Eukaryotes Fossil range: Proterozoic - Recent
Ostreococcus is the smallest known free living eukaryote with an average size of 0. The Proterozoic (ˌproʊtərəˈzoʊɪk is a geological eon representing a period before the first abundant complex life on Earth. Ostreococcus is a genus of unicellular coccoid Green alga belonging to the class Prasinophyceae. 8 µm.
Scientific classification
Superdomain: Neomura Domain: Eukaryota Whittaker & Margulis,1978
Kingdoms
Animalia - Animals Fungi Amoebozoa Plantae - Plants Chromalveolata Rhizaria Excavata
Alternative phylogeny
Unikonta Opisthokonta Metazoa Mesomycetozoa Choanozoa Eumycota Amoebozoa Bikonta Apusozoa Rhizaria Excavata Archaeplastida Chromalveolata

Animals, plants, fungi, and protists are eukaryotes (IPA: /juːˈkærɪɒt/ or IPA: /-oʊt/), organisms whose cells are organized into complex structures enclosed within membranes. Neomura is a speculative Clade composed of the two domains of life of Archaea and Eukarya. Robert Harding Whittaker (1920–1980 was an American Vegetation Ecologist, active in the 1950s to the 1970s Lynn Margulis (born March 5, 1938) is an American Biologist and University Professor in the Department of Geosciences In biological Taxonomy, a kingdom or regnum is a Taxonomic rank in either (historically the highest rank or (in the new three-domain system A fungus (ˈfʌŋgəs is a eukaryotic Organism that is a member of the kingdom Fungi (ˈfʌndʒaɪ The Amoebozoa are a major group of Amoeboid protozoa including the majority that move by means of internal Cytoplasmic flow Plants are living Organisms belonging to the kingdom Plantae. Chromalveolata is a Eukaryote supergroup first proposed by Thomas Cavalier-Smith as a refinement of his kingdom Chromista, which was first The Rhizaria are a species-rich supergroup of Protists They vary considerably in form but for the most part they are Amoeboids with filose reticulose or microtubule-supported The excavates are a major assemblage of Protists often known as Excavata. Alternative taxonomical classifications are those which differ from the commonly accepted classifications in fundamental ways Unikonts are members of the Unikonta a taxonomic group proposed by Thomas Cavalier-Smith. The opisthokonts ( Greek: (opisthō- = "rear posterior" + (kontos = "pole" i The Mesomycetozoea or DRIP Clade are a small group of Protists mostly Parasites of fish and other animals Choanozoa ( Greek: (choanos = "funnel" + (zōon = "animal" is the name of a Phylum of protists that belongs A fungus (ˈfʌŋgəs is a eukaryotic Organism that is a member of the kingdom Fungi (ˈfʌndʒaɪ The Amoebozoa are a major group of Amoeboid protozoa including the majority that move by means of internal Cytoplasmic flow A Bikont ("two flagella" is a eukaryotic cell with two Flagella, as its name suggests The Apusozoa comprise several genera of Flagellate protozoa They are usually around 5-20 μm in size and occur in soils and aquatic habitats where they feed on bacteria The Rhizaria are a species-rich supergroup of Protists They vary considerably in form but for the most part they are Amoeboids with filose reticulose or microtubule-supported The excavates are a major assemblage of Protists often known as Excavata. The Archaeplastida or Primoplantae are a major line of Eukaryotes comprising the land plants green and Red algae and a small Chromalveolata is a Eukaryote supergroup first proposed by Thomas Cavalier-Smith as a refinement of his kingdom Chromista, which was first Plants are living Organisms belonging to the kingdom Plantae. A fungus (ˈfʌŋgəs is a eukaryotic Organism that is a member of the kingdom Fungi (ˈfʌndʒaɪ Protists (ˈproʊtɨst are a diverse group of eukaryotic Microorganisms Historically protists were treated as the kingdom Protista but this The cell is the structural and functional unit of all known living Organisms It is the smallest unit of an organism that is classified as living and is often called The cell membrane (also called the plasma membrane, plasmalemma, or "phospholipid bilayer" is a Selectively permeable Lipid bilayer The defining membrane-bound structure which differentiates eukaryotic cells from prokaryotic cells is the nucleus. The prokaryotes (proʊˈkærioʊts singular prokaryote /proʊˈkæriət/ are a group of Organisms that lack a Cell nucleus (= karyon or any other In Cell biology, the nucleus (pl nuclei; from Latin la ''nucleus'' or la ''nuculeus'' "little nut" or kernel is a membrane-enclosed The presence of a nucleus gives these organisms their name, which comes from the Greek ευ, meaning "good/true", and κάρυον, "nut". Greek (el ελληνική γλώσσα or simply el ελληνικά — "Hellenic" is an Indo-European language, spoken today by 15-22 million people mainly Many eukaryotic cells contain other membrane-bound organelles such as mitochondria, chloroplasts and Golgi bodies. In Cell biology, an organelle (pronunciation /ɔː(rgəˡnɛl/ is a specialized subunit within a cell that has a specific function and is usually separately enclosed In Cell biology, a mitochondrion (plural mitochondria) is a membrane-enclosed Organelle found in most eukaryotic cells. Chloroplasts are Organelles found in Plant cells and eukaryotic Algae that conduct Photosynthesis. The Golgi apparatus (also called the Eukaryotes often have unique flagella made of microtubules in a 9+2 arrangement. A flagellum ( plural flagella) is a tail-like structure that projects from the Cell body of certain Prokaryotic and Eukaryotic cells and it Microtubules are one of the components of the Cytoskeleton. They have a diameter of 25 nm and length varying from 200 nanometers to 25 micrometers

