41-406: Eucarya may refer to: Eukaryotes , organisms whose cells contain a nucleus and complex structures inside the membranes. Eucarya , a formerly recognized genus of flowering plants that is now considered to be part of the genus Santalum . Topics referred to by the same term [REDACTED] This disambiguation page lists articles associated with
82-486: A female is any individual that produces the larger type of gamete called an ovum , and a male produces the smaller type, called a sperm cell or spermatozoon. Sperm cells are small and motile due to the presence of a tail-shaped structure, the flagellum , that provides propulsion. In contrast, each egg cell or ovum is relatively large and non-motile. Oogenesis , the process of female gamete formation in animals, involves meiosis (including meiotic recombination ) of
123-405: A microtubular spindle during nuclear division, in the distinctively eukaryotic process of mitosis . Eukaryotes differ from prokaryotes in multiple ways, with unique biochemical pathways such as sterane synthesis. The eukaryotic signature proteins have no homology to proteins in other domains of life, but appear to be universal among eukaryotes. They include the proteins of the cytoskeleton,
164-403: A zygote that develops into a new diploid organism. It is generally accepted that isogamy is the ancestral state from which anisogamy and oogamy evolved, although its evolution has left no fossil records. There are almost invariably only two gamete types, all analyses showing that intermediate gamete sizes are eliminated due to selection. Since intermediate sized gametes do not have
205-513: A "symbiosis-based phylogeny", giving the description "Eukarya (symbiosis-derived nucleated organisms)". By 2014, a rough consensus started to emerge from the phylogenomic studies of the previous two decades. The majority of eukaryotes can be placed in one of two large clades dubbed Amorphea (similar in composition to the unikont hypothesis) and the Diphoda (formerly bikonts), which includes plants and most algal lineages. A third major grouping,
246-430: A body, with its cells dividing by mitosis , and at some stage produce haploid gametes through meiosis , a division that reduces the number of chromosomes and creates genetic variability . There is considerable variation in this pattern. Plants have both haploid and diploid multicellular phases . Eukaryotes have lower metabolic rates and longer generation times than prokaryotes, because they are larger and therefore have
287-479: A bundle of microtubules arising from a centriole , characteristically arranged as nine doublets surrounding two singlets. Flagella may have hairs ( mastigonemes ), as in many stramenopiles . Their interior is continuous with the cell's cytoplasm . Centrioles are often present, even in cells and groups that do not have flagella, but conifers and flowering plants have neither. They generally occur in groups that give rise to various microtubular roots. These form
328-437: A diploid primary oocyte to produce a haploid ovum . Spermatogenesis , the process of male gamete formation in animals, involves meiosis in a diploid primary spermatocyte to produce haploid spermatozoa . In animals, ova are produced in the ovaries of females and sperm develop in the testes of males. During fertilization, a spermatozoon and an ovum, each carrying half of the genetic information of an individual, unite to form
369-401: A life cycle involving alternation of diploid and haploid generations some differences from animal life cycles exist. Plants use meiosis to produce spores that develop into multicellular haploid gametophytes which produce gametes by mitosis. In animals there is no corresponding multicellular haploid phase. The sperm of plants that reproduce using spores are formed by mitosis in an organ of
410-406: A primary component of the cytoskeleton, 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 produce the spindle during nuclear division. The cells of plants, algae, fungi and most chromalveolates , but not animals, are surrounded by a cell wall. This is a layer outside the cell membrane , providing
451-522: A reproductive technique for same-sex male couples, although a surrogate mother would still be required for the gestation period. Women who have passed menopause may be able to produce eggs and bear genetically related children with artificial gametes. Robert Sparrow wrote, in the Journal of Medical Ethics , that embryos derived from artificial gametes could be used to derive new gametes and this process could be repeated to create multiple human generations in
SECTION 10
#1733066256375492-510: A smaller surface area to volume ratio. The evolution of sexual reproduction may be a primordial characteristic of eukaryotes. Based on a phylogenetic analysis, Dacks and Roger have proposed that facultative sex was present in the group's common ancestor. A core set of genes that function in meiosis is present in both Trichomonas vaginalis and Giardia intestinalis , two organisms previously thought to be asexual. Since these two species are descendants of lineages that diverged early from
