Elements of Life
The creation of life requires a set of chemical elements for making the components of cells. Life on Earth uses about 25 of the 92 naturally occurring chemical elements, although just 4 of these elements—oxygen, carbon, hydrogen, and nitrogen—make up about 96 percent of the mass of living organisms. Thus, a first requirement for life might be the presence of most or all of the elements used by life.
Interestingly, this requirement can probably be met by almost any world. Scientists have determined that all chemical elements in the universe besides hydrogen and helium (and a trace amount of lithium) were produced by stars. These are known as heavy elements because they are heavier than hydrogen and helium. Although all of these heavy elements are quite rare compared to hydrogen and helium, they are found just about everywhere.
Heavy elements are continually being manufactured by stars and released into space by stellar deaths, so their amount compared to hydrogen and helium gradually rises with time. Heavy elements make up about 2 percent of the chemical content (by mass) of our solar system, the other 98 percent is hydrogen and helium. In some very old star systems, which formed before many heavy elements were produced, the heavy-element share may be less than 0.1 percent. Nevertheless, every star system studied has at least some amount of all the elements used by life. Moreover, when planetesimals—small, solid objects formed in the early solar system that may accumulate to become planets—condense within a forming star system, they are inevitably made from heavy elements because the more common hydrogen and helium remain gaseous. Thus, planetesimals everywhere should contain the elements needed for life, which means that objects built from planetesimals—planets, moons, asteroids, and comets-also contain these elements. The nature of solar-system formation explains why Earth contains all the elements needed for life, and it is why we expect these elements to be present on other worlds throughout our solar system, galaxy, and universe.
Note that this argument does not change, even if we allow for life very different from life on Earth. Life on Earth is carbon based, and most biologists believe that life elsewhere is likely to be carbon based as well. However, we cannot absolutely rule out the possibility of life with another chemical basis, such as silicon or nitrogen. The set of elements (or their relative proportions) used by life based on some other element might be somewhat different from that used by carbon-based life on Earth. But the elements are still products of stars and would still be present in planetesimals everywhere. No matter what kinds of life we are looking for, we are likely to find the necessary elements on almost every planet, moon, asteroid, and comet in the universe.
A somewhat stricter requirement is the presence of these elements in molecules that can be used as ready-made building blocks for life, just as early Earth probably had an organic soup of amino acids and other complex molecules. Earth's organic molecules likely came from some combination of three sources: chemical reactions in the atmosphere, chemical reactions near deep-sea vents in the oceans, and molecules carried to Earth by asteroids and comets. The first two sources can occur only on worlds with atmospheres or oceans, respectively. But the third source should have brought similar molecules to nearly all worlds in our solar system.
Studies of meteorites and comets suggest that organic molecules are widespread among both asteroids and comets. Because each body in the solar system was repeatedly struck by asteroids and comets during the period known as the heavy bombardment (about 4 billion years ago), each body should have received at least some organic molecules. However, these molecules tend to be destroyed by solar radiation on surfaces unprotected by atmospheres. Moreover, while these molecules might stay intact beneath the surface (as they evidently do on asteroids and comets), they probably cannot react with each other unless some kind of liquid or gas is available to move them about. Thus, if we limit our search to worlds on which organic molecules are likely to be involved in chemical reactions, we can probably rule out any world that lacks both an atmosphere and a surface or subsurface liquid medium, such as water.
29. The word ''components" in the passage is closest in meaning to
A. parts
B. bodies
C. combinations
D. characteristics
关联段落 paragraph1
30. According to paragraphs 1 and 2, living cells contain which of the following?
A. All chemical elements in the universe except lithium
B. About 25 different elements
C. About 96 percent of all known elements
D. Ninety-two naturally occurring elements
关联段落 paragraph1 & 2
31. Why does the author provide the information that "Heavy elements are continually being manufactured by stars and released into space by stellar deaths"?
A. To explain how it is that the elements required for life can be found everywhere.
B. To provide evidence that our solar system is relatively young.
C. To argue that some solar systems are more likely to support life than others.
D. To explain why heavy elements have greater mass than hydrogen and helium.
关联段落 paragraph3
32. Paragraph 3 suggests that which of the following may be a difference between very old star systems and newer star systems?
A. Older star systems are likely to have fewer planets, moons, asteroids, and comets than newer star systems.
B. Newer star systems probably contain more hydrogen and helium than older star systems.
C. Newer star systems probably contain more heavy elements than older star systems.
D. The process of solar-system formation may have been fundamentally different in older star systems than in newer star systems.