Cell division in eukaryotes is different from organisms without a nucleus (prokaryotes). Cell division is a process by which a cell, called the parent cell divides into two or more cells called daughter cells. It involves separating the duplicated chromosomes, through movements directed by microtubules. A chromosome is an organized structure of DNA and Protein that is found in cells. There are two types of division processes. In mitosis, one cell divides to produce two genetically-identical cells. Mitosis is the process in which a Eukaryotic cell separates the Chromosomes in its Cell nucleus, into two identical sets in two daughter nuclei In meiosis, which is required in sexual reproduction, one diploid cell (having two instances of each chromosome, one from each parent) undergoes recombination of each pair of parental chromosomes, and then two stages of cell division, resulting in four haploid cells (gametes). In Biology or life science meiosis (pronounced my-oh-sis is a process of reductional division in which the number of chromosomes per cell is cut in half The Evolution of sexual reproduction is a major puzzle The first Fossilized evidence of sexually reproducing Organisms is from Eukaryotes of the Stenian "Haplo" redirects here For the fictional character see The Death Gate Cycle. Genetic recombination is the process by which a strand of genetic material (usually DNA; but can also be RNA) is broken and then joined to a different DNA molecule "Haplo" redirects here For the fictional character see The Death Gate Cycle. A gamete (from Ancient Greek γαμέτης; translated gamete = wife gametes = husband is a cell that fuses with another gamete Each gamete has just one complement of chromosomes, each a unique mix of the corresponding pair of parental chromosomes.

Eukaryotes appear to be monophyletic, and so make up one of the three domains of life. A clade is a taxonomic group comprising a single Common ancestor and all the descendants of that ancestor In biological Taxonomy, a domain (also superregnum, superkingdom, or empire) is the highest Taxonomic rank of Organisms The two other domains, bacteria and archaea, are prokaryotes, and have none of the above features. The Bacteria ( singular: bacterium) are a large group of unicellular Microorganisms Typically a few Micrometres in length bacteria have But eukaryotes do share some aspects of their biochemistry with archaea, and so are grouped with archaea in the clade Neomura. A clade is a taxonomic group comprising a single Common ancestor and all the descendants of that ancestor Neomura is a speculative Clade composed of the two domains of life of Archaea and Eukarya.

Cell features

Eukaryotic cells are typically much larger than prokaryotes. The prokaryotes (proʊˈkærioʊts singular prokaryote /proʊˈkæriət/ are a group of Organisms that lack a Cell nucleus (= karyon or any other They have a variety of internal membranes and structures, called organelles, and a cytoskeleton composed of microtubules, microfilaments, and intermediate filaments, which play an important role in defining the cell's organization and shape. In Cell biology, an organelle (pronunciation /ɔː(rgəˡnɛl/ is a specialized subunit within a cell that has a specific function and is usually separately enclosed cytoskeleton (also CSK is a cellular " Scaffolding " or " Skeleton " contained within the Cytoplasm. Microtubules are one of the components of the Cytoskeleton. They have a diameter of 25 nm and length varying from 200 nanometers to 25 micrometers Microfilaments (or actin filaments) are the thinnest filaments of the Cytoskeleton found in the cytoplasm of all Eukaryotic cells. Intermediate filaments (IFs are cytoskeletal structures formed by members of a family of related proteins called Keratin. Eukaryotic DNA is divided into several linear bundles called chromosomes, which are separated by a microtubular spindle during nuclear division. Deoxyribonucleic acid ( DNA) is a Nucleic acid that contains the genetic instructions used in the development and functioning of all known A chromosome is an organized structure of DNA and Protein that is found in cells.

