Which of the following describes bacteria?

Bacteria are classified as prokaryotic organisms, which means they are single-celled and lack a true nucleus. Instead of a well-defined nucleus surrounded by a nuclear membrane, their genetic material is found in a region of the cell called the nucleoid. This characteristic is fundamental to bacteria, distinguishing them from eukaryotic organisms that possess a nucleus and often display more complex multicellularity.

The description emphasizes that bacteria are single-celled, which aligns with their classification in the prokaryotic domain. Bacteria can be found in a multitude of environments, not just aquatic ones, which makes it inaccurate to state that they are only multi-celled or exclusively found in water. Additionally, bacteria do not contain chitin; this substance is primarily found in the cell walls of fungi and some other organisms, further clarifying why the other options do not accurately describe bacteria.