关联段落 paragraph3
33. The word "Nevertheless" in the passage is closest in meaning to
A. additionally
B. however
C. in particular
D. on the contrary
关联段落 paragraph3
34. The word "inevitably" in the passage is closest in meaning to
A. typically
B. unsurprisingly
C. necessarily
D. naturally
关联段落 paragraph3
35. Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information
A. Planetesimals may remain in star systems when hydrogen and helium combine with less common heavier elements.
B. Planetesimals are composed of heavy elements because hydrogen and helium stay in the form of gases.
C. Planetesimals are small, solid objects that condense within a forming star system and may become planets.
D. When planetesimals accumulate to form planets, they inevitably contain gaseous as well as heavy elements.
关联段落 paragraph3
高亮: Moreover, when planetesimals—small, solid objects formed in the early solar system that may accumulate to become planets—condense within a forming star system, they are inevitably made from heavy elements because the more common hydrogen and helium remain gaseous.
36. According to paragraph 4, which of the following is true about possible life on other planets?
A. It cannot be based on silicon or nitrogen.
B. It could not survive on Earth.
C. It probably would not be made of elements produced by stars.
D. It is likely to have carbon as its chemical basis.
关联段落 paragraph4
37. According to paragraph 5, all of the following are true of the organic molecules on early Earth EXCEPT:
A. Some of them were probably brought to Earth by asteroids or comets.
B. Some of them probably formed in the atmosphere and oceans.
C. They were probably significantly different from the organic molecules present on other planets in the solar system.
D. They included complex molecules.
关联段落 paragraph5
38. The word “intact” in the passage is closest in meaning to
A. buried
B. whole
C. confined
D. active
关联段落 paragraph6
39. According to paragraph 6, why is life unlikely to be found on any planet that lacks both an atmosphere and a surface or subsurface liquid medium?
A. Organic molecules must be protected from solar radiation by a surface layer of liquid.
B. Planets that lack both of these features are probably too small to have been hit by many asteroids or comets carrying organic matter.
C. Organic molecules need a liquid or gaseous environment to bring them together so they can interact.
D. An atmosphere is needed to protect organic molecules from being destroyed by asteroids and comets.
关联段落 paragraph6
40. Look at the four squares [■] that indicate where the following sentence could be added to the passage.
To answer the question “Could life exist on other planets?” we must first look at the necessary preconditions for life.
Where would the sentence best fit? Click on a square [■] to add the sentence to the passage.
关联段落 paragraph1
41. Directions: An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. Some sentences do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points.
Drag your answer choices to the spaces where they belong. To remove an answer choice, click on it
To review the passage, click VIEW TEXT
关联全篇
The chemical elements that make up cells are likely to be available on just about any planet.
• D.The most common elements used by life-oxygen, carbon, hydrogen, and nitrogen—are also some of the most widely distributed elements in the universe.
• E.Planets, moons, asteroids, and comets are all composed of heavy elements, which means they contain the basis for any life form, carbon based or otherwise.
• F.Organic molecules are widely available but chemical reactions among these molecules probably require either an atmosphere or a liquid medium.
Answer Choices
A. Somewhere between 4 and 25 naturally occurring elements are necessary for life, depending on the complexity of the organism.
B.Life is most likely to be found in the oldest star systems, where heavy elements have been continually produced since those systems were formed.
C.Life is most likely to exist on those bodies that were not heavily bombarded with asteroids and comets during the formation of the solar system.
D.The most common elements used by life-oxygen, carbon, hydrogen, and nitrogen—are also some of the most widely distributed elements in the universe.
E.Planets, moons, asteroids, and comets are all composed of heavy elements, which means they contain the basis for any life form, carbon based or otherwise.
F.Organic molecules are widely available, but chemical reactions among these molecules probably require either an atmosphere or a liquid medium.
真题解析
29.
答案：A
题型：词汇题
解析：本题为词汇题。“part”的意思是“部分、片段、组成”,它所在的句子“The creation of life requires a set of chemical elements for making the components of cells.”意思是“生命的创造需要一套用于制造细胞成分的化学元素”，其中“component”的意思为“成分、组件”，根据同义转换，可知答案为A。
A选项“parts”意思是“部分、片段、组成”，意思最为贴切，故正确。
B选项“bodies”意思是“身体、主体、主要部分”,代入可知，句意不符，排除。
C选项“combinations”意思是“结合，组合”，代入可知，句意不符，排除。
D选项“characteristics”意思是“特点、特性”,代入可知，句意不符，排除。
30.
