What are bacteria?

Bacteria are indeed microscopic, one-celled organisms that are classified as prokaryotes. This classification means that bacteria do not have a nucleus and are structurally simpler compared to eukaryotic cells, which have a defined nucleus and organelles. The characteristics of bacteria include their small size, typically ranging from 0.5 to 5 micrometers, and their ability to live in diverse environments, including extreme conditions. They reproduce asexually through a process called binary fission, where one cell divides into two identical cells. This versatility allows them to play vital roles in various ecosystems, such as decomposing organic matter, fixing nitrogen in the soil, and even assisting in fermentation processes used in food production.

The other options describe different biological categories. Multicellular organisms consist of many cells working together, which is not applicable to bacteria. Single-celled fungi refers to organisms like yeasts, which are different from bacteria as they belong to the kingdom Fungi, not Bacteria. Complex viruses consist of a core of genes surrounded by a protein coat and, unlike bacteria, they cannot carry out metabolic processes on their own or reproduce independently. Each of these distinctions emphasizes the unique status of bacteria as one-celled organisms within their own domain