Detail of the endomembrane system and its components

Internal membrane

Eukaryotic cells include a variety of membrane-bound structures, collectively referred to as the endomembrane system. The endomembrane system is composed of the different membranes that are suspended in the Cytoplasm within a Eukaryotic cell. Simple compartments, called vesicles or vacuoles, can form by budding off other membranes. A vesicle is a small bubble of liquid within a cell A more formal definition in Cell biology, would be that a vesicle is a relatively small intracellular membrane-enclosed In general vacuole functions include Removing unwanted structural debris Isolating materials that might be harmful or a threat to the cell Containing Many cells ingest food and other materials through a process of endocytosis, where the outer membrane invaginates and then pinches off to form a vesicle. Endocytosis is a process where cells absorb material ( Molecules such as proteins from the outside by engulfing it with their Cell membrane. It is probable that most other membrane-bound organelles are ultimately derived from such vesicles.

The nucleus is surrounded by a double membrane (commonly referred to as a nuclear envelope), with pores that allow material to move in and out. The nuclear envelope (NE(also known as the perinuclear envelope, nuclear membrane, nucleolemma or karyotheca) is a double lipid bilayer that Various tube- and sheet-like extensions of the nuclear membrane form what is called the endoplasmic reticulum or ER, which is involved in protein transport and maturation. The endoplasmic reticulum (Greek endo = "within" (prefix plásma = "formed entity" Latin reticulum = "little net" or ER, is an Organelle It includes the Rough ER where ribosomes are attached, and the proteins they synthesize enter the interior space or lumen. Ribosomes ( from ribo nucleic acid and "Greek soma ( meaning body") are complexes of RNA and Protein that Subsequently, they generally enter vesicles, which bud off from the Smooth ER. In most eukaryotes, this protein-carrying vesicles are released and further modified in stacks of flattened vesicles, called Golgi bodies or dictyosomes. The Golgi apparatus (also called the

Vesicles may be specialized for various purposes. For instance, lysosomes contain enzymes that break down the contents of food vacuoles, and peroxisomes are used to break down peroxide, which is toxic otherwise. Lysosomes are Organelles that contain Digestive enzymes (acid Hydrolases. Peroxisomes are Ubiquitous Organelles in Eukaryotes that participate in the metabolism of Fatty acids and other metabolites A peroxide is a compound containing an Oxygen -oxygen single bond. Many protozoa have contractile vacuoles, which collect and expel excess water, and extrusomes, which expel material used to deflect predators or capture prey. Extrusomes are membrane-bound structures in some Eukaryotes which under certain conditions discharge their contents outside the cell In multicellular organisms, hormones are often produced in vesicles. Hormones (from Greek ὁρμή - "impetus" are chemicals released by cells that affect cells in other parts of the body In higher plants, most of a cell's volume is taken up by a central vacuole, which primarily maintains its osmotic pressure.

Mitochondria structure:
1) Inner membrane
2) Outer membrane
3) Crista
4) Matrix

Mitochondria and plastids

Mitochondria are organelles found in nearly all eukaryotes. The inner membrane is the Biological membrane (phospholipid bilayer of an Organelle or Gram-negative Bacteria that is within an Outer The outer membrane refers to the outside membranes of Gram-negative bacteria, the Chloroplast, or the Mitochondria. Cristae (singular crista) are the internal compartments formed by the inner membrane of a Mitochondrion. In Biology, matrix (plural matrices) is the material between animal or plant cells, the material (or tissue in which more specialized structures are embedded In Cell biology, a mitochondrion (plural mitochondria) is a membrane-enclosed Organelle found in most eukaryotic cells. They are surrounded by double membranes (known as the phospholipid bi-layer), the inner of which is folded into invaginations called cristae, where aerobic respiration takes place. A lipid bilayer or bilayer lipid membrane ( BLM) is a membrane composed of Lipid molecules (usually Phospholipids. Cellular respiration is the set of the metabolic reactions and processes that take place in Organisms cells to convert biochemical energy from They contain their own DNA and are only formed by the fission of other mitochondria. They are now generally held to have developed from endosymbiotic prokaryotes, probably proteobacteria. An endosymbiont is any Organism that lives within the body or cells of another organism i The Proteobacteria are a major group ( Phylum) of Bacteria. They include a wide variety of Pathogens such as Escherichia, The few protozoa that lack mitochondria have been found to contain mitochondrion-derived organelles, such as hydrogenosomes and mitosomes. A hydrogenosome is a membrane-enclosed Organelle of some anaerobic Ciliates trichomonads and Fungi. A mitosome is an Organelle found in some unicellular eukaryotic organisms

