"Experiments are done in the laboratory."
Translation:Déantar turgnaimh sa tsaotharlann.
I'm pretty sure that Duolingo didn't reject "experiments are done" in favour of "experiments are made".
Déan is used to translate both "do" and "make", but the most appropriate translation depends on the English idiom:
Déan do dhícheall - "Do your best" Tá na páistí ag déanamh glór - "The children are making noise" Sometimes it doesn't matter whether you use "do" or "make", but in these examples it does.