'Haben Insekten eine Lunge?'
This sentence in the German Body 2 skill is mistranslated as 'Do insects have a lung?' but there's no way to report it. If you click on the report button, there's only three options, and none of them are to report an unnatural English sentence.
I've noticed that a lot - why does it happen?
This is the discussion on that sentence: https://forum.duolingo.com/comment/11107946
For the reasons I wrote above.
But also bear this in mind: 'Eine Lunge' doesn't just mean 'a lung', it means 'lungs' or 'a pair of lungs', too.
Imagine a picture of some people. Each person is wearing a hat. Which sentence is correct?
- The people have hats.
- The people have a hat.
Imagine a language in which there were no plurals and the literal translation of the equivalent sentence is 'The people have (a) hat.' But it's the same picture - multiple people, multiple hats. The correct English translation would still be 'The people have hats', even if you could form a grammatically correct, word-for-word translation from the sentence in the other language.
Additionally, very few animals have a single lung - some snakes, the lungfish. The vast majority of animals have two lungs.
Do mammals have lungs? Yes, they do.
Do mammals have a lung? No - they have two lungs. Each.
Two remarks: "Lunge" is some kind of hybrid word that can mean both "a lung" and "(two) lungs" (like die Hose(n)). Also in German you can talk about "der Mensch hat zwei Lungen, die rechte Lunge, die linke Lunge" (common use in medicine), while colloquially both lungs are called "die Lunge". So without further assumptions the sentence can very well mean "Do insects have a(/one) lung". Anyway, the more common or likely interpretation of the sentence should be "Do insects have (any number of) lungs".
The second would be, in your example you talk about a certain group of people, while the sentence in question talks about insects in general. You can find enough examples of people asking "Do animals have a soul?", for example, alongside others (the majority, I'd say) who ask "Do animals have souls?". I don't think the first group intends a common soul of all animals, but one for each. In German we have a similar situation - you can say both - , but maybe the singular would be more common. Anyway, this kind of discussion seems to be Haarspalterei to me. Just to introduce a new word....
'Eine Lunge' doesn't just mean 'a lung', it means 'lungs' or 'a pair of lungs', too.