Plants and various groups of algae also have plastids. Algae ( sing. alga are a large and diverse group of simple typically Autotrophic organisms ranging from Unicellular to Multicellular forms Plastids are major Organelles found in plants and algae Plastids often contain pigments used in photosynthesis and the types of pigments present can change Again, these have their own DNA and developed from endosymbiotes, in this case cyanobacteria. Cyanobacteria, also known as blue-green algae, blue-green bacteria or Cyanophyta, is a phylum of Bacteria that obtain their energy They usually take the form of chloroplasts, which like cyanobacteria contain chlorophyll and produce energy through photosynthesis. Chloroplasts are Organelles found in Plant cells and eukaryotic Algae that conduct Photosynthesis. Chlorophyll is a green Pigment found in most Plants Algae and Cyanobacteria. Photosynthesis is a Metabolic pathway that converts Light Energy into Chemical energy. Others are involved in storing food. Although plastids likely had a single origin, not all plastid-containing groups are closely related. Instead, some eukaryotes have obtained them from others through secondary endosymbiosis or ingestion.

Endosymbiotic origins have also been proposed for the nucleus, for which see below, and for eukaryotic flagella, supposed to have developed from spirochaetes. A flagellum ( plural flagella) is a tail-like structure that projects from the Cell body of certain Prokaryotic and Eukaryotic cells and it Spirochaetes is a phylum of distinctive Gram-negative bacteria, which have long helically coiled cells This is not generally accepted, both from a lack of cytological evidence and difficulty in reconciling this with cellular reproduction.

Cytoskeletal structures

Many eukaryotes have long slender motile cytoplasmic projections, called flagella. A flagellum ( plural flagella) is a tail-like structure that projects from the Cell body of certain Prokaryotic and Eukaryotic cells and it These are composed mainly of tubulin and shorter cilia, both of which are variously involved in movement, feeding, and sensation. A Tubulin is one of several members of a small family of globular Proteins The most common members of the tubulin family are α-tubulin and β-tubulin the proteins that A cilium (plural cilia) is an Organelle found in eukaryotic cells Cilia are tail-like projections extending approximately These are entirely distinct from prokaryotic flagella. They are supported by a bundle of microtubules arising from a basal body, also called a kinetosome or centriole, characteristically arranged as nine doublets surrounding two singlets. A basal body (sometimes basal granule or kinetosome) is an Organelle formed from a Centriole, a short Cylindrical array A kinetosome in Biology, is the proper name for the Basal bodies found specifically in Ciliates The Axoneme arises from the kinetosome A Centriole is a barrel shaped Organelle found in most animal Eukaryotic cells though absent in Higher plants and Fungi. Flagella also may have hairs, or mastigonemes, and scales connecting membranes and internal rods. Mastigonemes are lateral "hairs" found covering the flagella of Heterokont and Cryptophyte Algae. Their interior is continuous with the cell's cytoplasm. The cytoplasm is the contents of a cell that is enclosed within the Plasma membrane. Microfilamental structures composed by actin and actin binding proteins, e. Actin is a globular roughly 42-kDa Protein found in all eukaryotic cells (except for Nematode sperm where it may be present at concentrations of g. , α-actinin, fimbrin, filamin are present in submembraneous cortical layers and bundles, as well. Actinin is a Microfilament protein α-Actinin is necessary for the attachment of Actin filaments to the Z-line membrane in muscle cells Fimbrin is an actin cross-linking protein To understand actin cross-linking in context one must first understand the function of Actin itself within the cell Motor proteins of microtubules, e. Motor proteins are a class of Molecular motors that are able to move along the surface of a suitable substrate g. , dynein or kinesin and actin, e. Dynein is a Motor protein (also called molecular motor or motor molecule in cells which converts the chemical Energy contained in ATP into the Kinesins are a class of Motor proteins found in Eukaryotic cells g. , myosins provide dynamic character of the network. Myosins are a large family of Motor proteins found in Eukaryotic tissues.

Centrioles are often present even in cells and groups that do not have flagella. A Centriole is a barrel shaped Organelle found in most animal Eukaryotic cells though absent in Higher plants and Fungi. They generally occur in groups of one or two, called kinetids, that give rise to various microtubular roots. These form a primary component of the cytoskeletal structure, and are often assembled over the course of several cell divisions, with one flagellum retained from the parent and the other derived from it. Centrioles may also be associated in the formation of a spindle during nuclear division.

