryotic and eukaryotic cells, and plays the dual role of locomotion and sense organ, being sensitive to chemicals and temperatures outside the cell. There are some notable differences between prokaryotic and...

 motility and chloroplast

Chloroplast

Chloroplasts are organelles found in plant cells and other eukaryotic organisms that conduct photosynthesis. Chloroplasts capture light energy to conserve free energy in the form of ATP and reduce NADP to NADPH through a complex set of processes called photosynthesis.Chloroplasts are green...

 dynamics, biogenesis, and genetics. One of the many striking features of Chlamydomonas is that it contains ion channel

Ion channel

Ion channels are pore-forming proteins that help establish and control the small voltage gradient across the plasma membrane of cells by allowing the flow of ions down their electrochemical gradient. They are present in the membranes that surround all biological cells...

s that are directly activated by light, such as channelrhodopsin

Channelrhodopsin

Channelrhodopsins are a subfamily of opsin proteins that function as light-gated ion channels. They serve as sensory photoreceptors in unicellular green algae, controlling phototaxis, i.e. movement in response to light. Expressed in cells of other organisms, they enable the use of light to control...

. Some regulatory systems of Chlamydomonas are more complex than their homolog

Homology (biology)

Homology forms the basis of organization for comparative biology. In 1843, Richard Owen defined homology as "the same organ in different animals under every variety of form and function". Organs as different as a bat's wing, a seal's flipper, a cat's paw and a human hand have a common underlying...

s in Gymnosperms, with evolutionary related regulatory proteins being larger and containing additional domains .

• Chlamydomonas reinhardtii
  Chlamydomonas reinhardtii
  Chlamydomonas reinhardtii is a single celled green alga about 10 micrometres in diameter that swims with two flagella. They have 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...
  
  
• Chlamydomonas caudata Wille
• Chlamydomonas moewusii
• Chlamydomonas nivalis
  Watermelon snow
  Watermelon snow, also called snow algae, red snow, or blood snow, is snow that is reddish or pink in color, with the slight scent of a fresh watermelon. Watermelon snow is caused by the presence mainly of Chlamydomonas nivalis, a species of green algae containing a secondary red carotenoid pigment ...
  
  

Most species are obligate phototrophs but C. reinhardtii

Chlamydomonas reinhardtii

Chlamydomonas reinhardtii is a single celled green alga about 10 micrometres in diameter that swims with two flagella. They have 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...

and C.