I'm a native speaker but no linguist, and I think this is the partitive case.
It kind of means "Is this [of the] cheese", as in "some of the cheese that exists".
The sentence "Onko tämä juusto" would also be correct, but only when referring to one whole cheese, as in "Is this a cheese".
So if you have one whole cheese, you use the latter, but if you have some amount of a substance in a sandwich, for example, you use the former.
Yes, it's partitive. By the way, it is spelt juusto (double u). It is a mass noun (ainesana in Finnish). You can read more about that here:
I recommend the above website to all Finnish learners.
If a moderator is reading this, I WILL keep bringing this up.
I'm not a moderator, but I don't think this is something a moderator can affect at all.
Isn't this a pretty basic feature of the Duolingo apps (Android and iOS)? And of any app, for that matter -- all the services I use which have both a web version and an app have a more limited number of functions in the app version.
Could you use the browser on your mobile device instead? I remember having done that with Duolingo at some point.
Thank you for the reply, annika! Perhaps you are quite correct and I am being unreasonable in my expectations. I do not know exactly what the mobile app is technically capable of, although the state that it is in is far above what it started out as. My hope is that a mod could forward a suggestion up the chain. While it is very true that an app usually has more limited features, surely they could do something as simple as have a card at the beginning of each level, couldn't they? Something outlining basic vocabulary and concepts that will be covered. Kind of like adding an extra slide into the exercises.
Example Category - Food, Level 0, Step 1: "Partitive Nouns and Adjectives add an a or ä to the end of a word, and are used for ideas including "part", "some of", and "any." Which of these sentences shows a Partitive case?" Then give to nearly identical sentences to choose between.
My computer access is limited by chronic arthritis (sitting in one spot is not practical for any length of time), thus I usually have to rely on the mobile app. It just pains me that something as wonderful as Duolingo is missing that little bit extra. My apologies for coming across as en okunnig röv.
Annika, my apologies, it wouldn't let me reply to your last response on my tablet web browser. I had to reply to my own comment, which made the reply button show up by your comment. I then had to copy and paste it to the reply under your comment. The web browser seems to have problems running Duolingo. Also, having a program that requires learners to access it via the web browser to see basic tips renders the App superfluous (pointless) doesn't it?