Significance of cytoskeletal structures is underlined in determination of shape of the cells, as well as their being essential components of migratory responses like chemotaxis and chemokinesis. Chemotaxis, a kind of Taxis, is the phenomenon in which bodily cells bacteria, and other single-cell or Multicellular organisms direct their movements Motile response of unicellular Prokaryotic or Eukaryotic organisms to chemicals that cause the cell to make some kind of change in their migratory/swimming behaviour Some protists have various other microtubule-supported organelles. These include the radiolaria and heliozoa, which produce axopodia used in flotation or to capture prey, and the haptophytes, which have a peculiar flagellum-like organelle called the haptonema. Radiolarians (also radiolaria) are Amoeboid Protozoa that produce intricate Mineral Skeletons typically with a central capsule Heliozoa, or sun Animalcules are roughly spherical Amoeboids with many stiff Microtubule -supported projections called Axopods radiating outward The haptophytes, classed either as the Prymnesiophyta or Haptophyta are a Phylum of Algae The Chloroplasts are pigmented similarly to those of the

Plant cell wall

Further information: Cell wall

Plant cells have a cell wall, a fairly rigid layer outside the cell membrane, providing the cell with structural support, protection, and a filtering mechanism. A cell wall is a tough flexible and sometimes fairly rigid layer surrounding a cell, located external to the Cell membrane, which provides the cell with structural The cell membrane (also called the plasma membrane, plasmalemma, or "phospholipid bilayer" is a Selectively permeable Lipid bilayer The cell wall also prevents over-expansion when water enters the cell. The major carbohydrates making up the primary cell wall are cellulose, hemicellulose, and pectin. Cellulose is an Organic compound with the formula, a Polysaccharide consisting of a linear chain of several hundred to over ten thousand β(1→4 A hemicellulose can be any of several Heteropolymers (matrix polysaccharides present in almost all plant cell walls along with Cellulose. Pectin (from Greek πηκτικός - pektikos, "congealed curdled" a white to light brown powder is a Heteropolysaccharide The cellulose microfibrils are linked via hemicellulosic tethers to form the cellulose-hemicellulose network, which is embedded in the pectin matrix. The microfibril is a very fine Fibril, or fiber-like strand consisting of Glycoproteins. The most common hemicellulose in the primary cell wall is xyloglucan. Xyloglucan is the main Hemicellulose in the primary Cell wall of dicotyledonous plants and occurs in the cell walls of all vascular plants

Differences between eukaryotic cells

There are many different types of eukaryotic cells, though animals and plants are the most familiar eukaryotes, and thus provide an excellent starting point for understanding eukaryotic structure. Fungi and many protists have some substantial differences, however.

Animal cell

Structure of a typical animal cell.

Structure of a typical plant cell. Plant cells are eukaryotic cells that differ in several key respects from the cells of other eukaryotic Organisms Their distinctive features

An animal cell is a form of eukaryotic cell that makes up many tissues in animals. Animals Plants fungi, and Protists are eukaryotes (juːˈkærɪɒt or -oʊt Organisms whose cells are organized into complex Tissue is a cellular organizational level intermediate between cells and a complete organism The animal cell is distinct from other eukaryotes, most notably plant cells, as they lack cell walls and chloroplasts, and they have smaller vacuoles. Plant cells are eukaryotic cells that differ in several key respects from the cells of other eukaryotic Organisms Their distinctive features A cell wall is a tough flexible and sometimes fairly rigid layer surrounding a cell, located external to the Cell membrane, which provides the cell with structural Chloroplasts are Organelles found in Plant cells and eukaryotic Algae that conduct Photosynthesis. In general vacuole functions include Removing unwanted structural debris Isolating materials that might be harmful or a threat to the cell Containing Due to the lack of a rigid cell wall, animal cells can adopt a variety of shapes, and a phagocytic cell can even engulf other structures. A cell wall is a tough flexible and sometimes fairly rigid layer surrounding a cell, located external to the Cell membrane, which provides the cell with structural Phagocytes are cells that are found in the blood bone marrow and other tissues of Vertebrates.

There are many different cell types. A cell type is a distinct morphological or functional form of cell. For instance, there are approximately 210 distinct cell types in the adult human body. There are about 210 known distinct human Cell types. Keratinizing epithelial cells Epidermal Keratinocyte (differentiating

Plant cell

Further information: Plant cell

Plant cells are quite different from the cells of the other eukaryotic organisms. Plant cells are eukaryotic cells that differ in several key respects from the cells of other eukaryotic Organisms Their distinctive features The cell is the structural and functional unit of all known living Organisms It is the smallest unit of an organism that is classified as living and is often called Their distinctive features are:

