The correct answer is option 'D': Mitochondria.

Prokaryotic cells are a type of cell that lack a nucleus and membrane-bound organelles. They are typically found in bacteria and archaea. Unlike eukaryotic cells, prokaryotic cells are much simpler in structure. They contain a few essential structures that carry out basic cellular functions. Let's discuss each of the structures mentioned in the options and why mitochondria is not found in prokaryotic cells.

a) Cell wall:
The cell wall is a rigid outer layer that provides support and protection to the cell. It is found in both prokaryotic and eukaryotic cells. However, the composition of the cell wall differs between prokaryotes and eukaryotes. In prokaryotic cells, the cell wall is mainly composed of peptidoglycan, a unique molecule that provides strength to the cell wall. On the other hand, eukaryotic cell walls can be made of various materials such as cellulose (in plants), chitin (in fungi), or silica (in diatoms).

b) Plasma membrane:
The plasma membrane is a thin, flexible barrier that surrounds the cell and separates the internal environment from the external environment. It is present in both prokaryotic and eukaryotic cells. The plasma membrane is composed of a phospholipid bilayer with embedded proteins that regulate the passage of molecules into and out of the cell.

c) Ribosomes:
Ribosomes are small cellular structures that are responsible for protein synthesis. They can be found in both prokaryotic and eukaryotic cells. However, there are slight differences in the structure of ribosomes in prokaryotes and eukaryotes. Prokaryotic ribosomes are smaller and have a different composition compared to eukaryotic ribosomes.

d) Mitochondria:
Mitochondria are membrane-bound organelles found in eukaryotic cells. They are often referred to as the "powerhouses" of the cell because they generate most of the cell's energy through the process of cellular respiration. Mitochondria have a double membrane structure and contain their own DNA. They are thought to have originated from symbiotic bacteria that were engulfed by a primitive eukaryotic cell.

In summary, mitochondria are not found in prokaryotic cells. They are a characteristic feature of eukaryotic cells and play a crucial role in energy production. Prokaryotic cells, on the other hand, have a simpler structure and lack membrane-bound organelles such as mitochondria.