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  1. Bacteria - Wikipedia

    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 …

  2. Bacteria | Cell, Evolution, & Classification | Britannica

    Dec 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, …

  3. Bacteria: Definition, Types, Benefits, Risks & Examples

    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.

  4. What Are Bacteria? Structure, Function, and Importance in Life

    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 …

  5. BACTERIUM Definition & Meaning - Merriam-Webster

    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 …

  6. Bacteria: Definition & Characteristics With Examples & Diagram

    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 …

  7. Bacteria - National Human Genome Research Institute

    3 days ago · Bacteria are small single-celled organisms. Bacteria are found almost everywhere on Earth and are vital to the planet's ecosystems. Some species can live under extreme …

  8. What are Bacteria?- A Complete Study Note and Guide

    May 21, 2025 · Bacteria, a singular bacterium, is derived from the Ancient Greek word “ backērion ” meaning “ cane ”, as the first bacteria observed were bacilli. The study of ‘Bacteria’ is called ‘ …

  9. Bacteria - National Geographic Society

    Oct 19, 2023 · Bacteria are microscopic infectious agents that have a long history of infecting humans, but they also play a vital role in supporting human health.

  10. Overview of Bacteria - Infections - Merck Manual Consumer Version

    Bacteria are microscopic, single-celled organisms. They are among the earliest known life forms on earth. There are millions of different kinds of bacteria, and they live in every conceivable …