In biology Biology is a natural science concerned with the study of life and living organisms, including their structure, function, growth, origin, evolution, distribution, and taxonomy, an organism is any contiguous living Life is a characteristic that distinguishes objects that have signaling and self-sustaining processes (biology) from those that do not, either because such functions have ceased (death), or else because they lack such functions and are classified as inanimate system System is a set of interacting or interdependent entities forming an integrated whole (such as animal Animals are a major group of mostly multicellular, eukaryotic organisms of the kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life. Most animals are motile, meaning they can move spontaneously and independently. All animals are also, plant Plants are living organisms belonging to the kingdom Plantae. They include familiar organisms such as trees, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The scientific study of plants, known as botany, has identified about 350,000 extant species of plants, defined as seed plants, bryophytes, ferns and fern allies. As of 2004,, fungus A fungus is a member of a large group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. The Fungi (pronounced /ˈfʌndʒaɪ/ or /ˈfʌŋɡaɪ/) are classified as a kingdom that is separate from plants, animals and bacteria. One major difference is that fungal cells have cell, or micro-organism A microorganism or microbe is an organism that is microscopic (too small to be seen by the naked human eye). The study of microorganisms is called microbiology, a subject that began with Anton van Leeuwenhoek's discovery of microorganisms in 1675, using a microscope of his own design). In at least some form, all organisms are capable of response to stimuli In physiology, a stimulus is a detectable change in the internal or external environment. The ability of an organism or organ to respond to external stimuli is called sensitivity. When a stimulus is applied to a sensory receptor, it elicits or influences a reflex via stimulus transduction. A stimulus is often the first component of a homeostatic, reproduction Reproduction is the biological process by which new "offspring" individual organisms are produced from their "parents". Reproduction is a fundamental feature of all known life; each individual organism exists as the result of reproduction. The known methods of reproduction are broadly grouped into two main types: sexual and, growth and development Developmental biology is the study of the process by which organisms grow and develop. Modern developmental biology studies the genetic control of cell growth, differentiation and "morphogenesis", which is the process that gives rise to tissues, organs and anatomy, and maintenance of homoeostasis as a stable whole. An organism may either be unicellular A microorganism or microbe is an organism that is microscopic (too small to be seen by the naked human eye). The study of microorganisms is called microbiology, a subject that began with Anton van Leeuwenhoek's discovery of microorganisms in 1675, using a microscope of his own design (single-celled) or be composed of, as in humans, many trillions of cells The cell is the functional basic unit of life. It was discovered by Robert Hooke and is the functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. Some organisms, such as most bacteria, are unicellular . Other organisms, such as humans, grouped into specialized tissues Tissue is a cellular organizational level intermediate between cells and a complete organism. Hence, a tissue is an ensemble of cells, not necessarily identical, but from the same origin, that together carry out a specific function. Organs are then formed by the functional grouping together of multiple tissues and organs In biology and anatomy, an organ is a collection of tissues joined in structural unit to serve a common function. The term multicellular Multicellular organisms are organisms that consist of more than one cell. Each cell is specialized to do a certain job for that organism. Most life that can be seen with the naked eye is multicellular, as are all members of the kingdoms Plantae and Animalia (many-celled) describes any organism made up of more than one cell The cell is the functional basic unit of life. It was discovered by Robert Hooke and is the functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. Some organisms, such as most bacteria, are unicellular . Other organisms, such as humans,.

The term "organism" (Greek Greek , an independent branch of the Indo-European family of languages, is the language of the Greeks. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. In its ancient form, it is the language of classical ancient Greek literature and the New Testament of ὀργανισμός - organismos, from Ancient Greek Ancient Greek is the historical stage in the development of the Greek language spanning the Archaic , Classical (c. 5th–4th centuries BC), and Hellenistic (c. 3rd century BC – 6th century AD) periods of ancient Greece and the ancient world. It is predated in the 2nd millennium BC by Mycenaean Greek. Its Hellenistic phase is known as Koine (& ὄργανον - organon "organ, instrument, tool") first appeared in the English language in 1701 and took on its current definition by 1834 (Oxford English Dictionary The Oxford English Dictionary , published by the Oxford University Press, is a dictionary of the English language. Two fully-bound print editions of the OED have been published under its current name, in 1928 and 1989. As of December 2008[update], the editors had completed one quarter of a third edition).

