ACT科学之细胞生物学详解（学科背景+单词+例题练习）

译文：所有的多细胞生物可以被归结为后生动物。大多数的后生动物是双边对称的（他们的左半边和右半边几乎是相同的）。生物学家们认为，在大约6亿年前，后生物从原生动物（单细胞生物）演变而来，但是他们对这如何发生的产生了分歧。生物学家们提出了三个理论。

• Cellularization Theory 细胞化理论

Some biologists believe that metazoans evolved from multinucleated protozoans (protozoans with many nuclei). Separate cells formed when membranes developed between adjacent nuclei. Later, cilia (hairlike strictures), used for movement, grew from each cell. These ciliated protozoan ancestors then evolved into aquatic, bilaterally symmetrical metazoans similar to modern flatworms. Later, other metazoans evolved from these flatworm-like creatures(see Figure 1)

译文：一些生物学家认为，后生动物是从多核的原生动物（有多个细胞核的原生动物）演变而来的。当两个相邻的细胞核之间形成薄膜时，分裂的细胞成形了。后来，纤毛（用来移动的毛状结构）从每一个细胞中生长出来。这些纤毛状的原生生物祖先随后演变成水生动物和与现代扁形虫相似的双边对称的后生动物。最后，其他的后生生物从这些扁形虫一样的生物中演变出来。（见图1）

（Figure 1）

• Colonial Theory菌落理论

Other biologists suggest that many protozoans grouped together into a hollow ball, or colony. This colony evolved into the first metazoan. Each cell in the colony had a flagellum (movable tail) for movement. Initially, some of these cells were better suited for reproduction, and these became the reproductive cells of the metazoan. The first metazoans were aquatic, flagellated, radially symmetrical organisms (body parts arranged symmetrically around a central point, as in modern jellyfish). All later metazoans evolved from these jellyfish-like organisms (see Figure 2).

译文：其他的一些生物学家提出，许多原生动物聚集在一起形成一个空心的球，或者叫做菌落。这个菌落演变成最初的后生动物。菌落的每一个细胞都有一个用来移动的鞭毛（可移动的尾状物）。最初，部分细胞非常适合再生，并且这些细胞变成了后生动物的可再生细胞。最初的后生动物是水生动物，有鞭毛的，放射对称的有机体（身体部分围绕一个中心对称排列，就像现代的水母）。所有后来的后生动物都是从这些水母状的有机体演变而来的（见图2）。

• Separate Line Theory分离线理论

Proponents of this theory argue that 2 separate protozoan lines led to metazoans. Radially symmetrical metazoans evolved form flagellated, colonial protozoans. Bilaterally symmetrical metazoans evolved from ciliated, multinucleated protozoans. The first metazoans of each group were jellyfish-like creatures and flatworm-like creatures, respectively. The 2 protozoan groups were only distantly related to each other, and the evolution of aquatic metazoans from the 2 protozoan groups occurred independently and at different times.

译文：这个理论的支持者认为，2个分离的原生动物排成线型产生后生动物。放射对称的后生动物是从有鞭毛的、菌落状的原生生物进化而来。双边对称的后生生物是从有纤毛的多核的原生生物进化而来。这些最初的后生生物分别是是水母状的生物和扁形虫状的生物。这两个原生生物组之间的关系不大，这两个组中的水生生物的演变是相互独立的并且发生在不同的时期。

★例题练习 1.1

The Cellularization Theory does NOT include the hypothesis that the earliest metazoans were:

F. ciliated.

G. aquatic.

H. hollow.

J. bilaterally symmetrical.

大家先思考一下，然后再看考点分析。

【考点分析】

• 观点（理论）冲突类文章 (单一观点题)
• 抓住定位词The Cellularization Theory ，直接定位到第二段部分，题目考察 The Cellularization Theory 不包括的假设。
• 根据第二段句子的描述“ Later, cilia (hairlike structures), used for movement, grew from each cell. These ciliated protozoan ancestors then evolved into aquatic, bilaterally symmetrical metazoans similar to modern flatworms. ”，蓝色三个单词一一对应三个选项，由此可知正确答案为H。

★例题练习 1.2

The development of which of the following characteristics is addressed in the passage by the Colonial Theory but NOT by the Cellularization Theory?

A. Body symmetry

B. Ciliated tissues

C. Multinucleated cells

D. Reproductive cells

【考点分析】

• 观点（理论）冲突类文章 (多观点冲突题)
• 抓住定位词The Cellularization Theory & the earliest metazoans ，直接定位到第二段和第三段部分，题目考察 The Cellularization Theory 不包括的特点。
• 用排除法，根据上一题，直接可以排除A&B选项；根据第二段句子的描述“Some biologists believe that metazoans evolved from multinucleated protozoans (protozoans with many nuclei). ” 排除C选项，由此可知正确答案为D。
• 同时D选项对应句子为“Initially, some of these cells were better suited for reproduction, and- these became the reproductive cells of the metazoan. ”。

★例题练习 1.3

Supporters of all 3 theories would agree with the conclusion that the first metazoans:

F. evolved from protozoans.

G. are older than the first protozoans.

H. had many nuclei in each cell.

J. were radially symmetrical.

【考点分析】

• 观点（理论）冲突类文章（综合观点题）
• 抓住定位词all 3 theories & the first metazoans，需要直接阅读全文，题目考察 the conclusion that the first metazoans。
• 根据第一段句子描述“Biologists agree that metazoans evolved from protozoans (single-celled organisms) over 600 million years ago, but they do not agree on how this occurred. ”，由此可知正确答案为F。
• 综合全文来看，G选项只有第二个理论明显提及，第二个理论没有阐述H选项，J选项只符合最后一个理论。

★例题练习 1.4

Which of the following types of organisms, if present today, would provide the most support for the Colonial Theory?

