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69-542: Incertae sedis : Ochrophytes , also known as heterokontophytes or stramenochromes , are a group of algae . They are the photosynthetic stramenopiles , a group of eukaryotes , organisms with a cell nucleus , characterized by the presence of two unequal flagella , one of which has tripartite hairs called mastigonemes . In particular, they are characterized by photosynthetic organelles or plastids enclosed by four membranes , with membrane-bound compartments called thylakoids organized in piles of three, chlorophyll

138-541: A and c as their photosynthetic pigments , and additional pigments such as β-carotene and xanthophylls . Ochrophytes are one of the most diverse lineages of eukaryotes, containing ecologically important algae such as brown algae and diatoms . They are classified either as phylum Ochrophyta or Heterokontophyta , or as subphylum Ochrophytina within phylum Gyrista . Their plastids are of red algal origin. Ochrophytes are eukaryotic organisms composed of cells that are either naked or covered by scales, lorica or

207-958: A cell wall . They can be single-celled , colonial , coenocytic or multicellular . Some Phaeophyceae develop as large multicellular thalli with differentiated tissues . All ochrophytes uniformly have tubular mitochondrial cristae . This is a common trait shared with their relatives, heterotrophic stramenopiles , as well as other closely related groups such as Rhizaria , Telonemia and Alveolata . As primarily photosynthetic eukaryotes, they are considered algae , distinguished from other groups of algae by specific morphological and ultrastructural traits, such as their flagella , chloroplasts and pigments . As stramenopiles (= heterokonts ), their swimming cells frequently display two markedly unequal flagella: an anterior flagellum ("tinsel") with straw-like hollow tripartite hairs called mastigonemes , and an immature posterior smooth flagellum ("whiplash") lacking these hairs. The ciliary transition zone of

276-474: A signal sequence . The N-terminus (one end) of a polypeptide chain (i.e., a protein) contains a few amino acids that work as an address tag, which are removed when the polypeptide reaches its destination. Nascent peptides reach the ER via the translocon , a membrane-embedded multiprotein complex. Proteins that are destined for places outside the endoplasmic reticulum are packed into transport vesicles and moved along

345-431: A 'cf.' (from Latin confer , compare, before a taxon name); such a convention is especially widespread in palaeontology. In zoological nomenclature, " incertae sedis " is not a nomenclatural term at all per se , but is used by taxonomists in their classifications to mean "of uncertain taxonomic position". In botany, a name is not validly published if it is not accepted by the author in the same publication. In zoology,

414-517: A causal link between obesity-induced increase in insulin secretion and peripheral insulin resistance. Abnormalities in XBP1 lead to a heightened endoplasmic reticulum stress response and subsequently causes a higher susceptibility for inflammatory processes that may even contribute to Alzheimer's disease . In the colon , XBP1 anomalies have been linked to the inflammatory bowel diseases including Crohn's disease . The unfolded protein response (UPR)

483-428: A cell can slowly interchange from one type to the other, depending on the changing metabolic activities of the cell. Transformation can include embedding of new proteins in membrane as well as structural changes. Changes in protein content may occur without noticeable structural changes. The surface of the rough endoplasmic reticulum (often abbreviated RER or rough ER ; also called granular endoplasmic reticulum )

552-399: A consortium of several plastids, each surrounded by two or three inner membranes respectively, is enveloped by a shared outer membrane. Ochrophyte chloroplasts contain chlorophylls a and c as photosynthetic pigments , in addition to fucoxanthin . Chlorophyll a binds to thylakoids, while the c pigment is present in the stroma. The most frequent accessory pigment in ochrophytes

621-639: A distinct plastid ultrastructure in comparison to other algal groups. Their chloroplasts originate from an event of secondary endosymbiosis from a red alga , which lead to four surrounding membranes : two inner membranes, corresponding to the primary plastid membranes; a third membrane, corresponding to the plasma membrane of the red alga; and an outermost layer, corresponding to the phagosome membrane. This characteristic differentiates them from archaeplastid algae ( glaucophytes , red algae and green algae ), whose chloroplasts have only two membranes. The two outer layers of ochrophyte plastids are continguous with

