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archaea

n. (plural of archaeon English)

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Archaea

The Archaea ( or or ; singular archaeon) constitute a domain and kingdom of single-celled microorganisms. These microbes are prokaryotes, meaning that they have no cell nucleus or any other membrane-bound organelles in their cells.

Archaea were initially classified as bacteria, receiving the name archaebacteria (in the Archaebacteria kingdom), but this classification is outdated. Archaeal cells have unique properties separating them from the other two domains of life, Bacteria and Eukaryota. The Archaea are further divided into multiple recognized phyla. Classification is difficult because the majority have not been isolated in the laboratory and have only been detected by analysis of their nucleic acids in samples from their environment.

Archaea and bacteria are generally similar in size and shape, although a few archaea have very strange shapes, such as the flat and square-shaped cells of Haloquadratum walsbyi. Despite this morphological similarity to bacteria, archaea possess genes and several metabolic pathways that are more closely related to those of eukaryotes, notably the enzymes involved in transcription and translation. Other aspects of archaeal biochemistry are unique, such as their reliance on ether lipids in their cell membranes, such as archaeols. Archaea use more energy sources than eukaryotes: these range from organic compounds, such as sugars, to ammonia, metal ions or even hydrogen gas. Salt-tolerant archaea (the Haloarchaea) use sunlight as an energy source, and other species of archaea fix carbon; however, unlike plants and cyanobacteria, no known species of archaea does both. Archaea reproduce asexually by binary fission, fragmentation, or budding; unlike bacteria and eukaryotes, no known species forms spores.

Archaea were initially viewed as extremophiles living in harsh environments, such as hot springs and salt lakes, but they have since been found in a broad range of habitats, including soils, oceans, marshlands and the human colon, oral cavity, and skin. Archaea are particularly numerous in the oceans, and the archaea in plankton may be one of the most abundant groups of organisms on the planet. Archaea are a major part of Earth's life and may play roles in both the carbon cycle and the nitrogen cycle. No clear examples of archaeal pathogens or parasites are known, but they are often mutualists or commensals. One example is the methanogens that inhabit human and ruminant guts, where their vast numbers aid digestion. Methanogens are also used in biogas production and sewage treatment, and enzymes from extremophile archaea that can endure high temperatures and organic solvents are exploited in biotechnology.

Usage examples of "archaea".

These were the Archaea, that third order of life along with bacteria and eucarya -and in this case, also citizens of the panspermic cloud which four billion years before fell on Mars from space, having flown many light-years from their point of spontaneous generation around an early second-generation star.

Then later Paul Bunyan, the distant descendant of these panspermic Archaea, came back to Mars to find it cold and ostensibly empty, though some of the old ones still persisted, golluming around in various submartian volcanic percolations.

It is suggested that these are stromatolites, and that the ovoid forms are archaea or nanobacteria, either dormant or slowed metabolically in response to a long-failing environment.

But the relationship between the little red people and the Archaea was clearly not a simple one.

The little red people interpreted their sullen bovine glares as subservience only, but all the while the Archaea were looking at them thinking, You cannibals, we are going to get you some day.

At the same time, they saw immediately what the resentful looks coming from their Archaea crops had meant - it was obvious on the face of it.

Dalai Lama would not eat cows on Earth, the little red people should not eat Archaea on Mars.

Meanwhile, just as the humans were coming down on them from above, the ungrateful Archaea were biting them from below.

At the same time, the Archaea could no longer be confined against their will in the cryptoendolitic world.

They had lots of water, lots of salt, lots of Archaea, and lots of humans.

Meanwhile the Archaea were experiencing a population explosion, and spoiling for a fight.

So she was a lot of things - big like Paul Bunyan, wild like Zo, rebellious like the archaea, happy like John, and as stormy and tempestuous as the Northern Sea.

Also, while the samples do contain magnetites, we question whether any indigenous archaea or nanobacteria would evolve to produce rnagnetites when Mars has a magnetic field so slight that it could not be registered for biological use.

No rnicrobacteria, nanobacteria, archaea or nanofossils was found in any retrieved rock, all of which was retrieved and handled using GEC-mandated sterilization techniques.

This indicates that the Terran archaea may have arrived on Earth in the SNC meteorites.