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TMS (tetramethylsilane) is commonly added to nuclear magnetic resonance (NMR) samples. It has a chemicalshift which is upfield of most organic signals, and it gives a strong, sharp singlet peak and can be easilyremoved. Why is TMS added to NMR samples?Section: Physical Sciences 

Several techniques have been developed to determine the order of a reaction. The rate of a reaction cannot bepredicted on the basis of the overall equation, but can be predicted on the basis of the rate-determining step.For instance, the following reaction can be broken down into three steps.A + D → F + GStep 1A → B + C(slow)Step 2B + D → E + F(fast)Step 3E + C → G(fast)Reaction 1In this case, the first step in the reaction pathway is the rate-determining step. Therefore, the overall rate of thereaction must equal the rate of the first step, k1 [A] where k1 is the rate constant for the first step. (Rateconstants of the different steps are denoted by kx, where x is the step number.)In some cases, it is desirable to measure the rate of a reaction in relation to only one species. In a secondorder reaction, for instance, a large excess of one species is included in the reaction vessel. Since a relativelysmall amount of this large concentration is reacted, we assume that the concentration essentially remainsunchanged. Such a reaction is called a pseudo first-order reaction. A new rate constant, k', is established, equalto the product of the rate constant of the original reaction, k, and the concentration of the species in excess.This approach is often used to analyze enzyme activity.In some cases, the reaction rate may be dependent on the concentration of a short-lived intermediate. This canhappen if the rate-determining step is not the first step. In this case, the concentration of the intermediate mustbe derived from the equilibrium constant of the preceding step. For redox reactions, the equilibrium can becorrelated with the voltage produced by two half-cells by means of the Nernst equation. This equation statesthat at any given moment:Equation 1Whena A + b B → c C + d DReaction 2Note: R = 8.314 J/K·mol; F = 9.6485 × 104 C/mol.)Catalysts are effective in increasing the rate of a reaction because they:Section: Physical Sciences

The sexual reproduction in Rhizopus isSection: Biological Sciences 

The Russia which emerged from the terrible civil war after the 1917 Revolution was far from the Bolsheviks’original ideal of a non-exploitative society governed by workers and peasants. By 1921, the regime wasweakened by widespread famine, persistent peasant revolts, a collapse of industrial production stemming fromthe civil war, and the consequent dispersal of the industrial working class – the Bolsheviks’ original base ofsupport. To buy time for recovery, the government in 1921 introduced the New Economic Policy, which allowedprivate trade in farm products (previously banned) and relied on a fixed grain tax instead of forced requisitionsto provide food for the cities. The value of the ruble was stabilized. Trade unions were again allowed to seekhigher wages and benefits, and even to strike. However, the Bolsheviks maintained a strict monopoly of powerby refusing to legalize other parties.After the death of the Revolution’s undisputed leader, Lenin, in January 1924, disputes over the long-rangedirection of policy led to an open struggle among the main Bolshevik leaders. Since open debate was stillpossible within the Bolshevik Party in this period, several groups with differing programs emerged in the courseof this struggle.The program supported by Nikolai Bukharin – a major ideological leader of the Bolsheviks with no power baseof his own – called for developing agriculture through good relations with wealthy peasants, or “kulaks.”Bukharin favored gradual industrial development, or “advancing towards Socialism at a snail’s pace.” In foreignaffairs, Bukharin’s policy was to ally with non-Socialist regimes and movements that were favorable to Russia.A faction led by Leon Trotsky, head of the Red Army and the most respected revolutionary leader after Lenin,called for rapid industrialization and greater central planning of the economy, financed by a heavy tax on thekulaks. Trotsky rejected the idea that a prosperous, human Socialist society could be built in Russia alone(Stalin’s slogan of “Socialism in One Country”), and therefore called for continued efforts to promote workingclass revolutions abroad. As time went on, he became bitterly critical of the new privileged elite emerging withinboth the Bolshevik Party and the Russian state.Joseph Stalin, General Secretary of the Bolshevik Party, was initially considered a “center,” conciliating figure,not clearly part of a faction. Stalin’s eventual supremacy was ensured by three successive struggles within theparty, and only during the last did his own program become clear.First, in 1924-25, Stalin isolated Trotsky, allying for this purpose with Grigori Zinoviev and Lev Kamenev,Bolshevik leaders better known than Stalin himself, whom Trotsky mistakenly considered his main rivals. Stalinmaneuvered Trotsky out of leadership of the Red Army, his main potential power base. Next, Stalin turned onZinoviev and Kamenev, using his powers as head of the Party organization to remove them from partyleadership in Leningrad and Moscow, their respective power bases. Trotsky, Zinoviev, and Kamenev thenbelatedly formed the “Joint Opposition” (1926-27). With Bukharin’s help, Stalin easily outmaneuvered theOpposition: Bukharin polemicized against Trotsky, while Stalin prevented the newspapers from printingTrotsky’s replies, organized gangs of toughs to beat up his followers, and transferred his supporters toadministrative posts in remote regions. At the end of 1927, Stalin expelled Trotsky from the Bolshevik Party andexiled him. (Later, in 1940, he had him murdered.) Zinoviev and Kamenev, meanwhile, recanted their views inorder to remain within the Party.The final act now began. A move by kulaks to gain higher prices by holding grain off the market touched off acampaign against them by Stalin. Bukharin protested, but with the tradition of Party democracy now all butdead, Stalin had little trouble silencing Bukharin. Meanwhile, he began a campaign to force all peasants – notjust kulaks – onto state-controlled “collective farms,” and initiated a crash industrialization program during whichhe deprived the trade unions of all rights and cut real wages by 50%. Out of the factional struggle in which heemerged by 1933 as sole dictator of Russia, Stalin’s political program of building up heavy industry on thebacks of both worker and peasant emerged with full clarity.The passage supports the idea that struggles within the Bolshevik Party were primarily:Section: Verbal Reasoning 

