The accusative case is particular in the sense that masculine nouns have two possible endings depending if they are одушевлённые (animate) or неодушевлённые (inanimate). If they are animate, we follow the same rules as with the genitive case, and if they are inanimate, the nominative case.
However, the division of nouns between animate and inanimate doesn’t match completely with the reality of living and non-living things in our world. There are several groups of words which are grammatically part of the “animate group”, but can’t be called living beings:
Nouns indicating a dead person: deadman, deceased, drowned person, etc.
Names of mythical creatures: dragon, goblin, house spirit, mermaid, etc.
Names of figures and accessories in some games: queen, knight, bishop (chess), ball (billard), jack, ace, king (cards game), etc.
Nouns refering to dolls: doll, puppet, matrioshka, etc.
Names of dishes prepare with meat.
In the opposite, there are cases where the grammatical form of inanimate nouns are not refering to inanimate objects:
Nouns denoting an number of people: army, crowd, delegation, friends, etc.
Nouns in plural, when used in special propositional constructions like:
When talking about biology, we use genitive case for a professional speech, and nominative case for a general andusual speech.
Prossional speech: for virus, bacteria, fungi, larva, microbe, etc.
Non-professional speech: for virus, bacteria, fungi, larva, microbe, etc.