Browning is the process of food turning brown due to the chemical reactions that take place within. The process of browning is one of the chemical reactions that take place in food chemistry and represents an interesting research topic regarding health and food technology. Though there are many different ways food chemically changes over time, browning in particular falls into 2 main categories: enzymatic versus non-enzymatic browning processes. Browning has many important implications on the food industry relating to nutrition and economic cost. Researchers are interested in studying the control of browning and the different methods that can be employed to maximize this inhibition and prolong the shelf life of food. Enzymatic browning is one of the most important reactions that takes place in most fruits and vegetables as well as in seafood; these processes affect the taste and value of such foods. It is a chemical reaction involving polyphenol oxidase, catechol oxidase, other enzymes that create melanins and benzoquinone from natural phenols.
Enzymatic browning requires exposure to oxygen. It begins with the oxidation of phenols by polyphenol oxidase into quinones, whose strong electrophilic state causes high susceptibility to a nucleophilic attack from other proteins; these quinones are polymerized in a series of reactions resulting in the formation of brown pigments on the surface of the food. The rate of enzymatic browning is reflected by the amount of active polyphenol oxidases present in the food. Hence most research investigating methods to inhibit enzymatic browning has focused on hindering polyphenol oxidase activity. However, not all browning of food produces negative effects. Examples of beneficial enzymatic browning: Developing color and flavor in Coffee, Cocoa beans, tea. Developing color and flavor in dried fruit such as figs and raisins. Examples of non-beneficial enzymatic browning: Fresh fruit and vegetables, including apples, potatoes and avocados. Polyphenols oxidases is the major reaction in the formation of Melanosis in crustaceans such as shrimp.
A variety of methods are used to prevent or slow down enzymatic browning of foods, each method aimed at targeting specific steps of the chemical reaction. The control of enzymatic browning has always been a challenge for the food industry. In addition, the use of chemicals to inhibit browning, such as sulfite have been reconsidered due to the potential hazards it causes along with its activity. Much research has been conducted regarding the exact types of control mechanisms that take place when confronted with these enzymatic process; the different types of enzymatic browning control can be classified into different groups. Lemon juice and other acids lower the pH and remove the copper cofactor necessary for the responsible enzymes to function Blanching or roasting of foods, to denature the enzymes, destroy to responsible reactants, as used in the "kill green" phase of tea processing. Low temperatures can prevent enzymatic browning by reducing rate of reaction. Use of ascorbic acid in certain pH's to control browning of apples under certain conditions by changing their phenolase activity.
Different pH values affect phenolase activity of apples differently. Proteins can exert an inhibitory effect on PPO activity by Chelating the essential copper at the active site of PPO through competitive inhibition, inhibiting its activity During wine synthesis, the use of Ion-exchange filtration is used to remove the brown color sediments in the solution. Arctic Apples have been genetically modified to avoid expressing polyphenol oxidase and thus do not brown The second type of browning, nonenzymatic browning, is a process that produces the brown pigmentation in foods, but without the activity of enzymes; the two main forms of non-enzymatic browning are the Maillard reaction. Both vary in the reaction rate as a function of water activity (in food chemistry, the standard state of water activity is most defined as the partial vapor pressure of pure water at the same temperature. Caramelization is a process involving the pyrolysis of sugar, it is used extensively in cooking for brown color. As the process occurs, volatile chemicals are released.
The other non-enzymatic reaction is the Maillard reaction. This reaction is responsible for the production of the flavor. Examples of foods that undergo Maillard reaction include breads and potatoes, it is a chemical reaction that takes place between the amine group of a free amino acid and the carbonyl group of a reducing sugar with the addition of heat. The sugar interacts with the amino acid, producing a variety of flavors; the Maillard reaction is the basis for producing artificial flavors for processed foods in the flavoring industry, since the type of amino acid involved determines the resulting flavor. Melanoidins are brown, high molecular weight heterogeneous polymers that are formed when sugars and amino acids combine through the Maillard reaction at high temperatures and low water activity. Melanoidins are present in foods that have undergone some form of non-enzymatic browning, such as barley malts, bread crust, bakery products and coffee, they are present in the wastewater of sugar refineries, necessitating treatment in order to avoid contamination around the outflow of these refineries.