Scientific classification Biological classification, or scientific classification in biology, is a method by which biologists group and categorize organisms by biological type, such as genus or species. Biological classification is a form of scientific taxonomy, but should be distinguished from folk taxonomy, which lacks scientific basis. Modern biological classification in biology considers organisms synonymous with life on Earth. Based on cell type, organisms may be divided into the prokaryotic The prokaryotes are a group of organisms that lack a cell nucleus (= karyon), or any other membrane-bound organelles. They differ from the eukaryotes, which have a cell nucleus. Most are unicellular, but a few prokaryotes such as myxobacteria have multicellular stages in their life cycles. The word prokaryote comes from the Greek πρό- (pro-) & and eukaryotic A eukaryote is an organism whose cells contain complex structures enclosed within membranes. The defining membrane-bound structure that sets eukaryotic cells apart from prokaryotic cells is the nucleus, or nuclear envelope, within which the genetic material is carried. The presence of a nucleus gives eukaryotes their name, which comes from the groups. The prokaryotes represent two separate domains The three-domain system is a biological classification introduced by Carl Woese in 1990 that divides cellular life forms into archaea, bacteria, and eukaryote domains. In particular, it emphasizes the separation of prokaryotes into two groups, originally called Eubacteria and Archaebacteria (now Archaea). Woese argued that, on the basis of, the Bacteria The bacteria ( [bækˈtɪəriə] ; singular: bacterium)[α] are a large group of single-celled, prokaryote microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals. Bacteria are ubiquitous in every habitat on Earth, growing in soil, acidic hot springs, radioactive waste, and Archaea The Archaea (/ɑrˈkiːə/ ar-KEE-ə) are a group of single-celled microorganisms. A single individual or species from this domain is called an archaeon (sometimes spelled "archeon"). They have no cell nucleus or any other organelles within their cells. In the past they were viewed as an unusual group of bacteria and named archaebacteria. Eukaryotic organisms, with a membrane-bounded cell nucleus In cell biology, the nucleus , also sometimes referred to as the "control center", is a membrane-enclosed organelle found in eukaryotic cells. It contains most of the cell's genetic material, organized as multiple long linear DNA molecules in complex with a large variety of proteins, such as histones, to form chromosomes. The genes, also contain organelles In cell biology, an organelle is a specialized subunit within a cell that has a specific function, and is usually separately enclosed within its own lipid bilayer, namely mitochondria In cell biology, a mitochondrion is a membrane-enclosed organelle found in most eukaryotic cells. These organelles range from 0.5 to 10 micrometers (μm) in diameter. Mitochondria are sometimes described as "cellular power plants" because they generate most of the cell's supply of adenosine triphosphate (ATP), used as a source of and (in plants) plastids Plastids are major organelles found in the cells of plants and algae. Plastids are the site of manufacture and storage of important chemical compounds used by the cell. Plastids often contain pigments used in photosynthesis, and the types of pigments present can change or determine the cell's colour, generally considered to be derived from endosymbiotic The endosymbiotic theory concerns the origins of mitochondria and plastids , which are organelles of eukaryotic cells. According to this theory, these organelles originated as separate prokaryotic organisms that were taken inside the cell as endosymbionts. Mitochondria developed from proteobacteria (in particular, Rickettsiales or close relatives) bacteria.^[1] Fungi A fungus is a member of a large group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. The Fungi (pronounced /ˈfʌndʒaɪ/ or /ˈfʌŋɡaɪ/) are classified as a kingdom that is separate from plants, animals and bacteria. One major difference is that fungal cells have cell, animals Animals are a major group of mostly multicellular, eukaryotic organisms of the kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life. Most animals are motile, meaning they can move spontaneously and independently. All animals are also and plants Plants are living organisms belonging to the kingdom Plantae. They include familiar organisms such as trees, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The scientific study of plants, known as botany, has identified about 350,000 extant species of plants, defined as seed plants, bryophytes, ferns and fern allies. As of 2004, are examples of species that are eukaryotes.

