Chalk- is a soft. white. porous sedimentary stone. a signifier of limestone composed of the mineral calcite. Calcite is calcium carbonate or CaCO3. It forms under moderately deep Marine conditions from the gradual accretion of minute calcite home bases shed from microorganism called coccolithophores. It is common to happen chert or flint nodules embedded in chalk. Chalk can besides mention to other compounds including Mg silicate and Ca sulphate. Chalk has greater opposition to enduring and slouching than the clays with which it is normally associated.
therefore organizing tall steep drops where chalk ridges meet the sea. Chalk hills. known as chalk down land. normally form where sets of chalk reach the surface at an angle. so organizing a scarp incline. Because chalk is porous it can keep a big volume of land H2O. supplying a natural reservoir that releases H2O easy through dry seasons. Chalk is composed largely of Ca carbonate with minor sums of silt and clay.
It is usually formed underwater. normally on the sea bed. so amalgamate and compressed during diagenesis into the signifier normally seen today. During diagenesis silicon oxide accumulates to organize chert or flint nodules within the carbonate stone Uses:
* Blackboard chalk is a substance used for pulling on unsmooth surfaces. as it readily crumbles go forthing atoms that stick slackly to these surfaces. Although traditionally composed of natural chalk. modern chalkboard chalk is by and large made from the mineral gypsum. frequently supplied in sticks of tight pulverization about 4 in ( 10 centimeter ) long. * Sidewalk chalk is similar to blackboard chalk. except that it is formed into larger sticks and frequently colored. It is used to pull on pavements. streets. and private roads. largely by kids. but besides by grownup creative persons. * In agribusiness chalk is used for raising pH in dirts with high sourness. The most common signifiers are CaCO3 and CaO. * Tailor’s chalk is traditionally a difficult chalk used to do impermanent markers on fabric. chiefly by seamsters. Nowadays it is normally made from talc. * Chalk is a beginning of calcium oxide by thermic decomposition. or slaked lime following slaking with H2O. * Polishing chalk is chalk prepared with a carefully controlled grain size. for really all right shining of metals * Woodworking articulations may be fitted by chalking one of the coupling surfaces. A test tantrum will go forth a chalk grade on the high musca volitanss of the corresponding surface. Chalk reassigning to cover the complete surface indicates a good tantrum.
A seashell or sea shell. besides known merely as a shell. is a difficult. protective outer bed created by an animate being that lives in the sea. The shell is portion of the organic structure of the animate being. Empty seashells are frequently found washed up on beaches by beachcombers. The shells are empty because the animate being has died and the soft parts have been eaten by another animate being or have rotted out. The term seashell normally refers to the exoskeleton of an invertebrate. Most shells that are found on beaches are the shells of Marine molluscs. partially because many of these shells endure better than other seashells. Apart from mollusc shells. other shells that can be found on beaches are those of cirripeds. horseshoe pediculosis pubis and lamp shells. Marine annelid worms in the household Serpulidae create shells made of chalky tubings cemented onto other surfaces. The shells of sea urchins are called trials. and the moulted shells of pediculosis pubis and lobsters are called exuviae. While most seashells are external. some cephalopods have internal shells. Seashells have been used by worlds for many different intents throughout history and pre-history. However. seashells are non the lone sort of shells ; in assorted home grounds it is possible to happen shells from fresh water animate beings such as fresh water mussels and fresh water snails. and it is besides possible to happen the shells of land snails.
When the word “seashells” is used to mention merely to the shells of Marine molluscs so analyzing seashells is portion of shell collecting. Conchologists or serious aggregators who have a scientific prejudice are in general careful non to upset life populations and home grounds: even though they may roll up a few unrecorded animate beings. most responsible aggregators do non frequently over-collect or otherwise disturb ecosystems. When analyzing the whole molluscan animate being is included every bit good as analyzing the shell. so the survey is known as malacology ; a individual who surveies mollusks is known as a malacologist.
Seashells are normally found in beach impetus. which is natural debris deposited along strandlines on beaches by the moving ridges and the tides. Shells are really frequently washed up onto a beach empty and clean. the carnal holding already died. and the soft parts holding rotted off or holding been eaten by either marauders or scavengers. Empty seashells are frequently picked up by beachcombers. However. the bulk of seashells which are offered for sale commercially have been collected alive ( frequently in majority ) and so killed and cleaned. specifically for the commercial trade. This type of large-scale development can sometimes hold a strong negative impact on local ecosystems. and sometimes can significantly cut down the distribution of rare species.
