托福阅读之生命起源

 　　针对托福考试中出现过不少关于生命起源的话题，小编为大家带来关于生命起源的托福阅读材料。

　　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 molecular¹ and cellular² components⁴ for life, which are listed in a rough order of postulated⁵ emergence⁶:

　　1. Plausible⁷ pre-biotic conditions result in the creation of certain basic small molecules⁸ (monomers) of life, such as amino acids. This was demonstrated in the Miller⁹-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 component³ of the cell membrane¹⁰.

　　3. The polymerization of nucleotides into random¹¹ 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 catalysts¹². Thus the first ribosome is born, and protein synthesis becomes more prevalent.

　　5. Protein out-compete ribozymes in catalytic ability, and therefore become the dominant¹³ 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 metabolism¹⁴. Many models fall into the "genes¹⁵-first" category or the "metabolism-first" category, but a recent trend is the emergence of hybrid¹⁶ 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 methane¹⁷ (CH4), ammonia (NH3), water (H2O), hydrogen sulfide (H2S), carbon dioxide (CO2) or carbon monoxide (CO), and phosphate (PO43-). Molecular oxygen (O2) and ozone¹⁸ (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 minimal¹⁹ 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.

　　本文中中难点词汇解析：

　　molecular ：adj. [化学] 分子的;由分子组成的

　　例句：You do not get this line from molecular hydrogen.

　　从氢分子中我们得不到这种光线。

　　demonstrated ：演示、展现

　　例句：Have they, for example, demonstrated a commitment to democracy?

　　例如，他们展现了对民主的奉献吗?

　　Phospholipids：n. 磷脂质

　　例句：What drove the transition from such membranes²⁰ to modern ones, which are based on the more complex phospholipids?

　　这种的简单膜结构转变成现代的基于磷脂的版本是由什么驱使的?

　　oligopeptides：n. [生化] 寡肽(oligopeptide的复数);寡生肽

　　例句：This paper reports preparation process of high Fischer ratio oligopeptides from corn gluten meal ( CGM ) by subtilisin and carboxypeptidase from Aspergillus oryzae in brief.

　　本文简述了酶法水解玉米醇溶蛋白制备高F值寡肽的主要工艺步骤。

　　predominantly：adv. 主要地; 显著地

　　例句：So, those are the reasons predominantly why people cannot get out themselves.

　　这就是人们为什么无法从利比亚撤出的主要原因。

　　progressively ：adv. 渐进地; 日益增多地

　　例句：Remember to take it easy, and your skill will progressively grow.

　　请记住，这些需要慢慢来，你的技能将逐步增长。

1 molecular   

adj.分子的；克分子的

参考例句：

• The research will provide direct insight into molecular mechanisms.这项研究将使人能够直接地了解分子的机理。
• For the pressure to become zero, molecular bombardment must cease.当压强趋近于零时，分子的碰撞就停止了。

2 cellular   

adj.移动的；细胞的，由细胞组成的

参考例句：

• She has a cellular telephone in her car.她的汽车里有一部无线通讯电话机。
• Many people use cellular materials as sensitive elements in hygrometers.很多人用蜂窝状的材料作为测量温度的传感元件。

3 component   

n.组成部分，成分，元件；adj.组成的，合成的

参考例句：

• Each component is carefully checked before assembly.每个零件在装配前都经过仔细检查。
• Blade and handle are the component parts of a knife.刀身和刀柄是一把刀的组成部分。

4 components   

（机器、设备等的）构成要素，零件，成分； 成分( component的名词复数 )； [物理化学]组分； [数学]分量； （混合物的）组成部分

参考例句：

• the components of a machine 机器部件
• Our chemistry teacher often reduces a compound to its components in lab. 在实验室中化学老师常把化合物分解为各种成分。

5 postulated   

v.假定，假设( postulate的过去式和过去分词 )

参考例句：

• They postulated a 500-year lifespan for a plastic container. 他们假定塑料容器的寿命为500年。
• Freud postulated that we all have a death instinct as well as a life instinct. 弗洛伊德曾假定我们所有人都有生存本能和死亡本能。 来自辞典例句

