[07 - 01] tpo2p1 - tpo3c1 - lecture

[ TOP17 - P1 ] Symbiotic Relationships

At times, it is actually possible to watch the effects of natural selection in host-parasite relationships. For example, Australia during the 1940's was overrun by hundreds of millions of European rabbits. The rabbits destroyed huge expanses of Australia and threatened the sheep and cattle industries. In 1950, myxoma virus, a parasite that affects rabbits, was deliberately introduced into Australia to control the rabbit population. Spread rapidly by mosquitoes, the virus devastated the rabbit population. The virus was less deadly to the offspring of surviving rabbits, however, and it caused less and less harm over the years. Apparently, genotypes (the genetic make-up of an organism) in the rabbit population were selected that were better able to resist the parasite. Meanwhile, the deadliest strains of the virus perished with their hosts as natural selection favored strains that could infect hosts but not kill them. Thus, natural selection stabilized this host-parasite relationship.

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        industries  n. 工业;行业;勤奋;勤劳;生产制造 industry的复数

        perished  v. 死亡;毁灭;丧失;(使橡胶等)老化，脆裂;湮灭;暴死 perish的过去分词和过去式

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According to paragraph 3, all of the following characterize the way natural selection stabilized the Australian rabbit population EXCEPT:

A. The most toxic viruses died with their hosts.

B. The surviving rabbits were increasingly immune to the virus.

C. The decline of the mosquito population caused the spread of the virus to decline.

D. Rabbits with specific genetic make-ups were favored.

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The third type of symbiosis, mutualism, benefits both partners in the relationship. Legume plants and their nitrogen-fixing bacteria, and the interactions between flowering plants and their pollinators, are examples of mutualistic association. In the first case, the plants provide the bacteria with carbohydrates and other organic compounds, and the bacteria have enzymes that act as catalysts that eventually add nitrogen to the soil, enriching it. In the second case, pollinators (insects, birds) obtain food from the flowering plant, and the plant has its pollen distributed and seeds dispersed much more efficiently than they would be if they were carried by the wind only. Another example of mutualism would be the bull's horn acacia tree, which grows in Central and South America. The tree provides a place to live for ants of the genus Pseudomyrmex. The ants live in large, hollow thorns and eat sugar secreted by the tree. The ants also eat yellow structures at the tip of leaflets; these are protein rich and seem to have no function for the tree except to attract ants. The ants benefit the host tree by attacking virtually anything that touches it. They sting other insects and large herbivores (animals that eat only plants) and even clip surrounding vegetation that grows near the tree. When the ants are removed, the trees usually die, probably because herbivores damage them so much that they are unable to compete with surrounding vegetation for light and growing space. The complex interplay of species in symbiotic relationships highlights an important point about communities: Their structure depends on a web of diverse connections among organisms.

According to paragraph 5, the relationship between legumes and bacteria benefits the soil by

A. adding enriching carbohydrates

B. speeding the decay of organic matter

C. destroying enzymes that pollute it

D. contributing nitrogen to it

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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. The relationship between flowering plants and pollinators provides pollinators with food and flowers with efficient reproduction.

B. In some cases birds obtain food from the seeds that are dispersed in the wind.

C. The wind not only helps the flowers distribute their seeds but enables birds to find more food.

D. Animals and insects are more effective in distributing pollen and seeds than the wind.

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According to paragraph 5, which of the following is NOT true of the relationship between the bull’s horn acacia tree and the Pseudomyrmex ants?

A. Ants defend the host trees against the predatory actions of insects and animals.

B. The acacia trees are a valuable source of nutrition for the ants.

C. The ants enable the acacia tree to produce its own chemical defenses.

D. The ants protect the acacia from having to compete with surrounding vegetation.

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        unforeseen  adj. 不可预见的;始料不及的;未想到的

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What is the main purpose of this passage?

