Classificationschemes are used by biologists to place the huge number of organisms on Earth into natural groupings. Ideally, these groupings are made by taxonomists on the basis of shared distinguishing features. Today taxonomists use such features asanatomy, developmental stages, andbiochemicalsimilarities tocategorizeorganisms. Earlyclassificationschemes placed all organisms into either the plant or animalkingdom. Later, close examination of theuniquestructure offungiand thediversityof single-celled organisms made it necessary toproposeadditionalkingdoms that recognized thefundamentaldifferences among plants, animals,fungi, andunicellularprokaryotes (organisms whose cells do not have adistinctmembrane-boundnucleus) and eukaryotes (organisms whose cells have adistinctmembrane-boundnucleus). Thecurrentschemeconsisting of five kingdoms— Monera, Protista, Animalia,Fungi, and Plantae—was devised inresponseto this need.

Scientists do not know how manyspeciesshare our world. Each year 7000 to 10,000 newspeciesare named. The total number of namedspeciesis currently around 1.4 million. However, many scientists believe that 7 million to 10 millionspeciesmay exist, and estimates range as high as 30 million. Of all of thespeciesthat have been identified, about 5 percent are in the Monera and Protista kingdoms. Anadditional22 percent are plants andfungi, and the rest are animals. Thisdistributionhas little to do with the actualabundanceof these organisms and a lot to do with the size of the organisms, how easy they are toclassify, and the number of scientists studying them.

ThekingdomProtista, defined as comprising all single-celled eukaryotic organisms, is not a natural grouping, and scientists disagree about which organisms it should include. Plants, animals, andfungiall have close protistan relatives, and the separation of single-celled organisms frommulticellularorganisms is sometimes problematic. It is especially so for thealgae, which have both single-celled andmulticellularrepresentativeswithinmost smaller taxonomic groupings. Can closely related organisms be placed intoseparatekingdoms, Protista and Plantae,simplyon the basis of multicellularity? If you look at different textbooks, you will see that thealgae,photosyntheticorganisms with simplereproduction，are sometimes placedentirelyinto Protista, and sometimes they aresplitbetween Protista and Plantae depending on whether they are single celled ormulticellular. Some taxonomistssplitthemulticellularalgaeinto two kingdoms, placing themulticellularbrown and redalgaewith the protists and themulticellulargreenalgaeinto the plantkingdom. These different attempts toclassifyclosely related organisms are good examples of how difficult it is to developstandardcriteriafor grouping organisms,evenat thekingdomlevel.

Oneapproachto this problem, enthusiastically endorsed by Lynn Margulis, a biologist at the University of Massachusetts, is the creation of thekingdomProtoctista. This taxonomiccategorywould include single-celled organisms and their close descendants (for example, themulticellularalgaebut not the animals,fungi, and plants). Margulis describes thekingdomProtoctista as “the entire motley and unruly group of nonplant, nonanimal, nonfungal organismsrepresentativeof lineages of the earliest descendants of the eukaryotes.”

It is conceptually difficult to group one of the largestmulticellularorganisms in the world, the brownalgaecalledgiantkelps, with simplemicroscopicsingle-celled organisms. Kelps, some of which are up to 60 meters long,possessa tissuelikeleveloforganizationthat isrelativelycomplexand cantransportmaterials over long distances, as can the tissues of higher plants. The cells in kelps and some otheralgaearespecializedand showdivisionof labor. However, kelpsreproducelike otheralgaeand differently from plants. Thomas Cavalier-Smith of the University of British Columbia has proposed that brownalgaemerit their ownkingdom(kingdomChromista) based on ultrastructural features and molecular comparisons of allalgae. So,evenamong thealgae, there arecleardifferences that some scientists believe aresufficienttojustifythestatusof aseparatekingdom.

As we learn more about the relationships between organisms andrefinethecriteriaused toclassifythem,classificationschemes will change. As thesuperficiallysimple question “In whichkingdomshould we place thealgae?” illustrates, the taxonomic categories in textbooks are tentative andsubjecttorevisionas we continue to discover more about life on Earth.

