在2014年6月15日的托福閱讀考試中有這樣一道題：雨林中動(dòng)物傳遞信息的方式。針對這道托?？碱}，出國留學(xué)網(wǎng)(www.liuxue86.com)小編來為大家普及一下關(guān)于生命起源的背景知識，這樣有助于考生在面對這類題目時(shí)方便作答。小編在此提醒大家：本文屬于生命起源類型，是托福閱讀資歷很老的話題之一，同學(xué)在閱讀中的難點(diǎn)是要克服對生僻詞匯和背景知識的恐懼心理。
托福真題再現(xiàn)：
版本一
1，地球早起大氣成分及生物 早起甲烷與二氧化碳占主要地位，沒有氧氣。因?yàn)橛辛藭?huì)光合作用的細(xì)菌，產(chǎn)生了大量氧氣，消耗二氧化碳，提供臭氧層，為當(dāng)今新生物鐘提供必要環(huán)境。
版本二
有一個(gè)講地球最早怎么產(chǎn)生生物的
大概有幾點(diǎn)，首先是太陽當(dāng)時(shí)不夠熱，地球當(dāng)時(shí)氣體組成像火山的，主要靠兩種氣體加溫度，似乎一種是二氧化碳另一種是m開頭的不認(rèn)識
那種氣體組成不適合生命也沒什么氧，當(dāng)時(shí)的organism有很大作用，進(jìn)行光合作用產(chǎn)生氧氣吸收二氧化碳，二氧化碳還有一部分被轉(zhuǎn)移成非氣態(tài)的，這樣就形成了后來的大氣組成
氧氣可以形成臭氧層，保護(hù)生物不受紫外線輻射，這塊提到了火星等其他星球就沒有臭氧層或者臭氧不夠多blabla不記得了，反正當(dāng)時(shí)生物都去海里了因?yàn)樗梢晕兆贤饩€輻射保護(hù)它們
解析：本文屬于生命起源類型，是托福閱讀資歷很老的話題之一，寫作角度涉及到巴斯德實(shí)驗(yàn)、生命起源的幾種假說，以及過程的描述，同學(xué)在閱讀中的難點(diǎn)是要克服對生僻詞匯和背景知識的恐懼心理，這些都可以通過多讀和精讀來實(shí)現(xiàn)。
參考閱讀：
There is no truly "standard" model of the origin of life. But most currently accepted models build in one way or another upon a number of discoveries about the origin of molecular and cellular components for life, which are listed in a rough order of postulated emergence:
1. Plausible pre-biotic conditions result in the creation of certain basic small molecules (monomers) of life, such as amino acids. This was demonstrated in the Miller-Urey experiment by Stanley L. Miller and Harold C. Urey in 1953, although it is now generally held that their laboratory conditions did not reflect the original Earth's atmosphere.
2. Phospholipids (of an appropriate length) can spontaneously form lipid bilayers, a basic component of the cell membrane.
3. The polymerization of nucleotides into random RNA molecules might have resulted in self-replicating ribozymes (RNA world hypothesis).
4. Selection pressures for catalytic efficiency and diversity result in ribozymes, which catalyse peptidyl transfer (hence formation of small proteins), since oligopeptides complex with RNA to form better catalysts. Thus the first ribosome is born, and protein synthesis becomes more prevalent.
5. Protein out-compete ribozymes in catalytic ability, and therefore become the dominant biopolymer. Nucleic acids are restricted to predominantly genomic use.
There are many different hypotheses regarding the path that might have been taken from simple organic molecules to protocells and metabolism. Many models fall into the "genes-first" category or the "metabolism-first" category, but a recent trend is the emergence of hybrid models.
The origin of the basic biomolecules, while not settled, is less controversial than the significance and order of steps 2 and 3. The basic chemicals from which life was thought to have formed are commonly held to be methane (CH4), ammonia (NH3), water (H2O), hydrogen sulfide (H2S), carbon dioxide (CO2) or carbon monoxide (CO), and phosphate (PO43-). Molecular oxygen (O2) and ozone (O3) typically are considered to have been either rare or absent.
As of 2007, no one had yet synthesized a "protocell" using basic components that would have the necessary properties of life (the so-called "bottom-up-approach"). Without such a proof-of-principle, explanations have tended to be short on specifics. However, some researchers working in this field have argued that a "top-down approach" is more feasible. One such approach involves engineering existing prokaryotic cells with progressively fewer genes, attempting to discern at which point the most minimal requirements for life were reached. The biologist John Desmond Bernal coined the term biopoesis for this process, and suggested that there were a number of clearly defined "stages" that could be recognized in explaining the origin of life.
Stage 1: The origin of biological monomers
Stage 2: The origin of biological polymers
Stage 3: The evolution from molecules to cell
Bernal suggested that Darwinian evolution may have commenced early, some time between Stage 1 and 2.
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