Like most fruit, grapes vary. This characteristic is used as a parameter in judging the quality of wine; the general process of winemaking is initiated by the enzymatic
In the fields of horticulture and botany, the term deciduous means "falling off at maturity" and "tending to fall off", in reference to trees and shrubs that seasonally shed leaves in the autumn. The term deciduous means "the dropping of a part, no longer needed" and the "falling away after its purpose is finished". In plants, it is the result of natural processes. "Deciduous" has a similar meaning when referring to animal parts, such as deciduous antlers in deer, deciduous teeth in some mammals. Wood from deciduous trees is used in a variety of ways in several industries including lumber for furniture and flooring, bowling pins and baseball bats and furniture, cabinets and paneling. In botany and horticulture, deciduous plants, including trees and herbaceous perennials, are those that lose all of their leaves for part of the year; this process is called abscission. In some cases leaf loss coincides with winter -- namely in polar climates. In other parts of the world, including tropical and arid regions, plants lose their leaves during the dry season or other seasons, depending on variations in rainfall.
The converse of deciduous is evergreen, where foliage is shed on a different schedule from deciduous trees, therefore appearing to remain green year round. Plants that are intermediate may be called semi-deciduous. Other plants are semi-evergreen and lose their leaves before the next growing season, retaining some during winter or dry periods; some trees, including a few species of oak, have desiccated leaves that remain on the tree through winter. Many deciduous plants flower during the period when they are leafless, as this increases the effectiveness of pollination; the absence of leaves improves wind transmission of pollen for wind-pollinated plants and increases the visibility of the flowers to insects in insect-pollinated plants. This strategy is not without risks, as the flowers can be damaged by frost or, in dry season regions, result in water stress on the plant. There is much less branch and trunk breakage from glaze ice storms when leafless, plants can reduce water loss due to the reduction in availability of liquid water during cold winter days.
Leaf drop or abscission involves complex physiological changes within plants. The process of photosynthesis degrades the supply of chlorophylls in foliage; when autumn arrives and the days are shorter or when plants are drought-stressed, deciduous trees decrease chlorophyll pigment production, allowing other pigments present in the leaf to become apparent, resulting in non-green colored foliage. The brightest leaf colors are produced when days grow short and nights are cool, but remain above freezing; these other pigments include carotenoids that are yellow and orange. Anthocyanin pigments produce red and purple colors, though they are not always present in the leaves. Rather, they are produced in the foliage in late summer, when sugars are trapped in the leaves after the process of abscission begins. Parts of the world that have showy displays of bright autumn colors are limited to locations where days become short and nights are cool. In other parts of the world, the leaves of deciduous trees fall off without turning the bright colors produced from the accumulation of anthocyanin pigments.
The beginnings of leaf drop starts when an abscission layer is formed between the leaf petiole and the stem. This layer is formed in the spring during active new growth of the leaf; the cells are sensitive to a plant hormone called auxin, produced by the leaf and other parts of the plant. When auxin coming from the leaf is produced at a rate consistent with that from the body of the plant, the cells of the abscission layer remain connected; the elongation of these cells break the connection between the different cell layers, allowing the leaf to break away from the plant. It forms a layer that seals the break, so the plant does not lose sap. A number of deciduous plants remove nitrogen and carbon from the foliage before they are shed and store them in the form of proteins in the vacuoles of parenchyma cells in the roots and the inner bark. In the spring, these proteins are used as a nitrogen source during the growth of new leaves or flowers. Plants with deciduous foliage have advantages and disadvantages compared to plants with evergreen foliage.
