Diagram of a fly from Robert Hooke's innovative Micrographia, 1665
The bacterium Escherichia coli (E. coli), is a single-celled prokaryote
In 1842, Charles Darwin penned his first sketch of On the Origin of Species.
An amoeba is a single-celled eukaryote
In the Bohr model of an atom, electrons (blue dot) orbit around an atomic nucleus (red-filled circle) in specific atomic orbitals (grey empty circles).
Polypore fungi and angiosperm trees are large multicellular eukaryotes.
Model of hydrogen bonds (1) between molecules of water
Precambrian stromatolites in the Siyeh Formation, Glacier National Park. In 2002, a paper in the scientific journal Nature suggested that these 3.5 Gya (billion years old) geological formations contain fossilized cyanobacteria microbes. This suggests they are evidence of one of the earliest known life forms on Earth.
Organic compounds such as glucose are vital to organisms.
LUCA may have used the Wood–Ljungdahl or reductive acetyl–CoA pathway to fix carbon.
A phospholipid bilayer consists of two adjacent sheets of phospholipids, with the hydrophilic tails facing inwards and the hydrophobic heads facing outwards.
The (a) primary, (b) secondary, (c) tertiary, and (d) quaternary structures of a hemoglobin protein
Structure of an animal cell depicting various organelles
Structure of a plant cell
Example of an enzyme-catalysed exothermic reaction
Respiration in a eukaryotic cell
Photosynthesis changes sunlight into chemical energy, splits water to liberate O2, and fixes CO2 into sugar.
In meiosis, the chromosomes duplicate and the homologous chromosomes exchange genetic information during meiosis I. The daughter cells divide again in meiosis II to form haploid gametes.
Punnett square depicting a cross between two pea plants heterozygous for purple (B) and white (b) blossoms
Bases lie between two spiraling DNA strands.
The extended central dogma of molecular biology includes all the processes involved in the flow of genetic information.
Regulation of various stages of gene expression
Composition of the human genome
Construction of recombinant DNA, in which a foreign DNA fragment is inserted into a plasmid vector
Model of concentration gradient building up; fine yellow-orange outlines are cell boundaries.
Natural selection for darker traits
Comparison of allopatric, peripatric, parapatric and sympatric speciation
Bacteria – Gemmatimonas aurantiaca (-=1 Micrometer)
Archaea – Halobacteria
Diversity of protists
Diversity of plants
Diversity of fungi. Clockwise from top left: Amanita muscaria, a basidiomycete; Sarcoscypha coccinea, an ascomycete; bread covered in mold; chytrid; Aspergillus conidiophore.
Bacteriophages attached to a bacterial cell wall
Root and shoot systems in a eudicot
The xylem (blue) transports water and minerals from the roots upwards whereas the phloem (orange) transports carbohydrates between organs.
Reproduction and development in sporophytes
Negative feedback is necessary for maintaining homeostasis such as keeping body temperature constant.
Diffusion of water and ions in and out of a freshwater fish
Different digestive systems in marine fishes
Respiratory system in a bird
Circulatory systems in arthropods, fish, reptiles, and birds/mammals
Asynchronous muscles power flight in most insects. a: Wings b: Wing joint c: Dorsoventral muscles power upstrokes d: Dorsolongitudinal muscles power downstrokes.
Mouse pyramidal neurons (green) and GABAergic neurons (red)
Sexual reproduction in dragonflies
Cleavage in zebrafish embryo
Processes in the primary immune response
Brood parasites, such as the cuckoo, provide a supernormal stimulus to the parenting species.
Terrestrial biomes are shaped by temperature and precipitation.
Reaching carrying capacity through a logistic growth curve
A (a) trophic pyramid and a (b) simplified food web. The trophic pyramid represents the biomass at each level.
Fast carbon cycle showing the movement of carbon between land, atmosphere, and oceans in billions of tons per year. Yellow numbers are natural fluxes, red are human contributions, white are stored carbon. Effects of the slow carbon cycle, such as volcanic and tectonic activity, are not included.
Efforts are made to preserve the natural characteristics of Hopetoun Falls, Australia, without affecting visitors' access.

In biology, an organism is any organic, living system that functions as an individual entity.

- Organism

For instance, all organisms are made up of cells that process hereditary information encoded in genes, which can be transmitted to future generations.

- Biology
Diagram of a fly from Robert Hooke's innovative Micrographia, 1665

17 related topics

Alpha

Life

Characteristic that distinguishes physical entities that have biological processes, such as signaling and self-sustaining processes, from those that do not, either because such functions have ceased or because they never had such functions and are classified as inanimate.

