Learn Finnish: Eläintarhassa on paljon eläimiä. - There are a lot of animals in the zoo.

This is a classic existential sentence (a "there is / there are" sentence). In Finnish, these sentences usually start with a location (eläintarhassa) followed by the verb on, which always stays in the singular third-person form, even if the things existing there (eläimiä) are plural.

Why is eläimiä in the partitive case?

The word paljon (a lot / much) is a quantity word that requires the noun following it to be in the partitive case. Since animals can be counted, we use the partitive plural form (eläimiä).

How does the basic word eläin (animal) change into eläimiä?

Nouns ending in -in, like eläin, change their stem to eläime- before taking most endings. To make it partitive plural, we add the plural marker -i- and the partitive ending -ä, resulting in eläimiä.

How is the word eläintarhassa formed?

It is a compound word made of eläin (animal) and tarha (enclosure, yard, or garden). The ending -ssa means "in" (the inessive case), so it translates literally to "in the animal garden" or "in the zoo".