Search results
Results from the WOW.Com Content Network
Non-cellular life, also known as acellular life, is life that exists without a cellular structure for at least part of its life cycle. [1] Historically, most definitions of life postulated that an organism must be composed of one or more cells, [2] but, for some, this is no longer considered necessary, and modern criteria allow for forms of life based on other structural arrangements.
NASA's 2015 strategy for astrobiology aimed to solve the puzzle of the origin of life – how a fully functioning living system could emerge from non-living components – through research on the prebiotic origin of life's chemicals, both in space and on planets, as well as the functioning of early biomolecules to catalyse reactions and support inheritance.
Polycyclic animals reproduce intermittently throughout their lives. Semelparous organisms reproduce only once in their lifetime, [27] such as annual plants (including all grain crops), and certain species of salmon, spider, bamboo and century plant. [28] Often, they die shortly after reproduction. This is often associated with r-strategists.
Prokaryotes (Archaea and Bacteria) reproduce asexually through binary fission, in which the parent organism divides in two to produce two genetically identical daughter organisms. Eukaryotes (such as protists and unicellular fungi) may reproduce in a functionally similar manner by mitosis; most of these are also capable of sexual reproduction.
According to this theory, living things may come forth from nonliving things in a manner roughly analogous to the "enformation of the female matter by the agency of the male seed" seen in sexual reproduction. [18] Nonliving materials, like the seminal fluid present in sexual generation, contain pneuma (πνεῦμα, "breath"), or "vital heat".
Abiotic components include physical conditions and non-living resources that affect living organisms in terms of growth, maintenance, and reproduction. Resources are distinguished as substances or objects in the environment required by one organism and consumed or otherwise made unavailable for use by other organisms.
From a physics perspective, an organism is a thermodynamic system with an organised molecular structure that can reproduce itself and evolve as survival dictates. [ 21 ] [ 22 ] Thermodynamically, life has been described as an open system which makes use of gradients in its surroundings to create imperfect copies of itself. [ 23 ]
Most Protozoa reproduce asexually through binary fission. [39] Many parasitic Protozoa reproduce both asexually and sexually. [38] However, sexual reproduction is rare among free-living protozoa and it usually occurs when food is scarce or the environment changes drastically. [40]