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46-437: Traditional groups: The embryophytes ( / ˈ ɛ m b r i ə ˌ f aɪ t s / ) are a clade of plants , also known as Embryophyta ( / ˌ ɛ m b r i ˈ ɒ f ə t ə , - oʊ ˈ f aɪ t ə / ) or land plants . They are the most familiar group of photoautotrophs that make up the vegetation on Earth 's dry lands and wetlands . Embryophytes have a common ancestor with green algae , having emerged within

92-485: A and b to harvest the light energy in sunlight for carbon fixation from carbon dioxide and water in order to synthesize carbohydrates while releasing oxygen as a byproduct . The Embryophytes emerged either a half-billion years ago, at some time in the interval between the mid- Cambrian and early Ordovician , or almost a billion years ago, during the Tonian or Cryogenian, probably from freshwater charophytes ,

138-419: A and b , generally giving them a bright green color. Embryophyte cells also generally have an enlarged central vacuole enclosed by a vacuolar membrane or tonoplast, which maintains cell turgor and keeps the plant rigid. In common with all groups of multicellular algae they have a life cycle which involves alternation of generations . A multicellular haploid generation with a single set of chromosomes –

184-479: A "ladder", with supposedly more "advanced" organisms at the top. Taxonomists have increasingly worked to make the taxonomic system reflect evolution. When it comes to naming , this principle is not always compatible with the traditional rank-based nomenclature (in which only taxa associated with a rank can be named) because not enough ranks exist to name a long series of nested clades. For these and other reasons, phylogenetic nomenclature has been developed; it

230-623: A clade can be described based on two different reference points, crown age and stem age. The crown age of a clade refers to the age of the most recent common ancestor of all of the species in the clade. The stem age of a clade refers to the time that the ancestral lineage of the clade diverged from its sister clade. A clade's stem age is either the same as or older than its crown age. Ages of clades cannot be directly observed. They are inferred, either from stratigraphy of fossils , or from molecular clock estimates. Viruses , and particularly RNA viruses form clades. These are useful in tracking

276-458: A clade of multicellular green algae similar to extant Klebsormidiophyceae . The emergence of the Embryophytes depleted atmospheric CO 2 (a greenhouse gas ), leading to global cooling , and thereby precipitating glaciations . Embryophytes are primarily adapted for life on land, although some are secondarily aquatic . Accordingly, they are often called land plants or terrestrial plants. On

322-464: A microscopic level, the cells of charophytes are broadly similar to those of chlorophyte green algae, but differ in that in cell division the daughter nuclei are separated by a phragmoplast . They are eukaryotic , with a cell wall composed of cellulose and plastids surrounded by two membranes. The latter include chloroplasts , which conduct photosynthesis and store food in the form of starch , and are characteristically pigmented with chlorophylls

368-705: A range of environmental conditions found on land, such as exposure to rain, tolerance of temperature variation, high levels of ultra-violet light, and seasonal dehydration. The preponderance of molecular evidence as of 2006 suggested that the groups making up the embryophytes are related as shown in the cladogram below (based on Qiu et al. 2006 with additional names from Crane et al. 2004). Liverworts [REDACTED] Mosses [REDACTED] Hornworts [REDACTED] Lycophytes [REDACTED] ( ferns and horsetails ) [REDACTED] Angiosperms ( flowering plants ) [REDACTED] Gymnosperms [REDACTED] An updated phylogeny of Embryophytes based on

414-422: A revised taxonomy based on a concept strongly resembling clades, although the term clade itself would not be coined until 1957 by his grandson, Julian Huxley . German biologist Emil Hans Willi Hennig (1913–1976) is considered to be the founder of cladistics . He proposed a classification system that represented repeated branchings of the family tree, as opposed to the previous systems, which put organisms on

460-441: A single cell. In the bryophytes the sporophyte remains dependent on the gametophyte, while in all other embryophytes the sporophyte generation is dominant and capable of independent existence. Embryophytes also differ from algae by having metamers . Metamers are repeated units of development, in which each unit derives from a single cell, but the resulting product tissue or part is largely the same for each cell. The whole organism

506-429: A suffix added should be e.g. "dracohortian". A clade is by definition monophyletic , meaning that it contains one ancestor which can be an organism, a population, or a species and all its descendants. The ancestor can be known or unknown; any and all members of a clade can be extant or extinct. The science that tries to reconstruct phylogenetic trees and thus discover clades is called phylogenetics or cladistics ,

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552-431: Is also required for cellular elongation: as the cell wall is partially degraded by the action of expansins , the less rigid wall is expanded by the pressure coming from within the vacuole. Turgor pressure exerted by the vacuole is also essential in supporting plants in an upright position. Another function of a central vacuole is that it pushes all contents of the cell's cytoplasm against the cellular membrane, and thus keeps

