Final answer:
The domain Bacteria includes the smallest known cells called mycoplasmas, which lack a cell wall. Unlike the rigid cell walls found in most bacteria, mycoplasmas have a flexible plasma membrane. These prokaryotic cells can be either free-living or pathogenic.
Step-by-step explanation:
The domain Bacteria includes the smallest known cells, the mycoplasmas, which lack a cell wall. These tiny bacteria are distinctive because they do not possess the rigid cell wall that is characteristic of most bacteria. Instead, they have a more flexible membrane, making them unique among prokaryotes. Some mycoplasmas are free-living, while others can be pathogenic, causing diseases in plants, animals, and humans.
Prokaryotic cells, such as those from the domains Archaea and Bacteria, are generally small (1-10 µm) and lack a nucleus and other membrane-bound organelles. They also reproduce asexually. While most prokaryotes have a cell wall that provides structural support and protection, mycoplasmas do not, making them one of the few exceptions within these domains.