Organism

The bacterium Escherichia coli (E. coli), is a single-celled prokaryote
An amoeba is a single-celled eukaryote
Polypore fungi and angiosperm trees are large multicellular eukaryotes.
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.
LUCA may have used the Wood–Ljungdahl or reductive acetyl–CoA pathway to fix carbon.

Organism is any organic, living system that functions as an individual entity.

- Organism
The bacterium Escherichia coli (E. coli), is a single-celled prokaryote

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A scanning electron microscope image of a single neutrophil (yellow/right), engulfing anthrax bacteria (orange/left) – scale bar is 5 µm (false color)

Immune system

A scanning electron microscope image of a single neutrophil (yellow/right), engulfing anthrax bacteria (orange/left) – scale bar is 5 µm (false color)
A scanning electron microscope image of normal circulating human blood. One can see red blood cells, several knobby white blood cells including lymphocytes, a monocyte, a neutrophil, and many small disc-shaped platelets.
Overview of the processes involved in the primary immune response
An antibody is made up of two heavy chains and two light chains. The unique variable region allows an antibody to recognize its matching antigen.
The time-course of an immune response begins with the initial pathogen encounter, (or initial vaccination) and leads to the formation and maintenance of active immunological memory.
Joints of a hand swollen and deformed by rheumatoid arthritis, an autoimmune disorder
Skeletal structural formula of the immunosuppressive drug dexamethasone
Polio vaccination in Egypt
Macrophages have identified a cancer cell (the large, spiky mass). Upon fusing with the cancer cell, the macrophages (smaller white cells) inject toxins that kill the tumor cell. Immunotherapy for the treatment of cancer is an active area of medical research.
Paul Ehrlich (1854–1915) was awarded a Nobel Prize in 1908 for his contributions to immunology.

The immune system is a network of biological processes that protects an organism from diseases.

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.

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Gene expression

Process by which information from a gene is used in the synthesis of a functional gene product that enables it to produce end products, protein or non-coding RNA, and ultimately affect a phenotype, as the final effect.

Process by which information from a gene is used in the synthesis of a functional gene product that enables it to produce end products, protein or non-coding RNA, and ultimately affect a phenotype, as the final effect.

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The process of transcription is carried out by RNA polymerase (RNAP), which uses DNA (black) as a template and produces RNA (blue).
Illustration of exons and introns in pre-mRNA and the formation of mature mRNA by splicing. The UTRs (in green) are non-coding parts of exons at the ends of the mRNA.
During the translation, tRNA charged with amino acid enters the ribosome and aligns with the correct mRNA triplet. Ribosome then adds amino acid to growing protein chain.
Protein before (left) and after (right) folding
The patchy colours of a tortoiseshell cat are the result of different levels of expression of pigmentation genes in different areas of the skin.
When lactose is present in a prokaryote, it acts as an inducer and inactivates the repressor so that the genes for lactose metabolism can be transcribed.
The lambda repressor transcription factor (green) binds as a dimer to major groove of DNA target (red and blue) and disables initiation of transcription. From.
In eukaryotes, DNA is organized in form of nucleosomes. Note how the DNA (blue and green) is tightly wrapped around the protein core made of histone octamer (ribbon coils), restricting access to the DNA. From.
Regulation of transcription in mammals. An active enhancer regulatory region is enabled to interact with the promoter region of its target gene by formation of a chromosome loop. This can initiate messenger RNA (mRNA) synthesis by RNA polymerase II (RNAP II) bound to the promoter at the transcription start site of the gene. The loop is stabilized by one architectural protein anchored to the enhancer and one anchored to the promoter and these proteins are joined to form a dimer (red zigzags). Specific regulatory transcription factors bind to DNA sequence motifs on the enhancer. General transcription factors bind to the promoter. When a transcription factor is activated by a signal (here indicated as phosphorylation shown by a small red star on a transcription factor on the enhancer) the enhancer is activated and can now activate its target promoter. The active enhancer is transcribed on each strand of DNA in opposite directions by bound RNAP IIs. Mediator (a complex consisting of about 26 proteins in an interacting structure) communicates regulatory signals from the enhancer DNA-bound transcription factors to the promoter.
DNA methylation is the addition of a methyl group to the DNA that happens at cytosine. The image shows a cytosine single ring base and a methyl group added on to the 5 carbon. In mammals, DNA methylation occurs almost exclusively at a cytosine that is followed by a guanine.
The identified areas of the human brain are involved in memory formation.
Neomycin is an example of a small molecule that reduces expression of all protein genes inevitably leading to cell death; it thus acts as an antibiotic.
The RNA expression profile of the GLUT4 Transporter (one of the main glucose transporters found in the human body)
In situ-hybridization of Drosophila embryos at different developmental stages for the mRNA responsible for the expression of hunchback. High intensity of blue color marks places with high hunchback mRNA quantity.
The three-dimensional structure of green fluorescent protein. The residues in the centre of the "barrel" are responsible for production of green light after exposing to higher energetic blue light. From.
Tet-ON inducible shRNA system

Regulation of gene expression is the basis for cellular differentiation, development, morphogenesis and the versatility and adaptability of any organism.