598-499: Is also used with a similar meaning in other fields besides biology, such as historical linguistics ; see Cladistics § In disciplines other than biology . The term "clade" was coined in 1957 by the biologist Julian Huxley to refer to the result of cladogenesis , the evolutionary splitting of a parent species into two distinct species, a concept Huxley borrowed from Bernhard Rensch . Many commonly named groups – rodents and insects , for example – are clades because, in each case,

644-471: Is in turn included in the mammal, vertebrate and animal clades. The idea of a clade did not exist in pre- Darwinian Linnaean taxonomy , which was based by necessity only on internal or external morphological similarities between organisms. Many of the better known animal groups in Linnaeus's original Systema Naturae (mostly vertebrate groups) do represent clades. The phenomenon of convergent evolution

690-515: Is responsible for many cases of misleading similarities in the morphology of groups that evolved from different lineages. With the increasing realization in the first half of the 19th century that species had changed and split through the ages, classification increasingly came to be seen as branches on the evolutionary tree of life . The publication of Darwin's theory of evolution in 1859 gave this view increasing weight. In 1876 Thomas Henry Huxley , an early advocate of evolutionary theory, proposed

736-489: Is still controversial. As an example, see the full current classification of Anas platyrhynchos (the mallard duck) with 40 clades from Eukaryota down by following this Wikispecies link and clicking on "Expand". The name of a clade is conventionally a plural, where the singular refers to each member individually. A unique exception is the reptile clade Dracohors , which was made by haplology from Latin "draco" and "cohors", i.e. "the dragon cohort "; its form with

782-409: Is surrounded by a membrane called the tonoplast (word origin: Gk tón(os) + -o-, meaning “stretching”, “tension”, “tone” + comb. form repr. Gk plastós formed, molded) and filled with cell sap . Also called the vacuolar membrane , the tonoplast is the cytoplasmic membrane surrounding a vacuole, separating the vacuolar contents from the cell's cytoplasm. As a membrane, it is mainly involved in regulating

828-465: Is the extrusion process of proteins and lipids from the cell. These materials are absorbed into secretory granules within the Golgi apparatus before being transported to the cell membrane and secreted into the extracellular environment. In this capacity, vacuoles are simply storage vesicles which allow for the containment, transport and disposal of selected proteins and lipids to the extracellular environment of

874-533: Is thus constructed from similar, repeating parts or metamers . Accordingly, these plants are sometimes termed 'metaphytes' and classified as the group Metaphyta (but Haeckel 's definition of Metaphyta places some algae in this group). In all land plants a disc-like structure called a phragmoplast forms where the cell will divide , a trait only found in the land plants in the streptophyte lineage, some species within their relatives Coleochaetales , Charales and Zygnematales , as well as within subaerial species of

920-641: The Latin form cladus (plural cladi ) is used rather than the English form. Clades are the fundamental unit of cladistics , a modern approach to taxonomy adopted by most biological fields. The common ancestor may be an individual, a population , or a species ( extinct or extant ). Clades are nested, one in another, as each branch in turn splits into smaller branches. These splits reflect evolutionary history as populations diverged and evolved independently. Clades are termed monophyletic (Greek: "one clan") groups. Over

966-702: The Phragmoplastophyta clade of freshwater charophyte green algae as a sister taxon of Charophyceae , Coleochaetophyceae and Zygnematophyceae . Embryophytes consist of the bryophytes and the polysporangiophytes . Living embryophytes include hornworts , liverworts , mosses , lycophytes , ferns , gymnosperms and angiosperms ( flowering plants ). Embryophytes have diplobiontic life cycles . The embryophytes are informally called "land plants" because they thrive primarily in terrestrial habitats (despite some members having evolved secondarily to live once again in semiaquatic / aquatic habitats ), while

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1012-592: The chloroplasts closer to light. Most plants store chemicals in the vacuole that react with chemicals in the cytosol. If the cell is broken, for example by a herbivore , then the two chemicals can react forming toxic chemicals. In garlic, alliin and the enzyme alliinase are normally separated but form allicin if the vacuole is broken. A similar reaction is responsible for the production of syn-propanethial-S-oxide when onions are cut. Vacuoles in fungal cells perform similar functions to those in plants and there can be more than one vacuole per cell. In yeast cells

1058-570: The gametophyte – produces sperm and eggs which fuse and grow into a diploid multicellular generation with twice the number of chromosomes – the sporophyte which produces haploid spores at maturity. The spores divide repeatedly by mitosis and grow into a gametophyte, thus completing the cycle. Embryophytes have two features related to their reproductive cycles which distinguish them from all other plant lineages. Firstly, their gametophytes produce sperm and eggs in multicellular structures (called ' antheridia ' and ' archegonia '), and fertilization of

