Questions & Answers about Chleb jest już pokrojony.
Chleb is in the nominative case because it is the subject of the sentence.
You can think of the structure as:
- chleb = the thing being talked about
- jest już pokrojony = what is being said about it
Even though in English bread might feel like the thing affected by the action, in this Polish sentence it is still grammatically the subject.
Jest is the 3rd person singular present form of być (to be).
Here it links the subject chleb with pokrojony. So the sentence has the structure:
- Chleb
- jest
- pokrojony
- jest
This is very common in Polish when describing a state or result:
- Drzwi są zamknięte = The door is closed.
- Obiad jest gotowy = Dinner is ready.
- Chleb jest już pokrojony = The bread is already sliced/cut.