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

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.

Circadian variation in body temperature, ranging from about 37.5 °C from 10 a.m. to 6 p.m., and falling to about 36.4 °C from 2 a.m. to 6 a.m.

Homeostasis

Circadian variation in body temperature, ranging from about 37.5 °C from 10 a.m. to 6 p.m., and falling to about 36.4 °C from 2 a.m. to 6 a.m.
Birds huddling for warmth
Negative feedback at work in the regulation of blood sugar. Flat line is the set-point of glucose level and sine wave the fluctuations of glucose.
The respiratory center
Calcium homeostasis
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In biology, homeostasis is the state of steady internal, physical, and chemical conditions maintained by living systems.

Branching tree diagram from Heinrich Georg Bronn's work (1858)

Phylogenetics

Branching tree diagram from Heinrich Georg Bronn's work (1858)
Phylogenetic tree suggested by Haeckel (1866)

In biology, phylogenetics (from Greek φυλή/φῦλον (phylé/phylon) "tribe, clan, race", and γενετικός (genetikós) "origin, source, birth") is the study of the evolutionary history and relationships among or within groups of organisms.

Cycle between autotrophs and heterotrophs. Autotrophs use light, carbon dioxide (CO2), and water to form oxygen and complex organic compounds, mainly through the process of photosynthesis (green arrow). Both types of organisms use such compounds via cellular respiration to both generate ATP and again form CO2 and water (two red arrows).

Heterotroph

Cycle between autotrophs and heterotrophs. Autotrophs use light, carbon dioxide (CO2), and water to form oxygen and complex organic compounds, mainly through the process of photosynthesis (green arrow). Both types of organisms use such compounds via cellular respiration to both generate ATP and again form CO2 and water (two red arrows).
Flowchart to determine if a species is autotroph, heterotroph, or a subtype

A heterotroph is an organism that cannot produce its own food, instead taking nutrition from other sources of organic carbon, mainly plant or animal matter.

Many of the internal organs of the human body

Organ (biology)

Organ is a collection of tissues joined in a structural unit to serve a common function.

Organ is a collection of tissues joined in a structural unit to serve a common function.

Many of the internal organs of the human body
The liver and gallbladder of a sheep
Relationship of major animal lineages with indication of how long ago these animals shared a common ancestor. On the left, important organs are shown, which allows us to determine how long ago these may have evolved.
The flower is the angiosperm's reproductive organ. This Hibiscus flower is hermaphroditic, and it contains stamen and pistils.
Strobilus of Equisetum telmateia
Human viscera

Organs exist in most multicellular organisms.

Cladogram (family tree) of a biological group. The last common ancestor is the vertical line stem at the bottom. The blue and red subgroups are clades; each shows its common ancestor stem at the bottom of the subgroup branch. The green subgroup is not a clade; it is a paraphyletic group, because it excludes the blue branch which has descended from the same common ancestor. The green and blue subgroups together form a clade again.

Clade

Cladogram (family tree) of a biological group. The last common ancestor is the vertical line stem at the bottom. The blue and red subgroups are clades; each shows its common ancestor stem at the bottom of the subgroup branch. The green subgroup is not a clade; it is a paraphyletic group, because it excludes the blue branch which has descended from the same common ancestor. The green and blue subgroups together form a clade again.
Early phylogenetic tree by Haeckel, 1866. Groups once thought to be more advanced, such as birds ("Aves"), are placed at the top.
Gavialidae, Crocodylidae and Alligatoridae are clade names that are here applied to a phylogenetic tree of crocodylians.
Cladogram of modern primate groups; all tarsiers are haplorhines, but not all haplorhines are tarsiers; all apes are catarrhines, but not all catarrhines are apes; etc.

A clade, also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree.

A phylogenetic tree: both blue and red groups are monophyletic. The green group is paraphyletic because it is missing a monophyletic group (the blue group) that shares a common ancestor—the lowest green vertical stem.

Monophyly

A phylogenetic tree: both blue and red groups are monophyletic. The green group is paraphyletic because it is missing a monophyletic group (the blue group) that shares a common ancestor—the lowest green vertical stem.
A cladogram of the primates, showing a monophyletic taxon: the simians (in yellow); a paraphyletic taxon: the prosimians (in cyan, including the red patch); and a polyphyletic group: the night-active primates, i.e., the lorises and the tarsiers (in red)
A cladogram of the vertebrates showing phylogenetic groups. A monophyletic taxon (in yellow): the group of "reptiles and birds", contains its most recent common ancestor and all descendants of that ancestor. A paraphyletic taxon (in cyan): the group of reptiles, contains its most recent common ancestor, but does not contain all the descendants (namely Aves) of that ancestor. A polyphyletic "group" (in red): the group of all warm-blooded animals (Aves and Mammalia), does not contain the most recent common ancestor of all its members; this group is not seen as a taxonomic unit and is not considered a taxon by modern systematists.

In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants.