tugas biology

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Organism

From Wikipedia, the free encyclopedia

Jump to: navigation,search"Life on Earth" redirects here. For the BBC series, see Life on Earth (TV series).Not to be confused with Orgasm.

Life on EarthFossil range:Archaean- Recent

TheseEscherichia colicells provide an example

of aprokaryoticmicroorganism

Scientific classification

(unranked):Life on Earth

(Gaeabionta)

Domains and Kingdoms

Cellular life

o Bacteria

o Archaea

o Eukarya

Bikonta Rhizaria

Excavata Heterokonta

Alveolata Plantae

Unikonta

Amoebozoa Fungi

Animalia

Non-cellular life (viruses) **
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Apolyporemushroom hasparasiticrelationship with its host

An ericoid mycorrhizalfungus

Herpes simplex virus

Inbiology, an organism is anylivingsystem (such as animal,plant,fungus, ormicro-organism). In at least some form, all organisms are capable ofresponse to stimuli,

reproduction, growth and development, and maintenance ofhomeostasisas a stable

whole. An organism may either be unicellular(single-celled) or be composed of, as inhumans, many billions ofcells grouped into specialized tissuesand organs. The termmulticellular(many-celled) describes any organism made up of more than onecell.

The term "organism" (Greek- organismos, from Ancient Greek -

organon "organ, instrument, tool") first appeared in the English language in 1701 and

took on its current definition by 1834 (Oxford English Dictionary).
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Scientific classificationin biology considers organisms synonymous with life on Earth.

Based on cell type, organisms may be divided into theprokaryoticandeukaryoticgroups.

The prokaryotes represent two separatedomains, the Bacteria and Archaea. Eukaryoticorganisms, with a membrane-bounded cell nucleus, also containorganelles, namely

mitochondria and (in plants)plastids, generally considered to be derived from

endosymbiotic bacteria.[1]

Fungi, animals andplants are examples of species that areeukaryotes.

More recently a clade,Neomura, has been proposed, which groups together theArchaea

andEukarya. Neomura is thought to have evolved from Bacteria, more specifically from

Actinobacteria.[2]

Semantics

The word "organism" may broadly be defined as an assembly ofmolecules that function

as a more or less stable whole and has the properties of life. However, many sources

propose definitions that excludeviruses and theoretically-possible man-made non-organiclife forms.[3]Viruses are dependent on the biochemical machinery of a host cell for

reproduction.

Chambers Online Reference provides a broad definition: "any living structure, such as a

plant, animal, fungus or bacterium, capable of growth and reproduction".[4]

In multicellular life the word "organism" usually describes the whole hierarchical

assemblage of systems (for example circulatory, digestive, orreproductive) themselves

collections oforgans; these are, in turn, collections of tissues, which are themselves made

ofcells. In some plants and the nematodeCaenorhabditis elegans, individual cells are

totipotent.

A superorganismis an organism consisting of many individuals working together as a

single functional orsocial unit.

[edit] Viruses

Viruses are not typically considered to be organisms because they are incapable of"independent" or autonomous reproduction ormetabolism. This controversy is

problematic because some cellular organisms also incapable of independent survival (but

not of independent metabolism and procreation) and live as obligatory intracellular

parasites. Although viruses have a few enzymesand molecules characteristic of livingorganisms, they have no metabolism of their own and cannot synthesize and organize the

organic compounds that form them. Naturally, this rules out autonomous reproduction

and they can only be passively replicated by the machinery of the host cell. In this sensethey are similar to inanimate matter. While viruses sustain no independent metabolism,

and thus are usually not accounted organisms, they do have their own genesand they do

evolve by similar mechanisms by which organisms evolve.
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[edit] Organizational terminology

The hierarchy ofbiological classification's eight majortaxonomic ranks. Intermediateminor rankings are not shown.

All organisms are classified by the science ofalpha taxonomy into eithertaxa orclades.

Taxa are ranked groups of organisms which run from the general (domain) to the specific

(species). A broad scheme of ranks in hierarchical order is:

Domain

Kingdom

Phylum

Class

Order Family

Genus

To give an example,Homo sapiensis the Latin binomial equating to modern humans. All

members of the speciessapiens are, at least in theory, genetically able to interbreed.Several species may belong to a genus, but the members of different species within a

genus are unable to interbreed to produce fertile offspring. Homo, however, only has one

surviving species (sapiens);Homo erectus,Homo neanderthalensis, &c. having becomeextinct thousands of years ago. Several genera belong to the same family and so on up the
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hierarchy. Eventually, the relevant kingdom (Animalia, in the case of humans) is placed

into one of the three domains depending upon certain genetic and structural

characteristics.

All living organisms known to science are given classification by this system such that

the species within a particular family are more closely related and genetically similar thanthe species within a particular phylum.

A crabis an example of an organism.

[edit] Chemistry

Organisms are complex chemical systems, organized in ways that promote reproduction

and some measure of sustainability or survival. The molecular phenomena of chemistryare fundamental in understanding organisms, but it is a philosophical error (reductionism)

to reduce organismal biology to mere chemistry. It is generally the phenomena of entire

organisms that determine their fitness to an environment and therefore the survivability of

theirDNA based genes.

Organisms clearly owe their origin, metabolism, and many other internal functions to

chemical phenomena, especially the chemistry of large organic molecules. Organisms are

complex systems ofchemical compounds which, through interaction with each other and

the environment, play a wide variety of roles.