A. To explain the concept of symbiosis by expanded descriptions of its principal types

B. To make a comparison between human relationships and symbiotic interactions in the natural world

C. To demonstrate the unforeseen benefits of natural processes that at first seem wholly destructive

D. To argue that parasitism is a problem that can be solved by scientific intervention

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At times, it is actually possible to watch the effects of natural selection in host-parasite relationships. For example, Australia during the 1940's was overrun by hundreds of millions of European rabbits. [ ] The rabbits destroyed huge expanses of Australia and threatened the sheep and cattle industries. [ ] In 1950, myxoma virus, a parasite that affects rabbits, was deliberately introduced into Australia to control the rabbit population. [ ] Spread rapidly by mosquitoes, the virus devastated the rabbit population. [ ] The virus was less deadly to the offspring of surviving rabbits, however, and it caused less and less harm over the years. Apparently, genotypes (the genetic make-up of an organism) in the rabbit population were selected that were better able to resist the parasite. Meanwhile, the deadliest strains of the virus perished with their hosts as natural selection favored strains that could infect hosts but not kill them. Thus, natural selection stabilized this host-parasite relationship.

Look at the four squares [ ] that indicate where the following sentence could be added to the passage.

This massive population began a century earlier as a mere twelve pairs of imported rabbits that reproduced quickly and developed into a major problem.

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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.

Answer Chiose:

A. Parasitic relationships involve the interplay of aggression by the parasite and resistance and adaptation by the host.

B. Parasitic damage to Australian rabbits was never reversed because the rabbits were unable to adapt to the parasites’ attacks.

C. Mutualism ordinarily involves an interaction between two members of the same species.

D. The rarity of commensal relationships stems from the difficulty of finding relationships that benefit one species without affecting the other.

E. Mutualism is unique among symbiotic relationships in that it benefits both partners involved in the relationship.

F. The structure of biological communities depends on the types of relationships that exist among the species within.

Symbiotic relationships involve the interaction of two or more organisms acting as partners.

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[ TOP23 - P2 ] Rock Art of the Australian Aborigines

Ever since Europeans first explored Australia, people have been trying to understand the ancient rock drawings and carvings created by the Aborigines, the original inhabitants of the continent. Early in the nineteenth century, encounters with Aboriginal rock art tended to be infrequent and open to speculative interpretation, but since the late nineteenth century, awareness of the extent and variety of Australian rock art has been growing. In the latter decades of the twentieth century there were intensified efforts to understand and record the abundance of Australian rock art.

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        approach  n. 方法;方式;(距离和时间上的)接近;要求;建议;进场;接洽;通路;相似

        examined  v. (仔细地)检查，检验;审查;调查;考察;考，测验

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According to paragraph 1, the twentieth-century approach to studying Australian rock art was different from earlier approaches because the twentieth-century approach

A. recognized that many different groups of Aborigines created Australian rock art

B. concentrated on a limited range of Aboriginal rock art

C. examined Aboriginal art from an Aboriginal rather than from a European perspective

D. focused more intensely on understanding and documenting rock art

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The word "discern" in the passage is closest in meaning to

A. indicate

B. apply

C. identify

D. repeat

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Although the remarkable antiquity of Australia`s rock art is now established, the sequences and meanings of its images have been widely debated. Since the mid-1970s a reasonably stable picture has formed of the organization of Australian rock art. In order to create a sense of structure to this picture, researchers have relied on a distinction that still underlies the forms of much indigenous visual culture-a distinction between geometric and figurative elements. Simple geometric repeated patterns-circles, concentric circles, and lines-constitute the iconography (characteristic images) of the earliest rock-art sites found across Australia. The frequency with which certain simple motifs appear in these oldest sites has led rock-art researchers to adopt a descriptive term-the Panaramitee style-a label which takes its name from the extensive rock pavements at Panaramitee North in desert South Australia, which are covered with motifs pecked into the surface. Certain features of these engravings lead to the conclusion that they are of great age-geological changes had clearly happened after the designs had been made and local Aboriginal informants, when first questioned about them, seemed to know nothing of their origins. Furthermore, the designs were covered with "desert varnish," a glaze that develops on rock surfaces over thousands of years of exposure to the elements. The simple motifs found at Panaramitee are common to many rock-art sites across Australia. Indeed, sites with engravings of geometric shapes are also to be found on the island of Tasmania, which was separated from the mainland of the continent some 10,000 years ago.

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. The oldest rock art sites have simpler motifs than the best known sites of Panaramitee North.

B. Because motifs primarily associated with the Panaramitee region are common in the oldest sites, the term Panaramitee style has become the general term for rock art of this type.

C. Because the Panaramitee style is so common in the older sites, researchers have described it most extensively.

D. The motifs carved in the rocky surface of the Panaramitee region make up the oldest form of rock art discovered in Australia.