690-447: A formal phylogenetic analysis is conducted that does not include a certain taxon, the authors might choose to label the taxon incertae sedis instead of guessing its placement. This is particularly common when molecular phylogenies are generated, since tissue for many rare organisms is hard to obtain. It is also a common scenario when fossil taxa are included, since many fossils are defined based on partial information. For example, if

759-429: A name proposed conditionally may be available under certain conditions. For uncertainties at lower levels, some authors have proposed a system of "open nomenclature", suggesting that question marks be used to denote a questionable assignment. For example, if a new species was given the specific epithet album by Anton and attributed with uncertainty to Agenus , it could be denoted " Agenus ? album Anton (?Anton)";

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828-542: A phylum-level taxon until 2017, when the same author lowered it to subphylum level and modified the name to Ochrophytina to match the -phytina suffix in botanical nomenclature, which corresponds to subdivisions. The phylum to which ochrophytes belong in his classification system is Gyrista , a clade that also contains some heterotrophic heterokonts, namely the Pseudofungi and the Bigyromonada . Gyrista and Bigyra compose

897-447: A recent phylogenomic study places one actinophryid, Actinophrys sol , as the probable sister group to ochrophytes. Although it lacks chloroplasts, plastidial genes have been found in the nuclear genome of this actinophryid, implying that its common ancestor with ochrophytes may have already begun domesticating plastids. In hierarchical classifications, where taxonomic ranks ( kingdom , phylum , class , order ...) are utilized,

966-521: A red alga was transformed into the chloroplast of the common ancestor of ochrophytes. The total group of ochrophytes is estimated to have evolved between 874 and 543 million years ago (Ma) through molecular clock inference. However, the earliest fossil remains, assigned to the billion-year-old xanthophyte Palaeovaucheria , suggest that ochrophytes had appeared by 1000 Ma. Other early putative representatives of photosynthetic stramenopiles are Jacutianema (750 Ma), Germinosphaera (750–700 Ma) and

1035-492: A retention motif . This motif is composed of four amino acids at the end of the protein sequence. The most common retention sequences are KDEL for lumen-located proteins and KKXX for transmembrane proteins. However, variations of KDEL and KKXX do occur, and other sequences can also give rise to endoplasmic reticulum retention. It is not known whether such variation can lead to sub-ER localizations. There are three KDEL ( 1 , 2 and 3 ) receptors in mammalian cells, and they have

1104-428: A state in which the folding of proteins slows, leading to an increase in unfolded proteins . This stress is emerging as a potential cause of damage in hypoxia/ischemia, insulin resistance, and other disorders. Secretory proteins, mostly glycoproteins , are moved across the endoplasmic reticulum membrane. Proteins that are transported by the endoplasmic reticulum throughout the cell are marked with an address tag called

1173-542: A stramenopile alga was that of the genus Fucus , by Linnaeus in his 1753 work Species Plantarum . Shortly after, unicellular chrysophytes were described by Otto Friedrich Müller . During this first era of scientific discovery, brown algae were described as plants , while microscopic algae were treated as animals under the name of infusoria . During the 20th century, evolutionary and phylogenetic discussions began including heterokont algae. Transmission electron microscopy and molecular phylogenetic analysis led to

1242-402: A taxon, which may be expressed, among others, by using a question mark after or before a taxon name. This should be distinguished from the situation where either it is uncertain how to use a name, often because the types have been lost ( nomen dubium , species inquirenda ), or whether a poorly preserved specimen should be included within a given species or genus, which is often expressed using

1311-420: A very high degree of sequence identity. The functional differences between these receptors remain to be established. The endoplasmic reticulum does not harbor an ATP-regeneration machinery, and therefore requires ATP import from mitochondria. The imported ATP is vital for the ER to carry out its house keeping cellular functions, such as for protein folding and trafficking. The ER ATP transporter, SLC35B1/AXER,

1380-567: A vesicular network. Within the CER, there is a prominent region of tight direct contacts between the periplastid membrane and the inner nuclear envelope, where lipid transfers might occur, and perhaps exchange of other molecules. Commonly, within the plastid stroma , three stacked thylakoids differentiate into the "girdle lamella", which runs around the periphery of the plastid, beneath the innermost membrane. The remaining thylakoids are arranged in stacks of three. In synchromophytes and aurearenophytes ,

