Microorganism

A microorganism is an organism too small to be seen clearly without a microscope. The group includes bacteria, archaea, many fungi, protists, and some algae.

Bacteria: Bacteria are single-celled organisms whose cells lack a membrane-bound nucleus. They are one of the largest and most familiar groups of microorganisms.
Binary fission: Binary fission is a form of cell division in which one cell divides into two daughter cells. Many bacteria and archaea reproduce by this process.
Fermentation: Fermentation is a metabolic process that releases energy from organic molecules without using oxygen as the final electron acceptor. Microorganisms carry out fermentations used to make foods and beverages.
Infectious disease: An infectious disease is an illness caused by a pathogen that can spread between hosts or from an environment. Some microorganisms cause disease, although most are not human pathogens.
Archaea: Archaea are single-celled organisms distinct from bacteria and eukaryotes in their evolutionary history and cellular machinery. Their small cells resemble bacteria, but their biology defines a separate domain of life.
Microbial metabolism: Microbial metabolism is the set of chemical reactions microorganisms use to obtain energy and build cellular material. Its varied energy sources let microorganisms occupy habitats unavailable to many larger organisms.
Antibiotic: An antibiotic is a substance that kills bacteria or inhibits their growth. Many antibiotics originated as microbial products or were developed from them.
Nitrogen cycle: The nitrogen cycle is the movement and transformation of nitrogen among organisms, soils, waters, and the atmosphere. Microorganisms perform essential transformations such as nitrogen fixation and denitrification.
Protist: A protist is a eukaryotic organism that is not classified as an animal, plant, or fungus. Many protists are microscopic, though the group is diverse and not a single evolutionary lineage.
Horizontal gene transfer: Horizontal gene transfer is the movement of genetic material between organisms outside parent-to-offspring inheritance. It helps explain how microbial traits can spread rapidly across lineages.

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