The word seashell is frequently used to intend merely the shell of a marine mollusc. Marine mollusc shells that are familiar to beachcombers and therefore most likely to be called “seashells” are the shells of marine species of pelecypods ( or boodles ) . univalves ( or snails ) . scaphopods ( or horn shells ) . polyplacophorans. and cephalopod. These shells are really frequently the most normally encountered. both in the natural state. and for sale as cosmetic objects. Marine species of univalves and pelecypods are more legion than land and fresh water species. and the shells are frequently larger and more robust. The shells of Marine species besides frequently have more sculpture and more colour. although this is by no agency ever the instance. In the tropical and sub-tropical countries of the planet. there are far more species of colorful. big. shallow H2O shelled Marine molluscs than there are in the temperate zones and the parts closer to the poles. Although there are a figure of species of shelled molluscs that are rather big. there are huge Numberss of highly little species excessively. see micro molluscs. Not all molluscs are marine nevertheless. there are legion land and fresh water molluscs. see for illustration snail and fresh water pelecypods. And non all molluscs have an external shell: some molluscs such as some cephalopods ( calamari and octopuses ) have an internal shell. and many molluscs have no shell. see for illustration bullet and sea slug.
Bivalves are frequently the most common seashells that wash up on big flaxen beaches or in sheltered lagunas. They can sometimes be highly legion. Very frequently the two valves become detached. There are more than 15. 000 species of pelecypods that live in both Marine and fresh water. Examples of pelecypods are boodles. crenations. mussels. and oysters. The bulk of pelecypods consist of two indistinguishable shells that are held together by a flexible flexible joint. Inside the shells holds the animal’s organic structure. Bivalves that do non hold two shells either have one shell or they lack a shell all together. The shells are made of Ca hydrogen carbonate and are secreted by the mantle. Bivalves. besides known as bivalves. are largely filter feeders ; they draw in H2O through their gills which so traps bantam nutrient atoms. Some pelecypods have eyes and even an unfastened circulatory system. Bivalves are used all over the universe as types of nutrient and as a manner of acquiring pearls. But in the H2O. the larvae of some fresh water mussels can be unsafe to angle and can even tire through wood. Shell Beach. Western Australia is a beach which is wholly made up of the shells of the cockle Fragum erugatum as shown here.
Certain species of univalve seashells ( the shells of sea snails ) can sometimes be common. washed up on flaxen beaches. and besides on beaches that are surrounded by bouldery Marine home ground.
Merely a few species of cephalopods have shells ( either internal or external ) that are sometimes found washed up on beaches. Some cephalopods such as Sepia. the cuttlefish. have a big internal shell. the cuttlefish bone. and this frequently washes up on beaches in parts of the universe where cuttlefish are common. Spirula Spirula peronii is a deep H2O squid-like cephalopod. It has an internal shell which is little ( about 1 in or 24 millimeter ) but really light and floaty. This chambered shell floats really good and hence washes up easy and is familiar to beachcombers in the Torrid Zones. Nautilus is the lone genus of cephalopod that has a well-developed external shell. Females of the cephalopod genus Argonauta create a papery egg instance which sometimes washes up on tropical beaches and is referred to as a “paper nautilus” . The largest group of shelled cephalopods. the ammonoids. is nonextant. but their shells are really common in certain countries as dodos.
There are legion popular books and field ushers on the topic of shell-collecting. Although there are a figure of books about land andfresh water molluscs. the bulk of popular books emphasizes. or focuses entirely on. the shells of Marine molluscs. Both the scientific discipline of analyzing mollusc shells and the avocation of roll uping and sorting them are known as shell collecting. The line between professionals and recreational partisans is frequently non good defined in this topic. because many amateurs have contributed to. and go on to lend to. shell collecting and the larger scientific discipline of malacology. Many shell aggregators belong to “shell clubs” where they can run into others who portion their involvements. A big figure of amateurs collect the shells of Marine molluscs. and this is partially because many shells wash up empty on beaches. or unrecorded in the intertidal or sub-tidal zones. and are hence easy found and preserved without much in the manner of specialised equipment or expensive supplies.
