Wheat is a grass cultivated for its seed, a cereal grain, a worldwide staple food. The many species of wheat together make up the genus Triticum; the archaeological record suggests that wheat was first cultivated in the regions of the Fertile Crescent around 9600 BCE. Botanically, the wheat kernel is a type of fruit called a caryopsis. Wheat is grown on more land area than any other food crop. World trade in wheat is greater than for all other crops combined. In 2016, world production of wheat was 749 million tonnes, making it the second most-produced cereal after maize. Since 1960, world production of wheat and other grain crops has tripled and is expected to grow further through the middle of the 21st century. Global demand for wheat is increasing due to the unique viscoelastic and adhesive properties of gluten proteins, which facilitate the production of processed foods, whose consumption is increasing as a result of the worldwide industrialization process and the westernization of the diet.
Wheat is an important source of carbohydrates. Globally, it is the leading source of vegetal protein in human food, having a protein content of about 13%, high compared to other major cereals but low in protein quality for supplying essential amino acids; when eaten as the whole grain, wheat is a source of dietary fiber. In a small part of the general population, gluten – the major part of wheat protein – can trigger coeliac disease, noncoeliac gluten sensitivity, gluten ataxia, dermatitis herpetiformis. Cultivation and repeated harvesting and sowing of the grains of wild grasses led to the creation of domestic strains, as mutant forms of wheat were preferentially chosen by farmers. In domesticated wheat, grains are larger, the seeds remain attached to the ear by a toughened rachis during harvesting. In wild strains, a more fragile rachis allows the ear to shatter and disperse the spikelets. Selection for these traits by farmers might not have been deliberately intended, but have occurred because these traits made gathering the seeds easier.
As the traits that improve wheat as a food source involve the loss of the plant's natural seed dispersal mechanisms domesticated strains of wheat cannot survive in the wild. Cultivation of wheat began to spread beyond the Fertile Crescent after about 8000 BCE. Jared Diamond traces the spread of cultivated emmer wheat starting in the Fertile Crescent sometime before 8800 BCE. Archaeological analysis of wild emmer indicates that it was first cultivated in the southern Levant, with finds dating back as far as 9600 BCE. Genetic analysis of wild einkorn wheat suggests that it was first grown in the Karacadag Mountains in southeastern Turkey. Dated archeological remains of einkorn wheat in settlement sites near this region, including those at Abu Hureyra in Syria, suggest the domestication of einkorn near the Karacadag Mountain Range. With the anomalous exception of two grains from Iraq ed-Dubb, the earliest carbon-14 date for einkorn wheat remains at Abu Hureyra is 7800 to 7500 years BCE. Remains of harvested emmer from several sites near the Karacadag Range have been dated to between 8600 and 8400 BCE, that is, in the Neolithic period.
With the exception of Iraq ed-Dubb, the earliest carbon-14 dated remains of domesticated emmer wheat were found in the earliest levels of Tell Aswad, in the Damascus basin, near Mount Hermon in Syria. These remains were dated by Willem van Zeist and his assistant Johanna Bakker-Heeres to 8800 BCE, they concluded that the settlers of Tell Aswad did not develop this form of emmer themselves, but brought the domesticated grains with them from an as yet unidentified location elsewhere. The cultivation of emmer reached Greece and Indian subcontinent by 6500 BCE, Egypt shortly after 6000 BCE, Germany and Spain by 5000 BCE. "The early Egyptians were developers of bread and the use of the oven and developed baking into one of the first large-scale food production industries." By 3000 BCE, wheat had reached Scandinavia. A millennium it reached China; the oldest evidence for hexaploid wheat has been confirmed through DNA analysis of wheat seeds, dating to around 6400-6200 BCE, recovered from Çatalhöyük.
