What characteristic features define bacteria?

Bacteria are defined primarily as single-celled organisms that lack a nucleus, categorizing them as prokaryotes. This absence of a defined nucleus differentiates them from eukaryotic cells, which contain a membrane-bound nucleus. Additionally, most bacteria possess a rigid cell wall that provides structural support and helps maintain their shape. The cell wall is significant for bacterial classification and protection from environmental stress.

The nature of bacteria being single-celled allows them to independently carry out all essential life processes, such as metabolism and reproduction. Bacteria can be found in a wide range of environments, including soil, water, and even extreme conditions; they are not limited to just vertebrates. Furthermore, bacteria have diverse reproductive mechanisms, and while some can reproduce under anaerobic conditions, many can reproduce aerobically as well, thus making the claim of reproduction being limited to anaerobic settings inaccurate. Understanding these fundamental features of bacteria is essential for appreciating their role in various biological processes and their impact on ecosystems and human health.