Organisms are semi-closed chemical systems. Although they are individual units of life

(as the definition requires) they are not closed to the environment around them. To

operate they constantly take in and release energy. Autotrophs produce usable energy (inthe form of organic compounds) using light from the sun or inorganic compounds while

heterotrophs take in organic compounds from the environment.

The primary chemical element in these compounds is carbon. The physical properties of

this element such as its great affinity for bonding with other small atoms, including othercarbon atoms, and its small size makes it capable of forming multiple bonds, make it

ideal as the basis of organic life. It is able to form small compounds containing three

atoms (such as carbon dioxide) as well as large chains of many thousands of atoms which

are able to store data (nucleic acids), hold cells together and transmit information(protein).

[edit] Macromolecules

The compounds which make up organisms may be divided into macromolecules and

other, smaller molecules. The four groups of macromolecule arenucleic acids,proteins,

carbohydratesand lipids. Nucleic acids (specificallydeoxyribonucleic acid, or DNA)
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store genetic data as a sequence ofnucleotides. The particular sequence of the four

different types of nucleotides (adenine,cytosine,guanine, and thymine) dictate the many

characteristics which constitute the organism. The sequence is divided up into codons,each of which is a particular sequence of three nucleotides and corresponds to a particular

amino acid. Thus a sequence of DNA codes for a particular protein which, due to the

chemical properties of the amino acids of which it is made,folds in a particular mannerand so performs a particular function.

The following functions of protein have been recognized:

1. Enzymes, which catalyze all of the reactions of metabolism;

2. Structural proteins, such as tubulin, orcollagen;

3. Regulatory proteins, such as transcription factorsor cyclins that regulate the cellcycle;

4. Signaling molecules or their receptors such as some hormonesand their receptors;

5. Defensive proteins, which can include everything from antibodies of the immune

system, to toxins (e.g.,dendrotoxins of snakes), to proteins that include unusualamino acids like canavanine.

Lipids make up the membrane of cells which constitutes a barrier, containing everything

within the cell and preventing compounds from freely passing into, and out of, the cell. Insome multicellular organisms they serve to store energy and mediate communication

between cells. Carbohydrates also store and transport energy in some organisms, but are

more easily broken down than lipids.

[edit] Structure

All organisms consist of monomeric units calledcells; some contain a single cell(unicellular) and others contain many units (multicellular). Multicellular organisms are

able to specialize cells to perform specific functions, a group of such cells is tissuethefour basic types of which are epithelium,nervous tissue,muscle tissue and connective

tissue. Several types of tissue work together in the form of anorgan to produce a

particular function (such as the pumping of the blood by the heart, or as a barrier to theenvironment as the skin). This pattern continues to a higher level with several organs

functioning as an organ systemto allow forreproduction,digestion, &c. Many

multicelled organisms comprise of several organ systems which coordinate to allow forlife.

[edit] The cell

The cell theory, first developed in 1839 by Schleiden and Schwann, states that all

organisms are composed of one or more cells; all cells come from preexisting cells; all

vital functions of an organism occur within cells, and cells contain thehereditary