The first identifiable bread wheat with sufficient gluten for yeasted breads has been identified using DNA analysis in samples from a granary dating to 1350 BCE at Assiros in Macedonia. From Asia, wheat continued to spread across Europe. In the British Isles, wheat straw was used for roofing in the Bronze Age, was in common use until the late 19th century. Technological advances in soil preparation and seed placement at planting time, use of crop rotation and fertilizers to improve plant growth, advances in harvesting methods have all combined to promote wheat as a viable crop; when the use of seed drills replaced broadcasting sowing of seed in the 18th century, another great increase in productivity occurred. Yields of pure wheat per unit area increased as methods of crop rotation were applied to long cultivated land, the use of fertilizers became widespread. Improved agricultural husbandry has more included threshing machines and reaping machines, tractor-drawn cultivators and planters, better varieties.
Great expansion of wheat production occurred as new arable land was farmed in the Americas and Australia in the 19th and 20th centuries. Leaves emerge from the shoot apical meristem in a telescoping fashion until the transition to reprod
Eukaryotes are organisms whose cells have a nucleus enclosed within membranes, unlike prokaryotes, which have no membrane-bound organelles. Eukaryotes belong to Eukarya, their name comes from the Greek εὖ and κάρυον. Eukaryotic cells contain other membrane-bound organelles such as mitochondria and the Golgi apparatus, in addition, some cells of plants and algae contain chloroplasts. Unlike unicellular archaea and bacteria, eukaryotes may be multicellular and include organisms consisting of many cell types forming different kinds of tissue. Animals and plants are the most familiar eukaryotes. Eukaryotes can reproduce both asexually through mitosis and sexually through meiosis and gamete fusion. In mitosis, one cell divides to produce two genetically identical cells. In meiosis, DNA replication is followed by two rounds of cell division to produce four haploid daughter cells; these act as sex cells. Each gamete has just one set of chromosomes, each a unique mix of the corresponding pair of parental chromosomes resulting from genetic recombination during meiosis.
The domain Eukaryota appears to be monophyletic, makes up one of the domains of life in the three-domain system. The two other domains and Archaea, are prokaryotes and have none of the above features. Eukaryotes represent a tiny minority of all living things. However, due to their much larger size, their collective worldwide biomass is estimated to be about equal to that of prokaryotes. Eukaryotes evolved 1.6–2.1 billion years ago, during the Proterozoic eon. The concept of the eukaryote has been attributed to the French biologist Edouard Chatton; the terms prokaryote and eukaryote were more definitively reintroduced by the Canadian microbiologist Roger Stanier and the Dutch-American microbiologist C. B. van Niel in 1962. In his 1937 work Titres et Travaux Scientifiques, Chatton had proposed the two terms, calling the bacteria prokaryotes and organisms with nuclei in their cells eukaryotes; however he mentioned this in only one paragraph, the idea was ignored until Chatton's statement was rediscovered by Stanier and van Niel.
In 1905 and 1910, the Russian biologist Konstantin Mereschkowski argued that plastids were reduced cyanobacteria in a symbiosis with a non-photosynthetic host, itself formed by symbiosis between an amoeba-like host and a bacterium-like cell that formed the nucleus. Plants had thus inherited photosynthesis from cyanobacteria. In 1967, Lynn Margulis provided microbiological evidence for endosymbiosis as the origin of chloroplasts and mitochondria in eukaryotic cells in her paper, On the origin of mitosing cells. In the 1970s, Carl Woese explored microbial phylogenetics, studying variations in 16S ribosomal RNA; this helped to uncover the origin of the eukaryotes and the symbiogenesis of two important eukaryote organelles and chloroplasts. In 1977, Woese and George Fox introduced a "third form of life", which they called the Archaebacteria. In 1979, G. W. Gould and G. J. Dring suggested that the eukaryotic cell's nucleus came from the ability of Gram-positive bacteria to form endospores. In 1987 and papers, Thomas Cavalier-Smith proposed instead that the membranes of the nucleus and endoplasmic reticulum first formed by infolding a prokaryote's plasma membrane.
