Biology help needed! Why do some prokaryotes have both DNA and plasmids?

If they can just use their plasmids to self-replicate, why do they need DNA?

If they can just use their plasmids to self-replicate, why do they need DNA?

They do not have a membrane-bound nucleus and their DNA is free in the cytoplasm.Bacteria have a single circular chromosome in the centre of the cell that holds all the genes needed for that bacterium. Bacteria also have extra circles of DNA called plasmids.

So when bacteria have both DNA and plasmids, they don't actually need the plasmids?