cell

Introduction & Top Questions
The nature and function of cells
- The molecules of cells
  - The structure of biological molecules
  - Coupled chemical reactions
    - Photosynthesis: the beginning of the food chain
    - ATP: fueling chemical reactions
- The genetic information of cells
  - DNA: the genetic material
  - RNA: replicated from DNA
- The organization of cells
  - Intracellular communication
  - Intercellular communication
The cell membrane
- Chemical composition and membrane structure
  - Membrane lipids
  - Membrane proteins
  - Membrane fluidity
- Transport across the membrane
  - Permeation
  - Membrane channels
  - Facilitated diffusion
    - The glucose transporter
    - The anion transporter
  - Secondary active transport
    - Counter-transport
    - Co-transport
  - Primary active transport
    - The sodium-potassium pump
    - Calcium pumps
    - Hydrogen ion pumps
  - Transport of particles
    - Endocytosis
    - Exocytosis
Internal membranes
- General functions and characteristics
- Cellular organelles and their membranes
  - The vacuole
  - The lysosome
  - Microbodies
  - The endoplasmic reticulum
    - The smooth endoplasmic reticulum
    - The rough endoplasmic reticulum
  - The Golgi apparatus
  - Secretory vesicles
- Sorting of products by chemical receptors
The nucleus
- Structural organization of the nucleus
  - DNA packaging
    - Nucleosomes: the subunits of chromatin
    - Organization of chromatin fiber
  - The nuclear envelope
- Genetic organization of the nucleus
  - The structure of DNA
  - Rearrangement and modification of DNA
- Genetic expression through RNA
  - RNA synthesis
  - Processing of mRNA
- Regulation of genetic expression
  - Regulation of RNA synthesis
  - Regulation of RNA after synthesis
The mitochondrion and the chloroplast
- Mitochondrial and chloroplastic structure
- Metabolic functions
  - The mitochondrion
    - Formation of the electron donors NADH and FADH₂
    - The electron-transport chain
    - The chemiosmotic theory
  - The chloroplast
    - Trapping of light
    - Fixation of carbon dioxide
- Evolutionary origins
  - The mitochondrion and chloroplast as independent entities
  - The endosymbiont hypothesis
The cytoskeleton
- Actin filaments
- Microtubules
- Intermediate filaments
The cell matrix and cell-to-cell communication
- The extracellular matrix
  - Matrix polysaccharides
  - Matrix proteins
  - Cell-matrix interactions
- Intercellular recognition and cell adhesion
  - Tissue and species recognition
  - Cell junctions
    - Adhering junctions
    - Tight junctions
    - Gap junctions
- Cell-to-cell communication via chemical signaling
  - Types of chemical signaling
  - Signal receptors
  - Cellular response
- The plant cell wall
  - Mechanical properties of wall layers
  - Components of the cell wall
    - Cellulose
    - Matrix polysaccharides
    - Proteins
    - Plastics
  - Intercellular communication
    - Plasmodesmata
    - Oligosaccharides with regulatory functions
Cell division and growth
- Duplication of the genetic material
- Cell division
  - Mitosis and cytokinesis
  - Meiosis
- The cell division cycle
  - Controlled proliferation
  - Failure of proliferation control
Cell differentiation
- The differentiated state
- The process of differentiation
- Errors in differentiation
The evolution of cells
- The development of genetic information
- The development of metabolism
The history of cell theory
- Formulation of the theory
  - Early observations
  - The problem of the origin of cells
  - The protoplasm concept
- Contribution of other sciences

References & Edit History Quick Facts & Related Topics

Images, Videos & Interactives

Artist's illustration of human nerve cells showing a central neuron with a green nucleus, branching dendrites, and glowing signals traveling along axons against a dark background.

How Are Plant Cells Different from Animal Cells?

Functions of cells

The video thumbnail image shows an illustration of an animal cell next to a photo of a whale swimming in the oean.