Some shell aggregators find their ain stuff and maintain careful records. or purchase lone “specimen shells” . which means shells which have full collectingdata: information including how. when. where. in what home ground. and by whom. the shells were collected. On the other manus. some aggregators buy the more widely available commercially-imported alien shells. the bulk of which have really small information. or none at all. To museum scientists. holding full roll uping informations ( when. where. and by whom it was collected ) with a specimen is far more of import than holding the shell right identified. Some proprietors of shell aggregations hope to be able to donate their aggregation to a major natural history or fauna museum at some point. nevertheless. shells with small or no collection informations are normally of no value to science. and are likely non to be accepted by a major museum. Apart from any harm to the shell that may hold happened before it was collected. shells can besides endure harm when they are stored or displayed.
For an illustration of one instead serious sort of harm see Byne’s disease. Cassava. besides called yuca. mogo. cassava. bitter cassava. tapioca and kamoteng kahoy. a woody bush of the Euphorbiaceae ( spurge household ) indigen to South America. is extensively cultivated as an one-year harvest in tropical and semitropical parts for its comestible starchy. tuberous root. a major beginning of saccharides. It differs from the similarly-spelled yucca. an unrelated fruit-bearing bush in the Asparagaceae household. Cassava. when dried to a starchy. powdery ( or pearly ) infusion is called tapioca. while its fermented. flakey version is named garri. Cassava is the third-largest beginning of nutrient saccharides in the Torrid Zones. Cassava is a major basic nutrient in the underdeveloped universe. supplying a basic diet for around 500 million people.
Cassava is one of the most drought-tolerant harvests. capable of turning on fringy dirts. Nigeria is the world’s largest manufacturer of manioc. Cassava root is a good beginning of saccharides. but a hapless beginning of protein. A preponderantly cassava root diet can do protein-energy malnutrition. Cassava is classified as Sweet or bitter. Like other roots and tubers. Cassava contains anti-nutrition factors and toxins. It must be decently prepared before ingestion. Improper readying of manioc can go forth adequate residuary nitrile to do acute nitrile poisoning and goitres. and may even do ataxy or partial palsy. Nevertheless. husbandmans frequently prefer the acrimonious assortments because they deter plagues. animate beings. and stealers. The more-toxic assortments of Cassava are a fall-back resource in times of dearth in some topographic points
Wild populations of M. esculenta races flabellifolia. shown to be the primogenitor of domesticated manioc. are centered in west-central Brazil. where it was likely first domesticated more than 10. 000 old ages BP. By 6. 600 BC. cassava pollen appears in the Gulf of Mexico Lowlandss. at the San Andres archeological site. The oldest direct grounds of cassava cultivation comes from a 1. 400-year-old Maya site. Joya de Ceren. in El Salvador. [ 12 ] but the species Manihot esculenta likely originated farther south in Brazil and Paraguay. With its high nutrient potency. it had become a staple nutrient of the native populations of northern South America. southern Mesoamerica. and the Caribbean by the clip of the Spanish conquering. and its cultivation was continued by the colonial Portuguese and Spanish. Forms of the modern domesticated species can be found turning in the natural state in the South of Brazil.
While several Manihot species are wild. all assortments of M. esculenta are cultigens. Cassava was a staple nutrient for pre-Columbian peoples in the Americas and is frequently portrayed in autochthonal art. The Moche people frequently depicted yuca in their ceramics. Since being introduced by Lusitanian bargainers from Brazil in the sixteenth century. maize and maniocs have replaced traditional African harvests as the continent’s most of import basic nutrient harvests. Cassava is sometimes described as the ‘bread of the tropics’ but should non to be confused with the tropical and equatorial B World production of cassava root was estimated to be 184 million tones in 2002. lifting to 230 million metric tons in 2008 ( FAO ) . The bulk of production in 2002 was in Africa. where 99. 1 million dozenss were grown ; 51. 5 million dozenss were grown in Asia and 33. 2 million dozenss in Latin America and the Caribbean. Nigeria is the world’s largest manufacturer of manioc. However. based on the statistics from the FAO of the United Nations. Thailand is the largest exporting state of dried manioc. with a sum of 77 % of universe export in 2005. The second-largest exporting state is Vietnam. with 13. 6 % . followed by Indonesia ( 5. 8 % ) and Costa Rica ( 2. 1 % ) .
Worldwide cassava production increased by 12. 5 % between 1988 and 1990. In 2010. the mean output of cassava harvests worldwide was 12. 5 dozenss per hectare. The most productive manioc farms in the universe were in India. with a countrywide mean output of 34. 8 dozenss per hectare in 2010. Cassava. yams and Sweet murphies are of import beginnings of nutrient in the Torrid Zones. The manioc works gives the highest output of saccharides per cultivated country among harvest workss. except for sugar cane and sugar Beta vulgariss. Cassava plays a peculiarly of import function in agribusiness in developing states. particularly in sub-Saharan Africa. because it does good on hapless dirts and with low rainfall. and because it is a perennial that can be harvested as required. Its broad harvest home window allows it to move as a dearth modesty and is priceless in pull offing labour agendas. It besides offers flexibleness to resource-poor husbandmans because it serves as either subsistence or a hard currency harvest. No continent depends every bit much on root and tuber harvests in feeding its population as does Africa.