• A large central vacuole (enclosed by a membrane, the tonoplast), which maintains the cell's turgor and controls movement of molecules between the cytosol and sap
• A primary cell wall containing cellulose, hemicellulose and pectin, deposited by the protoplast on the outside of the cell membrane; this contrasts with the cell walls of fungi, which contain chitin, and the cell envelopes of prokaryotes, in which peptidoglycans are the main structural molecules
• The plasmodesmata, linking pores in the cell wall that allow each plant cell to communicate with other adjacent cells; this is different from the functionally analogous system of gap junctions between animal cells. In general vacuole functions include Removing unwanted structural debris Isolating materials that might be harmful or a threat to the cell Containing In general vacuole functions include Removing unwanted structural debris Isolating materials that might be harmful or a threat to the cell Containing ' Turgor pressure' or turgidity is the main pressure of the cell contents against the Cell wall in Plant cells and bacteria cells determined by the water In Chemistry, a molecule is defined as a sufficiently stable electrically neutral group of at least two Atoms in a definite arrangement held together by The cytosol or intracellular fluid (or cytoplasmic matrix) is the liquid found inside cells. A cell wall is a tough flexible and sometimes fairly rigid layer surrounding a cell, located external to the Cell membrane, which provides the cell with structural Cellulose is an Organic compound with the formula, a Polysaccharide consisting of a linear chain of several hundred to over ten thousand β(1→4 A hemicellulose can be any of several Heteropolymers (matrix polysaccharides present in almost all plant cell walls along with Cellulose. Pectin (from Greek πηκτικός - pektikos, "congealed curdled" a white to light brown powder is a Heteropolysaccharide This article discusses protoplasts in the biological sense For the theological use see Adam and Eve Protoplast, from the Ancient Greek The cell membrane (also called the plasma membrane, plasmalemma, or "phospholipid bilayer" is a Selectively permeable Lipid bilayer A fungus (ˈfʌŋgəs is a eukaryotic Organism that is a member of the kingdom Fungi (ˈfʌndʒaɪ Chitin ( C 8 H 13 O 5 N)n (ˈkaɪtən is a long-chain Polymer of a N-acetylglucosamine The cell envelope is the Cell membrane and Cell wall plus an outer membrane if one is present The prokaryotes (proʊˈkærioʊts singular prokaryote /proʊˈkæriət/ are a group of Organisms that lack a Cell nucleus (= karyon or any other Not to be confused with Glycoprotein. Peptidoglycan, also known as murein, is a Polymer consisting of sugars and amino A gap junction or nexus is a specialized Intercellular connection between certain animal cell -types
• Plastids, especially chloroplasts that contain chlorophyll, the pigment that gives plants their green color and allows them to perform photosynthesis
• Higher plants, including conifers and flowering plants (Angiospermae) lack the flagellae and centrioles that are present in animal cells. Plastids are major Organelles found in plants and algae Plastids often contain pigments used in photosynthesis and the types of pigments present can change Chloroplasts are Organelles found in Plant cells and eukaryotic Algae that conduct Photosynthesis. Chlorophyll is a green Pigment found in most Plants Algae and Cyanobacteria. Plants are living Organisms belonging to the kingdom Plantae. Photosynthesis is a Metabolic pathway that converts Light Energy into Chemical energy. The flowering plants or angiosperms ( Angiospermae or Magnoliophyta) are the most widespread group A flagellum ( plural flagella) is a tail-like structure that projects from the Cell body of certain Prokaryotic and Eukaryotic cells and it A Centriole is a barrel shaped Organelle found in most animal Eukaryotic cells though absent in Higher plants and Fungi. Animals Plants fungi, and Protists are eukaryotes (juːˈkærɪɒt or -oʊt Organisms whose cells are organized into complex

Fungal cell

Fungal cells are most similar to animal cells, with the following exceptions:

• A cell wall containing chitin
• Less definition between cells; the hyphae of higher fungi have porous partitions called septa, which allow the passage of cytoplasm, organelles, and, sometimes, nuclei. Chitin ( C 8 H 13 O 5 N)n (ˈkaɪtən is a long-chain Polymer of a N-acetylglucosamine A hypha (plural hyphae) is a long branching filamentous cell of a Fungus, and also of unrelated Actinobacteria. A septum ( Latin: something that encloses; plural Septa) is a partition separating two cavities or spaces Primitive fungi have few or no septa, so each organism is essentially a giant multinucleate supercell; these fungi are described as coenocytic. A coenocyte is a Multinucleate cell. It can result from multiple nuclear divisions without accompanying Cell divisions or from cellular aggregation followed
• Only the most primitive fungi, chytrids, have flagella. Chytridiomycota is a Division of the Fungi kingdom. The name refers to the chytridium (from the Greek

Other eukaryotic cells

Eukaryotes are a very diverse group, and their cell structures are equally diverse. Many have cell walls; many do not. Many have chloroplasts, derived from primary, secondary, or even tertiary endosymbiosis; and many do not. Some groups have unique structures, such as the cyanelles of the glaucophytes, the haptonema of the haptophytes, or the ejectisomes of the cryptomonads. The glaucophytes, also known as glaucocystophytes or glaucocystids, are a small group of freshwater microscopic Algae. The haptophytes, classed either as the Prymnesiophyta or Haptophyta are a Phylum of Algae The Chloroplasts are pigmented similarly to those of the The cryptomonads are a small group of Flagellates most of which have Chloroplasts They are common in freshwater and also occur in marine and brackish habitats Other structures, such as pseudopods, are found in various eukaryote groups in different forms, such as the lobose amoebozoans or the reticulose foraminiferans. Pseudopods or pseudopodia (from the Greek word ψευδοπόδια, ψευδός "fake false" The Amoebozoa are a major group of Amoeboid protozoa including the majority that move by means of internal Cytoplasmic flow The Foraminifera, ("Hole Bearers" or forams for short are a large group of Amoeboid Protists with reticulating Pseudopods fine

