SUMMARY / RELATED TOPICS

Cell wall

A cell wall is a structural layer surrounding some types of cells, just outside the cell membrane. It can be tough and sometimes rigid, it provides the cell with both structural support and protection, acts as a filtering mechanism. Cell walls are present in most prokaryotes, in algae and eukaryotes including plants but are absent in animals. A major function is to act as pressure vessels, preventing over-expansion of the cell when water enters; the composition of cell walls varies between species and may depend on cell type and developmental stage. The primary cell wall of land plants is composed of the polysaccharides cellulose and pectin. Other polymers such as lignin, suberin or cutin are anchored to or embedded in plant cell walls. Algae possess cell walls made of glycoproteins and polysaccharides such as carrageenan and agar that are absent from land plants. In bacteria, the cell wall is composed of peptidoglycan; the cell walls of archaea have various compositions, may be formed of glycoprotein S-layers, pseudopeptidoglycan, or polysaccharides.

Fungi possess cell walls made of the N-acetylglucosamine polymer chitin. Unusually, diatoms have a cell wall composed of biogenic silica. A plant cell wall was first observed and named by Robert Hooke in 1665. However, "the dead excrusion product of the living protoplast" was forgotten, for three centuries, being the subject of scientific interest as a resource for industrial processing or in relation to animal or human health. In 1804, Karl Rudolphi and J. H. F. Link proved. Before, it had been thought that fluid passed between them this way; the mode of formation of the cell wall was controversial in the 19th century. Hugo von Mohl advocated the idea. Carl Nägeli believed that the growth of the wall in thickness and in area was due to a process termed intussusception; each theory was improved in the following decades: the apposition theory by Eduard Strasburger, the intussusception theory by Julius Wiesner. In 1930, Ernst Münch coined the term apoplast in order to separate the "living" symplast from the "dead" plant region, the latter of which included the cell wall.

By the 1980s, some authors suggested replacing the term "cell wall" as it was used for plants, with the more precise term "extracellular matrix", as used for animal cells, but others preferred the older term. Cell walls serve similar purposes in those organisms, they may give cells offering protection against mechanical stress. The chemical composition and mechanical properties of the cell wall are linked with plant cell growth and morphogenesis. In multicellular organisms, they permit the organism to hold a definite shape. Cell walls limit the entry of large molecules that may be toxic to the cell, they further permit the creation of stable osmotic environments by preventing osmotic lysis and helping to retain water. Their composition and form may change during the cell cycle and depend on growth conditions. In most cells, the cell wall is flexible, meaning that it will bend rather than holding a fixed shape, but has considerable tensile strength; the apparent rigidity of primary plant tissues is enabled by cell walls, but is not due to the walls' stiffness.

Hydraulic turgor pressure creates this rigidity, along with the wall structure. The flexibility of the cell walls is seen when plants wilt, so that the stems and leaves begin to droop, or in seaweeds that bend in water currents; as John Howland explains Think of the cell wall as a wicker basket in which a balloon has been inflated so that it exerts pressure from the inside. Such a basket is rigid and resistant to mechanical damage, thus does the prokaryote cell gain strength from a flexible plasma membrane pressing against a rigid cell wall. The apparent rigidity of the cell wall thus results from inflation of the cell contained within; this inflation is a result of the passive uptake of water. In plants, a secondary cell wall is a thicker additional layer of cellulose which increases wall rigidity. Additional layers may be formed by suberin in cork cell walls; these compounds are rigid and waterproof. Both wood and bark cells of trees have secondary walls. Other parts of plants such as the leaf stalk may acquire similar reinforcement to resist the strain of physical forces.

The primary cell wall of most plant cells is permeable to small molecules including small proteins, with size exclusion estimated to be 30-60 kDa. The pH is an important factor governing the transport of molecules through cell walls. Cell walls evolved independently in many groups; the photosynthetic eukaryotes is one group with cellulose cell walls, where the cell wall is related to the evolution of multicellularity, terrestrialization and vascularization. The CesA cellulose synthase evolved in Cyanobacteria and was part of Archaeplastida since endosymbiosis. Plants evolved various genes from CesA, including the Csl family of proteins and additional Ces proteins. Combined with the various glycosyltransferases, they enable more complex chemical structures to be built. Fungi use a chitin-glucan-protein cell wall, they share the 1,3-β-glucan synthesis pathway with plants, using homologous GT48 family 1,3-Beta-glucan synthases to perform the task, suggesting that such an e

