do sheep eat apples?
why not kuyunu?
Because that would put the poor sheep into accusative, effectively rendering the sentence without subject. Koyun is not an object but the subject in this sentence. Apple is the object so it is in the accusative.
I thank you for lingots, that's generous.
Bir kuyun yer elma
That is the wrong word order. In Turkish, verbs come at the end of the sentence :)
"elmayı" is a definite object in the sentence, so it's in the accusative position.
elma ----> elmayı