Characteristic that distinguishes physical entities that have biological processes, such as signaling and self-sustaining processes, from those that do not, either because such functions have ceased or because they never had such functions and are classified as inanimate.

Adenovirus as seen under an electron microscope
Definition of cellular life according to Budisa, Kubyshkin and Schmidt.
The structure of the souls of plants, animals, and humans, according to Aristotle
Cyanobacteria dramatically changed the composition of life forms on Earth by leading to the near-extinction of oxygen-intolerant organisms.
Deinococcus radiodurans is an extremophile that can resist extremes of cold, dehydration, vacuum, acid, and radiation exposure.
Animal corpses, like this African buffalo, are recycled by the ecosystem, providing energy and nutrients for living creatures

Biology is the science that studies life.

One popular definition is that organisms are open systems that maintain homeostasis, are composed of cells, have a life cycle, undergo metabolism, can grow, adapt to their environment, respond to stimuli, reproduce and evolve.

The structure of the DNA double helix. The atoms in the structure are colour-coded by element and the detailed structures of two base pairs are shown in the bottom right.

DNA

The structure of the DNA double helix. The atoms in the structure are colour-coded by element and the detailed structures of two base pairs are shown in the bottom right.
Chemical structure of DNA; hydrogen bonds shown as dotted lines. Each end of the double helix has an exposed 5' phosphate on one strand and an exposed 3' hydroxyl group (—OH) on the other.
A section of DNA. The bases lie horizontally between the two spiraling strands ([[:File:DNA orbit animated.gif|animated version]]).
DNA major and minor grooves. The latter is a binding site for the Hoechst stain dye 33258.
From left to right, the structures of A, B and Z DNA
DNA quadruplex formed by telomere repeats. The looped conformation of the DNA backbone is very different from the typical DNA helix. The green spheres in the center represent potassium ions.
A covalent adduct between a metabolically activated form of benzo[a]pyrene, the major mutagen in tobacco smoke, and DNA
Location of eukaryote nuclear DNA within the chromosomes
T7 RNA polymerase (blue) producing an mRNA (green) from a DNA template (orange)
DNA replication: The double helix is unwound by a helicase and topo­iso­merase. Next, one DNA polymerase produces the leading strand copy. Another DNA polymerase binds to the lagging strand. This enzyme makes discontinuous segments (called Okazaki fragments) before DNA ligase joins them together.
Interaction of DNA (in orange) with histones (in blue). These proteins' basic amino acids bind to the acidic phosphate groups on DNA.
The lambda repressor helix-turn-helix transcription factor bound to its DNA target
The restriction enzyme EcoRV (green) in a complex with its substrate DNA
Recombination involves the breaking and rejoining of two chromosomes (M and F) to produce two rearranged chromosomes (C1 and C2).
The DNA structure at left (schematic shown) will self-assemble into the structure visualized by atomic force microscopy at right. DNA nanotechnology is the field that seeks to design nanoscale structures using the molecular recognition properties of DNA molecules.
Maclyn McCarty (left) shakes hands with Francis Crick and James Watson, co-originators of the double-helix model.
Pencil sketch of the DNA double helix by Francis Crick in 1953
A blue plaque outside The Eagle pub commemorating Crick and Watson

Deoxyribonucleic acid (DNA) is a polymer composed of two polynucleotide chains that coil around each other to form a double helix carrying genetic instructions for the development, functioning, growth and reproduction of all known organisms and many viruses.

Modern biology and biochemistry make intensive use of these techniques in recombinant DNA technology.

Lucretius

Evolution

Change in the heritable characteristics of biological populations over successive generations.

Change in the heritable characteristics of biological populations over successive generations.

