泽熙美文Reading Comprehension
Sexual Reproduction
Birds do it. Bees do it. But dandelions don’t. The prodigious spread of these winsome weeds underscores a little-appreciated biological fact. Contrary to human experience, sex is not essential to reproduction. Asexual organisms can often churn out multiple generations of clones, gaining a distinct edge in the evolutionary numbers game. And therein lies the puzzle: If sex is such an inefficient way to reproduce, why is it so widespread?
Sex almost certainly originated nearly 3.5 billion years ago as a mechanism for repairing the DNA of bacteria. Because ancient earth was such a violent place, the genes of these unicellular organisms would have been frequently damaged by intense heat and ultraviolet radiation. “Conjugation”—the intricate process in which one bacterium infuses genetic material into another—provided an ingenious, if cumbersome, solution to this problem, although bacteria continued to rely on asexual reproduction to increase their numbers.
Animal sex, however, is a more recent invention. Biologist Lynn Margulis of the University of Massachusetts at Amherst believes the evolutionary roots of egg and sperm cells can be traced back to a group of organisms known as rotests that first appeared some 1.5 billion years ago. (Modern examples include protozoa, giant kelp and malaria parasite.) During periods of starvation, Margulis conjectures, one rotest was driven to devour another. Sometimes this cannibalistic meal was incompletely digested, and the nuclei of prey and predator fused. By joining forces, the fused cells were better able to survive adversity, and because they survived, their penchant for union was passed on to their distant descendants.
From this vantage point, human sexuality seems little more than a wondrous accident, born of a kind of original sin among protozoa. Most population biologists, however, believe sex was maintained over evolutionary time because it somehow enhanced survival. The mixing and matching of parental genes, they argue, provide organisms with a novel mechanism for generating genetically different offspring, thereby increasing the odds that their progeny could exploit new niches in a changing environment and, by virtue of their diversity, have a better chance of surviving the assaults of bacteria and other tiny germs that rapidly evolve tricks for eluding their hosts’ defenses.
1. The word “underscore” underlined in Paragraph 1 most probably means ______.
A.overestimate
B.underestimate
C.underline
D.underlie
正确答案：C
[解析] 词义题型。underscore此处意为“强调、凸显”，A选项意为“高估”，B选项意为“低估”，C选项意为“强调”，D选项意为“构成……的基础或原因”，故选C。本题核心：1．充分利用上下文语境推测词义；2．区分单词之间的细微差异。本题中underscore、underline、underlie前缀相同，对三者表意异同的甄别要依赖于平时对常见常用词汇的积累。
2. By “a little-appreciated biological fact”, the author means ______.
A.most people are not familiar with the reproduction of dandelions
B.most people are not familiar with asexual reproduction
C.sexual reproduction is seldom favored by biologists
D.asexual reproduction is seldom favored by biologists
正确答案：B
[解析] 句子主旨题型。本题考察对文中特定句子主旨的理解。考察句在词汇理解层面存在两个关键点：一是appreciate一词，该词为大家所熟悉的义项是“感激，欣赏”，而此句适合的义项则是“知晓，领会”，整句可直译为“一个鲜为人知的生物学事实”，C、D选项将appreciate错误理解为favor，将biological一词错误理解为“生物学家的”，故先排除；二是fact一词，该词行使的是指代功能，此句本身未说明所指，故需联系上下文加以理解。从冠词a一词可判断此概念在文中属于首次提及，可推知具体的阐释会出现在此句之前而非之后，而A选项“蒲公英的繁衍”出现在该句之前，为作者所要陈述事实的证据，故排除。紧随其后的Contrary to human experience, sex is not essential to reproduction. 一句对考察句进一步加以解释说明，可见大多数人认为性对于繁衍而言是必要条件，由此推定C选项“大多数人对无性繁衍不熟悉”符合作者的表意主旨。本题核心：留意常见词汇的特殊义项，同时善于运用语法知识锁定正确的信息点所在。
