biome vs grassland

biome and grassland both are nouns.

Word	Noun	Adjective	Verb	Adverb
biome	Yes	No	No	No
grassland	Yes	No	No	No

As nouns, grassland is a hyponym of biome; that is, grassland is a word with a more specific, narrower meaning than biome:

biome: a major biotic community characterized by the dominant forms of plant life and the prevailing climate
grassland: land where grass or grasslike vegetation grows and is the dominant form of plant life

Other hyponyms of biome include desert, forest, timber, timberland, woodland.

biome (noun)	grassland (noun)
a major biotic community characterized by the dominant forms of plant life and the prevailing climate	land where grass or grasslike vegetation grows and is the dominant form of plant life