Bacteria are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in …

For example, “ Clostridium botulinum ” is the scientific name for the bacterium that causes botulism. Within a species, scientists may discover different types, or strains, of a bacterium.

Nov 7, 2025 · Bacteria are microscopic single-celled organisms that live in almost every environment on Earth, from deep-sea vents to human digestive tracts. They are prokaryotes, …

Viruses differ from bacteria in several important ways. Viruses are not living organisms; they can only replicate in the cells of a host. By contrast, bacteria are single-celled organisms that can …

Aug 8, 2025 · Bacteria are disease-causing, microscopic, single-celled organisms with prokaryotic cell structures. They do not have membrane-bound organelles, including a true nucleus. Being …

Apr 18, 2025 · These tiny, single-celled organisms—bacteria—are among the most ancient, numerous, and influential forms of life on Earth. They are so small that millions can live in a …

Bacteria are single-celled microorganisms that differ from all other organisms (the eukaryotes) in lacking a true nucleus and organelles such as mitochondria, chloroplasts, and lysosomes.

BACTERIUM definition: 1. a type of very small organism that lives in air, earth, water, plants, and animals, often one…. Learn more.

A bacterium is defined as a primitive, relatively simple, single-celled organism that lacks a cell nucleus. AI generated definition based on: Molecular Biology (Third Edition), 2019

Feb 12, 2019 · Bacteria are microscopic, single-celled organisms that exist in their millions, in every environment, both inside and outside other organisms. Some bacteria are harmful, but …