Hirup

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Hirup ngarupakeun konsép multiharti tanpa dadaran nu basajan, sabab mindeng dilarapkeun kana rupa-rupa hal. WordNet méré opat welas harti pikeun kecap "life", sedengkeun Kamus Wéb Longman méré 35 harti.

Artikel ieu ngadadarkeun harti utama dina élmu hirup; tumbu ka harti séjén bisa ditempo di bagian artikel nu patali di handap.

Ngahartikeun konsép hirup[édit | sunting sumber]

Hirup mibanda sababaraha harti dina jihat biologi —

  • "hirup" nu nujul ka prosés nu keur lumangsung nu nu patali jeung mahluk hirup;
  • "hirup" nu nujul ka mangsa antara wedal jeung paéhna hiji organisme;
  • "hirup" nu nujul ka kaayaan/wujud nalika geus dilahirkeun saméméh paéh.

Sésa bagian ieu museur ka harti nu ahir — naon nu jadi dasar pikeun nyebutkeun yén hiji éntitas téh hirup (mahluk hirup)?

It would be relatively straightforward to offer a practical set of guidelines if one's only concern were life on Earth as we know it (see biosphere), but as soon as one considers questions about life's origins on Earth, or the possibility of extraterrestrial life, or the concept of artificial life, it becomes clear that the question is fundamentally difficult and comparable in many respects to the problem of defining intelligence.

Harti konvénsional[édit | sunting sumber]

Dina biologi, hiji éntitas dianggap hirup mun némbongkeun sakabéh peta di handap ieu:

  1. Kamekaran
  2. Métabolisme, 'barang hakan', ngarobah, sarta neundeun énérgi/massa; tumuwuh ku jalan nyerep jeung nata massa; miceun
  3. Ojah, boh dirina atawa di jero ragana
  4. Baranahan, boga kabisa nyiptakeun éntitas nu sarupa jeung dirina
  5. Némbal rangsangan - kabisa ngukur pasipatan lingkungan sabundeureunana, sarta ojah atawa meta nalika nyanghareupan hiji kaayaan.

Other definitions[édit | sunting sumber]

Other definitions include:

Descent with modification: a "useful" characteristic[édit | sunting sumber]

A useful characteristic upon which to base a definition of life is that of descent with modification: the ability of a life form to produce offspring that are like its parent or parents, but with the possibility of some variation due to chance. Descent with modification is sufficient by itself to allow evolution, assuming that the variations in the offspring allow for differential survival. The study of this form of heritability is called genetics. In all known life forms (assuming prions are not counted as such), the genetic material is primarily DNA or the related molecule, RNA. Another exception might be the software code of certain forms of viruses and programs created through genetic programming, but whether computer programs can be alive even by this definition is still a matter of some contention.

Exceptions to the common definition[édit | sunting sumber]

Note that many individual organisms are incapable of reproduction and yet are still generally considered to be "alive"; see mules and ants for examples. However, these exceptions can be accounted for by applying the definition of life on the level of entire species or of individual genes. (For example, see kin selection for information about one way by which non-reproducing individuals can still enhance the spread of their genes and the survival of their species.)

Viruses reproduce, flames grow, some software programs mutate and evolve, future software programs will probably evince (even high-order) behavior, machines move, and proto-life, consisting of metabolizing cells without reproduction apparatus, can have existed. Still, some would not call these entities alive. Generally, all five characteristics are required for a population to be considered alive.

Asal-usul hirup[édit | sunting sumber]

Artikel utama: Asal-usul hirup

Teu aya modél "baku" pikeun asal-usul hirup, tapi nu kiwari ditampa sacara umum diwangun dumasar papanggihan di handap ieu:

  1. Kaayaan nu ngarojong prabiotik ngahasilkeun kaciptana molekul leutik dasar kahirupan. Ieu dipetakeun dina percobaan Urey-Miller.
  2. Fosfolipid sacara spontan ngawangun lapis ganda lipid, struktur dasar mémbran sél.
  3. Procedures for producing random RNA molecules can produce "ribozymes", which are able to produce more of themselves under very specific conditions.

There are many different hypotheses regarding the path that might have been taken from simple organic molecules to protocells and metabolism. Many of the possibilities have tended to fall into either "genes-first" or "metabolism-first", a recent trend is the emergence of hybrid models that combine aspects of both.

The possibility of extraterrestrial life[édit | sunting sumber]

As of 2004, Earth is the only planet in the universe known by humans to support life. The question of whether life exists elsewhere in the universe remains open, but analyses such as the Drake equation have been used to estimate the probability of such life existing. There have been a number of false alarms of life elsewhere in the universe, but none of these apparent discoveries have so far survived scientific scrutiny.

Currently, the closest that scientists have come to finding extraterrestrial life is fossil evidence of possible bacterial life on Mars (via the ALH84001 meteorite). Searches for extraterrestrial life are presently focusing on planets and moons believed to possess liquid water, presently or in the past. Recent evidence from the NASA rovers Spirit and Opportunity supports the theory that Mars once had surface water. See Life on Mars for further discussion.

Jupiter's moons are also considered good candidates for extraterrestrial life, especially Europa, which seems to possess oceans of liquid water.

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