Reproduction

Nuclear division is often coordinated with cell division. Cell division is a process by which a cell, called the parent cell divides into two or more cells called daughter cells. This generally takes place by mitosis, a process that allows each daughter nucleus to receive one copy of each chromosome. Mitosis is the process in which a Eukaryotic cell separates the Chromosomes in its Cell nucleus, into two identical sets in two daughter nuclei In most eukaryotes, there is also a process of sexual reproduction, typically involving an alternation between haploid generations, wherein only one copy of each chromosome is present, and diploid generations, wherein two are present, occurring through nuclear fusion (syngamy) and meiosis. "Haplo" redirects here For the fictional character see The Death Gate Cycle. "Haplo" redirects here For the fictional character see The Death Gate Cycle. In Biology or life science meiosis (pronounced my-oh-sis is a process of reductional division in which the number of chromosomes per cell is cut in half There is considerable variation in this pattern, however.

Eukaryotes have a smaller surface to volume area ratio than prokaryotes, and thus have lower metabolic rates and longer generation times. In some multicellular organisms, cells specialized for metabolism will have enlarged surface areas, such as intestinal vili.

Origin and evolution

Phylogenetic tree showing the relationship between the eukaryotes and other forms of life. A phylogenetic tree, also called an evolutionary tree, is a tree showing the Evolutionary relationships among various biological Species or other ^[1] Eukaryotes are colored red, archaea green and bacteria blue. The Bacteria ( singular: bacterium) are a large group of unicellular Microorganisms Typically a few Micrometres in length bacteria have

The origin of the eukaryotic cell was a milestone in the evolution of life, since they include all complex cells and almost all multi-cellular organisms. The timing of this series of events is hard to determine; Knoll (1992) suggests they developed approximately 1. Andrew H Knoll (born 1947 is the Fisher Professor of Natural History and a Professor of Earth and Planetary Sciences at Harvard University. 6 - 2. 1 billion years ago. Some acritarchs are known from at least 1650 million years ago, and the possible alga Grypania has been found as far back as 2100 million years ago. Acritarchs are small organic Fossils present from approximately to the present Grypania is an early tube-shaped fossil from the Proterozoic Eon ^[2] Fossils that are clearly related to modern groups start appearing around 1. 2 billion years ago, in the form of a red alga. The red algae (Rhodophyta ˌroʊdəˈfaɪtə roʊˈdɒfɨtə from Greek: ῥόδον (rhodon = rose + φυτόν (phyton = plant thus red plant are

Biomarkers suggest that at least stem eukaryotes arose even earlier. A biomarker is a substance used as an indicator of a biologic state The presence of steranes in Australian shales indicates that eukaryotes were present 2. Steranes are a class of 4- Cyclic compounds derived from Steroids or Sterols via diagenetic and catagenetic degradation and saturation For a topic outline on this subject see List of basic Australia topics. Shale (also called mudstone) is a fine-grained Sedimentary rock whose original constituents were Clay minerals or Muds It is characterized by 7 billion years ago. ^{[3] [4]}

rRNA trees constructed during the 1980s and 1990s left most eukaryotes in an unresolved "crown" group (not technically a true crown), which was usually divided by the form of the mitochondrial cristae. Ribosomal RNA ( rRNA) is the central component of the Ribosome, the protein manufacturing machinery of all living cells. The Crown Group is a Catering and event caterer in the United Kingdom. The few groups that lack mitochondria branched separately, and so the absence was believed to be primitive; but this is now considered an artifact of long-branch attraction, and they are known to have lost them secondarily. In Cell biology, a mitochondrion (plural mitochondria) is a membrane-enclosed Organelle found in most eukaryotic cells. Long branch attraction (LBA is a phenomenon in Phylogenetic analyses (most commonly those employing Maximum parsimony) when rapidly evolving lineages are inferred ^[5][6]

Trees based on actin and other molecules have painted a different and more complete picture. Actin is a globular roughly 42-kDa Protein found in all eukaryotic cells (except for Nematode sperm where it may be present at concentrations of In Chemistry, a molecule is defined as a sufficiently stable electrically neutral group of at least two Atoms in a definite arrangement held together by Most eukaryotes are now included in one of the following supergroups, although the relationship between these groups, and the monophyly of each group, is not yet clear:^[7][8]