More recently a clade A clade[note 1] is a group consisting of an organism and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological classification. In, Neomura Neomura is a clade composed of the two domains of life of Archaea and Eukaryota. The group was first proposed by Thomas Cavalier-Smith and its name means "new walls"; so called because it is thought to have evolved from Bacteria, and one of the major changes was the replacement of peptidoglycan cell walls with other glycoproteins. The, has been proposed, which groups together the Archaea The Archaea (/ɑrˈkiːə/ ar-KEE-ə) are a group of single-celled microorganisms. A single individual or species from this domain is called an archaeon (sometimes spelled "archeon"). They have no cell nucleus or any other organelles within their cells. In the past they were viewed as an unusual group of bacteria and named archaebacteria and Eukarya A eukaryote is an organism whose cells contain complex structures inside the membranes. The defining membrane-bound structure that sets eukaryotic cells apart from prokaryotic cells is the nucleus, or nuclear envelope, within which the genetic material is carried. The presence of a nucleus gives eukaryotes their name, which comes from the Greek ε�. Neomura is thought to have evolved from Bacteria The bacteria ( [bækˈtɪəriə] ; singular: bacterium)[α] are a large group of single-celled, prokaryote microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals. Bacteria are ubiquitous in every habitat on Earth, growing in soil, acidic hot springs, radioactive waste,, more specifically from Actinobacteria Actinobacteria are a group of Gram-positive bacteria with high G+C ratio. They can be terrestrial or aquatic.^[2]

Semantics

The word "organism" may broadly be defined as an assembly of molecules A molecule is defined as an electrically neutral group of at least two atoms in a definite arrangement held together by very strong chemical bonds. Molecules are distinguished from polyatomic ions in this strict sense. In organic chemistry and biochemistry, the term molecule is used less strictly and also is applied to charged organic molecules that function as a more or less stable whole and has the properties of life. However, many sources propose definitions that exclude viruses A virus is a small infectious agent that can replicate only inside the living cells of organisms. Most viruses are too small to be seen directly with a light microscope. Viruses infect all types of organisms, from animals and plants to bacteria and archaea. Since the initial discovery of tobacco mosaic virus by Martinus Beijerinck in 1898, about 5, and theoretically-possible man-made non-organic life The hypothetical types of biochemistry are the different types of speculative biochemistries of alien life forms that differ radically from those known on Earth. It includes biochemistries that use elements other than carbon for its basic structural and physiological functions and/or use solvents other than water. Theories about extraterrestrial forms.^[3] Viruses A virus is a small infectious agent that can replicate only inside the living cells of organisms. Most viruses are too small to be seen directly with a light microscope. Viruses infect all types of organisms, from animals and plants to bacteria and archaea. Since the initial discovery of tobacco mosaic virus by Martinus Beijerinck in 1898, about 5, are dependent on the biochemical machinery of a host cell for reproduction.

Chambers Online Reference The Chambers Dictionary was first published by W. and R. Chambers as Chambers's English Dictionary in 1872. It was an expanded version of Chambers's Etymological Dictionary of 1867, compiled by James Donald. A second edition came out in 1898, and was followed in 1901 by a new compact edition called Chambers's Twentieth Century Dictionary provides a broad definition: "any living structure, such as a plant, animal, fungus or bacterium, capable of growth and reproduction".^[4]

In multicellular terms, "organism" usually describes the whole hierarchical assemblage of systems (for example circulatory The circulatory system is an organ system that passes nutrients , gases, hormones, blood cells, etc. to and from cells in the body to help fight diseases and help stabilize body temperature and pH to maintain homeostasis, digestive Digestion is the mechanical and chemical breaking down of food into smaller components that can be absorbed into a blood stream, for instance. Digestion is a form of catabolism: a break-down of larger food molecules to smaller ones, or reproductive The reproductive system or genital system is a system of organs within an organism which work together for the purpose of reproduction. Many non-living substances such as fluids, hormones, and pheromones are also important accessories to the reproductive system. Unlike most organ systems, the sexes of differentiated species often have significant) themselves collections of organs In biology and anatomy, an organ is a collection of tissues joined in structural unit to serve a common function; these are, in turn, collections of tissues, which are themselves made of cells The cell is the functional basic unit of life. It was discovered by Robert Hooke and is the functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. Some organisms, such as most bacteria, are unicellular . Other organisms, such as humans,. In some plants and the nematode The nematodes or roundworms (phylum Nematoda) are the most diverse phylum of pseudocoelomates, and one of the most diverse of all animals. Nematode species are very difficult to distinguish; over 28,000 have been described, of which over 16,000 are parasitic. It has been estimated[weasel words] that the total number of described and undescribed Caenorhabditis elegans, individual cells are totipotent.