Since deciduous plants lose their leaves to conserve water or to better survive winter weather conditions, they must regrow new foliage during the next suitable growing season. Evergreens suffer greater water loss during the winter and they can experience greater predation pressure when small. Losing leaves in winter may reduce damage from insects. Removing leaves reduces cavitation which can damage xylem vessels in plants; this allows deciduous plants to have xylem vessels with larger diameters and therefore a greater rate of transpiration during the summer growth period
Georgia is a country in the Caucasus region of Eurasia. Located at the crossroads of Western Asia and Eastern Europe, it is bounded to the west by the Black Sea, to the north by Russia, to the south by Turkey and Armenia, to the southeast by Azerbaijan; the capital and largest city is Tbilisi. Georgia covers a territory of 69,700 square kilometres, its 2017 population is about 3.718 million. Georgia is a unitary semi-presidential republic, with the government elected through a representative democracy. During the classical era, several independent kingdoms became established in what is now Georgia, such as Colchis and Iberia; the Georgians adopted Christianity in the early 4th century. The common belief had an enormous importance for spiritual and political unification of early Georgian states. A unified Kingdom of Georgia reached its Golden Age during the reign of King David IV and Queen Tamar in the 12th and early 13th centuries. Thereafter, the kingdom declined and disintegrated under hegemony of various regional powers, including the Mongols, the Ottoman Empire, successive dynasties of Iran.
In the late 18th century, the eastern Georgian Kingdom of Kartli-Kakheti forged an alliance with the Russian Empire, which directly annexed the kingdom in 1801 and conquered the western Kingdom of Imereti in 1810. Russian rule over Georgia was acknowledged in various peace treaties with Iran and the Ottomans and the remaining Georgian territories were absorbed by the Russian Empire in a piecemeal fashion in the course of the 19th century. During the Civil War following the Russian Revolution in 1917, Georgia became part of the Transcaucasian Federation and emerged as an independent republic before the Red Army invasion in 1921 which established a government of workers' and peasants' soviets. Soviet Georgia would be incorporated into a new Transcaucasian Federation which in 1922 would be a founding republic of the Soviet Union. In 1936, the Transcaucasian Federation was dissolved and Georgia emerged as a Union Republic. During the Great Patriotic War 700,000 Georgians fought in the Red Army against the German invaders.
After Soviet leader Joseph Stalin, a native Georgian, died in 1953, a wave of protest spread against Nikita Khrushchev and his de-Stalinization reforms, leading to the death of nearly one hundred students in 1956. From that time on, Georgia would become marred with blatant corruption and increased alienation of the government from the people. By the 1980s, Georgians were ready to abandon the existing system altogether. A pro-independence movement led to the secession from the Soviet Union in April 1991. For most of the following decade, post-Soviet Georgia suffered from civil conflicts, secessionist wars in Abkhazia and South Ossetia, economic crisis. Following the bloodless Rose Revolution in 2003, Georgia pursued a pro-Western foreign policy; this strengthened state institutions. The country's Western orientation soon led to the worsening of relations with Russia, culminating in the brief Russo-Georgian War in August 2008 and Georgia's current territorial dispute with Russia. Georgia is a member of the United Nations, the Council of Europe, the GUAM Organization for Democracy and Economic Development.
It contains two de facto independent regions and South Ossetia, which gained limited international recognition after the 2008 Russo-Georgian War. Georgia and most of the world's countries consider the regions to be Georgian territory under Russian occupation. "Georgia" stems from the Persian designation of the Georgians – gurğān, in the 11th and 12th centuries adapted via Syriac gurz-ān/gurz-iyān and Arabic ĵurĵan/ĵurzan. Lore-based theories were given by the traveller Jacques de Vitry, who explained the name's origin by the popularity of St. George amongst Georgians, while traveller Jean Chardin thought that "Georgia" came from Greek γεωργός; as Prof. Alexander Mikaberidze adds, these century-old explanations for the word Georgia/Georgians are rejected by the scholarly community, who point to the Persian word gurğ/gurğān as the root of the word. Starting with the Persian word gurğ/gurğān, the word was adopted in numerous other languages, including Slavic and West European languages; this term itself might have been established through the ancient Iranian appellation of the near-Caspian region, referred to as Gorgan.