Questions:
question_stem: Paragraph 1 mentions all of the following as features that taxonomists consider when grouping organisms EXCEPT
choices: tag: A
text: the size of the organism

tag: B
text: the physical structure of the organism

tag: C
text: the changes organisms undergo at specific stages

tag: D
text: biochemical characteristics that organisms have in common
answer_key: A
explanation: 题干问“分类学家在考虑分类有机体时会考虑那些特征，除了？”根据题目定位第一段的第三句，anatomy, developmental stages, and biochemical similarities to categorize organisms，句子内部的三个并列信息，选项 B the physical structure=anatomy，选项 C 对应 developmental stages，选项 D 对应 biochemical similarities；故选 A。

question_stem: The discussion of fungi in paragraph 1 suggests that the study of fungi was important for
choices: tag: A
text: establishing the earliest classification system

tag: B
text: improving our understanding of single-celled organisms

tag: C
text: recognizing the inadequacy of the early classification systems

tag: D
text: understanding the features that distinguish plants from animals
answer_key: C
explanation: 题干问“对于 fungi 的讨论表明 fungi 的研究对什么是重要的？”根据题目，定位原文第五句，“Later, examination of fungi made it necessary to，可得知答案句为 it necessary to propose additional kingdoms that recognized the fundamental differences，The current scheme consisting of five kingdoms was devised in response to this need.，意思是需要提出额外的“界”以便能识别出根本的区别，为了这个需求，目前的框架包括五个界，故选 C。

question_stem: The word “devised” in the passage is closest in meaning to
choices: tag: A
text: studied

tag: B
text: refined

tag: C
text: tested

tag: D
text: created
answer_key: D
explanation: devised 设计的，D. created 被创造的，符合意思，故选 D
A. studied 研究过的，B. refined 精确的，C. tested 被测试过的，都不符合原词意思，故不选

question_stem: According to paragraph 2, which of the following is the LEAST important reason why some kingdoms contain greater numbers of identified species than do other kingdoms?
choices: tag: A
text: Some kingdoms contain greater numbers of existing species than do other kingdoms.

tag: B
text: Organisms that are large in size are easier to identify than are smaller organisms.

tag: C
text: Some organisms are easier to classify than are other organisms.

tag: D
text: Some species have been studied by greater numbers of scientists than have other species.
answer_key: A
explanation: 题干文关于一些生态系统比另一些生态系统更具有多样性的原因中，最不重要的是哪个？根据题目定位2段最后一句话，This distribution has little to do with the actual abundance of these organisms，意为跟这些有机物的数量多没关系，故选 A，abundance 替换到 great number。BC 和 D 应该是比较重要的因素，且并列出现，故都不选。

question_stem: According to paragraph 3, multicellular algae that are closely related to each other are sometimes classified into two separate kingdoms in accordance with their
choices: tag: A
text: size

tag: B
text: color

tag: C
text: number of cells

tag: D
text: similarity to animal or plant protists
answer_key: B
explanation: 题干问“相近的 multicellular algae 有时被分为两个类别的根据是？”根据题目定位原文倒数第二句，把棕色海藻，红色海藻归类为原生生物，把绿藻归类为植物，可得知答案为 B。A,C,D 均不符合题目，故不选。

question_stem: According to paragraph 5, what is one reason why kelps should not be classified in the same kingdom as plants?
choices: tag: A
text: Kelps have a mode of reproduction that is similar to that of all other algae but differs from that of plants.

tag: B
text: Kelps have a level of organization that is more complex than that of plant tissue.

tag: C
text: Kelps, unlike plants, do not have the capacity to move materials from one part of their tissue to another.

tag: D
text: Kelps, unlike plants, do not have cells that are specialized to perform particular biological functions.
answer_key: A
explanation: 题干问“kelp 不能和 plant 分类在一起的原因是什么”，定位原文“However, kelps reproduce like other algae and differently from plants.”故选 A，like=similar; B 原文提到 complex 但没有比较级，不选；C 选项和原文矛盾，can transport materials，故不选；D 选项，原文明确说到 specialized and show division of labor 故不选。

question_stem: How do paragraphs 4 and 5 relate to each other?
choices: tag: A
text: The two paragraphs describe the work of two independent researchers who each arrived at the same conclusion

tag: B
text: Paragraph 4 describes a taxonomic problem, and paragraph 5 outlines a solution to that problem.

tag: C
text: Paragraph 4 proposes criteria for a new taxonomic category, and paragraph 5 provides support for the proposed category.

tag: D
text: Paragraph 4 describes an approach to a problem, and paragraph 5 points out the shortcomings of that approach and outlines an alternative.
answer_key: D
explanation: 题干问四段和五段的关联，原文第四段主要针对前段的问题提出了一个解决办法，即创建 kingdom Protoctista，第五段表达了 kingdom Protoctista 的缺陷，随即又提出了 Thomas Cavalier-Smith 的新观点，故选 D；A 选项的 same conclusion 错，B 选项说四段描述了一个问题，错，C 选项说第五段支持第四段，错。

question_stem: The word “tentative” in the passage is closest in meaning to
choices: tag: A
text: outdated

tag: B
text: uncertain

tag: C
text: misunderstood

tag: D
text: undefined
answer_key: B
explanation: tentative 试验性的，暂定的，B：uncertain 无把握的，正确； A：outdated 过时的，C：misunderstood 错解的；D：undefined 未被定义的，都不符合原词意思，故不选。