information necessary for regulating cell functions and for transmitting information to thenext generation of cells.
http://en.wikipedia.org/wiki/Nucleotidehttp://en.wikipedia.org/wiki/Adeninehttp://en.wikipedia.org/wiki/Cytosinehttp://en.wikipedia.org/wiki/Cytosinehttp://en.wikipedia.org/wiki/Guaninehttp://en.wikipedia.org/wiki/Guaninehttp://en.wikipedia.org/wiki/Thyminehttp://en.wikipedia.org/wiki/Codonhttp://en.wikipedia.org/wiki/Codonhttp://en.wikipedia.org/wiki/Amino_acidhttp://en.wikipedia.org/wiki/Protein_foldinghttp://en.wikipedia.org/wiki/Protein_foldinghttp://en.wikipedia.org/wiki/Enzymehttp://en.wikipedia.org/wiki/Tubulinhttp://en.wikipedia.org/wiki/Collagenhttp://en.wikipedia.org/wiki/Transcription_factorshttp://en.wikipedia.org/wiki/Transcription_factorshttp://en.wikipedia.org/wiki/Hormoneshttp://en.wikipedia.org/wiki/Hormoneshttp://en.wikipedia.org/wiki/Antibodieshttp://en.wikipedia.org/wiki/Immune_systemhttp://en.wikipedia.org/wiki/Immune_systemhttp://en.wikipedia.org/wiki/Dendrotoxinhttp://en.wikipedia.org/wiki/Dendrotoxinhttp://en.wikipedia.org/wiki/Canavaninehttp://en.wikipedia.org/wiki/Phospholipid_membranehttp://en.wikipedia.org/w/index.php?title=Organism&action=edit&section=6http://en.wikipedia.org/wiki/Cell_(biology)http://en.wikipedia.org/wiki/Cell_(biology)http://en.wikipedia.org/wiki/Unicellularhttp://en.wikipedia.org/wiki/Multicellularhttp://en.wikipedia.org/wiki/Biological_tissuehttp://en.wikipedia.org/wiki/Biological_tissuehttp://en.wikipedia.org/wiki/Epitheliumhttp://en.wikipedia.org/wiki/Epitheliumhttp://en.wikipedia.org/wiki/Nervous_tissuehttp://en.wikipedia.org/wiki/Musclehttp://en.wikipedia.org/wiki/Musclehttp://en.wikipedia.org/wiki/Connective_tissuehttp://en.wikipedia.org/wiki/Connective_tissuehttp://en.wikipedia.org/wiki/Organ_(anatomy)http://en.wikipedia.org/wiki/Organ_(anatomy)http://en.wikipedia.org/wiki/Hearthttp://en.wikipedia.org/wiki/Skinhttp://en.wikipedia.org/wiki/Organ_systemhttp://en.wikipedia.org/wiki/Organ_systemhttp://en.wikipedia.org/wiki/Reproductive_systemhttp://en.wikipedia.org/wiki/Digestive_systemhttp://en.wikipedia.org/wiki/Digestive_systemhttp://en.wikipedia.org/w/index.php?title=Organism&action=edit&section=7http://en.wikipedia.org/wiki/Cell_theoryhttp://en.wikipedia.org/wiki/Matthias_Jakob_Schleidenhttp://en.wikipedia.org/wiki/Theodor_Schwannhttp://en.wikipedia.org/wiki/Theodor_Schwannhttp://en.wikipedia.org/wiki/Geneticshttp://en.wikipedia.org/wiki/Geneticshttp://en.wikipedia.org/wiki/Geneticshttp://en.wikipedia.org/wiki/Nucleotidehttp://en.wikipedia.org/wiki/Adeninehttp://en.wikipedia.org/wiki/Cytosinehttp://en.wikipedia.org/wiki/Guaninehttp://en.wikipedia.org/wiki/Thyminehttp://en.wikipedia.org/wiki/Codonhttp://en.wikipedia.org/wiki/Amino_acidhttp://en.wikipedia.org/wiki/Protein_foldinghttp://en.wikipedia.org/wiki/Enzymehttp://en.wikipedia.org/wiki/Tubulinhttp://en.wikipedia.org/wiki/Collagenhttp://en.wikipedia.org/wiki/Transcription_factorshttp://en.wikipedia.org/wiki/Hormoneshttp://en.wikipedia.org/wiki/Antibodieshttp://en.wikipedia.org/wiki/Immune_systemhttp://en.wikipedia.org/wiki/Immune_systemhttp://en.wikipedia.org/wiki/Dendrotoxinhttp://en.wikipedia.org/wiki/Canavaninehttp://en.wikipedia.org/wiki/Phospholipid_membranehttp://en.wikipedia.org/w/index.php?title=Organism&action=edit&section=6http://en.wikipedia.org/wiki/Cell_(biology)http://en.wikipedia.org/wiki/Unicellularhttp://en.wikipedia.org/wiki/Multicellularhttp://en.wikipedia.org/wiki/Biological_tissuehttp://en.wikipedia.org/wiki/Epitheliumhttp://en.wikipedia.org/wiki/Nervous_tissuehttp://en.wikipedia.org/wiki/Musclehttp://en.wikipedia.org/wiki/Connective_tissuehttp://en.wikipedia.org/wiki/Connective_tissuehttp://en.wikipedia.org/wiki/Organ_(anatomy)http://en.wikipedia.org/wiki/Hearthttp://en.wikipedia.org/wiki/Skinhttp://en.wikipedia.org/wiki/Organ_systemhttp://en.wikipedia.org/wiki/Reproductive_systemhttp://en.wikipedia.org/wiki/Digestive_systemhttp://en.wikipedia.org/w/index.php?title=Organism&action=edit&section=7http://en.wikipedia.org/wiki/Cell_theoryhttp://en.wikipedia.org/wiki/Matthias_Jakob_Schleidenhttp://en.wikipedia.org/wiki/Theodor_Schwannhttp://en.wikipedia.org/wiki/Geneticshttp://en.wikipedia.org/wiki/Genetics


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There are two types of cells, eukaryotic and prokaryotic. Prokaryotic cells are usually

singletons, while eukaryotic cells are usually found in multi-cellular organisms.

Prokaryotic cells lack a nuclear membraneso DNA is unbound within the cell, eukaryoticcells have nuclear membranes.

All cells, whetherprokaryoticoreukaryotic, have a membrane, which envelops the cell,separates its interior from its environment, regulates what moves in and out, and

maintains the electric potential of the cell. Inside the membrane, asaltycytoplasm takesup most of the cell volume. All cells possessDNA, the hereditary material ofgenes, and

RNA, containing the information necessary tobuild variousproteins such as enzymes,

the cell's primary machinery. There are also other kinds ofbiomolecules in cells.

All cells share several abilities:[5]

Reproduction by cell division(binary fission, mitosis ormeiosis).

Use ofenzymes and otherproteinscoded forby DNAgenesand made via

messenger RNA intermediates and ribosomes. Metabolism, including taking in raw materials, building cell components,

converting energy, molecules and releasingby-products. The functioning of a cell

depends upon its ability to extract and use chemical energy stored in organic

molecules. This energy is derived from metabolic pathways. Response to external and internal stimulisuch as changes in temperature,pHor

nutrient levels.

Cell contents are contained within a cell surface membrane that contains proteinsand a lipid bilayer.

[edit] Life span

One of the basic parameters of organism is its life span. Some organisms live as short as

one day, while some plants can live thousands of years. Agingis important whendetermining life span of most organisms, bacterium, a virus or even aprion.[citation needed]

[edit] Evolution

See also: Common descent and Origin of life

In biology, the theory ofuniversal common descent proposes that all organisms on Earth

are descended from a common ancestor or ancestral gene pool. Evidence for commondescent may be found in traits shared between all living organisms. In Darwin's day, the

evidence of shared traits was based solely on visible observation of morphologic

similarities, such as the fact that all birds have wings, even those which do not fly.

