The cell (from
Latin ''cella'', meaning "small room"
) is the basic structural, functional, and biological unit of all known organisms. Cells are the smallest units of life, and hence are often referred to as the "building blocks of life". The study of cells is called
cell biology, cellular biology, or cytology.
Cells consist of
cytoplasm enclosed within a
membrane, which contains many
biomolecules such as
proteins and
nucleic acids.
[Cell Movements and the Shaping of the Vertebrate Body](_blank)
in Chapter 21 of
Molecular Biology of the Cell
' fourth edition, edited by Bruce Alberts (2002) published by Garland Science.
The Alberts text discusses how the "cellular building blocks" move to shape developing embryos. It is also common to describe small molecules such as amino acids as
molecular building blocks
. Most plant and animal cells are only visible under a
light microscope, with dimensions between 1 and 100
micrometres.
Electron microscopy gives a much higher resolution showing greatly detailed cell structure. Organisms can be classified as
unicellular (consisting of a single cell such as
bacteria) or
multicellular (including plants and animals).
Most
unicellular organisms are classed as
microorganisms.
The number of cells in plants and animals varies from species to species; it has been estimated that humans contain somewhere around 40 trillion (4×10
13) cells.
The human brain accounts for around 80 billion of these cells.
Cells were discovered by
Robert Hooke in 1665, who named them for their resemblance to cells inhabited by
Christian monks in a monastery.
Cell theory, first developed in 1839 by
Matthias Jakob Schleiden and
Theodor Schwann, states that all organisms are composed of one or more cells, that cells are the fundamental unit of structure and function in all living organisms, and that all cells come from pre-existing cells. Cells emerged on Earth at least 3.5 billion years ago.
Cell types
Cells are of two types:
eukaryotic, which contain a
nucleus, and
prokaryotic, which do not. Prokaryotes are
single-celled organisms, while eukaryotes can be either single-celled or
multicellular.
Prokaryotic cells
Prokaryotes include
bacteria and
archaea, two of the
three domains of life. Prokaryotic cells were the first form of
life on Earth, characterized by having vital
biological processes including
cell signaling. They are simpler and smaller than eukaryotic cells, and lack a
nucleus, and other membrane-bound
organelles. The
DNA of a prokaryotic cell consists of a single
circular chromosome that is in direct contact with the
cytoplasm. The nuclear region in the cytoplasm is called the
nucleoid. Most prokaryotes are the smallest of all organisms ranging from 0.5 to 2.0 μm in diameter.
A prokaryotic cell has three regions:
* Enclosing the cell is the
cell envelope – generally consisting of a
plasma membrane covered by a
cell wall which, for some bacteria, may be further covered by a third layer called a
capsule. Though most prokaryotes have both a cell membrane and a cell wall, there are exceptions such as ''
Mycoplasma'' (bacteria) and ''
Thermoplasma'' (archaea) which only possess the cell membrane layer. The envelope gives rigidity to the cell and separates the interior of the cell from its environment, serving as a protective filter. The cell wall consists of
peptidoglycan in bacteria, and acts as an additional barrier against exterior forces. It also prevents the cell from expanding and bursting (
cytolysis) from
osmotic pressure due to a
hypotonic environment. Some eukaryotic cells (
plant cells and
fungal cells) also have a cell wall.
* Inside the cell is the
cytoplasmic region that contains the
genome (DNA), ribosomes and various sorts of inclusions.
[ 30 March 2004.] The genetic material is freely found in the cytoplasm. Prokaryotes can carry
extrachromosomal DNA elements called
plasmids, which are usually circular. Linear bacterial plasmids have been identified in several species of
spirochete bacteria, including members of the genus ''
Borrelia'' notably ''
Borrelia burgdorferi'', which causes Lyme disease. Though not forming a nucleus, the
DNA is condensed in a
nucleoid. Plasmids encode additional genes, such as
antibiotic resistance genes.
* On the outside,
flagella and
pili project from the cell's surface. These are structures (not present in all prokaryotes) made of proteins that facilitate movement and communication between cells.