533-417: A system of domains rather than kingdoms as top level rank being put forward by Carl Woese , Otto Kandler , and Mark Wheelis in 1990, uniting all the eukaryote kingdoms in the domain "Eucarya", stating, however, that " 'eukaryotes' will continue to be an acceptable common synonym". In 1996, the evolutionary biologist Lynn Margulis proposed to replace kingdoms and domains with "inclusive" names to create
574-458: Is a haploid cell that fuses with another haploid cell during fertilization in organisms that reproduce sexually . Gametes are an organism's reproductive cells , also referred to as sex cells . The name gamete was introduced by the German cytologist Eduard Strasburger in 1878. Gametes of both mating individuals can be the same size and shape, a condition known as isogamy . By contrast, in
615-610: Is closer in structure to bacterial RNA than to eukaryote RNA. Some eukaryotes, such as the metamonads Giardia and Trichomonas , and the amoebozoan Pelomyxa , appear to lack mitochondria, but all contain mitochondrion-derived organelles, like hydrogenosomes or mitosomes , having lost their mitochondria secondarily. They obtain energy by enzymatic action in the cytoplasm. Plants and various groups of algae have plastids as well as mitochondria. Plastids, like mitochondria, have their own DNA and are developed from endosymbionts , in this case cyanobacteria . They usually take
656-618: Is much larger than that of prokaryotes. The eukaryotes seemingly emerged within the Asgard archaea , and are closely related to the Heimdallarchaeia . This implies that there are only two domains of life , Bacteria and Archaea, with eukaryotes incorporated among the Archaea. Eukaryotes first emerged during the Paleoproterozoic , likely as flagellated cells. The leading evolutionary theory
697-532: Is that their cells have nuclei . This gives them their name, from the Greek εὖ ( eu , "well" or "good") and κάρυον ( karyon , "nut" or "kernel", here meaning "nucleus"). Eukaryotic cells have a variety of internal membrane-bound structures, called organelles , and a cytoskeleton which defines the cell's organization and shape. The nucleus stores the cell's DNA , which is divided into linear bundles called chromosomes ; these are separated into two matching sets by
738-864: Is they were created by symbiogenesis between an anaerobic Asgard archaean and an aerobic proteobacterium , which formed the mitochondria . A second episode of symbiogenesis with a cyanobacterium created the plants, with chloroplasts . Eukaryotic cells contain membrane-bound organelles such as the nucleus , the endoplasmic reticulum , and the Golgi apparatus . Eukaryotes may be either unicellular or multicellular . In comparison, prokaryotes are typically unicellular. Unicellular eukaryotes are sometimes called protists . Eukaryotes can reproduce both asexually through mitosis and sexually through meiosis and gamete fusion ( fertilization ). Eukaryotes are organisms that range from microscopic single cells , such as picozoans under 3 micrometres across, to animals like
779-1354: The Excavata , has been abandoned as a formal group as it is paraphyletic . The proposed phylogeny below includes only one group of excavates ( Discoba ), and incorporates the 2021 proposal that picozoans are close relatives of rhodophytes. The Provora are a group of microbial predators discovered in 2022. Ancyromonadida [REDACTED] Malawimonada [REDACTED] CRuMs [REDACTED] Amoebozoa [REDACTED] Breviatea [REDACTED] Apusomonadida [REDACTED] Holomycota (inc. fungi) [REDACTED] Holozoa (inc. animals) [REDACTED] ? Metamonada [REDACTED] Discoba [REDACTED] Cryptista [REDACTED] Rhodophyta (red algae) [REDACTED] Picozoa [REDACTED] Glaucophyta [REDACTED] Viridiplantae (plants) [REDACTED] Hemimastigophora [REDACTED] Provora [REDACTED] Haptista [REDACTED] Telonemia [REDACTED] Rhizaria [REDACTED] Alveolata [REDACTED] Stramenopiles [REDACTED] [REDACTED] Gamete A gamete ( / ˈ ɡ æ m iː t / ; from Ancient Greek γαμετή ( gametḗ ) 'wife', ultimately from Ancient Greek γάμος ( gámos ) 'marriage')
820-518: The archaea —having a volume of around 10,000 times greater. Eukaryotes represent a small minority of the number of organisms , but, as many of them are much larger, their collective global biomass (468 gigatons) is far larger than that of prokaryotes (77 gigatons), with plants alone accounting for over 81% of the total biomass of Earth . The eukaryotes are a diverse lineage, consisting mainly of microscopic organisms . Multicellularity in some form has evolved independently at least 25 times within