6 emergence   

n.浮现，显现，出现，（植物）突出体

参考例句：

• The last decade saw the emergence of a dynamic economy.最近10年见证了经济增长的姿态。
• Language emerges and develops with the emergence and development of society.语言是随着社会的产生而产生，随着社会的发展而发展的。

7 plausible   

adj.似真实的，似乎有理的，似乎可信的

参考例句：

• His story sounded plausible.他说的那番话似乎是真实的。
• Her story sounded perfectly plausible.她的说辞听起来言之有理。

8 molecules   

分子( molecule的名词复数 )

参考例句：

• The structure of molecules can be seen under an electron microscope. 分子的结构可在电子显微镜下观察到。
• Inside the reactor the large molecules are cracked into smaller molecules. 在反应堆里，大分子裂变为小分子。

9 miller   

n.磨坊主

参考例句：

• Every miller draws water to his own mill.磨坊主都往自己磨里注水。
• The skilful miller killed millions of lions with his ski.技术娴熟的磨坊主用雪橇杀死了上百万头狮子。

10 membrane   

n.薄膜，膜皮，羊皮纸

参考例句：

• A vibrating membrane in the ear helps to convey sounds to the brain.耳膜的振动帮助声音传送到大脑。
• A plastic membrane serves as selective diffusion barrier.一层塑料薄膜起着选择性渗透屏障的作用。

11 random   

adj.随机的；任意的；n.偶然的(或随便的)行动

参考例句：

• The list is arranged in a random order.名单排列不分先后。
• On random inspection the meat was found to be bad.经抽查，发现肉变质了。

12 catalysts   

n.催化剂( catalyst的名词复数 )；触媒；促进因素；有感染力的人

参考例句：

• The first catalytic converters were called conventional oxidation catalysts. 最初的转化器叫做常规氧化催化器。 来自辞典例句
• Many processes that are essential to the chemical industry use heterogeneous catalysts. 很多重要的化学工业过程就是使用多相催化剂的。 来自辞典例句

13 dominant   

adj.支配的，统治的；占优势的；显性的；n.主因，要素，主要的人(或物)；显性基因

参考例句：

• The British were formerly dominant in India.英国人从前统治印度。
• She was a dominant figure in the French film industry.她在法国电影界是个举足轻重的人物。

14 metabolism   

n.新陈代谢

参考例句：

• After years of dieting,Carol's metabolism was completely out of whack.经过数年的节食，卡罗尔的新陈代谢完全紊乱了。
• All living matter undergoes a process of metabolism.生物都有新陈代谢。

15 genes   

n.基因( gene的名词复数 )

参考例句：

• You have good genes from your parents, so you should live a long time. 你从父母那儿获得优良的基因，所以能够活得很长。 来自《简明英汉词典》
• Differences will help to reveal the functions of the genes. 它们间的差异将会帮助我们揭开基因多种功能。 来自英汉非文学 - 生命科学 - 生物技术的世纪

16 hybrid   

n.(动，植）杂种，混合物

参考例句：

• That is a hybrid perpetual rose.那是一株杂交的四季开花的蔷薇。
• The hybrid was tall,handsome,and intelligent.那混血儿高大、英俊、又聪明。

17 methane   

n.甲烷，沼气

参考例句：

• The blast was caused by pockets of methane gas that ignited.爆炸是由数袋甲烷气体着火引起的。
• Methane may have extraterrestrial significance.甲烷具有星际意义。

18 ozone   

n.臭氧，新鲜空气

参考例句：

• The ozone layer is a protective layer around the planet Earth.臭氧层是地球的保护层。
• The capacity of ozone can adjust according of requirement.臭氧的产量可根据需要或调节。

19 minimal   

adj.尽可能少的，最小的

参考例句：

• They referred to this kind of art as minimal art.他们把这种艺术叫微型艺术。
• I stayed with friends, so my expenses were minimal.我住在朋友家，所以我的花费很小。

20 membranes   

n.（动物或植物体内的）薄膜( membrane的名词复数 )；隔膜；（可起防水、防风等作用的）膜状物

参考例句：

• The waste material is placed in cells with permeable membranes. 废液置于有渗透膜的槽中。 来自辞典例句
• The sarcoplasmic reticulum is a system of intracellular membranes. 肌浆网属于细胞内膜系统。 来自辞典例句