The native name is Sakartvelo, derived from the core central Georgian region of Kartli, recorded from the 9th century, in extended usage referring to the entire medieval Kingdom of Georgia by the 13th century. The self-designation used by ethnic Georgians is Kartvelebi; the medieval Georgian Chronicles present an eponymous ancestor of the Kartvelians, Kartlos, a great-grandson of Japheth. However, scholars agree that the word is derived from the Karts, the latter being one of the proto-Georgian tribes that emerged as a dominant group in ancient times; the name Sakartvelo consists of two parts. Its root, kartvel-i, specifies an inhabitant of the core central-eastern Georgian region of Kartli, or Iberia as it is known in sources of the Eastern Roman Empire. Ancient Greeks and Romans referred to early western Georgians as Colchians and eastern Georgians as Iberians; the Georgian circumfix sa-X-o is a standard geographic construction designating "the area where X dwell", where X is an ethnonym. To
Aphrodite is an ancient Greek goddess associated with love, pleasure and procreation. She is identified with the planet Venus, named after the Roman goddess Venus, with whom Aphrodite was extensively syncretized. Aphrodite's major symbols include myrtles, doves and swans; the cult of Aphrodite was derived from that of the Phoenician goddess Astarte, a cognate of the East Semitic goddess Ishtar, whose cult was based on the Sumerian cult of Inanna. Aphrodite's main cult centers were Cythera, Cyprus and Athens, her main festival was the Aphrodisia, celebrated annually in midsummer. In Laconia, Aphrodite was worshipped as a warrior goddess, she was the patron goddess of prostitutes, an association which led early scholars to propose the concept of "sacred prostitution", an idea, now seen as erroneous. In Hesiod's Theogony, Aphrodite is born off the coast of Cythera from the foam produced by Uranus's genitals, which his son Cronus has severed and thrown into the sea. In Homer's Iliad, she is the daughter of Zeus and Dione.
Plato, in his Symposium 180e, asserts that these two origins belong to separate entities: Aphrodite Ourania and Aphrodite Pandemos. Aphrodite had many other epithets, each emphasizing a different aspect of the same goddess, or used by a different local cult, thus she was known as Cytherea and Cypris, due to the fact that both locations claimed to be the place of her birth. In Greek mythology, Aphrodite was married to the god of blacksmiths and metalworking. Despite this, Aphrodite was unfaithful to him and had many lovers. In the First Homeric Hymn to Aphrodite, she seduces the mortal shepherd Anchises. Aphrodite was the surrogate mother and lover of the mortal shepherd Adonis, killed by a wild boar. Along with Athena and Hera, Aphrodite was one of the three goddesses whose feud resulted in the beginning of the Trojan War and she plays a major role throughout the Iliad. Aphrodite has been featured in western art as a symbol of female beauty and has appeared in numerous works of western literature.
She is a major deity in modern Neopagan religions, including the Church of Aphrodite and Hellenismos. Hesiod derives Aphrodite from aphrós "sea-foam", interpreting the name as "risen from the foam", but most modern scholars regard this as a spurious folk etymology. Early modern scholars of classical mythology attempted to argue that Aphrodite's name was of Greek or Indo-European origin, but these efforts have now been abandoned. Aphrodite's name is accepted to be of non-Greek Semitic, but its exact derivation cannot be determined. Scholars in the late nineteenth and early twentieth centuries, accepting Hesiod's "foam" etymology as genuine, analyzed the second part of Aphrodite's name as *-odítē "wanderer" or *-dítē "bright". Michael Janda accepting Hesiod's etymology, has argued in favor of the latter of these interpretations and claims the story of a birth from the foam as an Indo-European mytheme. Witczak proposes an Indo-European compound *abʰor- "very" and *dʰei- "to shine" referring to Eos.
Other scholars have argued that these hypotheses are unlikely since Aphrodite's attributes are different from those of both Eos and the Vedic deity Ushas. A number of improbable non-Greek etymologies have been suggested. One Semitic etymology compares Aphrodite to the Assyrian barīrītu, the name of a female demon that appears in Middle Babylonian and Late Babylonian texts. Hammarström looks to Etruscan, comparing prϑni "lord", an Etruscan honorific loaned into Greek as πρύτανις; this would make the theonym in origin an honorific, "the lady". Most scholars reject this etymology as implausible since Aphrodite appears in Etruscan in the borrowed form Apru; the medieval Etymologicum Magnum offers a contrived etymology, deriving Aphrodite from the compound habrodíaitos, "she who lives delicately", from habrós and díaita. The alteration from b to ph is explained as a "familiar" characteristic of Greek "obvious from the Macedonians"; the cult of Aphrodite in Greece was imported from, or at least influenced by, the cult of Astarte in Phoenicia, which, in turn, was influenced by the cult of the Mesopotamian goddess known as "Ishtar" to the East Semitic peoples and as "Inanna" to the Sumerians.