Lucretius
Alfred Russel Wallace
Thomas Robert Malthus
In 1842, Charles Darwin penned his first sketch of On the Origin of Species.
DNA structure. Bases are in the centre, surrounded by phosphate–sugar chains in a double helix.
Duplication of part of a chromosome
This diagram illustrates the twofold cost of sex. If each individual were to contribute to the same number of offspring (two), (a) the sexual population remains the same size each generation, where the (b) Asexual reproduction population doubles in size each generation.
Mutation followed by natural selection results in a population with darker colouration.
Simulation of genetic drift of 20 unlinked alleles in populations of 10 (top) and 100 (bottom). Drift to fixation is more rapid in the smaller population.
Homologous bones in the limbs of tetrapods. The bones of these animals have the same basic structure, but have been adapted for specific uses.
A baleen whale skeleton. Letters a and b label flipper bones, which were adapted from front leg bones, while c indicates vestigial leg bones, both suggesting an adaptation from land to sea.
Common garter snake (Thamnophis sirtalis sirtalis) has evolved resistance to the defensive substance tetrodotoxin in its amphibian prey.
The four geographic modes of speciation
Geographical isolation of finches on the Galápagos Islands produced over a dozen new species.
Tyrannosaurus rex. Non-avian dinosaurs died out in the Cretaceous–Paleogene extinction event at the end of the Cretaceous period.
The hominoids are descendants of a common ancestor.
As evolution became widely accepted in the 1870s, caricatures of Charles Darwin with an ape or monkey body symbolised evolution.

It is this process of evolution that has given rise to biodiversity at every level of biological organisation, including the levels of species, individual organisms and molecules.

Their discoveries have influenced not just the development of biology but numerous other scientific and industrial fields, including agriculture, medicine, and computer science.

Description of rare animals (写生珍禽图), by Song dynasty painter Huang Quan (903–965)

Taxonomy (biology)

Description of rare animals (写生珍禽图), by Song dynasty painter Huang Quan (903–965)
Title page of Systema Naturae, Leiden, 1735
Evolution of the vertebrates at class level, width of spindles indicating number of families. Spindle diagrams are typical for evolutionary taxonomy
The same relationship, expressed as a cladogram typical for cladistics
The basic scheme of modern classification. Many other levels can be used; domain, the highest level within life, is both new and disputed.
Type specimen for Nepenthes smilesii, a tropical pitcher plant
A comparison of phylogenetic and phenetic (character-based) concepts

In biology, taxonomy is the scientific study of naming, defining (circumscribing) and classifying groups of biological organisms based on shared characteristics.

All adult Eurasian blue tits share the same coloration, unmistakably identifying the morphospecies.

Species

All adult Eurasian blue tits share the same coloration, unmistakably identifying the morphospecies.
A region of the gene for the cytochrome c oxidase enzyme is used to distinguish species in the Barcode of Life Data Systems database.
The cladistic or phylogenetic species concept is that a species is the smallest lineage which is distinguished by a unique set of either genetic or morphological traits. No claim is made about reproductive isolation, making the concept useful also in palaeontology where only fossil evidence is available.
A chronospecies is defined in a single lineage (solid line) whose morphology changes with time. At some point, palaeontologists judge that enough change has occurred that two species (A and B), separated in time and anatomy, once existed.
A cougar, mountain lion, panther, or puma, among other common names: its scientific name is Puma concolor.
The type specimen (holotype) of Lacerta plica, described by Linnaeus in 1758
Ernst Mayr proposed the widely used Biological Species Concept of reproductive isolation in 1942.
Palaeontologists are limited to morphological evidence when deciding whether fossil life-forms like these Inoceramus bivalves formed a separate species.
Horizontal gene transfers between widely separated species complicate the phylogeny of bacteria.
John Ray believed that species breed true and do not change, even though variations exist.
Carl Linnaeus created the binomial system for naming species.
Blackberries belong to any of hundreds of microspecies of the Rubus fruticosus species aggregate.
The butterfly genus Heliconius contains many similar species.
The Hypsiboas calcaratus–fasciatus species complex contains at least six species of treefrog.
Carrion crow
Hybrid with dark belly, dark gray nape
Hybrid with dark belly
Hooded crow
Seven "species" of Larus gulls interbreed in a ring around the Arctic.
Opposite ends of the ring: a herring gull (Larus argentatus) (front) and a lesser black-backed gull (Larus fuscus) in Norway
A greenish warbler, Phylloscopus trochiloides
Presumed evolution of five "species" of greenish warblers around the Himalayas

In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity.

Nucleic acids RNA (left) and DNA (right).

Nucleic acid

Nucleic acids RNA (left) and DNA (right).
The Swiss scientist Friedrich Miescher discovered nucleic acid first naming it as nuclein, in 1868. Later, he raised the idea that it could be involved in heredity.

Nucleic acids are biopolymers, macromolecules, essential to all known forms of life.

Experimental studies of nucleic acids constitute a major part of modern biological and medical research, and form a foundation for genome and forensic science, and the biotechnology and pharmaceutical industries.

