【正文】 界的有機(jī)物才能被分解，才不會(huì)到處是生物遺體，才有了食物鏈（即有機(jī)物在自然界的不斷循環(huán)）。細(xì)菌將永遠(yuǎn)生活在我們身邊。有些種類和藻類共生 ,形成地衣 。 真菌與細(xì)菌的主要區(qū)別在于 :真菌是真核生物 ,而細(xì)菌是原核生物。真菌細(xì)胞內(nèi)有線粒體 ,高爾基復(fù)合體 ,內(nèi)質(zhì)網(wǎng)等細(xì)胞器 ,而細(xì)菌沒有。真菌與植物的主要區(qū)別在 于 :真菌貯藏的養(yǎng)料是肝糖 ,而綠色植物主要是淀粉。酵母可以用于制作面食和釀酒 (酵母在無氧的環(huán)境下可以把葡萄糖轉(zhuǎn)變?yōu)榫凭?,而面粉中或多或少都有一些葡萄糖 ,所以放久了的面團(tuán)會(huì)有酒味 ),曲霉也可以用于釀造業(yè) 。但總的來說 ,真菌對 人類還是大有益處的。但是它們的起源不詳。它的大小用納米（ nm )表示。我們衡 量一個(gè)原子的直徑用埃來表示。由此可見病毒是多么微小。二級(jí)分類：動(dòng)物病毒；植物病毒；細(xì)菌病毒。大多數(shù)病毒是由核酸和蛋白質(zhì)組成的。病毒的蛋白質(zhì)外殼 衣殼組成成分較復(fù)雜，上面有各種不 同類（如圖 :HIV 病毒 艾滋病病毒）型的受體，多糖等。它不能單獨(dú)進(jìn)行繁殖，必須在活細(xì)胞內(nèi)才能繁殖。概括起來分為：吸附，侵入，脫殼，生物合成，裝配與釋放等 5個(gè)步驟。 侵入和脫殼：病毒粒子被宿主細(xì)胞通過吞噬作用給“吞進(jìn)”了細(xì)胞。但有些 種類的病毒只是把它的核酸送入細(xì)胞，而把衣殼留在細(xì)胞外面。當(dāng)?shù)竭_(dá)一定的數(shù)量以后，會(huì)組成新的病毒粒子。有的是使宿主細(xì)胞破裂死亡，使病毒粒子釋放出來；有的以出芽的方式從細(xì)胞上“長”出來，比如流感病毒 病毒的用處：病毒雖然可以使人得病，但它們卻大有用處：它們是遺傳學(xué)研究的主要材料；細(xì)菌病毒可以使病原細(xì)菌死亡；昆蟲病毒可以殺死害蟲，而不會(huì)對環(huán)境造成破壞，害蟲也不容易產(chǎn)生抗藥性 . 托福聽力背 景知識(shí) (九 ) Dust Bowl Dust Bowl, mon name applied to a large area in the southern part of the Great Plains region of the United States, much of which suffered extensively from wind erosion during the 1930s. The area included parts of Kansas, Oklahoma, Texas, New Mexico, and Colorado. In its original state, the region was covered with hardy grasses that held the finegrained soil in place in spite of the long recurrent droughts and occasional torrential rains characteristic of the area. A large number of homesteaders settled in the region in the 30 years before World War I, planting wheat and row crops and raising cattle. Both of these land uses left the soil exposed to the danger of erosion by the winds that constantly sweep over the gently rolling land. Beginning in the early 1930s, the region suffered a period of severe droughts, and the soil began to blow away. The anic matter, clay, and silt in the soil were carried great distances by the winds, in some cases darkening the sky as far as the Atlantic coast, and sand and heavier materials drifted against houses, fences, and barns. In many places 8 to 10 cm (3 to 4 in) of topsoil were blown away. Many thousands of families, their farms ruined, migrated westward。 3year rotation of wheat and shum and of lying fallow。 and, in areas of greater rainfall, the planting of long “shelter belts” of trees to break the force of the wind. Dry spells in the 1950s, 39。70s were responsible for recurrences of dust storms in the region. 補(bǔ)充：由于 dust bowl 導(dǎo)致的洛杉磯地區(qū)的移民增加 In the 1930s and 1940s, the region also received two waves of major migrations: that of farm families from the southern Great Plains migrating west to escape the Dust Bowl, and that of African Americans moving out of the American South. During World War II (19391945) the need for labor, especially in ship and aircraft production, boosted the population even more. The population of Los Angeles County jumped from 3 million to million between 1940 and 1950. 托福聽力背景知識(shí) (十 ) 天上掉鉆石 Is It Raining Diamonds On Uranus？ Berkeley October 1, 1999 If experiments at the University of California, Berkeley, are any indication, future explorers of our solar system may well find diamonds hailing down through the atmospheres of Neptune and Uranus. These plas contain a high proportion of methane, which UC Berkeley researchers have now shown can turn into diamond at the high temperatures and pressures found inside these plas. Once these diamonds form, they fall like raindrops or hailstones toward the center of the pla, said Laura Robin Benedetti, a graduate student in physics at UC Berkeley. The team, led by Benedetti and Raymond Jeanloz, professor of geology and geophysics, produced these conditions inside a diamond anvil cell, squeezing liquid methane to several hundred thousand times atmospheric pressure. When they focused a laser beam on the pressurized liquid, heating it to some 5,000 degrees Fahrenheit, diamond dust appeared. They report their experimental findings in a paper in the Oct. 1 issue of Science. The demonstration that methane can convert to diamond as well as other plex hydrocarbons in the interiors of giant plas like Neptune hint at a plex chemistry inside gaseous plas and even brown dwarf stars. Brown dwarfs are small, dim stars barely larger than the largest gas giant plas. This is opening the door to study of the interesting types of chemical reactions taking place inside plas and brown dwarfs, Jeanloz said. Now that technology is able to reproduce the high pressures and temperatures found there, we are getting much better quality information on the chemical reactions taking place under these conditions. It is not amazing that chemistry like this happens inside plas, it39。t dealt with the chemical reactions that can occur, Benedetti said. The interior of these plas may be much more plicated that our current picture. A simple calculation, for example, shows that the energy released by diamonds settling to the pla39。s exciting to us is the application of this highpressure chemistry to understanding the outer plas, Jeanloz said. As more plas are found in unexpected orbits around other stars, the effects of internal chemical processes will need to be further clarified in order to obtain a general understanding of pla formation and evolution, the authors concluded in the Science paper. Our solar system39。s really cool to watch, said Benedetti. When you turn on the laser the methane turns black because of all the diamonds created. The black diamond specks float in a clear hydrocarbon liquid melted by the laser. Raman spectroscopy confirmed the identity of the suspended specks, as did subsequent analysis with Xray crystallography. The flecks were diamonds interspersed with hydrocarbons. Jeanloz said that the high temperature breaks up methane (CH4) into carbon and hydrogen, while high pressure condenses the carbon to diamond. Other types of hydrocarbons doubly and tr