…From a geological point of view, the Mediterranean is a tectonically mobile land-enclosed depression – small(about 3,000,000 square kilometers) in comparison to the major world oceans…Immediately obvious on allcharts is the highly variable topography and relief of both the seafloor and adjacent borderland. The coastline ishighly irregular and continental shelves, though generally narrow, are well developed off the major river deltas(Nile, Rhone, Po, and Ebro). Moreover, the deep-sea basins and trenches have distinctive relief, with basinplains ranging in depth from less than 1,000 meters to more than 4,000…Observation that rocks dredgedoffshore are similar to those on land raised a fundamental concept – the key to understanding Mediterraneanhistory lies in the adjacent emerged land masses, and vice-versa……Early paleographic reconstructions showed that the once-open communication with the Atlantic deterioratedduring the upper Miocene. Water-mass exchange continued for a while in the Rif Strait, but then ceasedcompletely prior to the beginning of the Pliocene……High relief near what is now the Strait of Gibraltar served as a barrier to the exchange of waters with theAtlantic. Exposed to a hot and dry climate, water evaporated and the then-dry basin elicited comparison with agigantic Death Valley…Microfossil studies suggested that the depth of the Mediterranean basin at these timeshad been “deep.” Estimates suggested a dry seafloor as far as 2,000 meters below ocean level… As aresponse to suddenly lowered sea level, rivers feeding the Mediterranean and canyons on the now-dry seafloorbegan a geologically dramatic phase of erosion. Deep, Grand Canyon-like gorges of the Nile and Rhone rivers,presently buried on land, were apparently cut during a great drawdown of water – when the Mediterranean floorlay exposed 1,000 meters or more below its present level…The sudden flooding through a gigantic waterfall atGibraltar drowned the exposed basin floor. These falls would have been 1,000 times bigger than NiagaraFalls…This flooding event is recorded by the Miocene Pliocene boundary, a time when open marine faunalassemblages were suddenly reintroduced from the Atlantic……Geological theories usually fall at a glacial pace into a sea of controversy, and this one is no exception. Today– charging that proof for the theory is lacking – many scientists believe that the Med always contained saltwater,with only the depth of the seafloor and the water being in question… Some of the tenets on which the theorywas formulated are, if not defective, very seriously in question. To interpret their findings, a respectable numberof geologists studying the surrounding emerged borderland as well as subsea sections indicate that alternative,more comprehensive concepts must be envisioned……It is not realistic to envision the Mediterranean seafloor of about 5 million years ago as a desert at 3,000meters below present ocean level. Several years ago…the Mediterranean [was compared] to a complexpicture-puzzle that comprises numerous intricate pieces, many of which are already in place. A general imageis emerging, although gaps in some areas of the picture remain fuzzy and indistinct.It can be inferred from the passage that geological theories tend to:Section: Verbal Reasoning