答案：B
题型：事实信息题
解析：本题为事实信息题,出题点是“The creation of life requires a set of chemical elements for making the components of cells. Life on Earth uses about 25 of the 92 naturally occurring chemical elements”，意思为“生命的创造需要一套用于制造细胞成分的化学元素。 “地球上的生命”使用了92种天然化学元素中的25种”。地球上的生命是由细胞组成的，则可知生命的细胞的组成部分包括大概25种不同的元素，则B项正确。
A选项的意思为：宇宙中除了锂以外的化学元素，A项的干扰因素来自于“Scientists have determined that all chemical elements in the universe besides hydrogen and helium (and a trace amount of lithium) were produced by stars”，这里只是说“科学家们已经确定，除了氢和氦(以及微量的锂)之外，宇宙中的所有化学元素都是由恒星产生的”，并没有说生命细胞是由除了锂以外的化学元素组成的，则A选项不正确。
C选项的意思为：大概96%的已知元素，C选项的干扰因素来自于“although just 4 of these elements—oxygen, carbon, hydrogen, and nitrogen—make up about 96 percent of the mass of living organisms”，意思为“尽管这些元素中只有4种：氧，碳，氢和氮 - 构成了大约96%的活生物体，”这里强调的是生物体的绝大部分都是由氧，碳，氢和氮4种元素组成的，但是不是说所有的细胞都是只由我们知道的元素中的96%组成的，则C项不正确。
D选项的意思为：92种已经存在的元素。D项的干扰因素来自于“Life on Earth uses about 25 of the 92 naturally occurring chemical elements”，这个应该注意到是92种中的25种，“of”说明并不是全部，则D项不正确。
31.
答案：A
题型：功能目的题
解析：本题的出题点为“Heavy elements are continually being manufactured by stars and released into space by stellar deaths, so their amount compared to hydrogen and helium gradually rises with time”，意思就是说“重元素不断由恒星制造并通过恒星死亡释放到太空中，因此它们的量与氢和氦相比随着时间的推移逐渐增加”这句话为一句有着因果关系的句子，前半句是后半句的原因，则可知A项正确。
B项的意思为：为了证明我们的太阳系是非常年轻的提供证据，B项中，本文的中心是宇宙中生命细胞的组成成分，并不是太阳系的生命长短，则B选项与文章的主旨不符，则B项不正确。
C项的意思为：为了证实一些太阳系比其他的星系更有可能存在生命，C项中，虽然在第三自然段能够推理出为什么太阳系中能够存在生命，但是其中并没有将太阳系与其他的星系相比较，没有比较关系，所以也就得不出这样的结论，则C项不正确。
D项的意思为：为了解释为什么重元素比氢和氦的质量更大，D项中，第三自然段并没有解释为什么重元素比氢和氦的质量更大，属于无中生有的现象，则D项不正确。
32.
答案：C
题型：推理题
解析：由“ In some very old star systems, which formed before many heavy elements were produced, the heavy-element share may be less than 0.1 percent”可知，“在一些非常古老的恒星系统中，这些恒星系统在许多重元素出现之前形成，重元素份额可能低于0.1%”，则可知C选项正确。
A选项的意思为：老的星系比新的星系可能拥有更少的行星、月亮、小行星以及彗星，A选项的干扰点来源于“Thus, planetesimals everywhere should contain the elements needed for life, which means that objects built from planetesimals—planets, moons, asteroids, and comets-also contain these elements”，就是说“因此，任何地方的星子都应该包含生命所需要的元素，这意味着由平行星 、行星、卫星、小行星和彗星等构成的物体也包含这些元素”，说明的是其他星系的组成部分，而不是将新的星系与老的星系之间进行比较，则A项不正确。
B选项的意思为：新的星系比老的星系可能包含更多的氢和氦元素，B选项，这个选项属于偷换概念，是将正确选项中的“heavy elements”换成了“hydrogen and helium”，而氢和氦并不属于重元素的范畴，则B选项不正确。
D选项的意思为：老的星系中的太阳系的形成过程与新的星系的形成过程可能有着本质的不同。
D选项，第三自然段并没有说明星系的形成过程，更没有将新的星系与旧的星系的形成过程进行比较，则D项不正确。
33.