Illustration comparing three cell types: a round animal cell and an irregularly shaped plant cell, both showing labeled organelles, and an elongated bacteria cell with labeled structures such as flagella and capsule.

How Do Organelles Work in Plant and Animal Cells?

Cutaway illustration of a eukaryotic animal cell showing labeled internal structures, including the nucleus, nucleolus, mitochondria, endoplasmic reticulum, Golgi apparatus, and other organelles.

The function of the cell membrane in biology explained

At a Glance

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cell: Media

biology

Videos

How Are Plant Cells Different from Animal Cells?

How Are Plant Cells Different from Animal Cells?

All living things are composed of cells.

Video: Encyclopædia Britannica, Inc.

Functions of cells

Functions of cells

Basic similarities between cells and ways cells may vary depending on their function.

Video: © Open University (A Britannica Publishing Partner)

The video thumbnail image shows an illustration of an animal cell next to a photo of a whale swimming in the oean.

The Major Parts of an Animal Cell

From teeny-tiny ants to 200-ton whales, all members of the animal kingdom are composed...

Video: Encyclopædia Britannica, Inc.

How Do Organelles Work in Plant and Animal Cells?

How Do Organelles Work in Plant and Animal Cells?

The nucleus, ribosomes, and mitochondria are all examples of organelles.

Video: Encyclopædia Britannica, Inc.

The function of the cell membrane in biology explained

The function of the cell membrane in biology explained

Cells ingest molecules through their plasma membranes.

Video: Encyclopædia Britannica, Inc.

The Process of Photosynthesis in Plants Explained

The Process of Photosynthesis in Plants Explained

The location, importance, and mechanisms of photosynthesis. Study the roles of chloroplasts,...

Video: Encyclopædia Britannica, Inc.

How does ATP provide energy to cells?

How does ATP provide energy to cells?

Adenosine triphosphate, or ATP, is the primary carrier of energy in cells. The water-mediated...

Video: Encyclopædia Britannica, Inc.

Study DNA's double helix structure to learn how the organic chemical determines an organism's traits

Study DNA's double helix structure to learn how the organic chemical determines an organism's traits

James Watson and Francis Crick revolutionized the study of genetics when they discovered...

Video: Encyclopædia Britannica, Inc.

What are the functions of different cell organelles?

What are the functions of different cell organelles?

Animal and plant cells house various types of internal membrane-bound compartments,...

Video: Encyclopædia Britannica, Inc.

Analyze the structure and motion of cilia and flagella

Analyze the structure and motion of cilia and flagella

Learn about the structure and movement of cilia and flagella.

Video: Encyclopædia Britannica, Inc.

Discover how the human endocrine system disperses hormones from glands through the bloodstream

Discover how the human endocrine system disperses hormones from glands through the bloodstream

Hormones secreted by the glands of the endocrine system are carried in the bloodstream...

Video: Encyclopædia Britannica, Inc.

See a movie illustrating wounded cells releasing signaling molecules causing a wave of calcium signaling

See a movie illustrating wounded cells releasing signaling molecules causing a wave of calcium signaling

This false-color movie, acquired by means of confocal microscopy, illustrates long-range...

Video: Nicholas Davenport/University of Wisconsin-Madison

Witness a living plant cell's chromosomes carrying genetic material duplicate during the process of mitosis

Witness a living plant cell's chromosomes carrying genetic material duplicate during the process of mitosis

Time-lapse photography of a live plant cell nucleus undergoing mitosis.

Video: Encyclopædia Britannica, Inc.

Watch: How cell division works

Watch: How cell division works

Learn about cell division in the developing embryo and in mature cells.

Video: Encyclopædia Britannica, Inc.

Consider how the invention of the microscope abetted the discovery and categorization of cells

Consider how the invention of the microscope abetted the discovery and categorization of cells

The discovery of cells was a revolution.

Video: Encyclopædia Britannica, Inc.

