Chemistry and Biology

About a century ago, the Swedish physical scientist Arrhenius proposed a low of classical chemistry that relates chemical reaction rate to temperature. According to his equation, chemical reactions are increasingly unlikely to occur as temperature approaches absolute zero, and at absolute zero, reactions stop. However, recent experiment evidence reveals that although the Arrhenius equation is generally accurate in describing the kind of chemical reaction that occurs at relatively high temperature, at temperatures closer to zero a quantum-mechanical effect known as tunneling comes into play; this effect accounts for chemical reactions that are forbidden by the principles of classical chemistry. Specifically, entire molecules can tunnel through the barriers of repulsive forces from other molecules and chemically react even though these molecules do not have sufficient energy, according to classical chemistry, to overcome the repulsive barrier.

The rate of any chemical reaction, regardless of the temperature at which it takes place, usually depends on a very important characteristic known as its activation energy. Any molecule can be imagined to reside at the bottom of a so-called potential well of energy. S chemical reaction corresponds to the transition of a molecule from the bottom of one potential well to the bottom of another. In classical chemistry, such a transition can be accomplished only by going over the potential barrier between the well, the height of which remain constant and is called the activation energy of the reaction. In tunneling, the reacting molecules tunnel from the bottom of one to the bottom of another well without having to rise over the barrier between the two wells. Recently researchers have developed the concept of tunneling temperature: the temperature below which tunneling transitions greatly outnumber Arrhenius transitions, and classical mechanics gives way to its quantum counterpart.

This tunneling phenomenon at very low temperatures suggested my hypothesis about a cold prehistory of life: formation of rather complex organic molecules in the deep cold of outer space, where temperatures usually reach only a few degrees Kelvin. Cosmic rays might trigger the synthesis of simple molecules, such as interstellar formaldehyde, in dark clouds of interstellar dust. Afterward complex organic molecules would be formed, slowly but surely, by means of tunneling. After I offered my hupothesis, Hoyle and Wickramashinghe argued that molecules of interstellar formaldehyde have indeed evolved into stable polysaccharides such as cellulose and starch. Their conclusions, although strongly disputed, have generated excitement among investigators such as myself who are proposing that the galactic clouds are the places where the prebiological evolution of compounds necessary to life occurred.

1. The author is mainly concerned with
[A] describing how the principles of classical chemistry were developed.
[B] initiating a debate about the kinds of chemical reaction required for the development of life.
[C] explaining how current research in chemistry may be related to broader biological concerns.
[D] clarifying inherent ambiguities in the laws of classical chemistry.

2. In which of the following ways are the mentioned chemical reactions and tunneling reactions alike?
[A] In both, reacting molecules have to rise over the barrier between the two wells.
[B] In both types of reactions, a transition is made from the bottom of one potential well to the bottom of another.
[C] In both types of reactions, reacting molecules are able to go through the barrier between the two wells.
[D] In neither type of reaction does the rate of a chemical reaction depend on its activation energy.

3. The author’s attitude toward the theory of a cold prehistory of life can best be described as
[A] neutral. ? ? ? ? ? [B] skeptical.
[C] mildly positive. [D] very supportive.

4. Which of the following best describes the hypothesis of Hoyle and Wickramasinghe?
[A] Molecules of interstellar formaldehyde can evolve into complex organic molecules.
[B] Interstellar formaldehyde can be synthesized by tunneling.
[C] Cosmic rays can directly synthesize complex organic molecules.
[D] The galactic clouds are the places where prebilogical evolution of compounds necessary to life occurred.

答案詳解（反白可見）：
1. C. 說明現(xiàn)在化學研究如何能和更廣泛的生物學領域有關。最后一段基本上都是談與生化的關系?！皹O低溫時的貫穿勢壘現(xiàn)象證明我對寒冷的史前生命的假說：在外層空間極其寒冷處，溫度一般只有K的幾度光景，有相當復雜的有機分子形成。宇宙射線可能激發(fā)諸如星際甲醛單分子在星際塵埃的烏云中綜合。以后，復雜的有機分子，慢慢的，但穩(wěn)定的通過貫穿勢壘的方式形成。”后又有兩位化學家提出“星際甲醛分子確實進化為類似纖維素和淀粉等多糖酶?！彼麄兊慕Y論雖有爭議，卻實在令人振奮，特別是文章之作者，因為他正提出“巨大的云塊這些地方，發(fā)生過生命所必須的前生物進化化合物?！?br> A. 描述經(jīng)典化學定理如何發(fā)展。 B. 開展一場有關生命進化所需的那種化學反應的辯論。 C. 搞清楚經(jīng)典化學定理所固有的模糊點。
2. B. 兩類反應中，都有一個從一個勢阱底部到另一個勢阱底部的躍遷。見第二段第三句起“化學反應跟分子從一個勢阱的底部到另一個勢阱的底部的躍遷相類似。在經(jīng)典化學中，這種躍遷只有跨過兩阱之間勢壘才能完成。位壘之高度為常數(shù)（固定不變）。這種躍遷叫做能量活化。在貫穿勢壘效應中作反應的分子從一個勢阱的底部通到另一個勢阱底部不需要上升跨越兩阱之間的位壘?！?br> A. 兩類反應中，反應中的分子都需跨越兩阱間的欄柵。 C. 兩類反應中，反應中的分子都能穿過兩阱之間的位壘。 D. 兩類反應中，沒有一種化學反應的速率取決于能量活化。 這三項都不對， 見上文。
3. C. 有點肯定。 見第1題答案注釋譯文。因為證實了作者之假設。
A. 中立。 B. 懷疑的。 D. 非常支持。
4. A. 星際甲醛分子可以進化到復雜的有機分子。見第1題C答案注釋譯文。
B. 星際甲醛分子可以通過貫穿勢壘方式加以綜合。 C. 宇宙射線可以直接綜合復雜的有機分子。 D. 大塊云團是生命所需復合物前生物進化發(fā)生的地方。這三項也可從第1題C答案注譯譯文看出其錯誤點。

翻頁查看詞匯及難句譯注>>>