答案：B
题型：词汇题
解析：“Nevertheless”的意思为“然而、不过、虽然如此”，表示转折，与B项的“however”的意思最为接近，表转折，意为“然而、但是”。
A选项的意思为：另外，加之，表示顺承;
B选项的意思为：然而，但是，表示转折;
C选项的意思为：尤其是，表示强调;
D选项的意思为：反之，指意思相反，表示对立面。
则A、C、D三项均不符合要求。
34.
答案：C
题型：词汇题
解析：“inevitably”意思为“必将，不可避免的”，原文中出现在“they are inevitably made from heavy elements ”，意思就是说“它们不可避免地由重元素制成”与C选项中的“necessarily”的意思相近，意为“一定地、必须地”，则C选项正确。
A选项的意思为：一般情况下，一般地;
B选项的意思为：勿庸置疑;
C选项的意思为：一定地、必须地;
D选项的意思为：自然地。
则A、B、D三项均不符合要求。
35.
答案：B
题型：句子简化题
解析：文中划出的句子的意思为“而且，当太阳系中早期太阳系中形成的可能积聚成行星的固体物体在形成恒星系统内凝聚时，它们不可避免地由重元素制成，因为更常见的氢和氦气保持气态”，理解了划线句的意思后就可得出B选项为正确答案。
A选项的意思为：当氢和氦与较不常见的较重元素结合时，平面星系可能保留在星系中;
B选项的意思为：星系由重元素组成，因为氢和氦以气体的形式存在;
C选项的意思为：星系是小而坚固的物体，凝聚在形成的恒星系统内，并可能成为行星;
D选项的意思为：当小行星积聚形成行星时，它们不可避免地含有气体和重元素。
将A、B、C、D选项进行比较，得出A、C、D三项均不符合要求。
36.
答案：D
题型：推理题
解析：由“ Life on Earth is carbon based, and most biologists believe that life elsewhere is likely to be carbon based as well”可知“地球上的生命是以碳为基础的，大多数生物学家认为其他地方的生活也可能以碳为基础”，则D选项是正确的。
A选项的意思为：它不能基于硅或氮;
B选项的意思为：它不能在地球上存活;
C选项的意思为：它不可能由星球产生的元素组成;
D选项的意思为：它可能是以碳元素为它的化学基础。
A项中的干扰点为“However, we cannot absolutely rule out the possibility of life with another chemical basis, such as silicon or nitrogen”，意思为“但是，我们不能完全排除使用另一种化学基础如硅或氮的生命的可能性”，则A项不正确;
B项，文章并没有提到它们是否能够在地球上存活，则B项是不正确的;
C项中的干扰点为“But the elements are still products of stars and would still be present in planetesimals everywhere”，意思为“但这些元素仍然是恒星的产物，并且仍然会以各种行星的形式出现”，则C选项不正确。
37.
答案：C
题型：否定事实信息题
解析：通过题干中的“EXCEPT”，我们判断这是一道否定事实信息题。我们在选项中寻找关键词，回到原位进行定位，用排除法找出正确答案。
由“Earth's organic molecules likely came from some combination of three sources: chemical reactions in the atmosphere, chemical reactions near deep-sea vents in the oceans, and molecules carried to Earth by asteroids and comets”可知，地球的有机分子可能来自三种来源的某一种组合：大气中的化学反应，海洋深海通风口附近的化学反应以及小行星和彗星携带到地球的分子，则A、B两项是正确的;
由第一句“A somewhat stricter requirement is the presence of these elements in molecules that can be used as ready-made building blocks for life, just as early Earth probably had an organic soup of amino acids and other complex molecules”，可知D选项是正确的。
综上所述，通过排除法，可得答案为C。
38.
答案：B
题型：词汇题
解析：“intact”的意思为“完整的”，强调整体性，与B选项中的“whole”意思接近，则B选项正确。
A选项的意思为：隐藏的，埋于地下的;
B选项的意思为：整个的额，整体的;
C选项的意思为：受限的，限制的;
D选项的意思为：积极的，有活力的。
比较A、B、C、D选项的意思，可得A、C、D选项均不符合要求。
39.