Today, there is debate over whether or not all organisms descended from a common

ancestor, or a "last universal ancestor" (LUA), also called the "last universal common

ancestor" (LUCA). The universality ofgenetic codingsuggests common ancestry. For
http://en.wikipedia.org/wiki/Nuclear_membranehttp://en.wikipedia.org/wiki/Nuclear_membranehttp://en.wikipedia.org/wiki/DNAhttp://en.wikipedia.org/wiki/Prokaryotichttp://en.wikipedia.org/wiki/Prokaryotichttp://en.wikipedia.org/wiki/Eukaryotichttp://en.wikipedia.org/wiki/Cell_membranehttp://en.wikipedia.org/wiki/Cell_potentialhttp://en.wikipedia.org/wiki/Salthttp://en.wikipedia.org/wiki/Salthttp://en.wikipedia.org/wiki/Cytoplasmhttp://en.wikipedia.org/wiki/DNAhttp://en.wikipedia.org/wiki/DNAhttp://en.wikipedia.org/wiki/Genehttp://en.wikipedia.org/wiki/RNAhttp://en.wikipedia.org/wiki/Gene_expressionhttp://en.wikipedia.org/wiki/Proteinhttp://en.wikipedia.org/wiki/Enzymehttp://en.wikipedia.org/wiki/Biomoleculehttp://en.wikipedia.org/wiki/Organism#cite_note-AlbertsCh1-4http://en.wikipedia.org/wiki/Cell_divisionhttp://en.wikipedia.org/wiki/Cell_divisionhttp://en.wikipedia.org/wiki/Binary_fissionhttp://en.wikipedia.org/wiki/Mitosishttp://en.wikipedia.org/wiki/Meiosishttp://en.wikipedia.org/wiki/Meiosishttp://en.wikipedia.org/wiki/Enzymehttp://en.wikipedia.org/wiki/Proteinhttp://en.wikipedia.org/wiki/Proteinhttp://en.wikipedia.org/wiki/Genetic_codehttp://en.wikipedia.org/wiki/DNAhttp://en.wikipedia.org/wiki/Genehttp://en.wikipedia.org/wiki/Genehttp://en.wikipedia.org/wiki/Messenger_RNAhttp://en.wikipedia.org/wiki/Ribosomehttp://en.wikipedia.org/wiki/Ribosomehttp://en.wikipedia.org/wiki/Metabolismhttp://en.wikipedia.org/wiki/Metabolismhttp://en.wikipedia.org/wiki/Moleculehttp://en.wikipedia.org/wiki/By-producthttp://en.wikipedia.org/wiki/Metabolic_pathwayhttp://en.wikipedia.org/wiki/Signal_transductionhttp://en.wikipedia.org/wiki/Signal_transductionhttp://en.wikipedia.org/wiki/PHhttp://en.wikipedia.org/wiki/PHhttp://en.wikipedia.org/wiki/PHhttp://en.wikipedia.org/wiki/Cell_membranehttp://en.wikipedia.org/wiki/Lipid_bilayerhttp://en.wikipedia.org/w/index.php?title=Organism&action=edit&section=8http://en.wikipedia.org/wiki/Life_spanhttp://en.wikipedia.org/wiki/Senescencehttp://en.wikipedia.org/wiki/Senescencehttp://en.wikipedia.org/wiki/Prionhttp://en.wikipedia.org/wiki/Prionhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/w/index.php?title=Organism&action=edit&section=9http://en.wikipedia.org/wiki/Common_descenthttp://en.wikipedia.org/wiki/Origin_of_lifehttp://en.wikipedia.org/wiki/Universal_common_descenthttp://en.wikipedia.org/wiki/Last_universal_ancestorhttp://en.wikipedia.org/wiki/Genetic_codinghttp://en.wikipedia.org/wiki/Genetic_codinghttp://en.wikipedia.org/wiki/Nuclear_membranehttp://en.wikipedia.org/wiki/DNAhttp://en.wikipedia.org/wiki/Prokaryotichttp://en.wikipedia.org/wiki/Eukaryotichttp://en.wikipedia.org/wiki/Cell_membranehttp://en.wikipedia.org/wiki/Cell_potentialhttp://en.wikipedia.org/wiki/Salthttp://en.wikipedia.org/wiki/Cytoplasmhttp://en.wikipedia.org/wiki/DNAhttp://en.wikipedia.org/wiki/Genehttp://en.wikipedia.org/wiki/RNAhttp://en.wikipedia.org/wiki/Gene_expressionhttp://en.wikipedia.org/wiki/Proteinhttp://en.wikipedia.org/wiki/Enzymehttp://en.wikipedia.org/wiki/Biomoleculehttp://en.wikipedia.org/wiki/Organism#cite_note-AlbertsCh1-4http://en.wikipedia.org/wiki/Cell_divisionhttp://en.wikipedia.org/wiki/Binary_fissionhttp://en.wikipedia.org/wiki/Mitosishttp://en.wikipedia.org/wiki/Meiosishttp://en.wikipedia.org/wiki/Enzymehttp://en.wikipedia.org/wiki/Proteinhttp://en.wikipedia.org/wiki/Genetic_codehttp://en.wikipedia.org/wiki/DNAhttp://en.wikipedia.org/wiki/Genehttp://en.wikipedia.org/wiki/Messenger_RNAhttp://en.wikipedia.org/wiki/Ribosomehttp://en.wikipedia.org/wiki/Metabolismhttp://en.wikipedia.org/wiki/Moleculehttp://en.wikipedia.org/wiki/By-producthttp://en.wikipedia.org/wiki/Metabolic_pathwayhttp://en.wikipedia.org/wiki/Signal_transductionhttp://en.wikipedia.org/wiki/PHhttp://en.wikipedia.org/wiki/Cell_membranehttp://en.wikipedia.org/wiki/Lipid_bilayerhttp://en.wikipedia.org/w/index.php?title=Organism&action=edit&section=8http://en.wikipedia.org/wiki/Life_spanhttp://en.wikipedia.org/wiki/Senescencehttp://en.wikipedia.org/wiki/Prionhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/w/index.php?title=Organism&action=edit&section=9http://en.wikipedia.org/wiki/Common_descenthttp://en.wikipedia.org/wiki/Origin_of_lifehttp://en.wikipedia.org/wiki/Universal_common_descenthttp://en.wikipedia.org/wiki/Last_universal_ancestorhttp://en.wikipedia.org/wiki/Genetic_coding