Consider how a single-celled organism contains the necessary structures to eat, grow, and reproduce

Consider how a single-celled organism contains the necessary structures to eat, grow, and reproduce

Cells are the basic units of life.

Video: Encyclopædia Britannica, Inc.

How different parts of a cell interact

How different parts of a cell interact

Learn about the different cell organelles, including the mitochondrion, the nucleus,...

Video: Encyclopædia Britannica, Inc.

See time-lapse microphotography of blastomeres created by mitotic cleavage of embryonic cells

See time-lapse microphotography of blastomeres created by mitotic cleavage of embryonic cells

Learn about mitotic cleavage of embryonic cells by watching this time-lapse microphotography...

Video: Encyclopædia Britannica, Inc.

Eukaryotic vs. Prokaryotic Cells: Key Differences Explained

Eukaryotic vs. Prokaryotic Cells: Key Differences Explained

Learn about the difference between prokaryotes and eukaryotes.

Video: Encyclopædia Britannica, Inc.

Study how bacteriophages replicate by injecting nucleic acid into a bacteria cell to create virions

Study how bacteriophages replicate by injecting nucleic acid into a bacteria cell to create virions

The cycle of infection results in the death of the host cell and the release of many...

Video: Encyclopædia Britannica, Inc.

Robert Hooke's Discovery: The Microscopic World of Cells

Robert Hooke's Discovery: The Microscopic World of Cells

This was a game-changer.

Video: Encyclopædia Britannica, Inc.

Images

Artist's illustration of human nerve cells showing a central neuron with a green nucleus, branching dendrites, and glowing signals traveling along axons against a dark background.

Neuron

Artist's conception of a human neuron.

© Sebastian Kaulitzki—Eraxion/Dreamstime.com

Animal cell

Animal cell

Principal structures of an animal cellCytoplasm...

© Merriam-Webster Inc.

Illustration comparing three cell types: a round animal cell and an irregularly shaped plant cell, both showing labeled organelles, and an elongated bacteria cell with labeled structures such as flagella and capsule.

Different types of cells

Animal cells and plant cells contain membrane-bound organelles, including a distinct...

Encyclopædia Britannica, Inc.

Cutaway illustration of a eukaryotic animal cell showing labeled internal structures, including the nucleus, nucleolus, mitochondria, endoplasmic reticulum, Golgi apparatus, and other organelles.

Eukaryotic cell

Cutaway drawing of a eukaryotic cell.

Encyclopædia Britannica, Inc.

Diagram of the eight-step tricarboxylic acid cycle showing the sequence of metabolites from acetyl CoA through citrate, isocitrate, alpha-ketoglutarate, succinyl CoA, succinate, fumarate, malate, and oxaloacetate, with arrows indicating the flow of reactions and production of ATP, NADH, FADH2, and CO2.

Tricarboxylic acid cycle

The eight-step tricarboxylic acid cycle.

Encyclopædia Britannica, Inc.

DNA structure

DNA structure

The initial proposal of the structure of DNA by James Watson and Francis Crick was...

Encyclopædia Britannica, Inc.

Diagram illustrating the process of protein synthesis: DNA unzips in the nucleus, messenger RNA (mRNA) forms on the DNA strands, and then mRNA moves to a ribosome where transfer RNA (tRNA) helps assemble amino acids into a protein chain.

Messenger RNA; translation

Molecular genetics emerged from the realization that DNA and RNA constitute the genetic...

Encyclopædia Britannica, Inc.

Diagram showing early human embryo development. The top row illustrates ovum cleavage from a single cell to a morula. The bottom row shows blastocyst formation and implantation, with labeled cell structures.

Early stages of human development

The ovum contains a small collection of cells in the early stages of human development....

Encyclopædia Britannica, Inc.

Detailed diagram of a plasma membrane's lipid bilayer showing two layers of phospholipid molecules with hydrophilic heads facing outward and hydrophobic tails inward, embedded cholesterol, integral (intrinsic) proteins spanning the membrane, peripheral (extrinsic) proteins attached to the surface, and sugar side chains extending from the outer face.

