All Polish nouns generally change (decline). But there are some exceptions, some nouns don't decline at all, e.g. salami, kiwi, emu. They are usually loanwords. Moreover "zupa" is a feminine noun. Feminine nouns always have different forms for accusative case. But thid rule is true for masculine inanimate nous, e.g. "komputer", "stół"

Mianownik, (kto?, co?) zupa; Dopełniacz (kogo? czego?) zupy; Celownik (komu? czemu?) zupie Biernik (kogo? co?) zupę; Narzędnik (z kim? z czym?) z zupą; Wołacz - o zupa!