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example, every living cell makes use of nucleic acids as its genetic material, and uses the

same twenty amino acids as the building blocks for proteins, although exceptions to the

basic twenty amino acids have been found. However, throughout history groupings basedon appearance or function of species have sometimes beenpolyphyleticdue to

convergent evolution.

A hypotheticalphylogenetic tree of all extant organisms, based on 16SrRNAgenesequence data, showing the evolutionary history of the three domains of life,bacteria,

archaea, and eukaryotes. Originally proposed by Carl Woese.

The "last universal ancestor" (LUA), or "last universal common ancestor" (LUCA), is thename given to the hypothetical single cellularorganismor single cell that gave rise to all

life on Earth 3.5 to 3.8 billion years ago[6]; however, this hypothesis has since been

refuted on many grounds. For example, it was once thought that the genetic codewasuniversal (see: universal genetic code), but many variations have been discovered[7]

including various alternative mitochondrial codes.[8] Back in the early 1970s, evolutionary

biologists thought that a given piece ofDNA specified the sameprotein subunit in everyliving thing, and that the genetic code was thus universal. This was interpreted as

evidence that every organism had inherited its genetic code from a single common

ancestor, aka, an LUCA. In 1979, however, exceptions to the code were found in

mitochondria, the tiny energy factories inside cells. Researchers studying humanmitochondrial genes discovered that they used an alternative code, and many slight

variants have been discovered since,[9] including various alternative mitochondrial codes,[10] as well as small variants such as Mycoplasma translating the codon UGA astryptophan. Biologists subsequently found exceptions inbacteria and in the nuclei of

algaeand single-celled animals. For example, certain proteins may use alternative

initiation (start) codons not normally used by that species.[11] In certain proteins, non-standard amino acids are substituted for standard stop codons, depending upon associated
http://en.wikipedia.org/wiki/Polyphyletichttp://en.wikipedia.org/wiki/Polyphyletichttp://en.wikipedia.org/wiki/Convergent_evolutionhttp://en.wikipedia.org/wiki/Phylogenetic_treehttp://en.wikipedia.org/wiki/Non-coding_RNAhttp://en.wikipedia.org/wiki/Non-coding_RNAhttp://en.wikipedia.org/wiki/Genehttp://en.wikipedia.org/wiki/Three-domain_systemhttp://en.wikipedia.org/wiki/Bacteriahttp://en.wikipedia.org/wiki/Bacteriahttp://en.wikipedia.org/wiki/Archaeahttp://en.wikipedia.org/wiki/Eukaryotehttp://en.wikipedia.org/wiki/Carl_Woesehttp://en.wikipedia.org/wiki/Unicellularhttp://en.wikipedia.org/wiki/Organismshttp://en.wikipedia.org/wiki/Organismshttp://en.wikipedia.org/wiki/Organismshttp://en.wikipedia.org/wiki/Life_on_Earthhttp://en.wikipedia.org/wiki/Organism#cite_note-5http://en.wikipedia.org/wiki/Genetic_codehttp://en.wikipedia.org/wiki/Genetic_codehttp://en.wikipedia.org/wiki/Genetic_code#Variations_to_the_standard_genetic_codehttp://en.wikipedia.org/wiki/Organism#cite_note-6http://en.wikipedia.org/wiki/Organism#cite_note-7http://en.wikipedia.org/wiki/DNAhttp://en.wikipedia.org/wiki/DNAhttp://en.wikipedia.org/wiki/Protein_subunithttp://en.wikipedia.org/wiki/Inheritedhttp://en.wikipedia.org/wiki/Mitochondriahttp://en.wikipedia.org/wiki/Human_mitochondrial_geneticshttp://en.wikipedia.org/wiki/Human_mitochondrial_geneticshttp://en.wikipedia.org/wiki/Organism#cite_note-8http://en.wikipedia.org/wiki/Organism#cite_note-9http://en.wikipedia.org/wiki/Mycoplasmahttp://en.wikipedia.org/wiki/Bacteriahttp://en.wikipedia.org/wiki/Cell_nucleushttp://en.wikipedia.org/wiki/Algaehttp://en.wikipedia.org/wiki/Algaehttp://en.wikipedia.org/wiki/Organism#cite_note-10http://en.wikipedia.org/wiki/File:Phylogenetic_tree.svghttp://en.wikipedia.org/wiki/Polyphyletichttp://en.wikipedia.org/wiki/Convergent_evolutionhttp://en.wikipedia.org/wiki/Phylogenetic_treehttp://en.wikipedia.org/wiki/Non-coding_RNAhttp://en.wikipedia.org/wiki/Genehttp://en.wikipedia.org/wiki/Three-domain_systemhttp://en.wikipedia.org/wiki/Bacteriahttp://en.wikipedia.org/wiki/Archaeahttp://en.wikipedia.org/wiki/Eukaryotehttp://en.wikipedia.org/wiki/Carl_Woesehttp://en.wikipedia.org/wiki/Unicellularhttp://en.wikipedia.org/wiki/Organismshttp://en.wikipedia.org/wiki/Life_on_Earthhttp://en.wikipedia.org/wiki/Organism#cite_note-5http://en.wikipedia.org/wiki/Genetic_codehttp://en.wikipedia.org/wiki/Genetic_code#Variations_to_the_standard_genetic_codehttp://en.wikipedia.org/wiki/Organism#cite_note-6http://en.wikipedia.org/wiki/Organism#cite_note-7http://en.wikipedia.org/wiki/DNAhttp://en.wikipedia.org/wiki/Protein_subunithttp://en.wikipedia.org/wiki/Inheritedhttp://en.wikipedia.org/wiki/Mitochondriahttp://en.wikipedia.org/wiki/Human_mitochondrial_geneticshttp://en.wikipedia.org/wiki/Human_mitochondrial_geneticshttp://en.wikipedia.org/wiki/Organism#cite_note-8http://en.wikipedia.org/wiki/Organism#cite_note-9http://en.wikipedia.org/wiki/Mycoplasmahttp://en.wikipedia.org/wiki/Bacteriahttp://en.wikipedia.org/wiki/Cell_nucleushttp://en.wikipedia.org/wiki/Algaehttp://en.wikipedia.org/wiki/Organism#cite_note-10