Eukaryotic cells
Plants,
animals,
fungi,
slime moulds,
protozoa, and
algae are all
eukaryotic. These cells are about fifteen times wider than a typical prokaryote and can be as much as a thousand times greater in volume. The main distinguishing feature of eukaryotes as compared to prokaryotes is
compartmentalization: the presence of membrane-bound
organelles (compartments) in which specific activities take place. Most important among these is a
cell nucleus,
an organelle that houses the cell's
DNA. This nucleus gives the eukaryote its name, which means "true kernel (nucleus)". Other differences include:
* The plasma membrane resembles that of prokaryotes in function, with minor differences in the setup. Cell walls may or may not be present.
* The eukaryotic DNA is organized in one or more linear molecules, called
chromosomes, which are associated with
histone proteins. All chromosomal DNA is stored in the
cell nucleus, separated from the cytoplasm by a membrane.
Some eukaryotic organelles such as
mitochondria also contain some DNA.
* Many eukaryotic cells are
ciliated with
primary cilia. Primary cilia play important roles in chemosensation,
mechanosensation, and thermosensation. Each cilium may thus be "viewed as a sensory cellular
antennae that coordinates a large number of cellular signaling pathways, sometimes coupling the signaling to ciliary motility or alternatively to cell division and differentiation."
* Motile eukaryotes can move using
motile cilia or
flagella. Motile cells are absent in
conifers and
flowering plants.
[PH Raven, Evert RF, Eichhorm SE (1999) Biology of Plants, 6th edition. WH Freeman, New York] Eukaryotic flagella are more complex than those of prokaryotes.
Subcellular components
All cells, whether
prokaryotic or
eukaryotic, have a
membrane that envelops the cell, regulates what moves in and out (selectively permeable), and maintains the
electric potential of the cell. Inside the membrane, the
cytoplasm takes up most of the cell's volume. All cells (except
red blood cells which lack a cell nucleus and most organelles to accommodate maximum space for
hemoglobin) 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. This article lists these primary
cellular components, then briefly describes their function.
Membrane
The
cell membrane, or plasma membrane, is a
biological membrane that surrounds the cytoplasm of a cell. In animals, the plasma membrane is the outer boundary of the cell, while in plants and prokaryotes it is usually covered by a
cell wall. This membrane serves to separate and protect a cell from its surrounding environment and is made mostly from a
double layer of phospholipids, which are
amphiphilic (partly
hydrophobic and partly
hydrophilic). Hence, the layer is called a
phospholipid bilayer, or sometimes a fluid mosaic membrane. Embedded within this membrane is a macromolecular structure called the
porosome the universal secretory portal in cells and a variety of
protein molecules that act as channels and pumps that move different molecules into and out of the cell.
The membrane is semi-permeable, and selectively permeable, in that it can either let a substance (
molecule or
ion) pass through freely, pass through to a limited extent or not pass through at all. Cell surface membranes also contain
receptor proteins that allow cells to detect external signaling molecules such as
hormones.
Cytoskeleton

The cytoskeleton acts to organize and maintain the cell's shape; anchors organelles in place; helps during
endocytosis, the uptake of external materials by a cell, and
cytokinesis, the separation of daughter cells after
cell division; and moves parts of the cell in processes of growth and mobility. The eukaryotic cytoskeleton is composed of
microtubules,
intermediate filaments and
microfilaments. In the cytoskeleton of a
neuron the intermediate filaments are known as
neurofilaments. There are a great number of proteins associated with them, each controlling a cell's structure by directing, bundling, and aligning filaments.
The prokaryotic cytoskeleton is less well-studied but is involved in the maintenance of cell shape,
polarity and cytokinesis. The subunit protein of microfilaments is a small, monomeric protein called
actin. The subunit of microtubules is a dimeric molecule called
tubulin. Intermediate filaments are heteropolymers whose subunits vary among the cell types in different tissues. But some of the subunit protein of intermediate filaments include
vimentin,
desmin,
lamin (lamins A, B and C),
keratin (multiple acidic and basic keratins), neurofilament proteins (NF–L, NF–M).
Genetic material

Two different kinds of genetic material exist:
deoxyribonucleic acid (DNA) and
ribonucleic acid (RNA). Cells use DNA for their long-term information storage. The biological information contained in an organism is
encoded in its DNA sequence.
RNA is used for information transport (e.g.,
mRNA) and
enzymatic functions (e.g.,
ribosomal RNA).
Transfer RNA (tRNA) molecules are used to add amino acids during protein
translation.