The Tasmanian tiger (Thylacinus cynocephalus) is an example of an extinct species.

Extinction

The Tasmanian tiger (Thylacinus cynocephalus) is an example of an extinct species.
External mold of the extinct Lepidodendron from the Upper Carboniferous of Ohio
Skeleton of various extinct dinosaurs; some other dinosaur lineages still flourish in the form of birds
The dodo of Mauritius, shown here in a 1626 illustration by Roelant Savery, is an often-cited example of modern extinction.
The passenger pigeon, one of the hundreds of species of extinct birds, was hunted to extinction over the course of a few decades.
Scorched land resulting from slash-and-burn agriculture
The golden toad was last seen on May 15, 1989. Decline in amphibian populations is ongoing worldwide.
The large Haast's eagle and moa from New Zealand
Tyrannosaurus, one of the many extinct dinosaur genera. The cause of the Cretaceous–Paleogene extinction event is a subject of much debate amongst researchers.
Georges Cuvier compared fossil mammoth jaws to those of living elephants, concluding that they were distinct from any known living species.
A great hammerhead caught by a sport fisherman. Human exploitation now threatens the survival of this species. Overfishing is the primary driver of shark population declines, which have fallen over 71% since 1970.

Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species.

Extinction is an important research topic in the field of zoology, and biology in general, and has also become an area of concern outside the scientific community.

Visual representation of the history of life on Earth as a spiral

Timeline of the evolutionary history of life

The timeline of the evolutionary history of life represents the current scientific theory outlining the major events during the development of life on planet Earth.

The timeline of the evolutionary history of life represents the current scientific theory outlining the major events during the development of life on planet Earth.

Visual representation of the history of life on Earth as a spiral
Moon
Fragment of the Acasta Gneiss exhibited at the Museum of Natural History in Vienna
The cyanobacterial-algal mat, salty lake on the White Sea seaside
Halobacterium sp. strain NRC-1
Detail of the eukaryote endomembrane system and its components
Dinoflagellate Ceratium furca
Blepharisma japonicum, a free-living ciliated protozoan
Dickinsonia costata, an iconic Ediacaran organism, displays the characteristic quilted appearance of Ediacaran enigmata.
Emergence of animals and plants
With only a handful of species surviving today, the Nautiloids flourished during the early Paleozoic era, from the Late Cambrian, where they constituted the main predatory animals.
Haikouichthys, a jawless fish, is popularized as one of the earliest fishes and probably a basal chordate or a basal craniate.
Ferns first appear in the fossil record about 360 million years ago in the late Devonian period.
Utatsusaurus is the earliest-known ichthyopterygian.
Plateosaurus engelhardti
Cycas circinalis
Mount of oxyaenid Patriofelis from the American Museum of Natural History
The bat Icaronycteris appeared 52.2 million years ago
Grass flowers
Caribbean monk seal
Illustration of a Baiji, declared functionally extinct by the Baiji.org Foundation in 2006.
Western black rhinoceros, holotype specimen of a female shot in 1911
Thylacine shot in 1936

In biology, evolution is any change across successive generations in the heritable characteristics of biological populations.

Evolutionary processes give rise to diversity at every level of biological organization, from kingdoms to species, and individual organisms and molecules, such as DNA and proteins.

The three-domains tree and the Eocyte hypothesis (Two domains tree), 2008.

Domain (biology)

The three-domains tree and the Eocyte hypothesis (Two domains tree), 2008.
Phylogenetic tree showing the relationship between the eukaryotes and other forms of life, 2006 Eukaryotes are colored red, archaea green, and bacteria blue.

In biological taxonomy, a domain ( or ) (Latin: regio ), also dominion, superkingdom, realm, or empire, is the highest taxonomic rank of all organisms taken together.

Chemical structure of a polypeptide macromolecule

Macromolecule

Very large molecule important to biophysical processes, such as a protein or nucleic acid.

Very large molecule important to biophysical processes, such as a protein or nucleic acid.

Chemical structure of a polypeptide macromolecule
Raspberry ellagitannin, a tannin composed of core of glucose units surrounded by gallic acid esters and ellagic acid units
Structure of a polyphenylene dendrimer macromolecule reported by Müllen, et al.

For example, while biology refers to macromolecules as the four large molecules comprising living things, in chemistry, the term may refer to aggregates of two or more molecules held together by intermolecular forces rather than covalent bonds but which do not readily dissociate.

All living organisms are dependent on three essential biopolymers for their biological functions: DNA, RNA and proteins.