Molecular view of the cell membrane

Intrinsic proteins penetrate and bind tightly to the lipid bilayer, which is made...

Encyclopædia Britannica, Inc.

Red blood cells

Red blood cells

Human red blood cells (erythrocytes).

© Steve Gschmeissner—Science Photo Library/Getty Images

Structural formula diagram of a glycerolphospholipid molecule, showing a glycerol backbone connected to a phosphate group and two long fatty acid chains labeled R1 and R2.

Glycerophospholipid structure

General structural formula of a glycerophospholipid. The composition of the specific...

Encyclopædia Britannica, Inc.

Cross-sectional diagram of a liposome, showing concentric bilayers formed by phospholipid molecules with pink heads and blue fatty acid tails, illustrating its structure in biochemistry.

Liposome

Phospholipids can be used to form artificial structures called liposomes, which are...

Encyclopædia Britannica, Inc.

Simple diagram of a lipid bilayer showing two layers of phospholipid molecules with round hydrophilic heads facing outward and hydrophobic tails facing inward, illustrating a cellular membrane structure.

Lipid bilayer; cell membrane

Phospholipid molecules, like molecules of many lipids, are composed of a hydrophilic...

Encyclopædia Britannica, Inc.

Endoplasmic reticulum; organelle

Endoplasmic reticulum; organelle

A scanning electron micrograph of a pancreatic acinar cell, showing mitochondria...

Pietro M. Motta & Tomonori Naguro/Science Source

Ligand-gated ion channel: nicotinic acetylcholine receptor

Ligand-gated ion channel: nicotinic acetylcholine receptor

The nicotinic acetylcholine receptor is an example of a ligand-gated ion channel....

Encyclopædia Britannica, Inc.

Diagram showing osmosis with two containers separated by a semipermeable membrane: at the top, water molecules move from pure water to a sugar solution, while sugar molecules cannot cross; at the bottom, water levels have shifted as equilibrium is reached.

Permeation and diffusion

The principle of permeation can be illustrated by differences in the diffusion of...

Encyclopædia Britannica, Inc.

Three-panel diagram showing the diffusion of chloride and potassium ions across a semipermeable membrane. Panel A illustrates movement driven by a concentration gradient, panel B shows both concentration gradient and opposing electrostatic force, and panel C depicts equilibrium potential where forces balance and ion flow is stable. Chloride ions are marked in blue, potassium ions in red, with direction arrows indicating ion movement.

Ion movement across a semipermeable membrane

Diffusion of ions across a semipermeable membrane. (A) A high concentration of potassium...

Encyclopædia Britannica, Inc.

Endocytosis and exocytosis

Endocytosis and exocytosis

The process of intracellular digestion involves endocytosis and exocytosis. Food...

Encyclopædia Britannica, Inc.

A four-step diagram shows a single-celled organism engulfing and digesting a food particle by phagocytosis, illustrating entrapment, vacuole formation, lysosome fusion, and digestion inside the cell.

Phagocytosis

The process by which cells engulf solid matter is called phagocytosis. There are...

Encyclopædia Britannica, Inc.

Diagram showing receptor-mediated endocytosis in a cell: a ligand binds to a receptor on the cell membrane, forming a coated pit that becomes a coated vesicle. The vesicle fuses with an endosome, where receptors are recycled and the contents are degraded in a lysosome.

Receptor-mediated endocytosis

Receptors play key roles in many cellular processes. For example, receptor-mediated...

Encyclopædia Britannica, Inc.

Structural diagram of a cholesterol molecule showing its four-ring steroid nucleus, labeled A through D, a hydroxyl group, and a hydrocarbon side chain branching from the main structure.

Cholesterol

Structural formula of cholesterol.

Encyclopædia Britannica, Inc.

Diagram of a basic plant cell showing labeled structures including the cell wall, cell membrane, chloroplast, nucleus, chromosomes, cytoplasm, organelles, and fluid-filled space.

