TOEFL | 生物/生态学相关习题精练+词汇整理

Biological invasions by exotic species are an escalating threat to biodiversity around the globe. Invasive species can displace native ones and irrevocably alter ecosystems. Most imported species either die or have limited growth in their new home, but a small percentage of the newcomers are opportunists whose growth is dangerously out of control. The story of how Caulerpa taxifolia became famous as one of these species began in 1989, when Dr. Alexandre Meinesz, a marine biologist at the University of Nice in France, learned that this exotic alga, which is native to the Caribbean and other tropical seas, was thriving in the Mediterranean waters off the coast of Monaco. Upon investigation, Meinesz discovered that a mutant variety of C. taxifolia was dumped into the Mediterranean with other aquarium refuse by the prestigious Oceanographic Institute of Monaco. Eventually, the C. taxifolia was traced back to a stock developed at the Wilhelma Zoological and Botanical Gardens in Stuttgart, Germany. This stock of C. taxifolia had caught the attention of amateur and professional aquarists for its exceptional beauty and hardiness and had been widely distributed in public and private aquaria in the 1980s.

Instead of dying in the cold winter waters of the Mediterranean Sea as the tropical variety of C. taxifolia does, the mutant variety can withstand several months at temperatures that range between 10° and 13° C. In addition, the alga grows equally well on a variety of ocean substrates—sand, mud, or rocks—and from near the surface to depths of 50 meters. When temperatures exceed 18°C, the mutant Caulerpa grows at a remarkable rate, capable of elongating by 2 centimeters in a single day and forming a new frond every 2 days. A single square meter of seafloor can be matted with 5,500 leafy fronds. All of this growth is asexual. Unlike the tropical form, the mutated form of C. taxifolia produces only male gametes in the Mediterranean and thus replicates only by fragmentation. Just a small piece can regenerate and colonize an area. In fact, it is believed that fishing nets and boat anchors as well as the ripping action of storms have helped the alga spread to new areas.

With such a rapid rate of growth, the Mediterranean Caulerpa grows quickly over the sea bottom, blanketing all other sea life such as marine angiosperms, native algae, corals, and sea fans. lt cuts off vital essentials such as sunlight for photosynthesis and currents for filter feeding of nutrients. The area becomes a Caulerpa lawn while species diversity is lost. In addition, C, taxifolia is inedible to most marine herbivores because of the presence of toxic compounds, primarily caulerpenyne. With no predator to inhibit its phenomenal growth, the alga had encompassed the Mediterranean coasts of Monaco, France, Italy, Spain, and the Croatian coast on the Adriatic Sea covering 30,000 hectares by 2002. Caulerpa infestations have also been found in southern Australia, in estuaries near Sydney and Adelaide.

Various methods have been tried to eradicate this deadly invader. Divers have been employed to rip the alga out by hand, but care must be taken because even a small fragment is capable of colonizing new areas. Black plastic tarps have been placed over the alga in an attempt to deprive it of life-giving sunlight. Chemicals such as copper, a conventional algicide, and toxic levels of salt have also been applied to Caulerpa fields. There has been limited success but only if the area of invasion is small.

One hopeful avenue is biological control. In biological control, a disease or predator of the invasive organism is introduced and allowed to destroy it. In the native range of the tropical C. taxiolie, two species of sea slug are immune to its poisons and feed on the alga exclusively. They suck the cytoplasm out of the leaves and incorporate the algal chloroplasts, the part of the plant that contains green photosynthetic pigment, into their skin. [█] The chloroplasts provide camouflage as the snails feed in the Caulerpa fields and, surprisingly, continue to photosynthesize, providing additional nutrition for the slugs. [█] Dr. Meinesz is suggesting the importation of these slugs to the Mediterranean as the only way to eliminate the immense area that Caulerpa now covers. [█] But many experts fear that another exotic importation may lead to more environmental damage. [√]

• According to paragraph 1, what event first caused Caulerpa taxifolia to become publicly known as a damaging species?

