Bacterial cells are single-celled organisms that belong to the domain Bacteria. They are prokaryotic, meaning they lack a nucleus and other membrane-bound organelles. Bacterial cells have a simple structure, typically consisting of a cell wall, cell membrane, cytoplasm, and genetic material in the form of a single circular DNA molecule. These cells can vary in shape, including cocci (spherical), bacilli (rod-shaped), and spirilla (spiral-shaped). Bacteria can reproduce rapidly through a process called binary fission, where one cell divides into two. They play essential roles in various ecosystems, including nutrient cycling and decomposition.