Plant cell

Membrane-bound organelles, including fluid-filled spaces, called vacuoles, are components...

Encyclopædia Britannica, Inc.

Formation of lysosomes

Formation of lysosomes

Lysosomes form by budding off from the membrane of the trans-Golgi network. Macromolecules...

Encyclopædia Britannica, Inc.

Diagram of a cell showing the process of protein processing and secretion, with proteins assembled by ribosomes, modified in the rough endoplasmic reticulum, transported in vesicles to the Golgi complex for further processing, and then released through the cell membrane.

Protein biosynthesis and the endoplasmic reticulum

The endoplasmic reticulum (ER) plays a major role in the biosynthesis of proteins....

Encyclopædia Britannica, Inc.

Diagram showing the chemical transmission of nerve impulses at a synapse, with labeled steps illustrating neurotransmitter release from the presynaptic terminal, movement across the synaptic cleft, binding to postsynaptic channel receptors, and resulting signal propagation in the nervous system.

Chemical transmission of a nerve impulse at the synapse

The arrival of a chemical stimulus at the presynaptic terminal stimulates the release...

Encyclopædia Britannica, Inc.

Centromere and chromatids in cell division

Centromere and chromatids in cell division

During the first stages of cell division, the recognizable double-stranded chromosome...

© Merriam-Webster Inc.

Diagram showing DNA winding around blue histone octamers to form nucleosomes, which coil together into a solenoid chromatin fiber. An inset highlights DNA wrapped around a single histone octamer.

Histones and nucleosomes

DNA wrapped around clusters of histone proteins to form nucleosomes, which can coil...

Encyclopædia Britannica, Inc.

Diagram of a DNA double helix showing its twisted ladder structure, with a close-up of the sugar-phosphate backbone, paired nitrogenous bases (adenine, thymine, cytosine, guanine), and labeled nucleotides and hydrogen bonds.

DNA

DNA molecule.

Encyclopædia Britannica, Inc.

Diagram of an antibody molecule showing two identical light chains and two identical heavy chains joined by disulfide bonds in a Y-shaped structure, with labeled regions for antigen binding and effector function.

Antibody structure

The structure of an antibody molecule represents the dramatic rearrangements of DNA...

Encyclopædia Britannica, Inc.

Diagram of a mitochondrion cut lengthwise, showing labeled parts including outer and inner membranes, intermembrane space, cristae, matrix, DNA, ribosomes, and membrane protein portions.

Mitochondrion

The internal membrane of a mitochondrion is elaborately folded into structures known...

Encyclopædia Britannica, Inc.

Chloroplast

Chloroplast

Internal structures of the chloroplast. The interior contains flattened sacs of photosynthetic...

© Merriam-Webster Inc.

Diagram of the respiratory chain in metabolism, showing the flow of electrons from NADH and FADH2 through complexes and cytochromes, ending with the reduction of oxygen to water. Key molecules, sites, and electron transfers are labeled.

electron-transport chain

The electron-transport chain embedded in the inner membrane of a mitochondrion is...

Encyclopædia Britannica, Inc.

spinach chloroplast

spinach chloroplast

Electron micrograph of an isolated spinach chloroplast.

Courtesy of the Lawrence Berkeley National Laboratory, University of California, Berkeley

A diagram shows the process of photosynthesis, where carbon dioxide and water, using light energy and chlorophyll in leaves, are converted into glucose and oxygen. The chemical equation 6CO2 plus 6H2O yields C6H12O6 plus 6O2 is displayed.

The reaction of photosynthesis

In photosynthesis, plants consume carbon dioxide and water and produce glucose and...

Encyclopædia Britannica, Inc.

Diagram of the reductive pentose phosphate cycle in photosynthesis, showing carbon dioxide fixation and reduction steps. Arrows trace the transformation of CO2 and RuBP through intermediates like PGA, DPGA, and Gal3P, with ATP and NADPH inputs and the net production of one Gal3P molecule for sugar or starch synthesis.