In the humid and subhumid countries of tropical Africa. it is either a primary basic nutrient or a secondary costaple. In Ghana. for illustration. manioc and yams occupy an of import place the agricultural economic system. and lend approximately 46 % of the agricultural gross domestic merchandise. Cassava histories for a day-to-day thermal consumption of 30 % in Ghana. and is grown by about every agriculture household. The importance of manioc to many Africans is epitomized in the Ewe ( a linguistic communication spoken in Ghana. Togo and Benin ) name for the works. agbeli. significance “there is life” . The monetary value of manioc has risen significantly in the last half decennary. and lower-income people have turned to other carbohydrate-rich nutrients. such as rice In Tamil Nadu. India. the National Highway 68 between Thalaivasal and Attur has many cassava-processing mills alongside it—indicating an copiousness of it locally. Cassava is widely cultivated and eaten as a basic nutrient in Andhra Pradesh and in Kerala. In the semitropical part of southern China. manioc is the fifth-largest harvest in term of production. after rice. sweet murphy. sugar cane and corn. China is besides the largest export market for manioc produced in Vietnam and Thailand. Over 60 % of cassava production in China is concentrated in a individual state. Guangxi. averaging over seven million dozenss yearly. read tree. the Artocarpus communis or the African Artocarpus communis.
Cassava-based dishes are widely consumed wherever the works is cultivated ; some have regional. national. or cultural importance. Cassava must be cooked decently to detoxicate it before it is eaten. Cassava can be cooked in assorted ways. The softhearted root has a delicate spirit and can replace boiled murphies in many utilizations: as an concomitant for meat dishes. or made into purees. dumplings. soups. frets. gravies. etc. This works is used in cholent. in some families. every bit good. Deep fried. it can replace fried murphies. with a typical spirit. In Brazil. detoxified cassava is land and cooked to a dry. frequently difficult or crunchy repast which is used as a condiment. toasted in butter. or eaten entirely as a side dish.
Cassava root is basically a saccharide beginning. Its composing shows 60–65 per centum wet. 20–31 per centum saccharide. 1–2 percent petroleum protein and a relatively low content of vitamins and minerals. However. the roots are rich in Ca and vitamin C and incorporate a nutritionally important measure of vitamin B1. vitamin B2 and nicotinic acid. Cassava amylum contains 70 per centum amylopectin and 20 per centum amylose. Cooked cassava amylum has a digestibleness of over 75 per centum. Cassava root is a hapless beginning of protein. Despite the really low measure. the quality of cassava root protein is reasonably good in footings of indispensable amino acids. Methionine. cysteine and cystine are. nevertheless. restricting aminic acids in cassava root. Cassava is attractive as nutrition beginning in certain ecosystems because manioc is one of the most drought-tolerant harvests. can be successfully grown on fringy dirts. and gives sensible outputs where many other harvests do non turn good.
Cassava is good adapted within latitudes 30° north and South of the equator. at lifts between sea degree and 2000 metres above sea degree. in equatorial temperatures. with rainfalls of 50 millimetres to five metres yearly. and to hapless dirts with a pH runing from acidic to alkaline. These conditions are common in certain parts of Africa and South America. Cassava is a extremely productive harvest in footings of nutrient Calories produced per unit land country per unit of clip. significantly higher than other staple harvests. Cassava can bring forth nutrient Calories at rates transcending 250. 000 cal/hectare/day compared with 176. 000 for rice. 110. 000 for wheat. and 200. 000 for corn ( maize ) . Cassava. like other nutrients. besides has ant nutritionary and toxic factors. Of peculiar concern are the cyanogenetic glucosides of manioc ( linamarin and lotaustralin ) . These. on hydrolysis. release hydrocyanic acid ( HCN ) . The presence of nitrile in manioc is of concern for homo and for carnal ingestion. The concentration of these ant nutritional and insecure glycosides varies well between assortments and besides with climatic and cultural conditions. Choice of manioc species to be grown. therefore. is rather of import. Once harvested. manioc must be treated and prepared decently prior to human or carnal ingestion.
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