"My entire family needs a refrigerator."
Translation:Cała moja rodzina potrzebuje lodówki.
In some sentences on Duolingo, you can say e.g. "odwiedzam siostrę" without specifying "odwiedzam moją siostrę", because it's supposed to be clear from context. For this one, if you say "cała rodzina potrzebuje lodówki" without "moja", it's rejected. Can somebody explain when "moja" is or isn't needed?
"potrzebować" is among those verb exceptions that take a direct object in Genitive, not Accusative.
And the Genitive singular form of feminine nouns is almost always identical to Nominative/Accusative plural form. That's why to a learner it might seem like plural is involved, but it's really singular.
If it was "needs new refrigerators", that would be "potrzebuje nowych lodówek".