Prokaryotic genetic material is organized in a simple
circular bacterial chromosome in the
nucleoid region of the cytoplasm. Eukaryotic genetic material is divided into different,
linear molecules called
chromosomes inside a discrete nucleus, usually with additional genetic material in some organelles like
mitochondria and
chloroplasts (see
endosymbiotic theory).
A
human cell has genetic material contained in the
cell nucleus (the
nuclear genome) and in the mitochondria (the
mitochondrial genome). In humans the nuclear genome is divided into 46 linear DNA molecules called
chromosomes, including 22
homologous chromosome pairs and a pair of
sex chromosomes. The mitochondrial genome is a circular DNA molecule distinct from the nuclear DNA. Although the
mitochondrial DNA is very small compared to nuclear chromosomes,
it codes for 13 proteins involved in mitochondrial energy production and specific tRNAs.
Foreign genetic material (most commonly DNA) can also be artificially introduced into the cell by a process called
transfection. This can be transient, if the DNA is not inserted into the cell's
genome, or stable, if it is. Certain
viruses also insert their genetic material into the genome.
Organelles
Organelles are parts of the cell which 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).
Both eukaryotic and prokaryotic cells have organelles, but prokaryotic organelles are generally simpler and are not membrane-bound.
There are several types of organelles in a cell. Some (such as the
nucleus and
golgi apparatus) are typically solitary, while others (such as
mitochondria,
chloroplasts,
peroxisomes and
lysosomes) can be numerous (hundreds to thousands). The
cytosol is the gelatinous fluid that fills the cell and surrounds the organelles.
Eukaryotic
thumb|3D rendering of a eukaryotic cell
* Cell nucleus: A cell's information center, the
cell nucleus is the most conspicuous organelle found in a
eukaryotic cell. It houses the cell's
chromosomes, and is the place where almost all
DNA replication and
RNA synthesis (
transcription) occur. The nucleus is spherical and separated from the cytoplasm by a double membrane called the
nuclear envelope. The nuclear envelope isolates and protects a cell's DNA from various molecules that could accidentally damage its structure or interfere with its processing. During processing,
DNA is
transcribed, or copied into a special
RNA, called
messenger RNA (mRNA). This mRNA is then transported out of the nucleus, where it is translated into a specific protein molecule. The
nucleolus is a specialized region within the nucleus where ribosome subunits are assembled. In prokaryotes, DNA processing takes place in the
cytoplasm.
* Mitochondria and chloroplasts: generate energy for the cell.
Mitochondria are self-replicating organelles that occur in various numbers, shapes, and sizes in the cytoplasm of all eukaryotic cells.
Respiration occurs in the cell mitochondria, which generate the cell's energy by
oxidative phosphorylation, using
oxygen to release energy stored in cellular nutrients (typically pertaining to
glucose) to generate
ATP. Mitochondria multiply by
binary fission, like prokaryotes. Chloroplasts can only be found in plants and algae, and they capture the sun's energy to make carbohydrates through
photosynthesis.

* Endoplasmic reticulum: The
endoplasmic reticulum (ER) is a transport network for molecules targeted for certain modifications and specific destinations, as compared to molecules that float freely in the cytoplasm. The ER has two forms: the rough ER, which has ribosomes on its surface that secrete proteins into the ER, and the smooth ER, which lacks ribosomes.
The smooth ER plays a role in calcium sequestration and release.
* Golgi apparatus: The primary function of the Golgi apparatus is to process and package the
macromolecules such as
proteins and
lipids that are synthesized by the cell.
* Lysosomes and peroxisomes:
Lysosomes contain
digestive enzymes (acid
hydrolases). They digest excess or worn-out
organelles, food particles, and engulfed
viruses or
bacteria.
Peroxisomes have enzymes that rid the cell of toxic
peroxides. The cell could not house these destructive enzymes if they were not contained in a membrane-bound system.
* Centrosome: the cytoskeleton organiser: The
centrosome produces the
microtubules of a cell – a key component of the
cytoskeleton. It directs the transport through the
ER and the
Golgi apparatus. Centrosomes are composed of two
centrioles, which separate during
cell division and help in the formation of the
mitotic spindle. A single centrosome is present in the
animal cells. They are also found in some fungi and algae cells.