861-583: The blue whale , weighing up to 190 tonnes and measuring up to 33.6 metres (110 ft) long, or plants like the coast redwood , up to 120 metres (390 ft) tall. Many eukaryotes are unicellular; the informal grouping called protists includes many of these, with some multicellular forms like the giant kelp up to 200 feet (61 m) long. The multicellular eukaryotes include the animals, plants, and fungi , but again, these groups too contain many unicellular species . Eukaryotic cells are typically much larger than those of prokaryotes —the bacteria and
SECTION 20
#1733066256375902-548: The domain of Eukaryota or Eukarya , organisms whose cells have a membrane-bound nucleus . All animals , plants , fungi , and many unicellular organisms are eukaryotes. They constitute a major group of life forms alongside the two groups of prokaryotes : the Bacteria and the Archaea . Eukaryotes represent a small minority of the number of organisms, but given their generally much larger size, their collective global biomass
943-461: The taxonomic rank of kingdom by Linnaeus in the 18th century. Though he included the fungi with plants with some reservations, it was later realized that they are quite distinct and warrant a separate kingdom. The various single-cell eukaryotes were originally placed with plants or animals when they became known. In 1818, the German biologist Georg A. Goldfuss coined the word Protozoa to refer to organisms such as ciliates , and this group
984-709: The cell to move, change shape, or transport materials. The motor structures are microfilaments of actin and actin-binding proteins , including α- actinin , fimbrin , and filamin are present in submembranous cortical layers and bundles. Motor proteins of microtubules, dynein and kinesin , and myosin of actin filaments, provide dynamic character of the network. Many eukaryotes have long slender motile cytoplasmic projections, called flagella , or multiple shorter structures called cilia . These organelles are variously involved in movement, feeding, and sensation. They are composed mainly of tubulin , and are entirely distinct from prokaryotic flagella. They are supported by
1025-404: The cell with structural support, protection, and a filtering mechanism. The cell wall also prevents over-expansion when water enters the cell. The major polysaccharides making up the primary cell wall of land plants are cellulose , hemicellulose , and pectin . The cellulose microfibrils are linked together with hemicellulose, embedded in a pectin matrix. The most common hemicellulose in
1066-427: The complex transcription machinery, the membrane-sorting systems, the nuclear pore , and some enzymes in the biochemical pathways. Eukaryote cells include a variety of membrane-bound structures, together forming the endomembrane system. Simple compartments, called vesicles and vacuoles , can form by budding off other membranes. Many cells ingest food and other materials through a process of endocytosis , where
1107-622: The cytoplasm. Mitochondria are organelles in eukaryotic cells. The mitochondrion is commonly called "the powerhouse of the cell", for its function providing energy by oxidising sugars or fats to produce the energy-storing molecule ATP . Mitochondria have two surrounding membranes , each a phospholipid bilayer , the inner of which is folded into invaginations called cristae where aerobic respiration takes place. Mitochondria contain their own DNA , which has close structural similarities to bacterial DNA , from which it originated, and which encodes rRNA and tRNA genes that produce RNA which
1148-406: The eukaryotes. Complex multicellular organisms, not counting the aggregation of amoebae to form slime molds , have evolved within only six eukaryotic lineages: animals , symbiomycotan fungi , brown algae , red algae , green algae , and land plants . Eukaryotes are grouped by genomic similarities, so that groups often lack visible shared characteristics. The defining feature of eukaryotes
1189-484: The eukaryotic evolutionary tree, core meiotic genes, and hence sex, were likely present in the common ancestor of eukaryotes. Species once thought to be asexual, such as Leishmania parasites, have a sexual cycle. Amoebae, previously regarded as asexual, may be anciently sexual; while present-day asexual groups could have arisen recently. In antiquity , the two lineages of animals and plants were recognized by Aristotle and Theophrastus . The lineages were given
1230-646: The form of chloroplasts which, like cyanobacteria, contain chlorophyll and produce organic compounds (such as glucose ) through photosynthesis . Others are involved in storing food. Although plastids probably 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. The capture and sequestering of photosynthetic cells and chloroplasts, kleptoplasty , occurs in many types of modern eukaryotic organisms. The cytoskeleton provides stiffening structure and points of attachment for motor structures that enable
