I do understand the educational purposes of Duolingo and the need of using the verb in genitive. The problem is, this "active" combination is seldom used (for existential or spiritual needs) and passive voice phrase is commonly used instead, where the noun depicting the everyday common need is in nominative (the subject of the phrase):
You need some bread/water/God - Potrzebujesz chleba/wody/Boga (genitive)
You need those women! - Potrzebne tobie/wam te kobiety! (plural nominative)
You need that woman! - Potrzebna tobie/wam ta kobieta! (sing. nominative)
In Russian, the accusative = genitive anyway for masculine animate nouns, so it works out. But feminine nouns take accusative, unless specifying "some quantity of," for which genitive is used. For Russian speakers, Polish verbs' inanimate objects taking the genitive case (for no reason) is very strange.