Identify and name the following cell structures.
$(a)$ The undefined nuclear region of a prokaryotic cell.
$(b)$ The site of energy release inside the cell.

(N/A) Nucleoid: In prokaryotic cells,the genetic material is not enclosed by a nuclear membrane. This undefined nuclear region containing only nucleic acids is known as the nucleoid.
$(b)$ Mitochondria: These are known as the powerhouses of the cell because they generate most of the cell's supply of adenosine triphosphate $(ATP)$,which is used as a source of chemical energy.