A microorganism is a living entity that is too small to be seen unaided. This term encompasses bacteria, archaea, microscopic fungi, algae, and protozoa; viruses and prions, although not truly living, are often studied alongside them.
Explanation
Microorganisms constitute a vast and diverse group of life forms that span all domains. Bacteria and archaea are prokaryotes that lack a membrane-bound nucleus. They vary in morphology, metabolism, and environmental tolerance, occupying niches from soil and oceans to hot springs. Fungi and algae are eukaryotic microbes; fungi include yeasts and molds that decompose organic matter, while microscopic algae perform photosynthesis in aquatic environments. Protozoa are single-celled eukaryotes that often move via cilia, flagella or pseudopodia and can be free‑living or parasitic. Viruses are acellular particles that replicate only inside host cells, making them obligate intracellular pathogens. Microorganisms reproduce rapidly through binary fission, budding or spore formation, allowing populations to adapt quickly through mutation and horizontal gene transfer. Their metabolic flexibility drives nutrient cycling, such as nitrogen fixation and decomposition, and some form symbiotic relationships with plants and animals. Others act as pathogens, causing diseases when they invade hosts or produce toxins.
Diversity and Examples
Escherichia coli is a common intestinal bacterium used extensively in research and biotechnology. The yeast Saccharomyces cerevisiae is central to bread and beer production and a model for eukaryotic cell biology. Plasmodium falciparum is a protozoan parasite responsible for severe malaria, while methanogenic archaea generate methane in anaerobic environments. Viruses such as influenza virus and bacteriophages illustrate the non-cellular agents studied in microbiology. These examples underscore the range of forms and lifestyles encompassed by the term microorganism.
Microorganisms dominate Earth’s biomass and influence every ecosystem. Understanding their biology is essential for health, agriculture, industry and environmental management.
Related Terms: Bacteria, Archaea, Protist, Virus, Microbiology