Carbon-based lifeform

A carbon-based lifeform is any lifeform, including flora and fauna, that depends upon carbon atoms, and is almost exclusively found on a M class planets. It is scientifically impossible for carbon-cycle lifeforms to inhabit a planet like Excalbia, which had a poisonous atmosphere and surface consisting mostly molten lava. 

Humans, for example, are carbon-based. The Starfleet Academy course "Exobiology 101" taught several basics on carbon-based life, such as that the Human immune system is unable to combat non-carbon elements, such as silicon and silicon-based viruses, which can attack the Human body in unpredictable ways. 

V'Ger and its Ilia probe used the term carbon unit to describe the humanoid crew of the USS Enterprise (NCC-1701). V'Ger considered carbon units to be inferior, and not true lifeforms. 

The internal environment of Gomtuu was suitable for carbon-based lifeforms. 

While scanning Suspiria's array for sporocystian lifeforms, the USS Voyager discovered instead the signatures of over 2,000 carbon-based lifeforms.