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signal sequences in the messenger RNA: UGA can code forselenocysteine and UAG can

code forpyrrolysine. Selenocysteine is now viewed as the 21st amino acid, and

pyrrolysine is viewed as the 22nd. A detailed description of variations in the genetic codecan be found at theNCBI web site.

It is now clear that the genetic code is not the same in all living things and this providescredence that all living things did not evolve on a firmly-rooted tree of life from a single

LUCA. Further support that there is no LUCA has been provided over the years byhorizontal/lateral gene transferin bothprokaryote and eukaryote single cell organisms.

This is whyphylogenetic trees cannot be rooted; why almost all phylogenetic trees have

different branching structures, particularly near the base of the tree; and why manyorganisms have been found with codons and sections of theirDNA sequence that are

sometimes unrelated to other species.[12]

Information about the early development of life includes input from many different

fields, including geology andplanetary science. These sciences provide information

about the history of the Earth and the changes produced by life. However, a great deal ofinformation about the early Earth has been destroyed by geological processes over the

course of time.

[edit] History of life

Main article: Timeline of evolution

The chemical evolutionfrom self-catalytic chemical reactionsto life (see Origin of life)

is not a part of biological evolution, but it is unclear at which point such increasingly

complex sets of reactions became what we would consider, today, to be living organisms.

Precambrianstromatolites in the Siyeh Formation, Glacier National Park. In 2002,

William Schopf ofUCLA published a controversial paper in the journalNature arguing

that formations such as this possess 3.5 billion year oldfossilizedalgae microbes. If true,

they would be the earliest known life on earth.
http://en.wikipedia.org/wiki/Selenocysteinehttp://en.wikipedia.org/wiki/Pyrrolysinehttp://en.wikipedia.org/wiki/Pyrrolysinehttp://www.ncbi.nlm.nih.gov/Taxonomy/Utils/wprintgc.cgi?mode=chttp://en.wikipedia.org/wiki/Horizontal_gene_transfer#Evolutionary_theoryhttp://en.wikipedia.org/wiki/Horizontal_gene_transfer#Evolutionary_theoryhttp://en.wikipedia.org/wiki/Prokaryotehttp://en.wikipedia.org/wiki/Eukaryotehttp://en.wikipedia.org/wiki/Phylogenetic_treeshttp://en.wikipedia.org/wiki/DNA_sequencehttp://en.wikipedia.org/wiki/Organism#cite_note-11http://en.wikipedia.org/wiki/Organism#cite_note-11http://en.wikipedia.org/wiki/Geologyhttp://en.wikipedia.org/wiki/Planetary_sciencehttp://en.wikipedia.org/w/index.php?title=Organism&action=edit&section=10http://en.wikipedia.org/wiki/Timeline_of_evolutionhttp://en.wikipedia.org/wiki/Chemical_evolutionhttp://en.wikipedia.org/wiki/Chemical_evolutionhttp://en.wikipedia.org/wiki/Catalysthttp://en.wikipedia.org/wiki/Catalysthttp://en.wikipedia.org/wiki/Origin_of_lifehttp://en.wikipedia.org/wiki/Precambrianhttp://en.wikipedia.org/wiki/Stromatolitehttp://en.wikipedia.org/wiki/Glacier_National_Park_(U.S.)http://en.wikipedia.org/wiki/University_of_California,_Los_Angeleshttp://en.wikipedia.org/wiki/Nature_(journal)http://en.wikipedia.org/wiki/Fossilhttp://en.wikipedia.org/wiki/Fossilhttp://en.wikipedia.org/wiki/Algaehttp://en.wikipedia.org/wiki/Algaehttp://en.wikipedia.org/wiki/File:Stromatolites.jpghttp://en.wikipedia.org/wiki/File:Stromatolites.jpghttp://en.wikipedia.org/wiki/Selenocysteinehttp://en.wikipedia.org/wiki/Pyrrolysinehttp://www.ncbi.nlm.nih.gov/Taxonomy/Utils/wprintgc.cgi?mode=chttp://en.wikipedia.org/wiki/Horizontal_gene_transfer#Evolutionary_theoryhttp://en.wikipedia.org/wiki/Prokaryotehttp://en.wikipedia.org/wiki/Eukaryotehttp://en.wikipedia.org/wiki/Phylogenetic_treeshttp://en.wikipedia.org/wiki/DNA_sequencehttp://en.wikipedia.org/wiki/Organism#cite_note-11http://en.wikipedia.org/wiki/Geologyhttp://en.wikipedia.org/wiki/Planetary_sciencehttp://en.wikipedia.org/w/index.php?title=Organism&action=edit&section=10http://en.wikipedia.org/wiki/Timeline_of_evolutionhttp://en.wikipedia.org/wiki/Chemical_evolutionhttp://en.wikipedia.org/wiki/Catalysthttp://en.wikipedia.org/wiki/Origin_of_lifehttp://en.wikipedia.org/wiki/Precambrianhttp://en.wikipedia.org/wiki/Stromatolitehttp://en.wikipedia.org/wiki/Glacier_National_Park_(U.S.)http://en.wikipedia.org/wiki/University_of_California,_Los_Angeleshttp://en.wikipedia.org/wiki/Nature_(journal)http://en.wikipedia.org/wiki/Fossilhttp://en.wikipedia.org/wiki/Algae