1104-444: The mosses (Bryophyta), hornworts (Anthocerotophyta), and liverworts (Marchantiophyta), are relatively small plants, often confined to environments that are humid or at least seasonally moist. They are limited by their reliance on water needed to disperse their gametes ; a few are truly aquatic. Most are tropical, but there are many arctic species. They may locally dominate the ground cover in tundra and Arctic–alpine habitats or

1150-652: The algae order Trentepohliales , and appears to be essential in the adaptation towards a terrestrial life style. The green algae and land plants form a clade , the Viridiplantae . According to molecular clock estimates, the Viridiplantae split 1,200  million years ago to 725  million years ago into two clades: chlorophytes and streptophytes . The chlorophytes, with around 700 genera, were originally marine algae, although some groups have since spread into fresh water . The streptophyte algae (i.e. excluding

1196-400: The cell membrane intact. Pinocytosis ("cell drinking") is essentially the same process, the difference being that the substances ingested are in solution and not visible under the microscope. Phagocytosis and pinocytosis are both undertaken in association with lysosomes which complete the breakdown of the material which has been engulfed. Salmonella is able to survive and reproduce in

1242-422: The cell. Endocytosis is the reverse of exocytosis and can occur in a variety of forms. Phagocytosis ("cell eating") is the process by which bacteria, dead tissue, or other bits of material visible under the microscope are engulfed by cells. The material makes contact with the cell membrane, which then invaginates. The invagination is pinched off, leaving the engulfed material in the membrane-enclosed vacuole and

1288-496: The cell. When the contractile vacuole is slowly taking water in, the contractile vacuole enlarges, this is called diastole and when it reaches its threshold, the central vacuole contracts then contracts (systole) periodically to release water. Food vacuoles (also called digestive vacuole ) are organelles found in Ciliates , and Plasmodium falciparum , a protozoan parasite that causes Malaria . In histopathology , vacuolization

1334-616: The destruction of invading bacteria and Robert B. Mellor proposed organ-specific forms have a role in 'housing' symbiotic bacteria. In protists, vacuoles have the additional function of storing food which has been absorbed by the organism and assisting in the digestive and waste management process for the cell. In animal cells, vacuoles perform mostly subordinate roles, assisting in larger processes of exocytosis and endocytosis . Animal vacuoles are smaller than their plant counterparts but also usually greater in number. There are also animal cells that do not have any vacuoles. Exocytosis

1380-429: The epiphyte flora in rain forest habitats. Clade In biological phylogenetics , a clade (from Ancient Greek κλάδος (kládos)  'branch'), also known as a monophyletic group or natural group , is a grouping of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree . In the taxonomical literature, sometimes

1426-413: The functions of the vacuole include: Vacuoles also play a major role in autophagy , maintaining a balance between biogenesis (production) and degradation (or turnover), of many substances and cell structures in certain organisms. They also aid in the lysis and recycling of misfolded proteins that have begun to build up within the cell. Thomas Boller and others proposed that the vacuole participates in

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1472-546: The group consists of a common ancestor with all its descendant branches. Rodents, for example, are a branch of mammals that split off after the end of the period when the clade Dinosauria stopped being the dominant terrestrial vertebrates 66 million years ago. The original population and all its descendants are a clade. The rodent clade corresponds to the order Rodentia, and insects to the class Insecta. These clades include smaller clades, such as chipmunk or ant , each of which consists of even smaller clades. The clade "rodent"

1518-513: The land plants) have around 122 genera; they adapted to fresh water very early in their evolutionary history and have not spread back into marine environments. Some time during the Ordovician , streptophytes invaded the land and began the evolution of the embryophyte land plants. Present day embryophytes form a clade. Becker and Marin speculate that land plants evolved from streptophytes because living in fresh water pools pre-adapted them to tolerate

1564-590: The last few decades, the cladistic approach has revolutionized biological classification and revealed surprising evolutionary relationships among organisms. Increasingly, taxonomists try to avoid naming taxa that are not clades; that is, taxa that are not monophyletic . Some of the relationships between organisms that the molecular biology arm of cladistics has revealed include that fungi are closer relatives to animals than they are to plants, archaea are now considered different from bacteria , and multicellular organisms may have evolved from archaea. The term "clade"

1610-518: The latter term coined by Ernst Mayr (1965), derived from "clade". The results of phylogenetic/cladistic analyses are tree-shaped diagrams called cladograms ; they, and all their branches, are phylogenetic hypotheses. Three methods of defining clades are featured in phylogenetic nomenclature : node-, stem-, and apomorphy-based (see Phylogenetic nomenclature§Phylogenetic definitions of clade names for detailed definitions). The relationship between clades can be described in several ways: The age of