* Vacuoles:
Vacuoles sequester waste products and in plant cells store water. They are often described as liquid filled space and are surrounded by a membrane. Some cells, most notably ''
Amoeba'', have contractile vacuoles, which can pump water out of the cell if there is too much water. The vacuoles of plant cells and fungal cells are usually larger than those of animal cells.
Eukaryotic and prokaryotic
* Ribosomes: The
ribosome is a large complex of
RNA and
protein molecules.
They each consist of two subunits, and act as an assembly line where RNA from the nucleus is used to synthesise proteins from amino acids. Ribosomes can be found either floating freely or bound to a membrane (the rough endoplasmatic reticulum in eukaryotes, or the cell membrane in prokaryotes).
Structures outside the cell membrane
Many cells also have structures which exist wholly or partially outside the cell membrane. These structures are notable because they are not protected from the external environment by the
semipermeable cell membrane. In order to assemble these structures, their components must be carried across the cell membrane by export processes.
Cell wall
Many types of prokaryotic and eukaryotic cells have a
cell wall. The cell wall acts to protect the cell mechanically and chemically from its environment, and is an additional layer of protection to the cell membrane. Different types of cell have cell walls made up of different materials; plant cell walls are primarily made up of
cellulose, fungi cell walls are made up of
chitin and bacteria cell walls are made up of
peptidoglycan.
Prokaryotic
Capsule
A gelatinous
capsule is present in some bacteria outside the cell membrane and cell wall. The capsule may be
polysaccharide as in
pneumococci,
meningococci or
polypeptide as ''
Bacillus anthracis'' or
hyaluronic acid as in
streptococci.
Capsules are not marked by normal staining protocols and can be detected by
India ink or
methyl blue; which allows for higher contrast between the cells for observation.
Flagella
Flagella are organelles for cellular mobility. The bacterial flagellum stretches from cytoplasm through the cell membrane(s) and extrudes through the cell wall. They are long and thick thread-like appendages, protein in nature. A different type of flagellum is found in archaea and a different type is found in eukaryotes.
Fimbriae
A
fimbria (plural fimbriae also known as a
pilus, plural pili) is a short, thin, hair-like filament found on the surface of bacteria. Fimbriae are formed of a protein called
pilin (
antigenic) and are responsible for the attachment of bacteria to specific receptors on human cells (
cell adhesion). There are special types of pili involved in
bacterial conjugation.
Cellular processes
Replication
Cell division involves a single cell (called a ''mother cell'') dividing into two daughter cells. This leads to growth in
multicellular organisms (the growth of
tissue) and to procreation (
vegetative reproduction) in
unicellular organisms.
Prokaryotic cells divide by
binary fission, while
eukaryotic cells usually undergo a process of nuclear division, called
mitosis, followed by division of the cell, called
cytokinesis. A
diploid cell may also undergo
meiosis to produce haploid cells, usually four.
Haploid cells serve as
gametes in multicellular organisms, fusing to form new diploid cells.
DNA replication, or the process of duplicating a cell's genome,
always happens when a cell divides through mitosis or binary fission. This occurs during the S phase of the
cell cycle.
In meiosis, the DNA is replicated only once, while the cell divides twice. DNA replication only occurs before
meiosis I. DNA replication does not occur when the cells divide the second time, in
meiosis II. Replication, like all cellular activities, requires specialized proteins for carrying out the job.
DNA repair
In general, cells of all organisms contain enzyme systems that scan their DNA for
damages and carry out
repair processes when damages are detected. Diverse repair processes have evolved in organisms ranging from bacteria to humans. The widespread prevalence of these repair processes indicates the importance of maintaining cellular DNA in an undamaged state in order to avoid cell death or errors of replication due to damages that could lead to
mutation.
''E. coli'' bacteria are a well-studied example of a cellular organism with diverse well-defined
DNA repair processes. These include: (1)
nucleotide excision repair, (2)
DNA mismatch repair, (3)
non-homologous end joining of double-strand breaks, (4)
recombinational repair and (5) light-dependent repair (
photoreactivation).
Growth and metabolism

Between successive cell divisions, cells grow through the functioning of cellular metabolism. Cell metabolism is the process by which individual cells process nutrient molecules. Metabolism has two distinct divisions:
catabolism, in which the cell breaks down complex molecules to produce energy and
reducing power, and
anabolism, in which the cell uses energy and reducing power to construct complex molecules and perform other biological functions.
