Antony van Leeuwenhoek essays

Antony van Leeuwenhoek essays The biologist I chose to report on is Antony van Leeuwenhoek. I chose to report on him because he made many great microscopic discoveries. Those discoveries include bacteria, free-living and parasitic microscopic protist, sperm cells, blood cells, and many Leeuwenhoek was born on October 24, 1632, in Delft. His mothers family were brewers and his father was a basket-maker. Antony was taught at Warmond and lived with his uncle in Benthuizen. He got his first job in a linen-drapers shop, in 1648. In 1654, he moved back to Delft, where he lived the rest of his life. He set up a drapery business for a while, but also worked as a surveyor, wine assayer, and a minor city official. In 1676, he was the trustee of a famous painter named Jan Vermeer. In 1668, Leeuwenhoek learned to grind lens and used them to make simple microscopes. Robert Hooke was his inspiration to use microscopes. Ten out of five hundred of Leeuwenhoeks scopes have survived up until today. His microscopes were basically a strong magnifying glass and not compound like the ones used today. Leeuwenhoeks scopes were composed of only one lens, mounted in a tiny hole, in the brass plate. The brass plate served as the base, also. Whatever was being viewed was placed on a sharp point, which was in front of the lens. To focus the object, two screws were turned. The entire scope was 3-4 inches long, and very difficult to use. Leeuwenhoek is often called, The inventor of the microscope, when in truth the compound microscope was invented many years The old compound microscope were not very good for viewing because they could only enlarge 20-30 times the original size. Leeuwenhoeks scopes however could magnify up to 200 times and more clearly then any other scopes at the time. Because Leeuwenhoeks scopes could magnify so well and clear many of his ...

Introduction to Monomers and Polymers in Chemistry

Introduction to Monomers and Polymers in Chemistry A monomer is a type of molecule that has the ability to chemically bond with other molecules in a long chain; a polymer is a chain of an unspecified number of monomers. Essentially, monomers are the building blocks of polymers, which are more complex type of molecules. Monomers- repeating molecular units- are connected into polymers by covalent bonds. Monomers The word monomer comes from mono- (one) and -mer (part). Monomers are small molecules which may be joined together in a repeating fashion to form more complex molecules called polymers. Monomers form polymers by forming chemical bonds or binding supramolecularly through a process called polymerization. Sometimes polymers are made from bound groups of monomer subunits (up to a few dozen monomers) called oligomers. To qualify as an oligomer, the properties of the molecule need to change significantly if one or a few subunits are added or removed. Examples of oligomers include collagen and liquid paraffin. A related term is monomeric protein, which is a protein that bonds to make a multiprotein complex. Monomers are not just building blocks of polymers, but are important molecules in their own right, which do not necessarily form polymers unless the conditions are right. Examples of Monomers Examples of monomers include vinyl chloride (which polymerizes into polyvinyl chloride or PVC), glucose (which polymerizes into starch, cellulose, laminarin, and glucans), and amino acids (which polymerize into peptides, polypeptides, and proteins). Glucose is the most abundant natural monomer, which polymerizes by forming glycosidic bonds. Polymers The word polymer comes from poly- (many) and -mer (part). A polymer may be a natural or synthetic macromolecule comprised of repeating units of a smaller molecule (monomers). While many people use the term polymer and plastic interchangeably, polymers are a much larger class of molecules which includes plastics, plus many other materials, such as cellulose, amber, and natural rubber. Lower molecular weight compounds may be distinguished by the number of monomeric subunits they contain. The terms dimer, trimer, tetramer, pentamer, hexamer, heptamer, octamer, nonamer, decamer, dodecamer, eicosamer reflects molecules containing 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, and 20 monomer units. Examples of Polymers Examples of polymers include plastics such as polyethylene, silicones such as silly putty, biopolymers such as cellulose and DNA, natural polymers such as rubber and shellac, and many other important macromolecules. Groups of Monomers and Polymers The classes of biological molecules may be grouped into the types of polymers they form and the monomers that act as subunits: Lipids - polymers called diglycerides, triglycerides; monomers are glycerol and fatty acidsProteins - polymers are known as polypeptides; monomers are amino acidsNucleic Acids - polymers are DNA and RNA; monomers are nucleotides, which are in turn consist of a nitrogenous base, pentose sugar, and phosphate groupCarbohydrates - polymers are polysaccharides and disaccharides*; monomers are monosaccharides (simple sugars) *Technically, diglycerides, and triglycerides are not true polymers because they form via dehydration synthesis of smaller molecules, not from the end-to-end linkage of monomers that characterizes true polymerization. How Polymers Form Polymerization is the process of covalently bonding the smaller monomers into the polymer. During polymerization, chemical groups are lost from the monomers so that they may join together. In the case of biopolymers of carbohydrates, this is a dehydration reaction in which water is formed. Resources and Further Reading Cowie, J.M.G. and Valeria Arrighi. Polymers: Chemistry and Physics of Modern Materials, 3rd ed. Boca Taton: CRC Press, 2007.  Sperling, Leslie H. Introduction to Physical Polymer Science, 4th ed. Hoboken, NJ: John Wiley Sons, 2006.  Ã‚  Young, Robert J., and Peter A. Lovell. Introduction to Polymers, 3rd ed. Boca Raton, LA: CRC Press, Taylor Francis Group, 2011.

The Realistic Theory of International Relations Research Paper

The Realistic Theory of International Relations - Research Paper Example Two options are available to the players in such a scenario. To gain power and to survive, countries can attack and capture other areas ruthlessly as Napoleon and Hitler did. The other option is to see that a balance of power is maintained. This can be done by diplomatic relations, alliances or by force. Bilateral trade agreements, aid to other countries are examples of diplomatic relations. NATO and the European Union are examples of alliances. There was a time when the US and the USSR were the two balancing powers of the world. The US attacked and also supplied arms to Vietnam fearing that the spread of communism in the country and other places may shift the balance of power in favour of the USSR. It would be effective to define realism at this point. A Cambridge University Press publication defines realism in three steps. An instance where this theory does not hold good or becomes ineffective is the case of terrorism. Terrorism is practically invisible even if countries who abet t errorists are identified. The terrorists do not come to the negotiating table nor do they work in visible organized structures. If the opponent is not available for negotiations or to fight with, it is not possible to think of survival or strength. A country may be hit by a terrorist attack at any time. Security becomes practically ineffective if suicide attacks are resorted to by the terrorists. Even a strong nation like the US can be shocked by attacks such as the September 11 suicide attacks on the Twin Towers. But there is practically nothing that can be effectively done by any country in such a situation. The US attacked Iraq and set up a new administration.