Table Tennis Victoria

Table Tennis Victoria is the State Sporting Organisation for the Sport of Table Tennis in Victoria. TTV was formed in 1925, it is affiliated with TTA, the ITTF and the OTTF. TTV has over 3,000 registered members. Members have represented Australia in Olympic Games, Commonwealth Games, World Championships, the World Cup and numerous other international competitions. At the 2000 Sydney Olympic Games Victoria's Miao Miao earned fifth place and took Silver at the 2002 Manchester Commonwealth Games. While at the 2002 Manchester Commonwealth Games Jian Fang Lay captured two Silver and one Bronze medal for Australia. Jiang Fang Lay combined with Miao Miao to win a Silver medal in the women's doubles and a Bronze medal in the women's teams event at the 2014 Commonwealth Games. Women: Jian Fang Lay Stephanie Sang Men: David Zalcberg Simon Gerada TTV sanctions multiple tournaments around Victoria throughout the year. There are Senior Tournaments and Veteran Tournaments. Division Events are restricted by Player Rating points TTV Super League Table Tennis Victoria Website

Francisco's Fight

Francisco's Fight is the name given to an alleged skirmish between a detachment of Tarleton's Raiders and Peter Francisco, a Continental Army soldier with a long service record, during the American Revolutionary War in July 1781. The skirmish, only known to be documented by Francisco, resulted in the death of at least one man and the wounding of several others. Historical accounts of the skirmish embellished the story with details not present in the documentary record. In early July 1781, General Charles Cornwallis, in command of British troops in Virginia, arrived at Portsmouth and prepared to embark some of the troops on transports. While en route to Portsmouth, he dispatched Banastre Tarleton and some of his British Legion on a raiding expedition into central Virginia. Moving Tarleton and his men left Suffolk on July 9, rode deep into the foothills of the Blue Ridge Mountains; the complete expedition ended up being a 400 miles trek that succeeded in raiding some military stores, although most of the targeted supplies had been sent off to Nathanael Greene's Continental Army in South Carolina.

Peter Francisco was a private. He was a striking figure, reported to be about six feet six inches and over 260 pounds, was known for his strength. In the northern campaigns, he was in the battles at Brandywine and Monmouth Court House, was the second man in the fortifications during the Battle of Stony Point, he served in the southern army under General Greene, where he was reported to have killed 11 men during the May 1781 Battle of Guilford Courthouse. He was injured in that battle, had returned to his home in Buckingham, Virginia to recuperate; the only documented primary sources for this action originate with Peter Francisco himself. One source is Francisco's 1829 application to the United States Congress for financial support, his request was rejected on the grounds that he was receiving a military pension. The other is a similar letter addressed to the Virginia State Assembly in 1820; the two accounts differ in some details, but much of the narrative is the same. No other sources are known to corroborate the events.

In the 1820 account Francisco describes how, while passing through Amelia County, Virginia on his way home, he encountered a band of dragoons from Tarleton's regimental cavalry at Benjamin Ward's tavern. One of the dragoons demanded that he give up his silver shoe buckles, he refused. As the dragoon bent down to take his buckles, unarmed, reached down and drew the man's sword from its scabbard, he used the sword to kill the man. According to the Virginia letter, he "wounded and drove off the others", taking eight of the nine horses. In the 1829 letter to Congress, he claims to have killed two more men and "frightened off the rest of the party, amounting in number to six." One of the most published accounts of Francisco's fight was that of Virginia historian Henry Howe, first published by him in 1845, appearing in an 1844 compendium of Revolutionary War anecdotes by John Lauris Blake. The version reprinted below contains details not present in Francisco's own written accounts, including the presence nearby of Tarleton's main body, an allegation of the tavernkeeper's assistance to the raiders.

Some of its details are visible in the 1814 engraving depicted above. While the British army were spreading havoc and desolation all around them, by their plundering and burnings in Virginia, in 1781, Francisco had been reconnoitring, while stopping at the house of a Mr. V--- in Amelia, now Nottoway county, nine of Tarleton's cavalry came up, with three negroes, told him he was their prisoner. Seeing he was overpowered by numbers, he made no resistance. Believing him to be peaceable, they all went into the house, leaving him and the paymaster together.'Give up all that you possess of value,' said the latter,'or prepare to die."I have nothing to give up,' said Francisco,'so use your pleasure."Deliver instantly,' rejoined the soldier,'those massy silver buckles which you wear in your shoes."They were a present from a valued friend,' replied Francisco,'and it would grieve me to part with them. Give them into your hands I never will. You have the power; the soldier put his sabre under his arm, bent down to take them.

Francisco, finding so favorable an opportunity to recover his liberty, stepped one pace in his rear, drew the sword with force from under his arm, gave him a blow across the scull.'My enemy,' observed Francisco,'was brave, though wounded, drew a pistol, and, in the same moment that he pulled the trigger, I cut his hand nearly off. The bullet grazed my side. Ben V---. Very ungenerously brought out a musket, gave it to one of the British soldiers, told him to make use of that, he mounted the only horse they could get, presented it at my breast. It missed fire. I rushed on the muzzle of the gun. A short struggle ensued. I wounded him. Tarleton's troop of four hundred men were in sight. All was hurry and confusion, which I increased by hallooing, as loud as I could, "Come on, my brave boys; the wounded man flew to the troop. I se