3. According to Paragraph 1, asexual reproduction is advantageous for its ______.
A.large offspring numbers
B.creation of offspring without a mate
C.creation of genetically identical offspring
D.creation of genetically different offspring
正确答案：A
[解析] 段落主旨题型。本题考察点“无性繁衍的优点”与段落的主旨密切相关。本段为全文引段，旨在点明主题。作者采用的具体策略是反面对照法，对照的两方分别为有性和无性繁衍，意在通过彰显无性繁衍的优点来引发读者思考有性繁衍存在的必要性。段中涉及无性繁衍的叙述有两处，一是The prodigious spread of these winsome weeds，二是Asexual organisms can often churn out multiple generations of clones, gaining a distinct edge in the evolutionary numbers game. 从prodigious spread(疯狂的传播)、churn out multiple generations(大量制造子子孙孙)和numbers game(数字游戏)等描述词可见作者意在突出其繁衍数量多这一优点，故选A。本题核心：B、C选择项的内容(无须交配；与后代基因相同)同样属于无性繁殖的特征，尽管在原文中亦有所提及，但甄选正确答案有赖于把握段落的论证逻辑，找准表意重心，明确作者在此处提及无性繁殖的用意。
4. We can infer from the passage that sex first appeared in ______.
A.bacteria
B.multicellular organisms
C.rotests
D.protozoa
正确答案：A
[解析] 细节题型。本题考察有性繁衍最早出现在哪种生物形态上。根据第二段第一句Sex almost certainly originated nearly 3.5 billion years ago as a mechanism for repairing the DNA of bacteria.中的originate一词可基本锁定A选项“细菌”。B选项中的organisms一词同样出现在第二段，但修饰词unicellular被置换为multicellular，为干扰项。C选项rotests出现在第三段，对应的时间点为1.5 billion years ago。D选项protozoa亦出现在第三段，对应的时间点为modern。依次排序可确定A为正确答案。本题核心：此题涉及时间排序，可通读全文寻找时间标识词确定答案。
5. Which statement is NOT true about conjugation? ______
A.Conjugation is a process whereby the genes of bacteria are transferred.
B.Conjugation is a process whereby the genes of bacteria are recombined.
C.Conjugation is a process whereby the genes of bacteria are repaired.
D.Conjugation is a process whereby the genes of bacteria are damaged.
正确答案：D
[解析] 概念主旨题型。此题考察对conjugation这一概念的理解。原文第三段将其描述为the intricate process in which one bacterium infuses genetic material into another(一个细菌将遗传物质注入另一个细菌的微妙过程)。选择项并未照搬原文文字，因此需基于原文的描述把握概念的实质。给出的四个选择项分别为：在这个过程中，细菌的遗传因子A“发生转移”、B“进行重组”、C“得到修复”、D“遭到损害”。A、B选项涉及过程描述，从定义本身可推定此两选项无误。C、D选项涉及结果/后果描述，从上下文可知，远古地球生存环境恶劣，细菌遗传因子常因高热和紫外线辐射而遭受损害，conjugation则提供了一种解决方案，可见结果应当是细菌的遗传因子得到修复，C选项描述无误。正确答案应为D。本题核心：1．注意题干是以否定形式出现的，要求选出的是描述不正确的选项；2．不可因原文中出现damage原词而断章取义将其视为正确理解，而应围绕正确的逻辑关系作答。
6. According to biologist Lynn Margulis, ______.
A.rotests have both egg and sperm cells
B.rotests devoured each other because of starvation
C.rotests devoured each other for the survival of its species
D.protozoans, like their distant ancestors, devour each other
正确答案：B
[解析] 观点主旨题型。本题考察生物学家Lynn Margulis的具体观点。原文给出的信息大意如下：精子和卵子产生的源头可追溯到rotests。该类生物因为饥饿而相互吞噬，由于吞噬不完全，吞噬者和被吞噬者的细胞核发生了聚合。两者的合力使得聚合后的细胞在恶劣环境中更容易存活，而这种相互结合的倾向也随着其存活被其继承下来。逐一对比选择项可见：A选项与原文不符，尽管原文出现了roots一词，但并非指rotests本身具有精子和卵子细胞，而是指这种生物在相互吞噬过程中产生了细胞核聚合，导致后来同类生物之间精子和卵子细胞存在结合的倾向。C选项与原文不符，根据原文逻辑，“物种存续”是“互相吞噬”的结果而非原因。D选项与原文不符，尽管根据modern examples一词可判定protozoa和rotests之间存在共性，但原文protozoa一词出现在作者探讨rotests的吞噬现象之前，可见其共性并非吞噬本能，而只是从物种分类上可大致划归一类。本题核心：完整理解段落逻辑，而非孤立依据单独字句断章取义。
7. Paragraph 4 implies that human sexuality is the result of ______.