A superorganism is an organism consisting of many individuals working together as a single functional or social unit.

Viruses

Viruses are not typically considered to be organisms because they are incapable of "independent" or autonomous reproduction or metabolism. This controversy is problematic because some cellular organisms are also incapable of independent survival (but not of independent metabolism and procreation) and live as obligatory intracellular parasites. Although viruses have a few enzymes and molecules characteristic of living organisms, 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 sense they are similar to inanimate matter. While viruses sustain no independent metabolism, and thus are usually not accounted organisms, they do have their own genes and they do evolve by similar mechanisms by which organisms evolve.

Organizational terminology

All organisms are classified by the science of alpha taxonomy into either taxa or clades.

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
• Species

To give an example, Homo sapiens is the Latin binomial equating to modern humans. All members of the species sapiens 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, etc. having become extinct thousands of years ago. Several genera belong to the same family and so on up the 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 than the species within a particular phylum.

Chemistry

Organisms are complex chemical systems, organized in ways that promote reproduction and some measure of sustainability or survival. The molecular phenomena of chemistry are 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 their DNA 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 of chemical 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 (in the 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 other carbon atoms, and its small size make it capable of forming multiple bonds, make it ideal as the basis of organic life. It is able to form small three-atom compounds (such as carbon dioxide), as well as large chains of many thousands of atoms that can store data (nucleic acids), hold cells together, and transmit information (protein).

Macromolecules

Compounds that make up organisms may be divided into macromolecules and other, smaller molecules. The four groups of macromolecule are nucleic acids, proteins, carbohydrates and lipids. Nucleic acids (specifically deoxyribonucleic acid, or DNA) store genetic data as a sequence of nucleotides. The particular sequence of the four different types of nucleotides (adenine, cytosine, guanine, and thymine) dictate the many characteristics that 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 manner and 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, or collagen;
3. Regulatory proteins, such as transcription factors or cyclins that regulate the cell cycle;
4. Signaling molecules or their receptors such as some hormones and 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 unusual amino acids like canavanine.

Lipids make up the membrane of cells that constitutes a barrier, containing everything within the cell and preventing compounds from freely passing into, and out of, the cell. In some 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.

Structure

All organisms consist of monomeric units called cells; 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 tissue the four basic types of which are epithelium, nervous tissue, muscle tissue and connective tissue. Several types of tissue work together in the form of an organ to produce a particular function (such as the pumping of the blood by the heart, or as a barrier to the environment as the skin). This pattern continues to a higher level with several organs functioning as an organ system to allow for reproduction, digestion, etc. Many multicelled organisms consist of several organ systems, which coordinate to allow for life.

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 the hereditary information necessary for regulating cell functions and for transmitting information to the next generation of cells.

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 membrane so DNA is unbound within the cell, eukaryotic cells have nuclear membranes.

All cells, whether prokaryotic or eukaryotic, 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, a salty cytoplasm takes up most of the cell volume. All cells possess DNA, the hereditary material of genes, and RNA, containing the information necessary to build various proteins such as enzymes, the cell's primary machinery. There are also other kinds of biomolecules in cells.

All cells share several abilities:^[5]

• Reproduction by cell division (binary fission, mitosis or meiosis).
• Use of enzymes and other proteins coded for by DNA genes and made via messenger RNA intermediates and ribosomes.
• Metabolism, including taking in raw materials, building cell components, converting energy, molecules and releasing by-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 stimuli such as changes in temperature, pH or nutrient levels.
• Cell contents are contained within a cell surface membrane that contains proteins and a lipid bilayer.