1656-466: The movements of ions around the cell, and isolating materials that might be harmful or a threat to the cell. Transport of protons from the cytosol to the vacuole stabilizes cytoplasmic pH , while making the vacuolar interior more acidic creating a proton motive force which the cell can use to transport nutrients into or out of the vacuole. The low pH of the vacuole also allows degradative enzymes to act. Although single large vacuoles are most common,

1702-437: The ovum takes place within the archegonium rather than in the external environment. Secondly, the initial stage of development of the fertilized egg (the zygote ) into a diploid multicellular sporophyte, takes place within the archegonium where it is both protected and provided with nutrition. This second feature is the origin of the term 'embryophyte' – the fertilized egg develops into a protected embryo, rather than dispersing as

1748-450: The related green algae are primarily aquatic. Embryophytes are complex multicellular eukaryotes with specialized reproductive organs . The name derives from their innovative characteristic of nurturing the young embryo sporophyte during the early stages of its multicellular development within the tissues of the parent gametophyte . With very few exceptions, embryophytes obtain biological energy by photosynthesis , using chlorophyll

1794-406: The size and number of vacuoles may vary in different tissues and stages of development. For example, developing cells in the meristems contain small provacuoles and cells of the vascular cambium have many small vacuoles in the winter and one large one in the summer. Aside from storage, the main role of the central vacuole is to maintain turgor pressure against the cell wall . Proteins found in

1840-590: The spread of viral infections . HIV , for example, has clades called subtypes, which vary in geographical prevalence. HIV subtype (clade) B, for example is predominant in Europe, the Americas and Japan, whereas subtype A is more common in east Africa. Vacuole Contractile vacuoles ("stars") were first observed by Spallanzani (1776) in protozoa , although mistaken for respiratory organs. Dujardin (1841) named these "stars" as vacuoles . In 1842, Schleiden applied

1886-417: The term for plant cells, to distinguish the structure with cell sap from the rest of the protoplasm . In 1885, de Vries named the vacuole membrane as tonoplast. The function and significance of vacuoles varies greatly according to the type of cell in which they are present, having much greater prominence in the cells of plants, fungi and certain protists than those of animals and bacteria. In general,

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1932-402: The tonoplast ( aquaporins ) control the flow of water into and out of the vacuole through active transport , pumping potassium (K ) ions into and out of the vacuolar interior. Due to osmosis , water will diffuse into the vacuole, placing pressure on the cell wall. If water loss leads to a significant decline in turgor pressure, the cell will plasmolyze . Turgor pressure exerted by vacuoles

1978-408: The vacuole ( Vac7 ) is a dynamic structure that can rapidly modify its morphology . They are involved in many processes including the homeostasis of cell pH and the concentration of ions, osmoregulation , storing amino acids and polyphosphate and degradative processes. Toxic ions, such as strontium ( Sr ), cobalt (II) ( Co ), and lead (II) ( Pb ) are transported into

2024-416: The vacuole to isolate them from the rest of the cell. A contractile vacuole is a specialized osmoregulatory organelle that is present in many free-living protists. The contractile vacuole is part of the contractile vacuole complex which includes radial arms and a spongiome. The contractile vacuole complex works periodically contracts to remove excess water and ions from the cell to balance water flow into

2070-423: The vacuoles of several mammal species after being engulfed. The vacuole probably evolved several times independently, even within the Viridiplantae . Most mature plant cells have one large vacuole that typically occupies more than 30% of the cell's volume, and that can occupy as much as 80% of the volume for certain cell types and conditions. Strands of cytoplasm often run through the vacuole. A vacuole

2116-973: The work by Novíkov & Barabaš-Krasni 2015 and Hao and Xue 2013 with plant taxon authors from Anderson, Anderson & Cleal 2007 and some additional clade names. Puttick et al./Nishiyama et al. are used for the basal clades. Anthocerotophytina (Hornworts) Bryophytina (Mosses) Marchantiophytina (Liverworts) † Horneophytopsida [Protracheophytes] † Cooksoniaceae † Aglaophyton † Rhyniopsida † Catenalis † Aberlemnia † Hsuaceae † Renaliaceae † Adoketophyton †? Barinophytopsida † Zosterophyllopsida † Hicklingia † Gumuia † Nothia Lycopodiopsida (Clubmosses, Spikemosses & Quillworts) † Zosterophyllum deciduum † Yunia † Eophyllophyton † Trimerophytopsida † Ibyka † Pauthecophyton † Cladoxylopsida Polypodiopsida (ferns) † Celatheca † Pertica † Progymnosperms (paraphyletic) Spermatophytes (seed plants) The non-vascular land plants, namely

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