In the 1990s, several other biologists proposed endosymbiotic origins for the nucleus reviving Mereschkowski's theory. Eukaryotic cells are much larger than those of prokaryotes having a volume of around 10,000 times greater than the prokaryotic cell, they have a variety of internal membrane-bound structures, called organelles, a cytoskeleton composed of microtubules and intermediate filaments, which play an important role in defining the cell's organization and shape. Eukaryotic DNA is divided into several linear bundles called chromosomes, which are separated by a microtubular spindle during nuclear division. Eukaryote cells include a variety of membrane-bound structures, collectively referred to as 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 the outer membrane invaginates and pinches off to form a vesicle, it is probable that most other membrane-bound organelles are derived from such vesicles.
Alternatively some products produced by the cell can leave in a vesicle through exocytosis. The nucleus is surrounded with pores that allow material to move in and out. Various tube- and sheet-like extensions of the nuclear membrane form the endoplasmic reticulum, involved in protein transport and maturation, it includes the rough endoplasmic reticulum where ribosomes are attached to synthesize proteins, which enter the interior space or lumen. Subsequently, they 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, the Golgi apparatus. Vesicles may be specialized for various purposes. For instance, lysosomes contain digestive enzymes that break down most biomolecules in the cytoplasm. Peroxisomes are used to break down peroxide, otherwise toxic. Many protozoans have contractile vacuoles, which collect and expel excess water, extrusomes, which expel material used to deflect predators or capture prey.
In higher plants, most of a cell's volume is taken up by a central vacuole, whi
The Rhizaria are a species-rich supergroup of unicellular eukaryotes. A multicellular form has been described; this supergroup was proposed by Cavalier-Smith in 2002. Being described from rDNA sequences, they vary in form, having no clear morphological distinctive characters, but for the most part they are amoeboids with filose, reticulose, or microtubule-supported pseudopods. Many produce shells or skeletons, which may be quite complex in structure, these make up the vast majority of protozoan fossils. Nearly all have mitochondria with tubular cristae; the three main groups of Rhizaria are: Cercozoa – various amoebae and flagellates with filose pseudopods and common in soil Foraminifera – amoeboids with reticulose pseudopods, common as marine benthos Radiolaria – amoeboids with axopods, common as marine planktonA few other groups may be included in the Cercozoa, but on some trees appear closer to the Foraminifera. These are the Phytomyxea and Ascetosporea, parasites of plants and animals and the peculiar amoeba Gromia.
The different groups of Rhizaria are considered close relatives based on genetic similarities, have been regarded as an extension of the Cercozoa. The name Rhizaria for the expanded group was introduced by Cavalier-Smith in 2002, who included the centrohelids and Apusozoa. Another order that appears to belong to this taxon is the Mikrocytida; these are parasites of oysters. Rhizaria are part of the Diaphoretickes clade along with Archaeplastida, Cryptista and Halvaria. Many rhizarians were considered animals because of their motility and heterotrophy. However, when a simple animal-plant dichotomy was superseded by a recognition of additional kingdoms, taxonomists placed rhizarians in the kingdom Protista; when scientists began examining the evolutionary relationships among eukaryotes using molecular data, it became clear that the kingdom Protista was paraphyletic. Rhizaria appear to share a common ancestor with Stramenopiles and Alveolates forming part of the SAR super assemblage. Rhizaria has been supported by molecular phylogenetic studies as a monophyletic group.
