Organism

The term "organism" (from the Ancient Greek , derived from , meaning , , or ) It is related to the verb "organize". == Whether criteria exist, or are needed ==

stated this as "the quality of being sufficiently heterogeneous in form to be rendered non-functional if cut in half". • an immune response, separating self from foreign • "anti-entropy", the ability to maintain order, a concept first proposed by Erwin Schrödinger; or in another form, that Claude Shannon's information theory can be used to identify organisms as capable of self-maintaining their information content Other scientists think that the concept of the organism is inadequate in biology; that the concept of individuality is problematic; and from a philosophical point of view, question whether such a definition is necessary. Problematic cases include colonial organisms: for instance, a colony of eusocial insects fulfills criteria such as adaptive organisation and germ-soma specialisation. If so, the same argument, or a criterion of high co-operation and low conflict, would include some mutualistic (e.g. lichens) and sexual partnerships (e.g. anglerfish) as organisms. If group selection occurs, then a group could be viewed as a superorganism, optimized by group adaptation. Another view is that attributes like autonomy, genetic homogeneity and genetic uniqueness should be examined separately, rather than requiring that an organism possess all of them. On this view, there are multiple dimensions to biological individuality, resulting in several types of organism. == Organisms at differing levels of biological organisation ==

consists of a body formed mainly by fungi, with unicellular algae or cyanobacteria (green) interspersed within the structure, and a bacterial microbiome. The species are mutually interdependent, like cells within a multicellular organism. A multicellular organism such as an animal, plant, fungus, or alga is composed of many cells, often specialised. The evolutionary biologists David Queller and Joan Strassmann state that "organismality" has evolved socially, as groups of simpler units (from cells upwards) came to cooperate without conflicts. They propose that cooperation should be used as the "defining trait" of an organism. == Boundary cases ==

Viruses is not a cell; it contains only its genetic material, and a protein coat. Viruses are not typically considered to be organisms, because they are incapable of autonomous reproduction, growth, metabolism, or homeostasis. Although viruses have a few enzymes and molecules like those in living organisms, they have no metabolism of their own; they cannot synthesize the organic compounds from which they are formed. In this sense, they are similar to inanimate matter. Viruses have their own genes, and they evolve. Thus, an argument that viruses should be classed as living organisms is their ability to undergo evolution and replicate through self-assembly. However, some scientists argue that viruses neither evolve nor self-reproduce. Instead, viruses are evolved by their host cells, meaning that there was co-evolution of viruses and host cells. If host cells did not exist, viral evolution would be impossible. As for reproduction, viruses rely on hosts' machinery to replicate. The discovery of viruses with genes coding for energy metabolism and protein synthesis fuelled the debate about whether viruses are living organisms, but the genes have a cellular origin. Most likely, they were acquired through horizontal gene transfer from viral hosts. According to this hypothesis "organisms" emerged when RNA chains began to self-replicate, initiating the three mechanisms of Darwinian selection: heritability, variation of type and differential reproductive output. The fitness of an RNA replicator (its per capita rate of increase) would presumably have been a function of its intrinsic adaptive capacities, determined by its nucleotide sequence, and the availability of external resources. The three primary adaptive capacities of these early "organisms" may have been: (1) replication with moderate fidelity, giving rise to both heritability while allowing variation of type, (2) resistance to decay, and (3) acquisition of and processing of resources An evolved organism takes its form by the partially understood mechanisms of evolutionary developmental biology, in which the genome directs an elaborated series of interactions to produce successively more elaborate structures. The existence of chimaeras and hybrids demonstrates that these mechanisms are "intelligently" robust in the face of radically altered circumstances at all levels from molecular to organismal. Synthetic organisms already take diverse forms, and their diversity will increase. What they all have in common is a teleonomic or goal-seeking behaviour that enables them to correct errors of many kinds so as to achieve whatever result they are designed for. Such behaviour is reminiscent of intelligent action by organisms; intelligence is seen as an embodied form of cognition. == References ==