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Not much is known about the earliest developments in life. However, all existing

organisms share certain traits, including cellular structure and genetic code. Most

scientists interpret this to mean all existing organisms share a common ancestor, whichhad already developed the most fundamental cellular processes, but there is no scientific

consensus on the relationship of the three domains of life (Archaea,Bacteria, Eukaryota)

or the origin of life. Attempts to shed light on the earliest history of life generally focuson the behavior ofmacromolecules, particularlyRNA, and the behavior ofcomplex

systems.

The emergence of oxygenicphotosynthesis (around 3 billion years ago) and the

subsequent emergence of an oxygen-rich, non-reducing atmosphere can be traced throughthe formation ofbanded iron deposits, and laterred bedsof iron oxides. This was a

necessary prerequisite for the development ofaerobiccellular respiration, believed to

have emerged around 2 billion years ago.

In the last billion years, simple multicellular plants and animals began to appear in the

oceans. Soon after the emergence of the first animals, the Cambrian explosion (a periodof unrivaled and remarkable, but brief, organismal diversity documented in the fossils

found at the Burgess Shale) saw the creation of all the major body plans, orphyla, ofmodern animals. This event is now believed to have been triggered by the development

of the Hox genes. About 500 million years ago, plants and fungicolonized the land, and

were soon followed by arthropods and other animals, leading to the development of landecosystems with which we are familiar.

The evolutionary process may be exceedingly slow. Fossil evidence indicates that the

diversity and complexity of modern life has developed over much of the history of the

earth. Geological evidence indicates that the Earth is approximately 4.6 billion years old.

Studies on guppies by David Reznick at the University of California, Riverside, however,have shown that the rate of evolution through natural selection can proceed 10 thousand

to 10 million times faster than what is indicated in the fossil record.[13]. Such comparative

studies however are invariably biased by disparities in the time scales over whichevolutionary change is measured in the laboratory, field experiments, and the fossil

record.

[edit] Horizontal gene transfer, and the history of life

The ancestry of living organisms has traditionally been reconstructed from morphology,

but is increasingly supplemented with phylogenetics - the reconstruction of phylogenies

by the comparison of genetic (DNA) sequence.

"Sequence comparisons suggest recent horizontal transferof many genes among diverse

species including across the boundaries ofphylogenetic'domains'. Thus determining the