Calvin cycle

Pathway of carbon dioxide fixation and reduction in photosynthesis, the Calvin cycle....

Encyclopædia Britannica, Inc.

Diagram showing the structure of human striated or skeletal muscle, with labeled cross-sections from whole muscle to fascicle, muscle fiber, myofibril, and sarcomere, highlighting actin and myosin filaments.

Striated muscle

The structure of striated, or skeletal, muscle. Striated muscle tissue, such as the...

Encyclopædia Britannica, Inc.

multicellular animal

multicellular animal

Marine sponges are multicellular animals that can regenerate from single cells. The...

© Royalty-free/Corbis

Diagram of a typical endocrine cell showing labeled internal structures, including the nucleus, endoplasmic reticulum, Golgi apparatus, cytoplasm, and secretory granules, with arrows illustrating the pathway of hormone synthesis and exocytosis.

cell surface receptor

Hormones and active metabolites bind to different types of receptors. Water-soluble...

Encyclopædia Britannica, Inc.

A step-by-step diagram shows the stages of mitosis in a somatic cell, illustrating chromosome duplication, alignment, separation, and the formation of two identical daughter cells, with labeled cell structures and brief descriptions of each phase.

mitosis

Mitosis, the process in which a cell gives rise to two genetically identical daughter...

Encyclopædia Britannica, Inc.

stages of mitosis

stages of mitosis

Stages of mitosisA. Prophase. Replicated...

© Merriam-Webster Inc.

A step-by-step diagram of meiosis, showing the stages of sex cell division. Illustrated cells depict chromosome behavior, cell membrane changes, and the formation of four daughter cells, each with half the chromosome number of the original cell. Labels and brief descriptions explain key processes such as homologous chromosome pairing, crossing over, and separation of chromatids.

Gamete formation in meiosis

Meiosis, the process in which gametes (sex cells) form.

Encyclopædia Britannica, Inc.

Diagram showing how acutely and slowly transforming retroviruses can cause cancer by infecting normal cells, integrating viral genes, and triggering neoplastic transformation into cancer cells.

Cancer-causing retroviruses

Retroviral insertion can convert a proto-oncogene, integral to the control of cell...

Encyclopædia Britannica, Inc.

Diagram showing the anatomy of the small intestine with labeled regions (duodenum, jejunum, ileum), a cross-section highlighting muscle and mucosa layers, an enlargement of mucosal folds (plicae circulares), and a detailed view of a villus structure with epithelial, goblet, endocrine, and Paneth cells, microvilli, blood capillaries, and lacteal.

small intestine

The small intestine contains many distinct types of cells, each of which serves a...

Encyclopædia Britannica, Inc.

Leaf anatomy

Leaf anatomy

Structures of a leaf. The epidermis is often covered with a waxy protective cuticle...

© Merriam-Webster Inc.

This diagram illustrates the cloning process of Dolly the sheep in 1996, showing how a nucleus from an adult Finn Dorset ewe was fused with an enucleated egg cell from a Scottish Blackface ewe, then implanted into a surrogate to produce Dolly.

How was Dolly cloned?

Dolly the sheep was successfully cloned in 1996 by fusing the nucleus from a mammary-gland...

Encyclopædia Britannica, Inc.

Illustration comparing three cell types: a round animal cell and an irregularly shaped plant cell, both showing labeled organelles, and an elongated bacteria cell with labeled structures such as flagella and capsule.

Bacterial, animal, and plant cells compared

Bacterial cells differ from animal cells and plant cells in several ways. One fundamental...

Encyclopædia Britannica, Inc.

A composite diagram shows the structural formulas, space-filling models, and simplified depictions of lipid molecules including stearic acid and phosphatidylcholine, and how these assemble into a micelle and lipid bilayer, with labels identifying hydrophilic heads and hydrophobic tails.