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. Aging is important when determining life span of most organisms, bacterium, a virus or even a prion.^{[citation needed]}

Evolution

In biology, the theory of universal common descent proposes that all organisms on Earth are descended from a common ancestor or ancestral gene pool. Evidence for common descent 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 that 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 of genetic coding suggests common ancestry. For 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 based on appearance or function of species have sometimes been polyphyletic due to convergent evolution.^[6]

The "last universal ancestor" (LUA), or "last universal common ancestor" (LUCA), is the name given to the hypothetical single cellular organism or single cell that gave rise to all life on Earth 3.5 to 3.8 billion years ago^[7]; however, this hypothesis has since been refuted on many grounds. For example, it was once thought that the genetic code was universal (see: universal genetic code), but many variations have been discovered^[8] including various alternative mitochondrial codes.^[9] Back in the early 1970s, evolutionary biologists thought that a given piece of DNA specified the same protein subunit in every living 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 human mitochondrial genes discovered that they used an alternative code, and many slight variants have been discovered since,^[10] including various alternative mitochondrial codes,^[11] as well as small variants such as Mycoplasma translating the codon UGA as tryptophan. Biologists subsequently found exceptions in bacteria and in the nuclei of algae and single-celled animals. For example, certain proteins may use alternative initiation (start) codons not normally used by that species.^[12] In certain proteins, non-standard amino acids are substituted for standard stop codons, depending upon associated signal sequences in the messenger RNA: UGA can code for selenocysteine and UAG can code for pyrrolysine. Selenocysteine is now viewed as the 21st amino acid, and pyrrolysine is viewed as the 22nd. A detailed description of variations in the genetic code can be found at the NCBI web site.

It is now clear that the genetic code is not the same in all living things and this provides credence 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 by horizontal/lateral gene transfer in both prokaryote and eukaryote single cell organisms. This is why phylogenetic trees cannot be rooted; why almost all phylogenetic trees have different branching structures, particularly near the base of the tree; and why many organisms have been found with codons and sections of their DNA sequence that are sometimes unrelated to other species.^[13]

Information about the early development of life includes input from many different fields, including geology and planetary science. These sciences provide information about the history of the Earth and the changes produced by life. However, a great deal of information about the early Earth has been destroyed by geological processes over the course of time.

History of life

The chemical evolution from self-catalytic chemical reactions to 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.

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, which had 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 focus on the behavior of macromolecules, particularly RNA, and the behavior of complex systems.

The emergence of oxygenic photosynthesis (around 3 billion years ago) and the subsequent emergence of an oxygen-rich, non-reducing atmosphere can be traced through the formation of banded iron deposits, and later red beds of iron oxides. This was a necessary prerequisite for the development of aerobic cellular 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 period of 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, or phyla, of modern animals. This event is now believed to have been triggered by the development of the Hox genes. About 500 million years ago, plants and fungi colonized the land, and were soon followed by arthropods and other animals, leading to the development of today's land ecosystems.

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.^[14]. Such comparative studies however are invariably biased by disparities in the time scales over which evolutionary change is measured in the laboratory, field experiments, and the fossil record.

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 transfer of many genes among diverse species including across the boundaries of phylogenetic 'domains'. Thus determining the phylogenetic history of a species can not be done conclusively by determining evolutionary trees for single genes."^[15]

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 of a net to visualize the rich exchange and cooperative effects of HGT among microbes."^[16]

Future of life (cloning and synthetic organisms)

In modern terms, the category of organism 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 the subject of much ethical debate (see Bioethics, Ethics of cloning, and Designer baby articles).

The J. Craig Venter Institute has recently assembled a synthetic yeast genome, Mycoplasma genitalium, by recombination of 25 overlapping DNA fragments in a single step. "The use of yeast recombination greatly simplifies the assembly of large DNA molecules from both synthetic and natural fragments."^[17] Other companies, such as Synthetic Genomics, have already been formed to take advantage of the many commercial uses of custom designed genomes.