Pausanias states that the first to establish a cult of Aphrodite were the Assyrians, after the Assyrians, the Paphians of Cyprus, the Phoenicians at Ascalon. The Phoenicians, in turn, taught her worship to the people of Cythera. Aphrodite took on Inanna-Ishtar's associations with procreation. Furthermore, she was known as Ourania, which means "heavenly", a title corresponding to Inanna's role as the Queen of Heaven. Early artistic and literary portrayals of Aphrodite are similar on Inanna-Ishtar. Like Inanna-Ishtar, Aphrodite was a warrior goddess, he mentions that Aphrodite's most ancient cult statues in Sparta and on Cythera showed her bearing arms. Modern scholars note that Aphrodite's warrior-goddess aspects appear in the oldest strata of her worship and see it as an indication of her Near Eastern origins. Nineteenth century classical scholars had a general aversion to the idea that ancient Greek religion was at all influenced by the cultures of the Near East, but Friedrich Got
The Maleae are the apple tribe in the rose family, Rosaceae. The group includes a number of plants bearing commercially important fruits, such as apples and pears, while others are cultivated as ornamentals. Older taxonomies separated some of this group as tribe Crataegeae, as the Cydonia group, or some genera were placed in family Quillajaceae; the tribe consists of shrubs and small trees. Most have a type of accessory fruit that does not occur in other Rosaceae. All except Vauquelinia have a basal haploid chromosome count of 17, instead of 7, 8, or 9 as in the other Rosaceae. There are 28 genera that contain about 1100 species worldwide, with most species occurring in the temperate Northern Hemisphere; the name Maleae is required by the International Code of Nomenclature for algae and plants, for any group at the tribal level that includes the genus Malus, but not either of the genera Rosa or Amygdalus. A traditional circumscription of Maleae includes the following genera: Amelanchier - serviceberry, juneberry Aria Aronia - chokeberry Chaenomeles - Japanese quince Chamaemeles Chamaemespilus Cormus Cydonia - quince Dichotomanthes Docynia Docyniopsis Eriobotrya -loquat Eriolobus Hesperomeles Heteromeles - toyon Malacomeles Malus - apple, crabapple Osteomeles Peraphyllum Photinia Pseudocydonia - Chinese quince Pyrus - pear Rhaphiolepis - hawthorn Sorbus - rowan, service tree Stranvaesia Torminalis intergeneric hybrids: × Amelasorbus ×Malosorbus ×Sorbaronia × Sorbopyrusand graft hybrids:+Pyrocydonia A recent taxonomic treatment includes the following genera in Maleae that were earlier separated as tribe Crataegeae: Cotoneaster - cotoneaster Crataegus - hawthorn Mespilus - medlar Pyracantha - firethornintergeneric hybrids: × Crataemespilus × Crataegosorbus × Sorbocotoneasterand the graft hybrid: +Crataegomespilus The following genera were placed in tribe Quillajaceae in Rosaceae, or in family Quillajaceae.
Their fruit are dry capsules, not pomes. Kageneckia Vauquelinia Lindleya The Cydonia group within the Maloid Rosaceae was a tentative grouping of pome-fruited genera with many ovules per carpel; the genera involved were: Cydonia Chaenomeles Docynia PseudocydoniaIt is not yet clear whether this group is monophyletic within the Maleae. Molecular data indicate a close relationship between Pseudocydonia. Multiple ovules per carpel occur in Kageneckia, a non-pome-bearing genus. Chloroplast DNA analysis, but not nuclear DNA, shows a tight relationship between Cydonia and Dichotomanthes, a non-pome-bearing genus
Western Asia, West Asia, Southwestern Asia or Southwest Asia is the westernmost subregion of Asia. The concept is in limited use, as it overlaps with the Middle East, the main difference being the exclusion of the majority of Egypt and the inclusion of the Caucasus; the term is sometimes used for the purposes of grouping countries in statistics. The total population of Western Asia is an estimated 300 million as of 2015. Although the term "Western Asia" is used as a convenient division of contemporary sovereign states into a manageable number of world regions for statistical purposes, it is sometimes used instead of the more geopolitical term "Middle East". In an unrelated context, the term is used in ancient history and archaeology to divide the Fertile Crescent into the "Asiatic" or "Western Asian" cultures as opposed to ancient Egypt; as a geographic concept, Western Asia includes the Levant, Anatolia, the Armenian Highlands, the South Caucasus, the Arabian peninsula as well as the Sinai Peninsula, making Egypt a transcontinental country.