答案：C
题型：推理题
解析：由“each body should have received at least some organic molecules. However, these molecules tend to be destroyed by solar radiation on surfaces unprotected by atmospheres. Moreover, while these molecules might stay intact beneath the surface (as they evidently do on asteroids and comets), they probably cannot react with each other unless some kind of liquid or gas is available to move them about”，就是说，“所以每个个体至少应该接受一些有机分子。 然而，这些分子往往被不受大气保护的表面上的太阳辐射破坏。此外，尽管这些分子可能会在表面下保持完整(因为它们明显对小行星和彗星有影响)，但除非某种液体或气体可用于移动它们，否则它们可能无法相互反应”，即气体和液体的环境，对于有机分子的合成是非常重要的，则C项正确。
A选项的意思为：有机分子必须由液体层的表面保护其不受太阳射线的辐射;
B选项的意思为：不具备这两个特点的行星有可能因为太小以至于会被带有有机物质的陨石和彗星所击中;
C选项的意思为：有机分子需要有一个液体或者气体环境，使得它们能够相互反应;
D选项的意思为：对于保护有机分子不被陨石或者彗星所损坏来说大气层是非常重要的。
A选项虽然说法正确，但是，题目问的是“为什么在缺少大气层和液体介质的行星上不可能发现生命?”显然，答非所问，则A项不正确;
B选项，第六自然段并没有提到相关的观点，属于无中生有，则B项不正确;
D选项，由“ these molecules tend to be destroyed by solar radiation on surfaces unprotected by atmospheres”可知，有机分子会收到太阳射线的损坏，并不是陨石和彗星。
则A、B、D三项均不正确。
40.
答案：A
题型：句子插入题
解析：“To answer the question “Could life exist on other planets?” we must first look at the necessary preconditions for life”的意思为“为了回答生命能够存活在其它行星上这个问题，我们首先必须看看生命存在的前提条件是什么”，首先这句话是一个具有启示下文的作用的句子，则我们将它放在位置A，看看是否符合要求，发现是满足要求的，因为通过阅读可知，后文讲的都是生命的组成成分，也就是生命存在的基本要求，结合本段的最后一句话“Thus, a first requirement for life might be the presence of most or all of the elements used by life”，这是一个总结性的话，与所给句子相呼应，则一头一尾对应，则答案为A。
本段的基本机构呢为提出问题，解释问题，总结问题，若将所给句子填入其它的三个位置，则会破坏文章的结构。
41.
答案：DEF
题型：总结题
解析：本题为总结题，对同学们的阅读速度和能力都提出很高的要求。下面我们逐一来看选项。
A选项的意思为：根据生物体的复杂程度，4至25之间的某些天然存在的元素对于生命是必需的。文章中并没有提到这个问题，属于无中生有，文章提到的是“Life on Earth uses about 25 of the 92 naturally occurring chemical elements”，也就是说““地球上的生命”使用了92种天然化学元素中的25种”，则A项不正确;
B选项的意思为：生命最容易在最古老的恒星系统中找到，自那些系统形成以来，重元素一直在不断产生。文章中说“ In some very old star systems, which formed before many heavy elements were produced, the heavy-element share may be less than 0.1 percent”，即古老的星系上的重元素的含量是很少的，并没有不断产生，则B项不正确;
C选项的意思为：生命最有可能存在于这些行星上，它们在太阳系的形成过程中没有受到陨石和彗星的严重轰炸。由文章中最后一段的“Because each body in the solar system was repeatedly struck by asteroids and comets during the period known as the heavy bombardment (about 4 billion years ago), each body should have received at least some organic molecules”可知C项不正确;
D选项的意思为：最常见的用于形成生命的元素是氧、碳、氢和氦，它们也是宇宙中分布最广的元素。由“although just 4 of these elements—oxygen, carbon, hydrogen, and nitrogen—make up about 96 percent of the mass of living organisms”可知D项正确;
E选项的意思为：行星，卫星，小行星和彗星都由重元素组成，这意味着它们包含任何生命形式，都是以碳元素为基础或其他为基础的。由“Thus, planetesimals everywhere should contain the elements needed for life, which means that objects built from planetesimals—planets, moons, asteroids, and comets-also contain these elements”可得E选项正确;
F选项的意思为：有机分子广泛存在，但这些分子之间的化学反应可能需要大气或液体介质。由“However, these molecules tend to be destroyed by solar radiation on surfaces unprotected by atmospheres. Moreover, while these molecules might stay intact beneath the surface (as they evidently do on asteroids and comets), they probably cannot react with each other unless some kind of liquid or gas is available to move them about”可知F选项正确。
综上所需，D、E、F三项均正确。
通过对TPO54托福阅读passage3的文本和真题解析内容分享我们可以发现，托福阅读近来对推理题和词汇题的考察力度逐渐加大，最后一大题更是频繁出现对文章总结题的考察，这说明