1271-402: The gametophyte known as the antheridium and the egg cells by mitosis in a flask-shaped organ called the archegonium . Plant sperm cells are their only motile cells, often described as flagellate, but more correctly as ciliate. Bryophytes have 2 flagella, horsetails have up to 200 and the mature spermatozoa of the cycad Zamia pumila has up to 50,000 flagella. Cycads and Ginkgo biloba are
Eucarya - Misplaced Pages Continue
1312-506: The genes during meiosis ensures that the chromosomes of gametes are not exact duplicates of either of the sets of chromosomes carried in the parental diploid chromosomes but a mixture of the two. Artificial gametes, also known as in vitro derived gametes (IVD), stem cell-derived gametes (SCDGs), and in vitro generated gametes (IVG), are gametes derived from stem cells . The use of such artificial gametes would "necessarily require IVF techniques". Research shows that artificial gametes may be
1353-444: The laboratory. This technique could be used to create cell lines for medical applications and for studying the heredity of genetic disorders . Additionally, this technique could be used for human enhancement by selectively breeding for a desired genome or by using recombinant DNA technology to create enhancements that have not arisen in nature. Plants that reproduce sexually also produce gametes. However, since plants have
1394-511: The majority of species, the gametes are of different sizes, a condition known as anisogamy or heterogamy that applies to humans and other mammals. The human ovum has approximately 100,000 times the volume of a single human sperm cell. The type of gamete an organism produces determines its sex and sets the basis for the sexual roles and sexual selection . In humans and other species that produce two morphologically distinct types of gametes, and in which each individual produces only one type ,
1435-410: The only gymnosperms with motile sperm. In the flowering plants , the female gametophyte is produced inside the ovule within the ovary of the flower. When mature, the haploid gametophyte produces female gametes which are ready for fertilization. The male gametophyte is produced inside a pollen grain within the anther and is non-motile, but can be distributed by wind, water or animal vectors. When
1476-449: The outer membrane invaginates and then pinches off to form a vesicle. Some cell products can leave in a vesicle through exocytosis . The nucleus is surrounded by a double membrane known as the nuclear envelope , with nuclear pores that allow material to move in and out. Various tube- and sheet-like extensions of the nuclear membrane form the endoplasmic reticulum , which is involved in protein transport and maturation. It includes
1517-417: The primary cell wall is xyloglucan . Eukaryotes have a life cycle that involves sexual reproduction , alternating between a haploid phase, where only one copy of each chromosome is present in each cell, and a diploid phase, with two copies of each chromosome in each cell. The diploid phase is formed by fusion of two haploid gametes, such as eggs and spermatozoa , to form a zygote ; this may grow into
1558-498: The rough endoplasmic reticulum, covered in ribosomes which synthesize proteins; these enter the interior space or lumen. Subsequently, they generally enter vesicles, which bud off from the smooth endoplasmic reticulum. In most eukaryotes, these protein-carrying vesicles are released and further modified in stacks of flattened vesicles ( cisternae ), the Golgi apparatus . Vesicles may be specialized; for instance, lysosomes contain digestive enzymes that break down biomolecules in
1599-406: The same advantages as small or large ones, they do worse than small ones in mobility and numbers, and worse than large ones in supply. In contrast to a gamete, which has only one set of chromosomes, a diploid somatic cell has two sets of homologous chromosomes , one of which is a copy of the chromosome set from the sperm and one a copy of the chromosome set from the egg cell. Recombination of
1640-566: The title Eucarya . If an internal link led you here, you may wish to change the link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=Eucarya&oldid=1198240942 " Category : Disambiguation pages Hidden categories: Short description is different from Wikidata All article disambiguation pages All disambiguation pages Eukaryote The eukaryotes ( / j uː ˈ k ær i oʊ t s , - ə t s / yoo- KARR -ee-ohts, -əts ) constitute
1681-498: Was expanded until Ernst Haeckel made it a kingdom encompassing all single-celled eukaryotes, the Protista , in 1866. The eukaryotes thus came to be seen as four kingdoms: The protists were at that time thought to be "primitive forms", and thus an evolutionary grade , united by their primitive unicellular nature. Understanding of the oldest branchings in the tree of life only developed substantially with DNA sequencing , leading to