The term is used pragmatically and has no "correct" or agreed-upon definition. The National Geographic Style Manual as well as Maddison's The World Economy: Historical Statistics by the Organisation for Economic Co-operation and Development only includes Bahrain, Iraq, Jordan, Lebanon, Qatar, Palestinian territories, Saudi Arabia, Turkey, UAE, Yemen as West Asian countries. In contrast to this definition, the United Nations Industrial Development Organization in its 2015 yearbook includes Armenia and Azerbaijan, excludes Israel and Turkey. Unlike the UNIDO, the United Nations Statistics Division excludes Iran from Western Asia and includes Turkey and Cyprus in the region. In the United Nation's geopolitical Eastern European Group and Georgia are included in Eastern Europe, whereas Cyprus and East Thracian Turkey are in Southern Europe; these three nations are listed in the European category of the United Nations Educational and Cultural Organisation. National members of West Asian sports governing bodies are limited to Bahrain, Iraq, Kuwait, Syria, Palestine, Saudi Arabia, United Arab Emirates, Yemen.
The Olympic Council of Asia's multi-sport event West Asian Games are contested by athletes representing these thirteen countries. Among the region's sports organisations are the West Asia Basketball Association, West Asian Billiards and Snooker Federation, West Asian Football Federation, the West Asian Tennis Federation. "Western Asia" was in use as a geographical term in the early 19th century before "Near East" became current as a geopolitical concept. In the context of the history of classical antiquity, "Western Asia" could mean the part of Asia known in classical antiquity, as opposed to the reaches of "interior Asia", i.e. Scythia, "Eastern Asia" the easternmost reaches of geographical knowledge in classical authors, i.e. Transoxania and India. In the 20th century, "Western Asia" was used to denote a rough geographical era in the fields of archaeology and ancient history as a shorthand for "the Fertile Crescent excluding Ancient Egypt" for the purposes of comparing the early civilizations of Egypt and the former.
Use of the term in the context of contemporary geopolitics or world economy appears to date from at least the mid-1960s. Western Asia is located directly south of Eastern Europe; the region is surrounded by seven major seas. To the north, the region is delimited from Europe by the Caucasus Mountains, to the southwest, it is delimited from Africa by the Isthmus of Suez, while to the east, the region adjoins Central Asia and South Asia; the Dasht-e Kavir and Dasht-e Lut deserts in eastern Iran delimit the region somewhat from Asia itself. Three major tectonic plates converge on Western Asia, including the African and Arabian plates; the boundaries between the tectonic plates make up the Azores-Gibraltar Ridge, extending across North Africa, the Red Sea, into Iran. The Arabian Plate is moving northward into the Anatolian plate at the East Anatolian Fault, the boundary between the Aegean and Anatolian plate in eastern Turkey is seismically active. Several major aquifers provide water to large portions of Western Asia.
In Saudi Arabia, two large aquifers of Palaeozoic and Triassic origins are located beneath the Jabal Tuwayq mountains and areas west to the Red Sea. Cretaceous and Eocene-origin aquifers are located beneath large portions of central and eastern Saudi Arabia, including Wasia and Biyadh which contain amounts of both fresh water and saline water. Flood or furrow irrigation, as well as sprinkler methods, are extensively used for irrigation, covering nearly 90,000 km2 across Western Asia for agriculture; the Tigris and Euphrates rivers contribute well. Western Asia is arid and semi-arid, can be subject to drought, but it contains vast expanses of forest and fertile valleys; the region consists of grasslands, rangelands and mountains. Water shortages are a problem in many parts of West Asia, with growing populations increasing demands for water, while salinization and pollution threaten water supplies. Major rivers, including the Tigris and Euphrates, provide sources for irrigation water to support agriculture.