Notes

1. ^ T.Cavalier-Smith (1987) The origin of eukaryote and archaebacterial cells, Annals of the New York Academy of Sciences 503, 17–54
2. ^ T. Cavalier-Smith (2002) The neomuran origin of archaebacteria, the negibacterial root of the universal tree and bacterial megaclassification. International Journal of Systematic and Evolutionary Microbiology 52, 7–76
3. ^ "organism". Oxford English Dictionary (online ed.). 2004.
4. ^ "organism". Chambers 21st Century Dictionary (online ed.). 1999.
5. ^ The Universal Features of Cells on Earth in Chapter 1 of Molecular Biology of the Cell fourth edition, edited by Bruce Alberts (2002) published by Garland Science.
6. ^ Villarreal LP, Witzany G (2010). Viruses are essential agents within the roots and stem of the tree of life. J Theor Biol 262: 698-710.
7. ^ Doolittle, W. Ford (February, 2000). Uprooting the tree of life. Scientific American 282 (6): 90–95.
8. ^ NCBI: "The Genetic Codes", Compiled by Andrzej (Anjay) Elzanowski and Jim Ostell
9. ^ Jukes TH, Osawa S, The genetic code in mitochondria and chloroplasts., Experientia. 1990 Dec 1;46(11-12):1117-26.
10. ^ NCBI: "The Genetic Codes", Compiled by Andrzej (Anjay) Elzanowski and Jim Ostell
11. ^ Jukes TH, Osawa S, The genetic code in mitochondria and chloroplasts., Experientia. 1990 Dec 1;46(11-12):1117-26.
12. ^ Genetic Code page in the NCBI Taxonomy section (Downloaded 27 April 2007.)
13. ^ Syoso Osawa (1995). Evolution of the Genetic Code. Oxford University Press. pp. 232. ISBN 978-0198547815.
14. ^ Evaluation of the Rate of Evolution in Natural Populations of Guppies (Poecilia reticulata) "[1]"
15. ^ Oklahoma State - Horizontal Gene Transfer
16. ^ esalenctr.org
17. ^ Gibsona, Daniel G., Gwynedd A. Benders, Kevin C. Axelroda, Jayshree Zaveria, Mikkel A. Algirea, Monzia Moodiea, Michael G. Montaguea, J. Craig Ventera, Hamilton O. Smith, and Clyde A. Hutchison III (2008). "One-step assembly in yeast of 25 overlapping DNA fragments to form a complete synthetic Mycoplasma genitalium genome". PNAS 105 (51): 20404–20409. doi:10.1073/pnas.0811011106. http://www.pnas.org/content/105/51/20404.full.pdf.

External links

• BBCNews: 27 September, 2000, When slime is not so thick Citat: "It means that some of the lowliest creatures in the plant and animal kingdoms, such as slime and amoeba, may not be as primitive as once thought"
  • SpaceRef.com, July 29, 1997: Scientists Discover Methane Ice Worms On Gulf Of Mexico Sea Floor
    • The Eberly College of Science: Methane Ice Worms discovered on Gulf of Mexico Sea Floor download Publication quality photos
  • Artikel, 2000: Methane Ice Worms: Hesiocaeca methanicola. Colonizing Fossil Fuel Reserves
  • SpaceRef.com, May 04, 2001: Redefining "Life as We Know it" Hesiocaeca methanicola In 1997, Charles Fisher, professor of biology at Penn State, discovered this remarkable creature living on mounds of methane ice under half a mile of ocean on the floor of the Gulf of Mexico.
• BBCNews, 18 December, 2002, 'Space bugs' grown in lab Citat: "Bacillus simplex and Staphylococcus pasteuri...Engyodontium album The strains cultured by Dr Wainwright seemed to be resistant to the effects of UV - one quality required for survival in space"
• BBCNews, 19 June, 2003, Ancient organism challenges cell evolution Citat: "It appears that this organelle has been conserved in evolution from prokaryotes to eukaryotes, since it is present in both"
• Interactive Syllabus for General Biology - BI 04, Saint Anselm College, Summer 2003
• Jacob Feldman: Stramenopila
• NCBI Taxonomy entry: root (rich)
• Saint Anselm College: Survey of representatives of the major Kingdoms Citat: "Number of kingdoms has not been resolved...Bacteria present a problem with their diversity...Protista present a problem with their diversity...",
• Species 2000 Indexing the world's known species. Species 2000 has the objective of enumerating all known species of plants, animals, fungi and microbes on Earth as the baseline dataset for studies of global biodiversity. It will also provide a simple access point enabling users to link from here to other data systems for all groups of organisms, using direct species-links.
• The largest organism in the world may be a fungus carpeting nearly 10 square kilometers of an Oregon forest, and may be as old as 10500 years.
• The Tree of Life.
• Frequent questions from kids about life and their answers

Categories: Life | Organisms | Greek loanwords

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