Biosynthesis of 24-isopropyl cholestane precursors in various rhizaria suggests a relevant ecological role during the Ediacaran. Phylogeny based on al.. 2009, Howe et al. 2011, Silar 2016. In 2019, the Cercozoa were recognized as sister of the Retaria. Molecular Phylogeny of Amoeboid Protists - Tree of Rhizaria Tree of Life Eukaryotes
The Cercozoa are a group of single-celled eukaryotes. They lack shared morphological characteristics at the microscopic level, being defined by molecular phylogenies of rRNA and actin or polyubiquitin; the group flagellates that feed by means of filose pseudopods. These may be restricted to part of the cell surface, but there is never a true cytostome or mouth as found in many other protozoa, they show a variety of forms and have proven difficult to define in terms of structural characteristics, although their unity is supported by genetic studies. Cercozoa are related to Foraminifera and Radiolaria, amoeboids that have complex shells, together with them form a supergroup called the Rhizaria, they are sometimes grouped by whether they are "filose" or "reticulose". The best-known Cercozoa are the euglyphids, filose amoebae with shells of siliceous scales or plates, which are found in soils, nutrient-rich waters, on aquatic plants; some other filose amoebae produce organic shells, including Gromia.
They were classified with the euglyphids as the Testaceafilosia. This group is not monophyletic, but nearly all studied members fall in or near the Cercozoa, related to shelled flagellates. Other notable filose cercozoans include the cercomonads. Another important group placed here are the chlorarachniophytes, strange amoebae that form a reticulating net, they are set apart by the presence of chloroplasts, which developed from an ingested green alga. They still possess a vestigial nucleus, called a nucleomorph; as such, they have been of great interest to researchers studying the endosymbiotic origins of organelles. Chlorarachniophytes are sometimes considered Filosa, rather than Endomyxa, while groups such as Gromia are considered Endomyxa. Filosa is a monophyletic group, but Endomyxa is paraphyletic. In addition, three groups that are traditionally considered heliozoans belong here: the Heliomonadida and Gymnosphaerida, which were grouped into the new class of Granofilosea. Cercozoans include the Phaeodarea, marine protozoa that were considered radiolarians.
The exact composition and classification of the Cercozoa are still being worked out. A general scheme is: In addition two groups of parasites, the Phytomyxea and Ascetosporea, the shelled amoeba Gromia may be basal Cercozoa, although some trees place them closer to the Foraminifera; the spongomonads have been included here, but more have been considered Amoebozoa. Some other small groups of protozoans are considered Cercozoa but are of uncertain placement, it is many obscure genera will turn out to be cercozoans with further study. Phylogeny based on al.. 2009, Howe etal. 2011 and Silar 2016. In 2019, Cercozoa were recognized as sister to Retaria in Rhizaria. Phylum Cercozoa Family? Gymnophrydiidae Family? Gymnophryidae Mikrjukov & Mylnikov 1996 Family? Rhizoplasmidae Cavalier-Smith & Bass 2009 Order? Gymnosphaerida Poche 1913 emend. Mikrjukov 2000 Family Gymnosphaeridae Poche 1913 Clade Marimyxia Cavalier-Smith 2017 Order Reticulosida Cavalier-Smith 2003 emend. Bass et al. 2009 Family Filoretidae Cavalier-Smith & Bass 2009 Class Gromiidea Cavalier-Smith 2003 Order Gromiida Claparède & Lachmann 1856 s.s.
Class Ascetosporea Desportes & Ginsburger-Vogel, 1977 emend. Cavalier-Smith 2009 Order Claustrosporida Cavalier-Smith 2003 Order Paradiniida Cavalier-Smith 2009 Order Mikrocytida Hartikainen et al. 2014 Order Paramyxida Chatton 1911 Order Haplosporida Caullery & Mesnil 1899 Class Phytomyxea Engler & Prantl 1897 em. Cavalier-Smith 1993 Order Phagomyxida Cavalier-Smith 1993 Order Plasmodiophorida Cook 1928 em. Cavalier-Smith 1993 Class Vampyrellidea Cavalier-Smith 2017 Order Vampyrellida West 1901 emend. Hess et al. 2012 Subphylum Filosa Leidy 1879 emend. Cavalier-Smith 2003 Class Skiomonadea Cavalier-Smith 2012 Order Tremulida Cavalier-Smith & Howe 2011 Class Chlorarachnea Hibberd & Norris 1984 Order Minorisida Cavalier-Smith 2017 Order Chlorarachniida Hibberd & Norris 1984 Class Granofilosea Cavalier-Smith & Bass 2009 Family? Microgromiidae De Saedeleer 1934 Order? Axomonadida Order Desmothoracida Honigberg et al. 1964 Order Cryptofilida Cavalier-Smith & Bass 2009 Order Limnofilida Cavalier-Smith & Bass 2009 Order Leucodictyida Cavalier-Smith 1993 emend.
