The bacterium Escherichia coli (E. coli), is a single-celled prokaryote
Many of the internal organs of the human body
An amoeba is a single-celled eukaryote
The liver and gallbladder of a sheep
Polypore fungi and angiosperm trees are large multicellular eukaryotes.
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.
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.
The flower is the angiosperm's reproductive organ. This Hibiscus flower is hermaphroditic, and it contains stamen and pistils.
LUCA may have used the Wood–Ljungdahl or reductive acetyl–CoA pathway to fix carbon.
Strobilus of Equisetum telmateia
Human viscera

Beetles, squids, tetrapods, mushrooms, and vascular plants are examples of multicellular organisms that differentiate specialized tissues and organs during development.

- Organism

Organs exist in most multicellular organisms.

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

3 related topics

Alpha

(A) Electron micrograph of Halothiobacillus neapolitanus cells, arrows highlight carboxysomes. (B) Image of intact carboxysomes isolated from H. neapolitanus. Scale bars are 100 nm.

Organelle

Organelle is a specialized subunit, usually within a cell, that has a specific function.

Organelle is a specialized subunit, usually within a cell, that has a specific function.

(A) Electron micrograph of Halothiobacillus neapolitanus cells, arrows highlight carboxysomes. (B) Image of intact carboxysomes isolated from H. neapolitanus. Scale bars are 100 nm.
Structure of Candidatus Brocadia anammoxidans, showing an anammoxosome and intracytoplasmic membrane

The name organelle comes from the idea that these structures are parts of cells, as organs are to the body, hence organelle, the suffix -elle being a diminutive.

In biology organs are defined as confined functional units within an organism.

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

Biology

Scientific study of life.

Scientific study of life.

Diagram of a fly from Robert Hooke's innovative Micrographia, 1665
In 1842, Charles Darwin penned his first sketch of On the Origin of Species.
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).
Model of hydrogen bonds (1) between molecules of water
Organic compounds such as glucose are vital to organisms.
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.

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

The cell cycle is a vital process by which a single-celled fertilized egg develops into a mature organism, as well as the process by which hair, skin, blood cells, and some internal organs are renewed.

Onion (Allium cepa) root cells in different phases of the cell cycle (drawn by E. B. Wilson, 1900)

Cell (biology)

Basic structural and functional unit of life forms.

Basic structural and functional unit of life forms.

Onion (Allium cepa) root cells in different phases of the cell cycle (drawn by E. B. Wilson, 1900)
Structure of a typical prokaryotic cell
Structure of a typical animal cell
Structure of a typical plant cell
Detailed diagram of lipid bilayer of cell membrane
A fluorescent image of an endothelial cell. Nuclei are stained blue, mitochondria are stained red, and microfilaments are stained green.
Deoxyribonucleic acid (DNA)
Human cancer cells, specifically HeLa cells, with DNA stained blue. The central and rightmost cell are in interphase, so their DNA is diffuse and the entire nuclei are labelled. The cell on the left is going through mitosis and its chromosomes have condensed.
Diagram of the endomembrane system
Prokaryotes divide by binary fission, while eukaryotes divide by mitosis or meiosis.
An outline of the catabolism of proteins, carbohydrates and fats
An overview of protein synthesis.
Within the nucleus of the cell (light blue), genes (DNA, dark blue) are transcribed into RNA. This RNA is then subject to post-transcriptional modification and control, resulting in a mature mRNA (red) that is then transported out of the nucleus and into the cytoplasm (peach), where it undergoes translation into a protein. mRNA is translated by ribosomes (purple) that match the three-base codons of the mRNA to the three-base anti-codons of the appropriate tRNA. Newly synthesized proteins (black) are often further modified, such as by binding to an effector molecule (orange), to become fully active.
Staining of a Caenorhabditis elegans highlights the nuclei of its cells.
Stromatolites are left behind by cyanobacteria, also called blue-green algae. They are the oldest known fossils of life on Earth. This one-billion-year-old fossil is from Glacier National Park in the United States.
Robert Hooke's drawing of cells in cork, 1665

Organelles are parts of the cell that are adapted and/or specialized for carrying out one or more vital functions, analogous to the organs of the human body (such as the heart, lung, and kidney, with each organ performing a different function).

Multicellular organisms are organisms that consist of more than one cell, in contrast to single-celled organisms.