What is the nucleus of a bacterium known as?

Identify the correct terms for the following analogy-based questions:
$(i)$ Smallest cell : $Mycoplasma$ :: Largest cell : ......
$(ii)$ Loose sheath in bacteria : $Slime$ layer :: Thick and tough sheath : ....

What is the primary difference between prokaryotic and eukaryotic cells regarding their internal structure?

Which of the following structures is present only in a prokaryotic cell?

Glycocalyx is loose - $P$
Glycocalyx is thick and tough - $Q$
Select the correct option for $P$ and $Q$.

$PPLO$ stands for ...