The bacterium Escherichia coli (E. coli), is a single-celled prokaryote
A Caenorhabditis elegans stained to highlight the nuclei of its cells
An amoeba is a single-celled eukaryote
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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.

A multicellular organism is an organism that consists of more than one cell, in contrast to a unicellular organism.

- Multicellular organism

Organisms are classified by taxonomy into groups such as multicellular animals, plants, and fungi; or unicellular microorganisms such as protists, bacteria, and archaea.

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

8 related topics

Alpha

Eukaryote

The endomembrane system and its components
Simplified structure of a mitochondrion
Longitudinal section through the flagellum of Chlamydomonas reinhardtii
Structure of a typical animal cell
Structure of a typical plant cell
Fungal Hyphae cells: 1 – hyphal wall, 2 – septum, 3 – mitochondrion, 4 – vacuole, 5 – ergosterol crystal, 6 – ribosome, 7 – nucleus, 8 – endoplasmic reticulum, 9 – lipid body, 10 – plasma membrane, 11 – spitzenkörper, 12 – Golgi apparatus
This diagram illustrates the twofold cost of sex. If each individual were to contribute the same number of offspring (two), (a) the sexual population remains the same size each generation, where the (b) asexual population doubles in size each generation.
Phylogenetic and symbiogenetic tree of living organisms, showing a view of the origins of eukaryotes and prokaryotes
One hypothesis of eukaryotic relationships – the Opisthokonta group includes both animals (Metazoa) and fungi, plants (Plantae) are placed in Archaeplastida.
A pie chart of described eukaryote species (except for Excavata), together with a tree showing possible relationships between the groups
The three-domains tree and the Eocyte hypothesis
Phylogenetic tree showing a possible relationship between the eukaryotes and other forms of life; eukaryotes are colored red, archaea green and bacteria blue
Eocyte tree.
Diagram of the origin of life with the Eukaryotes appearing early, not derived from Prokaryotes, as proposed by Richard Egel in 2012. This view implies that the UCA was relatively large and complex.

Eukaryotes are organisms whose cells have a nucleus enclosed within a nuclear envelope.

Eukaryotes may be either unicellular or multicellular, and include many cell types forming different kinds of tissue; in comparison, prokaryotes are typically unicellular.

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

Organisms can be classified as unicellular (consisting of a single cell such as bacteria) or multicellular (including plants and animals).

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

Two mitochondria from mammalian lung tissue displaying their matrix and membranes as shown by electron microscopy

Mitochondrion

Double-membrane-bound organelle found in most eukaryotic organisms.

Double-membrane-bound organelle found in most eukaryotic organisms.

Two mitochondria from mammalian lung tissue displaying their matrix and membranes as shown by electron microscopy
Simplified structure of a mitochondrion.
Cross-sectional image of cristae in a rat liver mitochondrion to demonstrate the likely 3D structure and relationship to the inner membrane
Electron transport chain in the mitochondrial intermembrane space
Transmission electron micrograph of a chondrocyte, stained for calcium, showing its nucleus (N) and mitochondria (M).
Typical mitochondrial network (green) in two human cells (HeLa cells)
Model of the yeast multimeric tethering complex, ERMES
Evolution of MROs
The circular 16,569 bp human mitochondrial genome encoding 37 genes, i.e., 28 on the H-strand and 9 on the L-strand.

Some cells in some multicellular organisms lack mitochondria (for example, mature mammalian red blood cells).

The number of mitochondria in a cell can vary widely by organism, tissue, and cell type.

Modern stromatolites in Shark Bay, Western Australia. It can take a century for a stromatolite to grow 5 cm.

Unicellular organism

Modern stromatolites in Shark Bay, Western Australia. It can take a century for a stromatolite to grow 5 cm.
A bottom-dwelling community found deep in the European Arctic.
Paramecium tetraurelia, a ciliate, with oral groove visible
A scanning electron microscope image of a diatom
Transmission electron microscope image of budding Ogataea polymorpha

A unicellular organism, also known as a single-celled organism, is an organism that consists of a single cell, unlike a multicellular organism that consists of multiple cells.

Algae

False-color scanning electron micrograph of the unicellular coccolithophore Gephyrocapsa oceanica
title page of Gmelin's Historia Fucorum, dated 1768
The kelp forest exhibit at the Monterey Bay Aquarium: A three-dimensional, multicellular thallus
Rock lichens in Ireland
Floridian coral reef
Algae on coastal rocks at Shihtiping in Taiwan
Phytoplankton, Lake Chūzenji
Harvesting algae
Seaweed-fertilized gardens on Inisheer
Dulse, a type of edible seaweed
Algae bladder

Algae (singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms.

Included organisms range from unicellular microalgae, such as Chlorella, Prototheca and the diatoms, to multicellular forms, such as the giant kelp, a large brown alga which may grow up to 50 m in length.

Protist

Phylogenetic and symbiogenetic tree of living organisms, showing the origins of eukaryotes
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A protist is any eukaryotic organism (that is, an organism whose cells contain a cell nucleus) that is not an animal, plant, or fungus.

In the five-kingdom system of Lynn Margulis, the term protist is reserved for microscopic organisms, while the more inclusive kingdom Protoctista (or protoctists) included certain large multicellular eukaryotes, such as kelp, red algae, and slime molds.

Cell division in prokaryotes (binary fission) and eukaryotes (mitosis and meiosis)

Cell division

Process by which a parent cell divides, when a mother cell divides into two or more daughter cells.

Process by which a parent cell divides, when a mother cell divides into two or more daughter cells.

Cell division in prokaryotes (binary fission) and eukaryotes (mitosis and meiosis)
Divisome and elongasome complexes responsible for peptidoglycan synthesis during lateral cell-wall growth and division.
Image of the mitotic spindle in a human cell showing microtubules in green, chromosomes (DNA) in blue, and kinetochores in red
Cell division over 42. The cells were directly imaged in the cell culture vessel, using non-invasive quantitative phase contrast time-lapse microscopy.
Kurt Michel with his phase-contrast microscope

For simple unicellular microorganisms such as the amoeba, one cell division is equivalent to reproduction – an entire new organism is created.

On a larger scale, mitotic cell division can create progeny from multicellular organisms, such as plants that grow from cuttings.

Martinus Beijerinck in his laboratory in 1921

Virus

Martinus Beijerinck in his laboratory in 1921
Antigenic shift, or reassortment, can result in novel and highly pathogenic strains of human flu
A typical virus replication cycle
Some bacteriophages inject their genomes into bacterial cells (not to scale)
The Baltimore Classification of viruses is based on the method of viral mRNA synthesis
Overview of the main types of viral infection and the most notable species involved
Transmission electron microscope image of a recreated 1918 influenza virus
Two rotaviruses: the one on the right is coated with antibodies that prevent its attachment to cells and infecting them.
The structure of the DNA base guanosine and the antiviral drug acyclovir
Peppers infected by mild mottle virus
Transmission electron micrograph of multiple bacteriophages attached to a bacterial cell wall
Scientist studying the H5N1 influenza virus

A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism.

In multicellular organisms, if enough cells die, the whole organism will start to suffer the effects.