Final answer:
Prokaryotes are simple cells without a nucleus, most commonly found in spherical (cocci), rod-shaped (bacilli), and spiral (spirilla) forms. These cells may have flagella, pili, and other structures affecting their movement and attachment.
Step-by-step explanation:
Prokaryote Cell Structures and Shapes:
The structure of prokaryotes is simple but varies in shape, with the most common shapes being helices, spheres, and rods. An uncommon shape in prokaryotic cells is star-shaped, which belongs to a few select groups of bacteria. These bacterial shapes correspond to: (a) cocci, or spherical; (b) bacilli, or rod-shaped; and (c) spirilla, or spiral-shaped. Prokaryotic cells lack membrane-bound organelles and thus do not have a nucleus but have a nucleoid where their DNA resides. They usually have a cell wall that determines their shape and may have additional structures such as flagella for movement and pili for attachment.
Common Prokaryotic Cell Shapes:
Cocci: Spherical cells which can appear in pairs, chains, or clusters, depending on their pattern of division and growth.
Bacilli: Rod-shaped cells that can be found singly or in chains.
Spirilla: Spiral-shaped cells that often move via flagella.