Lipid structure

Structure and properties of two representative lipids. Both stearic acid (a fatty...

Encyclopædia Britannica, Inc.

Oil painting by Jan Verkolje showing Antonie van Leeuwenhoek seated at a table with a globe, papers, inkstand, and a compass in hand, wearing a brown robe and white shirt.

Antonie van Leeuwenhoek

Antonie van Leeuwenhoek, detail of a portrait by Jan Verkolje; in the Rijksmuseum,...

Rijksmuseum, Amsterdam (SK-A-957)

Portrait of Scottish botanist Robert Brown seated, wearing a dark suit and cravat, with papers resting on the table beside him.

Robert Brown

Hulton Archive/Getty Images

Portrait of Theodor Schwann, a middle-aged man with short hair and sideburns, wearing a dark suit, waistcoat, and bow tie, facing slightly to the left.

Theodor Schwann

© Hulton Archive/Getty Images

Matthias Jakob Schleiden

Matthias Jakob Schleiden

Matthias Jakob Schleiden.

From The Popular Science Monthly, Volume XXII, by E.L and W.J. Youmans, November 1882-April 1883, published by D. Appleton and Company, New York.

Rudolf Virchow

Rudolf Virchow

German pathologist and statesman Rudolf Virchow.

Bildarchiv Preussischer Kulturbesitz, Berlin

Louis Pasteur

Louis Pasteur

French chemist and microbiologist Louis Pasteur.

Archives Photographiques, Paris

Karl Ernst von Baer

Karl Ernst von Baer

Prussian-Estonian embryologist Karl Ernst von Baer.

News About the Life and Writings of the Privy Councilor Dr. Karl Ernst Baer/Wellcome Collection, London (CC BY 4.0)

Chromosomes are inside the cells of every living thing. They are so small that they can only be seen through a powerful microscope.

Chromosomes are inside the cells of every living thing. They are so small that they...

© James Cavallini—BSIP/age fotostock

Fluorescent confocal image of HeLa cells with green microtubules outlining cell shapes, red mitochondria, and blue nuclei.

Microtubules (shown in green) play an important role in cytoplasmic streaming.

© defun—iStock/Getty Images

plant cells and tissues

plant cells and tissues

Figure 5: Cell types and tissues.

Encyclopædia Britannica, Inc.

Labeled diagram of a bacillus-shaped bacterial cell showing capsule, cell wall, cell membrane, cytoplasm, nuclear matter, pili, and a single long flagellum extending from one end.

Bacillus-type bacterial cell

Schematic drawing of the structure of a typical bacterial cell of the bacillus type.

Encyclopædia Britannica, Inc.

endocytosis

endocytosis

Adsorption to and entry into a cell of an enveloped animal virus by the process of...

Encyclopædia Britannica, Inc.

Side-by-side labeled diagrams of a typical animal cell and a plant cell, showing internal structures such as nucleus, mitochondrion, endoplasmic reticulum, and unique features like chloroplasts and cell wall in the plant cell.

Organelles of eukaryotic cells

A defining feature of eukaryotic cells is the presence of membrane-bound organelles...

Encyclopædia Britannica, Inc.

A step-by-step diagram shows viruses attaching to and entering a body cell, releasing their genetic material, taking over the cell's machinery to produce new viruses, and releasing them to infect other cells.

virus invading a cell

Virus invading a cell and reproducing.

Encyclopædia Britannica, Inc.

Cutaway illustration of a plant cell showing labeled internal structures including the nucleus, nucleolus, chloroplast, mitochondrion, vacuole, endoplasmic reticulum, ribosomes, Golgi apparatus, cell wall, and other key organelles.

Plant cell

Cutaway drawing of a plant cell, showing the cell wall and internal organelles.

Encyclopædia Britannica, Inc.

Interactives

Animal cell

Animal cell

Can you label the major parts of an animal cell? Test your knowledge.

EB owned. Book Buddy Digitial Media, Inc.

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