A. Flagellated protozoans living in dense colonies

B. Flagellated protozoans living in hollow colonies

C. Ciliated protozoans living in dense colonies

D. Ciliated protozoans living in hollow colonies

【考点分析】

• 观点（理论）冲突类文章（单一观点题）
• 抓住定位词the Colonial Theory，直接定位到第三段部分，题目考察最支持the Colonial Theory 的结构证据。
• 根据第二段句子的描述“Other biologists suggest that many protozoans grouped together into a hollow ball, or colony.”，排除选项A&C，根据“The first metazoans were aquatic, flagellated, radially…“，排除选项D，由此可知正确答案为B。
• 还可以根据 Figure 2 来作答，根据图中所示，明显具备 hollow & flagella 元素，故可以得出正确答案。

★例题练习 1.5

Assuming that the Separate Line Theory is correct, which of the following conclusions can be made about modern hydras, which are radially symmetrical, and modern flukes, which are bilaterally symmetrical?

F. Hydras and flukes evolved from radially symmetrical metazoans.

G. Hydras and flukes evolved from bilaterally symmetrical metazoans.

H. Hydras and flukes are more closely related to each other than to protozoans.

J. Hydras and flukes are only distantly related through protozoans.

【考点分析】

• 观点（理论）冲突类文章（单一观点题）
• 抓住定位词the Separate Line Theory ，直接定位到最后一段，题目考察对此理论的理解。
• 根据最后一段中句子的描述“Proponents of this theory argue that 2 separate protozoan lines led to metazoans. Radially symmetrical metazoans evolved from flagellated, colonial protozoans. Bilaterally symmetrical metazoans evolved from ciliated, multinucleated protozoans. ”和题干得出F&G是错误选项，根据最后一段中句子的描述“The 2 protozoan groups were only distantly related to each other”，由此可知正确答案为J，H选项文章中未提及。

★例题练习 1.6

Which of the following questions is raised by the Colonial Theory, but is NOT answered in the passage?

A. Why did the first flatworm-like metazoans have cilia?

B. Why were some colonial cells better suited for reproduction?

C. How could 2 lines of metazoans evolve from protozoans?

D. How were multinucleated cells transformed into cells with single nuclei?

【考点分析】

• 观点（理论）冲突类文章（综合信息题）
• 抓住定位词the Colonial Theory & NOT answered in the passage，须知是以第三段为主，并且结合全文，考察对the Colonial Theory 的理解以及全文把控 。
• 直接看选项，A选项题眼 the first flatworm-like metazoans have cilia，明显可知为第一个理论内容，文章中“Later, other metazoans evolved from these flatworm-like creatures (see Figure 1).”为依据；B选项题眼为 reproduction，为the Colonial Theory 提到的内容，文章中“Initially, some of these cells were better suited for reproduction, and- these became the reproductive cells of the metazoan. ”为依据，提出了此观点，但全文中未给出解释，所以B为正确答案；C选项明显可知由第三种理论提出，文章中“Proponents of this theory argue that 2 separate protozoan lines led to metazoans. ”为依据，并且从第二段可知与第二种理论无关；D选项文章未涉及。

★例题练习 1.7

Proponents of all 3 theories would agree with which of the following, conclusions about the evolution of metazoans?

F. Bilaterally and radially symmetrical metazoans evolved at different times.

G. The first metazoan was a jellyfish-like organism with flagella.

H. The evolution of metazoans led to the extinction of protozoans.

J. Bilaterally symmetrical metazoans are more advanced than radially symmetrical metazoans.

【考点分析】

• 观点（理论）冲突类文章（综合观点题）
• 抓住定位词Proponents of all 3 theories ，考察对全文的掌握。
• 排除法来做，先看F选项，从最后一段最后一句可以找到支持，同时另外两种理论也未就此进行反驳，故而F选项应为正确；G选项为第二个理论观点，根据文章中“The first metazoans were aquatic, flagellated, radially symmetrical organisms (body parts arranged symmetrically around a central point, as in modern jellyfish).” ，可找到依据，但从第二段可知，第一个理论支持 flatworm-like 结构，与G选项不同；H&J选项全文并未提及。

知识拓展——后生动物

• 后生动物(Metazoa)是除原生动物外所有其他动物的总称（后生动物亚界）。动物界除原生动物门以外的所有多细胞动物门类的总称。其特征是体躯由大量形态有分化、机能有分工的细胞构成；与群体原生动物的兼有营养和生殖功能的细胞不同，其生殖细胞和营养细胞有明显的分化；依体制形态的对称情况，后生动物可分为不对称动物（多孔动物门）、辐射对称动物（腔肠动物门、栉水母动物门、棘皮动物门；后者的对称是次生的、栉水母和某些珊瑚是左右辐射对称）和两侧对称动物（其他所有门类）。

• 后生动物系来自原生动物的祖先已毫无疑问，但什么样的原生动物是其祖先则议论很多。大致可分： （1）是多核原生动物的细胞分化结果[纤毛虫类起源说，认为从多核纤毛类产生原始的扁形动物，腔肠动物是由此而来的次生性动物]； （2）从老的学说来看，认为是从团藻那样的鞭毛虫群体演化而来。在这两种学说中，一般认为前者的论据不足，赞成后者的人比较多。后者的论点：认为这种群体构造是后生动物没有变化的胚芽；构成群体中的个体，按照极轴产生构造上的变化；分化成营养个员和生殖个员；在形成群体的过程中，特别类似于海绵动物的个体发生；后生动物的雄性生殖细胞保持着鞭毛虫的形态等等。

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