biology vs facultative

biology is a noun but facultative is not a noun.

Word	Noun	Adjective	Verb	Adverb
biology	Yes	No	No	No
facultative	No	Yes	No	No

biology (noun)	facultative (noun)
the science that studies living organisms
all the plant and animal life of a particular region
characteristic life processes and phenomena of living organisms

biology (adjective)	facultative (adjective)
	able to exist under more than one set of conditions
	of or relating to the mental faculties
	granting a privilege or permission or power to do or not do something
	optional