Complex sugars consumed by the organism can be broken down into simpler sugar molecules called
monosaccharides such as
glucose. Once inside the cell, glucose is broken down to make adenosine triphosphate (
ATP),
a molecule that possesses readily available energy, through two different pathways.
Protein synthesis
Cells are capable of synthesizing new proteins, which are essential for the modulation and maintenance of cellular activities. This process involves the formation of new protein molecules from
amino acid building blocks based on information encoded in DNA/RNA. Protein synthesis generally consists of two major steps:
transcription and
translation.
Transcription is the process where genetic information in DNA is used to produce a complementary RNA strand. This RNA strand is then processed to give
messenger RNA (mRNA), which is free to migrate through the cell. mRNA molecules bind to protein-RNA complexes called
ribosomes located in the
cytosol, where they are translated into polypeptide sequences. The ribosome mediates the formation of a polypeptide sequence based on the mRNA sequence. The mRNA sequence directly relates to the polypeptide sequence by binding to
transfer RNA (tRNA) adapter molecules in binding pockets within the ribosome. The new polypeptide then folds into a functional three-dimensional protein molecule.
Motility
Unicellular organisms can move in order to find food or escape predators. Common mechanisms of motion include
flagella and
cilia.
In multicellular organisms, cells can move during processes such as wound healing, the immune response and
cancer metastasis. For example, in wound healing in animals, white blood cells move to the wound site to kill the microorganisms that cause infection. Cell motility involves many receptors, crosslinking, bundling, binding, adhesion, motor and other proteins. The process is divided into three steps – protrusion of the leading edge of the cell, adhesion of the leading edge and de-adhesion at the cell body and rear, and cytoskeletal contraction to pull the cell forward. Each step is driven by physical forces generated by unique segments of the cytoskeleton.
Navigation, control and communication
In August 2020, scientists described one way cells – in particular cells of a slime mold and mouse pancreatic cancer–derived cells – are able to
navigate efficiently through a body and identify the best routes through complex mazes: generating gradients after breaking down diffused
chemoattractants which enable them to sense upcoming maze junctions before reaching them, including around corners.
Multicellularity
Cell specialization/differentiation

Multicellular organisms are
organisms that consist of more than one cell, in contrast to
single-celled organisms.
In complex multicellular organisms, cells specialize into different
cell types that are adapted to particular functions. In mammals, major cell types include
skin cells,
muscle cells,
neurons,
blood cells,
fibroblasts,
stem cells, and others. Cell types differ both in appearance and function, yet are
genetically identical. Cells are able to be of the same
genotype but of different cell type due to the differential
expression of the
genes they contain.
Most distinct cell types arise from a single
totipotent cell, called a
zygote, that
differentiates into hundreds of different cell types during the course of
development. Differentiation of cells is driven by different environmental cues (such as cell–cell interaction) and intrinsic differences (such as those caused by the uneven distribution of
molecules during
division).
Origin of multicellularity
Multicellularity has evolved independently at least 25 times,
including in some prokaryotes, like
cyanobacteria,
myxobacteria,
actinomycetes, ''
Magnetoglobus multicellularis'' or ''
Methanosarcina''. However, complex multicellular organisms evolved only in six eukaryotic groups: animals, fungi, brown algae, red algae, green algae, and plants.
It evolved repeatedly for plants (
Chloroplastida), once or twice for
animals, once for
brown algae, and perhaps several times for
fungi,
slime molds, and
red algae. Multicellularity may have evolved from
colonies of interdependent organisms, from
cellularization, or from organisms in
symbiotic relationships.
The first evidence of multicellularity is from
cyanobacteria-like organisms that lived between 3 and 3.5 billion years ago.
Other early fossils of multicellular organisms include the contested
Grypania spiralis and the fossils of the black shales of the
Palaeoproterozoic Francevillian Group Fossil B Formation in
Gabon.
The evolution of multicellularity from unicellular ancestors has been replicated in the laboratory, in
evolution experiments using predation as the
selective pressure.
Origins
The origin of cells has to do with the
origin of life, which began the
history of life on Earth.
Origin of the first cell

There are several theories about the origin of small molecules that led to life on the
early Earth. They may have been carried to Earth on meteorites (see
Murchison meteorite), created at
deep-sea vents, or synthesized by lightning in a reducing atmosphere (see
Miller–Urey experiment). There is little experimental data defining what the first self-replicating forms were.