There are two wind phenomena in Western Asia: the shamal. The sharqi is a wind that comes from the south and southea
Plants are multicellular, predominantly photosynthetic eukaryotes of the kingdom Plantae. Plants were treated as one of two kingdoms including all living things that were not animals, all algae and fungi were treated as plants. However, all current definitions of Plantae exclude the fungi and some algae, as well as the prokaryotes. By one definition, plants form the clade Viridiplantae, a group that includes the flowering plants and other gymnosperms and their allies, liverworts and the green algae, but excludes the red and brown algae. Green plants obtain most of their energy from sunlight via photosynthesis by primary chloroplasts that are derived from endosymbiosis with cyanobacteria, their chloroplasts contain b, which gives them their green color. Some plants are parasitic or mycotrophic and have lost the ability to produce normal amounts of chlorophyll or to photosynthesize. Plants are characterized by sexual reproduction and alternation of generations, although asexual reproduction is common.
There are about 320 thousand species of plants, of which the great majority, some 260–290 thousand, are seed plants. Green plants provide a substantial proportion of the world's molecular oxygen and are the basis of most of Earth's ecosystems on land. Plants that produce grain and vegetables form humankind's basic foods, have been domesticated for millennia. Plants have many cultural and other uses, as ornaments, building materials, writing material and, in great variety, they have been the source of medicines and psychoactive drugs; the scientific study of plants is known as a branch of biology. All living things were traditionally placed into one of two groups and animals; this classification may date from Aristotle, who made the distincton between plants, which do not move, animals, which are mobile to catch their food. Much when Linnaeus created the basis of the modern system of scientific classification, these two groups became the kingdoms Vegetabilia and Animalia. Since it has become clear that the plant kingdom as defined included several unrelated groups, the fungi and several groups of algae were removed to new kingdoms.
However, these organisms are still considered plants in popular contexts. The term "plant" implies the possession of the following traits multicellularity, possession of cell walls containing cellulose and the ability to carry out photosynthesis with primary chloroplasts; when the name Plantae or plant is applied to a specific group of organisms or taxon, it refers to one of four concepts. From least to most inclusive, these four groupings are: Another way of looking at the relationships between the different groups that have been called "plants" is through a cladogram, which shows their evolutionary relationships; these are not yet settled, but one accepted relationship between the three groups described above is shown below. Those which have been called "plants" are in bold; the way in which the groups of green algae are combined and named varies between authors. Algae comprise several different groups of organisms which produce food by photosynthesis and thus have traditionally been included in the plant kingdom.
The seaweeds range from large multicellular algae to single-celled organisms and are classified into three groups, the green algae, red algae and brown algae. There is good evidence that the brown algae evolved independently from the others, from non-photosynthetic ancestors that formed endosymbiotic relationships with red algae rather than from cyanobacteria, they are no longer classified as plants as defined here; the Viridiplantae, the green plants – green algae and land plants – form a clade, a group consisting of all the descendants of a common ancestor. With a few exceptions, the green plants have the following features in common, they undergo closed mitosis without centrioles, have mitochondria with flat cristae. The chloroplasts of green plants are surrounded by two membranes, suggesting they originated directly from endosymbiotic cyanobacteria. Two additional groups, the Rhodophyta and Glaucophyta have primary chloroplasts that appear to be derived directly from endosymbiotic cyanobacteria, although they differ from Viridiplantae in the pigments which are used in photosynthesis and so are different in colour.
These groups differ from green plants in that the storage polysaccharide is floridean starch and is stored in the cytoplasm rather than in the plastids. They appear to have had a common origin with Viridiplantae and the three groups form the clade Archaeplastida, whose name implies that their chloroplasts were derived from a single ancient endosymbiotic event; this is the broadest modern definition of the term'plant'. In contrast, most other algae not only have different pigments but have chloroplasts with three or four surrounding membranes, they are not close relatives of the Archaeplastida having acquired chloroplasts separately from ingested or symbiotic green and red algae. They are thus not included in the broadest modern definition of the plant kingdom, although they were in the past; the green plants or Viridiplantae were traditionally divided into the green algae (including