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Noun, pl. bacteria

1. A member of a large group of unicellular microorganisms lacking organelles and an organized nucleus, including some that can cause disease. (Google Dictionary)

2. Constitutes a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals. Bacteria were among the first life forms to appear on Earth, and are present in most habitats on the planet, growing in soil, water, acidic hot springs, radioactive waste, and deep in the Earth’s crust, as well as in organic matter and the live bodies of plants and animals, providing outstanding examples of mutualism in the digestive tracts of humans, termites and cockroaches. (

3. (Science: Microbiology)
Microscopic, single-celled organisms belonging to Kingdom Monera that possess a prokaryotic type of cell structure, which means their cells are noncompartmentalized, and their DNA (usually circular) can be found throughout the cytoplasm rather than within a membrane-bound nucleus. They reproduce by fission or by forming spores. They can practically live everywhere. They can inhabit all kinds of environment, such as in soil, acidic hot springs, radioactive waste, seawater, deep in the Earth’s crust, in stratosphere, and even in the bodies of other organisms. (

Syn: germ, microbe, bacteria

Word origin: From New Latin, from Ancient Greek βακτήριον (bakterion, “small stuff”) + -ium

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