  • Marine biologist Alexandre Meinesz identified a variety of C. taxiolia growing in the Mediterranean near Monaco
  • The Oceanographic Institute of Monaco disposed of a variety of C. taxiolia in the Mediterranean
  • The Wilhelma Zoological and Botanical Gardens developed a new variety of C. taxifolia
  • A variety of C. taxifolia became widely distributed in public and private aquaria

• According to paragraph 2, which of the following is true of the mutant variety of C. taxifolia?

  • It grows more rapidly on ocean substrates than near the surface of the sea
  • It thrives only when temperatures rise above 18°C
  • It dies when the temperature drops below 13°C
  • It reproduces through fragmentation

• What can be inferred from paragraph 2 about the reproduction of the tropical form of C. taxifolia?

  • It is accomplished asexually and at a slower pace than that of the mutant form of C taxifolia.
  • It may be accomplished sexually, from the union of male and female gametes.
  • It occurs due to fragmentation caused by both human activity and storms.
  • It takes place only in winter, when temperatures are colder.

• Which of the following is true of Caulerpa in the Mediterranean, as described in paragraph 3?

  • It grows over native species, depriving them of sunlight and nutrients
  • It poisons native plant species with its toxic compounds
  • It feeds on native marine herbivores
  • It grows on the surface of the sea

• According to paragraphs 4 and 5, which of the following is NOT a method that has been used in trying to eliminate C. taxifolia from Mediterranean waters?

  • Having divers pull it out by hand
  • Putting dark plastic tarps over it
  • Applying algicides and salt to it
  • Importing toxin-immune sea slugs to feed on it

• The word “exclusively” in the passage is closest in meaning to

  • entirely
  • heavily
  • mostly
  • frequently

• The word “immense” in the passage is closest in meaning to

  • general
  • vast
  • additional
  • primary

• Which of the following statements best describes the organization of the passage?

  • A description of an ecological problem is followed by a discussion of some possible solutions of the problem.
  • A general statement about an ecological problem is followed by a discussion of several species examples that support the general statement.
  • An argument about the hazards of certain ecological practices is followed by a discussion of alternatives to those practices.
  • A description of certain harmful ecological practices is followed by a discussion of the origins of the practices.

• Look at the four squares[█] that indicate where the following sentence can be added to the passage.Where would the sentence best fit?Click on a square[█] to insert the sentence in the passage.
  How can we predict that the presence of the sea slugs will not harm a native Mediterranean species?

• 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 answer choices 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 questions is worth 2 points.
  Caulerpa taxifolia is an invasive imported species that threatens the biodiversity of the Mediterranean.

  • C. taxifolia first caught the attention of amateur and professional aquarists after it was widely distributed in public and private aquaria in the 1980s.
  • Unlike the tropical variety, the mutant variety of C. taxifolia can endure both cold and warm temperatures and can reproduce extremely quickly.
  • C. taxiolia threatens sea life in the Mediterranean by cutting off access to life essentials such as sunlight and nutrients.
  • Some experts believe that fishing nets, boat anchors, and even violent storms are to blame for the rapid spread of C. taxifolia.
  • Attempts to eliminate C. taxifolia from the Mediterranean have met with only limited success, and an untried method of biological control is risky, some experts say.
  • Not only are the algal chloroplasts of C. taxifolia harmless to the sea slugs that eat it, but they also provide additional nutrition for the predators.

Some of the least costly defenses, in terms of energy use, available to plants are structures that make penetration by predators difficult, if not impossible. These include tough leaves, spines, and epidermal hairs on leaves, which may trap, impale, or fence out insects and discourage browsing by vertebrate herbivores, as well as hard-coated seeds. These structures may have evolved early in the history of the plants, when they might have been subject to even greater predatory pressures. Because they represent little investment, plants still retain them.

Many seeds have thick, hard seed coats that provide protection from seed-eating animals. The problem with such seed defense is that the seeds need to be scarified—the hard seed needs scratching or scoring of the seed coat to weaken it—so the seedling itself can escape. If the seed is not scarified, the seedling embryo is sealed in, never to germinate. Many plants, however, have turned seed predation into a mechanism for seed dispersal, such as the transport and caching of seeds by squirrels, jays, mice, and ants.