2003 Infraphylum Monadofilosa Cavalier-Smith 1997 Family? Katabiidae Cavalier-Smith 2012 Family? Krakenidae Dumack, Mylnikov & Bonkowski 2017 Order? Pseudodimorphida Class Helkesea Cavalier-Smith 2017 Order Ventricleftida Cavalier-Smith 2011 Order Helkesida Cavalier-Smith 2017 Order Cercomonadida Poche 1913 emend. Karpov et al. 2006 Class Metromonadea Cavalier-Smith 2007 s.s. Order Metromonadida Bass & Cavalier-Smith 2004 Order Metopiida Cavalier-Smith 2003 Clade Glissomonadida-Pansomonadida Order Glissomonadida Howe & Cavalie
Protist is a peer-reviewed scientific journal focusing on protists. It was founded as Archiv für Protistenkunde by editor Fritz Shaudinn in 1902, published by Gustav Fischer and Jena; the journal is now published by Elsevier, is edited by Michael Melkonian. The journal changed its name to Protist in 1998; the journal is abstracted and indexed in the following bibliographic databases: According to the Journal Citation Reports, the journal has a 2017 impact factor of 2.702. E. A. M.. "Archiv für Protistenkunde". Nature. 66: 627–628. Doi:10.1038/066627a0. G. N. C.. "Archiv fur Protistenkunde". Science. 16: 981–982. Doi:10.1126/science.16.416.981. Official website
Spirogyra is a genus of filamentous charophyte green algae of the order Zygnematales, named for the helical or spiral arrangement of the chloroplasts, characteristic of the genus. It is found in freshwater habitats, there are more than 400 species of Spirogyra in the world. Spirogyra measures 10 to 100 μm in width and may grow to several centimetres in length. Spirogyra is common in clean eutrophic water, developing slimy filamentous green masses. In spring Spirogyra grows under water, but when there is enough sunlight and warmth they produce large amounts of oxygen, adhering as bubbles between the tangled filaments; the filamentous masses become visible as slimy green mats. Spirogyra has a cell wall, nucleus and spiral chloroplasts, it is rare among the plant-like protists. Spirogyra can reproduce both sexually and asexually. In vegetative reproduction, fragmentation takes place, Spirogyra undergoes intercalary cell division to extend the length of the new filaments. Sexual reproduction is of two types: Scalariform conjugation requires association of two or more different filaments lined side by side either or throughout their length.
One cell each from opposite lined filaments emits tubular protuberances known as conjugation tubes, which elongate and fuse, to make a passage called the conjugation canal. The cytoplasm of the cell acting as the male travels through this tube and fuses with the female cytoplasm, the gametes fuse to form a zygospore. In lateral conjugation, gametes are formed in a single filament. Two adjoining cells near the common transverse wall give out protuberances known as conjugation tubes, which further form the conjugation canal upon contact; the male cytoplasm migrates through fusing with the female. The rest of the process proceeds as in scalariform conjugation; the essential difference is that scalariform conjugation occurs between two filaments and lateral conjugation occurs between two adjacent cells on the same filament. The following species are accepted: Spirogyra at microscopy-uk.org.uk John Whitton, B. A. and Brook, A. J. 2002. The Freshwater Algal Flora of the British Isles. Cambridge University Press, Cambridge.