1449-486: Is a cellular stress response related to the endoplasmic reticulum. The UPR is activated in response to an accumulation of unfolded or misfolded proteins in the lumen of the endoplasmic reticulum. The UPR functions to restore normal function of the cell by halting protein translation , degrading misfolded proteins, and activating the signaling pathways that lead to increasing the production of molecular chaperones involved in protein folding . Sustained overactivation of

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1518-464: Is a separate region that in other algal groups (i.e. cryptomonads and chlorarachniophytes ) contains a nucleomorph , the vestigial nucleus of the secondary endosymbiont; however, no nucleomorphs are known within the ochrophytes. Instead, other structures have been observed within the PC, similarly to those seen in haptophytes and chromerid algae: "blob-like structures" where PC proteins are localized, and

1587-411: Is common in cold, clear, fast-flowing mountain streams, where it attaches to a firm substrate. Xanthophycean genera commonly found in rivers include Vaucheria , Tribonema and Bumilleria , either freely floating or attached to filamentous algae and plants. Diatoms are more diverse, with more than 60 genera commonly found in rivers. Many river diatoms have developed different strategies to attach to

1656-399: Is estimated that they amount to more than 100,000 species, of which the majority are diatoms. Below is the present classification of ochrophytes according to the 2019 revision of eukaryotic classification, with the inclusion of classes of algae described in posterior years as well as the number of described species for each class. According to the aforementioned 2019 revision by protistologists,

1725-514: Is indicative of their functions: The endoplasmic reticulum synthesizes molecules, while the sarcoplasmic reticulum stores calcium ions and pumps them out into the sarcoplasm when the muscle fiber is stimulated. After their release from the sarcoplasmic reticulum, calcium ions interact with contractile proteins that utilize ATP to shorten the muscle fiber. The sarcoplasmic reticulum plays a major role in excitation-contraction coupling . The endoplasmic reticulum serves many general functions, including

1794-464: Is studded with protein-manufacturing ribosomes giving it a "rough" appearance (hence its name). The binding site of the ribosome on the rough endoplasmic reticulum is the translocon . However, the ribosomes are not a stable part of this organelle's structure as they are constantly being bound and released from the membrane. A ribosome only binds to the RER once a specific protein-nucleic acid complex forms in

1863-463: Is the class Heterokontæ , introduced by Finnish biologist Alexander Ferdinand Luther  [ fi ] in 1899 to include the orders Chloromonadales and Confervales , later separated into Xanthophyceae and Raphidophyceae . This name referenced, among other traits, the two unequal flagella characteristic of all Stramenopiles , also known as heterokonts. After several electron microscopy discoveries, Christiaan van den Hoek introduced in 1978

1932-434: Is the yellow β-carotene . The golden-brown or brown pigmentation in diatoms , brown algae , golden algae and others is conferred by the xanthophyll fucoxanthin. In the yellow-green or yellow-brown raphidophyceans , eustigmatophyceans and xanthophyceans , vaucheriaxanthin is dominant instead. These pigment combinations extend their photosynthetic ability beyond chlorophyll a alone. Additionally, xanthophylls protect

2001-404: Is used only by paleontologists. Endoplasmic reticulum The two types of ER share many of the same proteins and engage in certain common activities such as the synthesis of certain lipids and cholesterol . Different types of cells contain different ratios of the two types of ER depending on the activities of the cell. RER is found mainly toward the nucleus of the cell and SER towards

2070-872: The brown alga Miaohephyton (600–550 Ma). Scales similar to modern chrysophyte scales, and valves resembling the modern centric diatom valves, have been found in 800–700 million-years-old sediments. Xanthophyceae Chrysoparadoxophyceae Phaeosacciophyceae Schizocladiophyceae Phaeophyceae (brown algae) Aurearenophyceae Phaeothamniophyceae Raphidophyceae Actinophryida Olisthodiscophyceae Chrysophyceae (golden algae) Synurophyceae Synchromophyceae / Picophagea Eustigmatophyceae Pinguiophyceae Dictyochophyceae Pelagophyceae Bolidophyceae Diatomeae (diatoms) Actinophryida Pseudofungi Relationships among many classes of ochrophytes remain unresolved, but three main clades (called SI, SII and SIII) are supported in most phylogenetic analyses . The SI lineage, containing