Several authorities recognize two larger clades, the unikonts and the bikonts, that derive from an ancestral uniflagellar organism and a biflagellate respectively. A Bikont ("two flagella" is a eukaryotic cell with two Flagella, as its name suggests The Apusozoa comprise several genera of Flagellate protozoa They are usually around 5-20 μm in size and occur in soils and aquatic habitats where they feed on bacteria The Archaeplastida or Primoplantae are a major line of Eukaryotes comprising the land plants green and Red algae and a small Chromalveolata is a Eukaryote supergroup first proposed by Thomas Cavalier-Smith as a refinement of his kingdom Chromista, which was first The Rhizaria are a species-rich supergroup of Protists They vary considerably in form but for the most part they are Amoeboids with filose reticulose or microtubule-supported The excavates are a major assemblage of Protists often known as Excavata. Unikonts are members of the Unikonta a taxonomic group proposed by Thomas Cavalier-Smith. The Amoebozoa are a major group of Amoeboid protozoa including the majority that move by means of internal Cytoplasmic flow The opisthokonts ( Greek: (opisthō- = "rear posterior" + (kontos = "pole" i Choanozoa ( Greek: (choanos = "funnel" + (zōon = "animal" is the name of a Phylum of protists that belongs A fungus (ˈfʌŋgəs is a eukaryotic Organism that is a member of the kingdom Fungi (ˈfʌndʒaɪ Unikonts are members of the Unikonta a taxonomic group proposed by Thomas Cavalier-Smith. A Bikont ("two flagella" is a eukaryotic cell with two Flagella, as its name suggests In this system, the opisthokonts and amoebozoans are considered unikonts, and the rest bikonts. The chromalveolates were originally thought to be two separate groups, the chromists and the alveolates, but the former was proved to be paraphyletic to the latter, and the two groups combined. Chromalveolata is a Eukaryote supergroup first proposed by Thomas Cavalier-Smith as a refinement of his kingdom Chromista, which was first The Chromista are a eukaryotic supergroup probably Polyphyletic, The alveolates ("with cavities" are a major line of Protists There are three phyla, which are very divergent in form but are now known to be close relatives Some small protist groups have not been related to any of these supergroups, in particular the centrohelids. The centrohelids or centroheliozoa are a large group of Heliozoan protists

Eukaryotes are closely related to Archaea, at least in terms of nuclear DNA and genetic machinery, and some place them with Archaea in the clade Neomura. Neomura is a speculative Clade composed of the two domains of life of Archaea and Eukarya. In other respects, such as membrane composition, they are similar to eubacteria. The Bacteria ( singular: bacterium) are a large group of unicellular Microorganisms Typically a few Micrometres in length bacteria have Three main explanations for this have been proposed:

• Eukaryotes resulted from the complete fusion of two or more cells, where the cytoplasm formed from a eubacterium, and the nucleus from an archaeon or from a virus. Viral eukaryogenesis is the Hypothesis that the Cell nucleus of Eukaryotic life forms evolved from a large DNA virus in a form of endosymbiosis
• Eukaryotes developed from Archaea, and acquired their eubacterial characteristics from the proto-mitochondrion.
• Eukaryotes and Archaea developed separately from a modified eubacterium.

The origin of the endomembrane system and mitochondria are also disputed. The phagotrophic hypothesis states the membranes originated with the development of endocytosis and later specialized; mitochondria were acquired by ingestion, like plastids. The syntrophic hypothesis states that the proto-eukaryote relied on the proto-mitochondrion for food, and so ultimately grew to surround it; the membranes originate later, in part thanks to mitochondrial genes (the hydrogen hypothesis is one particular version). The hydrogen hypothesis is a model proposed by William Martin and Miklós Müller in 1998 that describes a possible way in which the Mitochondrion arose as an endosymbiont

In a study using genomes to construct supertrees, Pisani et al (2007) suggest that, along with evidence that there was never a mitochondrion-less eukaryote, eukaryotes evolved from a syntrophy between an archaea closely related to Thermoplasmatales and an α-proteobacterium, likely a symbiosis driven by sulfur or hydrogen. Syntrophy is the phenomenon that one species lives off the products of another species In taxonomy, the Thermoplasmatales are an order of the Thermoplasmata. The Proteobacteria are a major group ( Phylum) of Bacteria. They include a wide variety of Pathogens such as Escherichia, This article is about the biological phenomenon for other uses see Symbiosis (disambiguation The term symbiosis (from the Greek The mitochondrion and its genome is a remnant of the α-proteobacterial endosymbiont. ^[9]

See also

• List of sequenced eukaryotic genomes

References

External links

• Eukaryotes (Tree of Life web site)
• Prokaryote versus eukaryote, BioMineWiki