phylogenetic history of a species can not be done conclusively by determiningevolutionary trees for single genes."[14]
http://en.wikipedia.org/wiki/Genetic_codehttp://en.wikipedia.org/wiki/Genetic_codehttp://en.wikipedia.org/wiki/Scientific_consensushttp://en.wikipedia.org/wiki/Scientific_consensushttp://en.wikipedia.org/wiki/Archaeahttp://en.wikipedia.org/wiki/Archaeahttp://en.wikipedia.org/wiki/Bacteriumhttp://en.wikipedia.org/wiki/Eukaryotahttp://en.wikipedia.org/wiki/Origin_of_lifehttp://en.wikipedia.org/wiki/Origin_of_lifehttp://en.wikipedia.org/wiki/Macromoleculehttp://en.wikipedia.org/wiki/Macromoleculehttp://en.wikipedia.org/wiki/RNAhttp://en.wikipedia.org/wiki/RNAhttp://en.wikipedia.org/wiki/Complex_systemhttp://en.wikipedia.org/wiki/Complex_systemhttp://en.wikipedia.org/wiki/Photosynthesishttp://en.wikipedia.org/wiki/Photosynthesishttp://en.wikipedia.org/wiki/Banded_iron_formationhttp://en.wikipedia.org/wiki/Red_bedhttp://en.wikipedia.org/wiki/Red_bedhttp://en.wikipedia.org/wiki/Aerobic_respirationhttp://en.wikipedia.org/wiki/Aerobic_respirationhttp://en.wikipedia.org/wiki/Cellular_respirationhttp://en.wikipedia.org/wiki/Cambrian_explosionhttp://en.wikipedia.org/wiki/Burgess_Shalehttp://en.wikipedia.org/wiki/Phylum_(biology)http://en.wikipedia.org/wiki/Phylum_(biology)http://en.wikipedia.org/wiki/Phylum_(biology)http://en.wikipedia.org/wiki/Homeoboxhttp://en.wikipedia.org/wiki/Fungihttp://en.wikipedia.org/wiki/Fungihttp://en.wikipedia.org/wiki/Arthropodhttp://en.wikipedia.org/wiki/Ecosystemhttp://en.wikipedia.org/wiki/History_of_Earthhttp://en.wikipedia.org/wiki/History_of_Earthhttp://en.wikipedia.org/wiki/Age_of_the_Earthhttp://en.wikipedia.org/wiki/Organism#cite_note-12http://en.wikipedia.org/w/index.php?title=Organism&action=edit&section=11http://en.wikipedia.org/wiki/Horizontal_gene_transferhttp://en.wikipedia.org/wiki/Horizontal_gene_transferhttp://en.wikipedia.org/wiki/Genehttp://en.wikipedia.org/wiki/Specieshttp://en.wikipedia.org/wiki/Phylogeneticshttp://en.wikipedia.org/wiki/Phylogeneticshttp://en.wikipedia.org/wiki/Organism#cite_note-13http://en.wikipedia.org/wiki/Genetic_codehttp://en.wikipedia.org/wiki/Scientific_consensushttp://en.wikipedia.org/wiki/Scientific_consensushttp://en.wikipedia.org/wiki/Archaeahttp://en.wikipedia.org/wiki/Bacteriumhttp://en.wikipedia.org/wiki/Eukaryotahttp://en.wikipedia.org/wiki/Origin_of_lifehttp://en.wikipedia.org/wiki/Macromoleculehttp://en.wikipedia.org/wiki/RNAhttp://en.wikipedia.org/wiki/Complex_systemhttp://en.wikipedia.org/wiki/Complex_systemhttp://en.wikipedia.org/wiki/Photosynthesishttp://en.wikipedia.org/wiki/Banded_iron_formationhttp://en.wikipedia.org/wiki/Red_bedhttp://en.wikipedia.org/wiki/Aerobic_respirationhttp://en.wikipedia.org/wiki/Cellular_respirationhttp://en.wikipedia.org/wiki/Cambrian_explosionhttp://en.wikipedia.org/wiki/Burgess_Shalehttp://en.wikipedia.org/wiki/Phylum_(biology)http://en.wikipedia.org/wiki/Homeoboxhttp://en.wikipedia.org/wiki/Fungihttp://en.wikipedia.org/wiki/Arthropodhttp://en.wikipedia.org/wiki/Ecosystemhttp://en.wikipedia.org/wiki/History_of_Earthhttp://en.wikipedia.org/wiki/History_of_Earthhttp://en.wikipedia.org/wiki/Age_of_the_Earthhttp://en.wikipedia.org/wiki/Organism#cite_note-12http://en.wikipedia.org/w/index.php?title=Organism&action=edit&section=11http://en.wikipedia.org/wiki/Horizontal_gene_transferhttp://en.wikipedia.org/wiki/Genehttp://en.wikipedia.org/wiki/Specieshttp://en.wikipedia.org/wiki/Phylogeneticshttp://en.wikipedia.org/wiki/Organism#cite_note-13


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Biologist Gogarten suggests "the original metaphor of a tree no longer fits the data from

recent genome research", therefore "biologists [should] use the metaphor of a mosaic to

describe the different histories combined in individual genomes and use [the] metaphor ofa net to visualize the rich exchange and cooperative effects of HGT among microbes."[15]

[edit] Future of life (cloning and synthetic organisms)

In modern terms, the category oforganism cloning refers to the procedure of creating a

new multicellular organism, genetically identical to another. However, cloning also has

the potential of creating entirely new species of organisms. Organism cloning is thesubject of much ethical debate (see Bioethics,Ethics of cloning, and Designer baby

articles).

The J. Craig Venter Institute has recently assembled a synthetic yeastgenome,Mycoplasma genitalium, by recombination of 25 overlapping DNA fragments in a singlestep. "The use of yeast recombination greatly simplifies the assembly of large DNA

molecules from both synthetic and natural fragments."[16]

Other companies, such asSynthetic Genomics, have already been formed to take advantage of the manycommercial uses of custom designed genomes.
http://en.wikipedia.org/wiki/Organism#cite_note-14http://en.wikipedia.org/w/index.php?title=Organism&action=edit&section=12http://en.wikipedia.org/wiki/Cloning#Organism_cloninghttp://en.wikipedia.org/wiki/Bioethicshttp://en.wikipedia.org/wiki/Ethics_of_cloninghttp://en.wikipedia.org/wiki/Ethics_of_cloninghttp://en.wikipedia.org/wiki/Designer_babyhttp://en.wikipedia.org/wiki/J._Craig_Venter_Institutehttp://en.wikipedia.org/wiki/Yeasthttp://en.wikipedia.org/wiki/Genomehttp://en.wikipedia.org/wiki/Mycoplasma_genitaliumhttp://en.wikipedia.org/wiki/Organism#cite_note-Venter-15http://en.wikipedia.org/wiki/Synthetic_Genomicshttp://en.wikipedia.org/wiki/Organism#cite_note-14http://en.wikipedia.org/w/index.php?title=Organism&action=edit&section=12http://en.wikipedia.org/wiki/Cloning#Organism_cloninghttp://en.wikipedia.org/wiki/Bioethicshttp://en.wikipedia.org/wiki/Ethics_of_cloninghttp://en.wikipedia.org/wiki/Designer_babyhttp://en.wikipedia.org/wiki/J._Craig_Venter_Institutehttp://en.wikipedia.org/wiki/Yeasthttp://en.wikipedia.org/wiki/Genomehttp://en.wikipedia.org/wiki/Mycoplasma_genitaliumhttp://en.wikipedia.org/wiki/Organism#cite_note-Venter-15http://en.wikipedia.org/wiki/Synthetic_Genomics

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