2139-448: The cytoskeleton toward their destination. In human fibroblasts, the ER is always co-distributed with microtubules and the depolymerisation of the latter cause its co-aggregation with mitochondria, which are also associated with the ER. The endoplasmic reticulum is also part of a protein sorting pathway. It is, in essence, the transportation system of the eukaryotic cell. The majority of its resident proteins are retained within it through

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2208-455: The endoplasmic reticulum (ER), together composing the chloroplast endoplasmic reticulum (CER), also known as the periplastidial endoplasmic reticulum (PER), which is often connected to the nuclear envelope . The tripartite flagellar hairs, characteristic of stramenopiles, are produced within either the PER or the nuclear envelope. The periplastid compartment (PC), between the second and third layers,

2277-553: The genus may be assigned incertae sedis . This excerpt from a 2007 scientific paper about crustaceans of the Kuril–Kamchatka Trench and the Japan Trench describes typical circumstances through which this category is applied in discussing: ...the removal of many genera from new and existing families into a state of incertae sedis. Their reduced status was attributed largely to poor or inadequate descriptions but it

2346-475: The nascent (new) protein forming into the RER lumen and/or membrane. The protein is processed in the ER lumen by an enzyme (a signal peptidase ), which removes the signal peptide. Ribosomes at this point may be released back into the cytosol; however, non-translating ribosomes are also known to stay associated with translocons. The membrane of the rough endoplasmic reticulum is in the form of large double-membrane sheets that are located near, and continuous with,

2415-875: The photosystems from high intensity light. Ochrophyte algae accumulate chrysolaminarin , a carbohydrate consisting of short chains of β-1,3-linked glucose molecules, as a storage product. It is stored in vesicles located within the cytoplasm , outside plastids, unlike other algae. Cytoplasmic lipid droplets are also common. They lack starch , which is the common storage product in green algae and plants. Ochrophytes are capable of asexual reproduction by fragmentation , propagules , vegetative cell division , sporogenesis or zoosporogenesis. In addition, they are capable of sexual reproduction through gametes , by three different modes: isogamy , anisogamy or oogamy . Ochrophytes are present in nearly all environments. Some classes are more common in marine habitats, while others are more frequent in freshwater or soil. Among

2484-467: The silicoflagellates ) and Pelagophyceae . A new class of algae, Olisthodiscophyceae , was described in 2021 and recovered as part of the SII lineage. One group of heterotrophic heliozoan protists, Actinophryida , is included in some classifications as the sister lineage to the raphidophytes , and both groups are treated as one class Raphidomonadea on the basis of 18S rDNA phylogenetic analyses. However,

2553-480: The "(?Anton)" indicates the author that assigned the question mark. So if Anton described Agenus album , and Bruno called the assignment into doubt, this could be denoted " Agenus ? album (Anton) (?Bruno)", with the parentheses around Anton because the original assignment (to Agenus ) was modified (to Agenus ?) by Bruno. This practice is not included in the International Code of Zoological Nomenclature , and

2622-538: The Golgi apparatus and COPI marks them to be brought back to the rough endoplasmic reticulum. The rough endoplasmic reticulum works in concert with the Golgi complex to target new proteins to their proper destinations. The second method of transport out of the endoplasmic reticulum involves areas called membrane contact sites , where the membranes of the endoplasmic reticulum and other organelles are held closely together, allowing

2691-473: The action or storage of key enzymes and the products of these enzymes. The sarcoplasmic reticulum (SR), from the Greek σάρξ sarx ("flesh"), is smooth ER found in muscle cells . The only structural difference between this organelle and the smooth endoplasmic reticulum is the composition of proteins they have, both bound to their membranes and drifting within the confines of their lumens. This fundamental difference

2760-444: The cell membrane or plasma membrane of cell. The outer ( cytosolic ) face of the RER is studded with ribosomes that are the sites of protein synthesis . The RER is especially prominent in cells such as hepatocytes . The SER lacks ribosomes and functions in lipid synthesis but not metabolism , the production of steroid hormones , and detoxification . The SER is especially abundant in mammalian liver and gonad cells. The ER

