What structure in a prokaryotic cell is responsible for maintaining its shape?

The cell wall in a prokaryotic cell is essential for maintaining the cell's shape and providing structural support. It is a rigid layer that surrounds the cell membrane, composed of peptidoglycan in bacteria. This structure not only contributes to the mechanical strength of the cell, allowing it to withstand osmotic pressure and environmental stresses, but it also plays a critical role in determining the overall shape of the cell, whether it be cocci (spherical), bacilli (rod-shaped), or spirilla (spiral).

In prokaryotes, which lack a membrane-bound nucleus, the cell wall helps define the organism's form and protects the integrity of its cytoplasmic contents. Without a well-functioning cell wall, prokaryotic cells would be susceptible to lysis in hypotonic environments.

While the cell membrane is involved in regulating what enters and exits the cell and is important for cellular processes, it does not provide the same structural support that the cell wall does. The nucleus is present in eukaryotic cells and is not a feature of prokaryotes. Flagella are appendages that aid in movement but do not contribute to the overall shape of the cell itself.