RNA is thought to be the earliest self-replicating molecule, as it is capable of both storing genetic information and catalyzing chemical reactions (see
RNA world hypothesis), but some other entity with the potential to self-replicate could have preceded RNA, such as
clay or
peptide nucleic acid.
Cells emerged at least 3.5 billion years ago.
The current belief is that these cells were
heterotrophs. The early cell membranes were probably more simple and permeable than modern ones, with only a single fatty acid chain per lipid. Lipids are known to spontaneously form bilayered
vesicles in water, and could have preceded RNA, but the first cell membranes could also have been produced by catalytic RNA, or even have required structural proteins before they could form.
Origin of eukaryotic cells
The eukaryotic cell seems to have evolved from a
symbiotic community of prokaryotic cells. DNA-bearing organelles like the
mitochondria and the
chloroplasts are descended from ancient symbiotic oxygen-breathing
proteobacteria and
cyanobacteria, respectively, which were
endosymbiosed by an ancestral
archaean prokaryote.
There is still considerable debate about whether organelles like the
hydrogenosome predated the origin of
mitochondria, or vice versa: see the
hydrogen hypothesis for the origin of eukaryotic cells.
History of research

* 1632–1723:
Antonie van Leeuwenhoek taught himself to make
lenses, constructed basic
optical microscopes and drew protozoa, such as ''
Vorticella'' from rain water, and
bacteria from his own mouth.
* 1665:
Robert Hooke discovered cells in
cork, then in living plant tissue using an early compound microscope. He coined the term ''cell'' (from
Latin ''cella'', meaning "small room"
) in his book ''
Micrographia'' (1665).
[" ... I could exceedingly plainly perceive it to be all perforated and porous, much like a Honey-comb, but that the pores of it were not regular ..these pores, or cells, ..were indeed the first microscopical pores I ever saw, and perhaps, that were ever seen, for I had not met with any Writer or Person, that had made any mention of them before this ... " – Hooke describing his observations on a thin slice of cork. See also:]
Robert Hooke
/ref>
* 1839: Theodor Schwann and Matthias Jakob Schleiden elucidated the principle that plants and animals are made of cells, concluding that cells are a common unit of structure and development, and thus founding the cell theory.
* 1855: Rudolf Virchow stated that new cells come from pre-existing cells by cell division (''omnis cellula ex cellula'').
* 1859: The belief that life forms can occur spontaneously (''generatio spontanea'') was contradicted by Louis Pasteur (1822–1895) (although Francesco Redi had performed an experiment in 1668 that suggested the same conclusion).
* 1931: Ernst Ruska built the first transmission electron microscope (TEM) at the University of Berlin. By 1935, he had built an EM with twice the resolution of a light microscope, revealing previously unresolvable organelles.
* 1953: Based on Rosalind Franklin's work, Watson and Crick made their first announcement on the double helix structure of DNA.
* 1981: Lynn Margulis published ''Symbiosis in Cell Evolution'' detailing the endosymbiotic theory.
See also
* Cell cortex
* Cell culture
* Cellular model
* Cytorrhysis
* Cytoneme
* Cytotoxicity
* Human cell
* Lipid raft
* Outline of cell biology
* ''Parakaryon myojinensis''
* Plasmolysis
* Syncytium
* Tunneling nanotube
* Vault (organelle)
References
Notes
Further reading
*
* ; Th
fourth edition is freely available
from National Center for Biotechnology Information Bookshelf.
*
*
External links
MBInfo – Descriptions on Cellular Functions and Processes
MBInfo – Cellular Organization
Inside the Cell
– a science education booklet by National Institutes of Health, in PDF and ePub.
Cells Alive!
in "The Biology Project" of University of Arizona.
Centre of the Cell online
!-- Partly by Queen Mary University. -->
The Image & Video Library of The American Society for Cell Biology
a collection of peer-reviewed still images, video clips and digital books that illustrate the structure, function and biology of the cell.
HighMag Blog
still images of cells from recent research articles.
March 4, 2011 – Howard Hughes Medical Institute.
WormWeb.org: Interactive Visualization of the ''C. elegans'' Cell lineage
– Visualize the entire cell lineage tree of the nematode ''C. elegans''
Cell Photomicrographs
{{DEFAULTSORT:Cell (Biology)
Category:1665 in science