2829-411: The cytosol. This special complex forms when a free ribosome begins translating the mRNA of a protein destined for the secretory pathway . The first 5–30 amino acids polymerized encode a signal peptide , a molecular message that is recognized and bound by a signal recognition particle (SRP). Translation pauses and the ribosome complex binds to the RER translocon where translation continues with

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2898-484: The description of many new groups and several classes well into the 21st century. The sequencing of the first ochrophyte genome, belonging to Thalassiosira pseudonana , began in 2002. Incertae sedis Incertae sedis ( Latin for 'of uncertain placement') or problematica is a term used for a taxonomic group where its broader relationships are unknown or undefined. Alternatively, such groups are frequently referred to as "enigmatic taxa". In

2967-477: The diatoms (Diatomeae) do not form a single class Bacillariophyceae, but numerous classes to reflect the phylogenetic advances over the previous decade. Multicellular seaweeds , in the class Phaeophyceae , were described in early Chinese (around 3000 BC), Greek (300 BC, such as Theophrastus ) and Japanese (ca. 500 AD) writings. Knowledge of them likely predates recorded history, being used as food , dyes , and for medicinal purposes. The first formal description of

3036-533: The diverse and multicellular class Phaeophyceae , or brown algae, experienced an evolutionary radiation during the late Paleozoic (around 310 million years ago). The class Schizocladiophyceae is the sister lineage to brown algae, followed by a clade of closely related classes Xanthophyceae , Phaeosacciophyceae and Chrysoparadoxophyceae . This is in turn the sister lineage to a clade containing Aurearenophyceae and Phaeothamniophyceae , which are sometimes treated as one class Aurophyceae. The Raphidophyceae are

3105-474: The division Heterokontophyta for five algal classes: Chrysophyceae , Xanthophyceae , Bacillariophyceae , Phaeophyceae , and Chloromonadophyceae . Several other names were used to group heterokont algae with ambiregnal organisms, such as Chromophyta , Heterokonta and lastly Stramenopiles , which is not a validly published name under the ICN . Several phycologists currently advocate the use of Heterokontophyta as

3174-530: The endoplasmic reticulum is a network of membranes called cisternae . These sac-like structures are held together by the cytoskeleton . The phospholipid membrane encloses the cisternal space (or lumen), which is continuous with the perinuclear space but separate from the cytosol . The functions of the endoplasmic reticulum can be summarized as the synthesis and export of proteins and membrane lipids, but varies between ER and cell type and cell function. The quantity of both rough and smooth endoplasmic reticulum in

3243-485: The enzyme glucose-6-phosphatase , which converts glucose-6-phosphate to glucose, a step in gluconeogenesis . It is connected to the nuclear envelope and consists of tubules that are located near the cell periphery. These tubes sometimes branch forming a network that is reticular in appearance. In some cells, there are dilated areas like the sacs of rough endoplasmic reticulum. The network of smooth endoplasmic reticulum allows for an increased surface area to be devoted to

3312-417: The flagellum generally has a transitional helix. The ochrophytes are mostly photosynthetic. As such, they may possess one or more photosynthetic plastids ( chloroplasts ) per cell. Some groups contain species with leucoplasts , chloroplasts that have lost photosynthetic capacity and pigments but presumably continue to play a role in the synthesis of amino acids , lipids and heme groups. Ochrophytes have

3381-491: The folding of protein molecules in sacs called cisternae and the transport of synthesized proteins in vesicles to the Golgi apparatus . Rough endoplasmic reticulum is also involved in protein synthesis. Correct folding of newly made proteins is made possible by several endoplasmic reticulum chaperone proteins, including protein disulfide isomerase (PDI), ERp29, the Hsp70 family member BiP/Grp78 , calnexin , calreticulin , and

3450-490: The heterokont algae are commonly regarded as an entire phylum (or division in botanical nomenclature ) by the name of Ochrophyta , within the Stramenopila or Heterokonta . The phylum was first described by protozoologist Thomas Cavalier-Smith in 1986, as Ochrista , later renamed to Ochrophyta in 1996 in accordance to recommendations of the International Code of Nomenclature for algae, fungi, and plants (ICN). It remained

