biology vs underwater

biology is a noun but underwater is not a noun.

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

biology (noun)	underwater (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)	underwater (adjective)
	growing or remaining under water
	beneath the surface of the water