What are microbes commonly defined as?

Microbes are commonly defined as single-celled organisms that are too small to be seen with the naked eye and require a microscope for observation. This definition encompasses a wide range of organisms, including bacteria, archaea, some fungi, and protozoa, which are primarily unicellular. The distinguishing feature of microbes is their microscopic size, which sets them apart from multicellular organisms that can be seen without magnification.

The focus on single-celled organisms is important because it highlights their simplicity and the diversity of life forms that can exist at such a small scale. Though some exceptions exist, like certain fungi which can be multicellular, the central theme within the context of microbes pertains to their unicellular nature. This classification helps in the understanding of biology and ecology, particularly in how these organisms interact with larger life forms and their environment.