3519-421: The metabolism of carbohydrates, detoxification of natural metabolism products and of alcohol and drugs, attachment of receptors on cell membrane proteins, and steroid metabolism . In muscle cells, it regulates calcium ion concentration. Smooth endoplasmic reticulum is found in a variety of cell types (both animal and plant), and it serves different functions in each. The smooth endoplasmic reticulum also contains

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3588-624: The most basal within the SI. The SII lineage contains the golden algae or Chrysophyceae , as well as smaller classes Synurophyceae , Eustigmatophyceae , Pinguiophyceae and Picophagea (also known as Synchromophyceae). Both clades, SI and SII, compose the Chrysista lineage. The remaining classes are grouped within the sister lineage Diatomista , equivalent to the SIII lineage; these are the diatoms or Bacillariophyceae, Bolidophyceae , Dictyochophyceae (including

3657-433: The nature and action of their toxins is not resolved. Freshwater Gonyostomum species are capable of mucilage secretion at high amounts detrimental to fish gills. Within the diatoms ( Bacillariophyta ), harmful effects can be due to physical damage or to toxin production. Centric diatoms like Chaetoceros live as colonial chains of cells with long spines (setae) that can clog fish gills, causing their death. Among diatoms,

3726-1011: The ochrophyte lineages are the diatoms, the most abundant photosynthetic eukaryotes worldwide in marine habitats; multicellular seaweeds, such as brown algae (e.g., kelp ) and golden algae; and an array of microscopic single-celled lineages that are also abundant, as evidenced by environmental sequencing . Regarding nutrition, various ochrophytes are mixotrophic , usually through phagocytosis . Several classes of heterokont algae are exclusively known from marine habitats, such as Bolidophyceae , Pelagophyceae , Pinguiophyceae and Schizocladiophyceae . The brown algae (Phaeophyceae) are almost exclusively marine, with very few freshwater genera. Chrysophyceae , Phaeothamniophyceae and Xanthophyceae are predominantly freshwater classes. In lotic habitats (rivers, streams), golden algae (Chrysophyceae) and yellow-green algae (Xanthophyceae) are common and occasionally abundant. The golden algal genus Hydrurus , in particular, can be widespread in some drainage basins and

3795-663: The only toxin producers have been found among pennate diatoms, almost entirely within the genus Pseudonitzschia . More than a dozen species of Pseudonitzschia are capable of producing a neurotoxin , domoic acid , the cause of amnesiac shellfish poisoning. The ochrophytes constitute a highly diverse clade within Stramenopila , a eukaryotic supergroup that also includes several heterotrophic lineages of protists such as oomycetes , hyphochytrids , labyrinthuleans , opalines and bicosoecids . This lineage of stramenopiles originated from an event of secondary endosymbiosis where

3864-517: The outer layer of the nuclear envelope . The double membrane sheets are stacked and connected through several right- or left-handed helical ramps, the "Terasaki ramps", giving rise to a structure resembling a parking garage . Although there is no continuous membrane between the endoplasmic reticulum and the Golgi apparatus , membrane-bound transport vesicles shuttle proteins between these two compartments. Vesicles are surrounded by coating proteins called COPI and COPII. COPII targets vesicles to

3933-411: The peptidylprolyl isomerase family. Only properly folded proteins are transported from the rough ER to the Golgi apparatus – unfolded proteins cause an unfolded protein response as a stress response in the ER. Disturbances in redox regulation, calcium regulation, glucose deprivation, and viral infection or the over-expression of proteins can lead to endoplasmic reticulum stress response (ER stress),

4002-478: The phylogeny was constructed using soft tissue and vertebrae as principal characters and the taxon in question is only known from a single tooth, it would be necessary to label it incertae sedis . If conflicting results exist or if there is not a consensus among researchers as to how a taxon relates to other organisms, it may be listed as incertae sedis until the conflict is resolved. The term incertae sedis refers to uncertainty about phylogenetic position of

4071-492: The phylum name for heterokont algae. However, the original use by Hoek in 1978 did not provide a Latin description, which was a requirement for valid publication under the ICN until 2011. Phycologists Michael Guiry , Øjvind Moestrup and Robert Andersen validly published Heterokontophyta as a phylum in 2023. As opposed to the hierarchical classification, the cladistic classification only recognizes clades as valid groups, rejecting