A fungus is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separate from the other eukaryotic life kingdoms of plants and animals. A characteristic that places fungi in a different kingdom from plants and some protists is chitin in their cell walls. Similar to animals, fungi are heterotrophs. Fungi do not photosynthesize. Growth is their means of mobility, except for spores, which may travel through the water. Fungi are the principal decomposers in ecological systems; these and other differences place fungi in a single group of related organisms, named the Eumycota, which share a common ancestor, an interpretation, strongly supported by molecular phylogenetics. This fungal group oomycetes; the discipline of biology devoted to the study of fungi is known as mycology. In the past, mycology was regarded as a branch of botany, although it is now known fungi are genetically more related to animals than to plants.
Abundant worldwide, most fungi are inconspicuous because of the small size of their structures, their cryptic lifestyles in soil or on dead matter. Fungi include symbionts of plants, animals, or other fungi and parasites, they may become noticeable when fruiting, either as molds. Fungi perform an essential role in the decomposition of organic matter and have fundamental roles in nutrient cycling and exchange in the environment, they have long been used in the form of mushrooms and truffles. Since the 1940s, fungi have been used for the production of antibiotics, more various enzymes produced by fungi are used industrially and in detergents. Fungi are used as biological pesticides to control weeds, plant diseases and insect pests. Many species produce bioactive compounds called mycotoxins, such as alkaloids and polyketides, that are toxic to animals including humans; the fruiting structures of a few species contain psychotropic compounds and are consumed recreationally or in traditional spiritual ceremonies.
Fungi can break down manufactured materials and buildings, become significant pathogens of humans and other animals. Losses of crops due to fungal diseases or food spoilage can have a large impact on human food supplies and local economies; the fungus kingdom encompasses an enormous diversity of taxa with varied ecologies, life cycle strategies, morphologies ranging from unicellular aquatic chytrids to large mushrooms. However, little is known of the true biodiversity of Kingdom Fungi, estimated at 2.2 million to 3.8 million species. Of these, only about 120,000 have been described, with over 8,000 species known to be detrimental to plants and at least 300 that can be pathogenic to humans. Since the pioneering 18th and 19th century taxonomical works of Carl Linnaeus, Christian Hendrik Persoon, Elias Magnus Fries, fungi have been classified according to their morphology or physiology. Advances in molecular genetics have opened the way for DNA analysis to be incorporated into taxonomy, which has sometimes challenged the historical groupings based on morphology and other traits.
Phylogenetic studies published in the last decade have helped reshape the classification within Kingdom Fungi, divided into one subkingdom, seven phyla, ten subphyla. The English word fungus is directly adopted from the Latin fungus, used in the writings of Horace and Pliny; this in turn is derived from the Greek word sphongos, which refers to the macroscopic structures and morphology of mushrooms and molds. The word mycology is derived from the Greek logos, it denotes the scientific study of fungi. The Latin adjectival form of "mycology" appeared as early as 1796 in a book on the subject by Christiaan Hendrik Persoon; the word appeared in English as early as 1824 in a book by Robert Kaye Greville. In 1836 the English naturalist Miles Joseph Berkeley's publication The English Flora of Sir James Edward Smith, Vol. 5. Refers to mycology as the study of fungi. A group of all the fungi present in a particular area or geographic region is known as mycobiota, e.g. "the mycobiota of Ireland". Before the introduction of molecular methods for phylogenetic analysis, taxonomists considered fungi to be members of the plant kingdom because of similarities in lifestyle: both fungi and plants are immobile, have similarities in general morphology and growth habitat.
Like plants, fungi grow in soil and, in the case of mushrooms, form conspicuous fruit bodies, which sometimes resemble plants such as mosses. The fungi are now considered a separate kingdom, distinct from both plants and animals, from which they appear to have diverged around one billion years ago; some morphological and genetic features are shared with other organisms, while others are unique to the fungi separating them from the other kingdoms: Shared features: With other euka