4140-424: The substrate to avoid being displaced by water currents. The most basic strategy is to produce extracellular polymeric substances , varied carbohydrate structures formed from the cell membrane. In faster-flowing waters, some diatoms (e.g., Cocconeis ) grow directly attached to the substrate through adhesive films. Others (e.g., Eunotia , Nitzschia ) grow stalks or colonial tubes capable of reaching higher into

4209-611: The system of open nomenclature , uncertainty at specific taxonomic levels is indicated by incertae familiae (of uncertain family), incerti subordinis (of uncertain suborder), incerti ordinis (of uncertain order) and similar terms. When formally naming a taxon, uncertainty about its taxonomic classification can be problematic. The International Code of Nomenclature for algae, fungi, and plants , stipulates that "species and subdivisions of genera must be assigned to genera, and infraspecific taxa must be assigned to species, because their names are combinations", but ranks higher than

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4278-399: The transfer of lipids and other small molecules. The rough endoplasmic reticulum is key in multiple functions: In most cells the smooth endoplasmic reticulum (abbreviated SER ) is scarce. Instead there are areas where the ER is partly smooth and partly rough, this area is called the transitional ER. The transitional ER gets its name because it contains ER exit sites. These are areas where

4347-487: The transport vesicles which contain lipids and proteins made in the ER, detach from the ER and start moving to the Golgi apparatus . Specialized cells can have a lot of smooth endoplasmic reticulum and in these cells the smooth ER has many functions. It synthesizes lipids , phospholipids , and steroids . Cells which secrete these products, such as those in the testes , ovaries , and sebaceous glands have an abundance of smooth endoplasmic reticulum. It also carries out

4416-413: The two main branches of stramenopiles, which are regarded as the superphylum Heterokonta within the kingdom Chromista . However, this classification system is in disuse due to the kingdom's non- monophyletic nature. While Ochrophyta is the preferred name by general protistologists and protozoologists, the name Heterokontophyta is considered more familiar among phycologists . The origin of this name

4485-681: The use of paraphyletic or polyphyletic groups. This method of classification is preferred among protistologists. The latest revision of the International Society of Protistologists, in 2019, recognizes Ochrophyta as a valid taxon within the higher Stramenopiles group, within the SAR supergroup . The subdivision of ochrophytes between Chrysista and Diatomista is fully accepted by the scientific community and backed up by phylogenetic analyses. As of 2024, ochrophytes amount to 23,314 described species, with 490 species of uncertain position. However, it

4554-529: The water column to acquire more nutrients. Brown algae (Phaeophyceae), although highly diversified, contain only seven species present in rivers. These lack any complex multicellular thalli, and instead exist as benthic filamentous forms that have evolved independently from marine ancestors. Two main lineages of photosynthetic stramenopiles include many toxic species. Within the class Raphidophyceae , strains of Heterosigma and Chattonella at high concentrations are responsible for fish mortality, although

4623-430: Was accepted that some of the vagueness in the analysis was due to insufficient character states. It is also evident that a proportion of the characters used in the analysis, or their given states for particular taxa, were inappropriate or invalid. Additional complexity, and factors that have misled earlier authorities, are intrusion by extensive homoplasies , apparent character state reversals and convergent evolution . If

4692-401: Was observed by light microscopy by Garnier in 1897, who coined the term ergastoplasm . The lacy membranes of the endoplasmic reticulum were first seen by electron microscopy in 1945 by Keith R. Porter , Albert Claude , and Ernest F. Fullam. Later, the word reticulum , which means "network", was applied by Porter in 1953 to describe this fabric of membranes. The general structure of

4761-614: Was recently cloned and characterized, and the mitochondria supply ATP to the ER through a Ca -antagonized transport into the ER ( CaATiER ) mechanism. The CaATiER mechanism shows sensitivity to cytosolic Ca ranging from high nM to low μM range, with the Ca -sensing element yet to be identified and validated. Increased and supraphysiological ER stress in pancreatic β cells disrupts normal insulin secretion, leading to hyperinsulinemia and consequently peripheral insulin resistance associated with obesity in humans. Human clinical trials also suggested

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