The role of structural defenses in plants was largely presumed until experimental evidence was sought to demonstrate the effectiveness of such apparent defensive structures against grazing herbivores. Researchers investigated experimentally the effects of plant spinescence on the feeding habits of three large browsing mammalian herbivores of Africa. These were the kudu, a large African antelope attaining a female body weight of 180 kilograms; the impala, a medium-sized African antelope attaining a female body weight of 50 kg; and the Boer goat, a domestic ungulate weighing about 35 kg. The experimenters hand reared the antelope from calves to allow observation of feeding habits from very close range, 1 to 5 meters, under natural conditions, to determine biting rates the animals employed. They converted the bites to dry biomass by collecting samples of leaves and shoots of a size similar to those eaten and drying them to a constant weight. They calculated eating rate as the product of bite size (dry mass) and biting rate.

Another one of their experiments involved a detailed study to examine the influence of spinescence. They selected ten plants each of five species of trees at a height accessible to impalas outside the enclosure. The woody plants exhibited three basic types of spinescence : paired prickles or thorns situated in or close to the leaf axils ; short, sharp-tipped branchlets or spines, sometimes carrying small leaves ; and prickles of various kinds on leaves. Thorns were either straight and long, up to 70 millimeters, or short and sharply curved (hooked). On each tree, two branches were matched for size, shape, density of leaf cover, and ease of access to impalas. These paired branches were labeled and the thorns were removed from one of the branches in each pair. Two months later, researchers visually estimated the relative loss of foliage from browsing.

Results clearly showed that thorns and spines affected the feeding behavior of the three ungulates. These structures restricted bite sizes to mostly single leaves or leaf clusters, and hooked thorns retarded biting rates. Acceptability of leaves of those plant species offering small leaf size along with prickles was lower, at least for kudu, than those of other palatable plant species. The inhibitory effect of prickles was greater for impalas and goats than for kudu, which bit off the shoot ends in spite of the prickles. For certain straight-thorned species, kudu compensated partially for their slow eating rates by spending more time gathering the leaves. Most spinescent species were similar to unarmed palatable species in their acceptability to the ungulates, even though the armed species had a higher crude protein to their foliage. Probably these spinescent species, especially species of Acacia plants, would be preferred over unarmed species but for the thorns.

[█] The main effect of these armed structural defense features is to restrict bite size, thus increasing handling time. Thorns, spines, and prickles restrict foliage losses to large herbivores. [√] In addition, the animals may incur scar tissue in the esophagus and scratches in the mouth and throat. [█] These experiments show that at least in some cases structural plant defenses are effective at protecting plants. [█]

• The word “retain” in the passage is closest in meaning to

  • keep
  • need
  • defend
  • develop

• Paragraph 1 supports which of the following statements about the defense system of plants?

  • Its development requires lots of energy on the part of the plant.
  • Its design is less elaborate today than at the time of its origin.
  • It was probably of greater necessity in the early stages of plant evolution.
  • It developed relatively late in the plant’s evolutionary history.

• What can be inferred from paragraph 2 about seed-producing plants?

  • They depend on one particular animal species to disperse their seeds.
  • Some of them have turned seed predation into an action that benefits them.
  • Most are quite vulnerable to attacks by predatory animals.
  • Most have seedlings that automatically emerge out of the seed coats.

• According to paragraph 3, which of the following claims is true about research into plant defenses?

  • It revealed that bite size and biting rates vary depending on how dry the vegetation is.
  • It has generally focused on the effects of plant defense structures on herbivores living in the wild.
  • It has shown that plant spinescence is most effective at stopping predation by young female herbivores.
  • It attempted to find evidence that plant structures affect the feeding of herbivores.

• The word “retarded” in the passage is closest in meaning to

  • slowed
  • controlled
  • increased
  • determined

• According to paragraph 4, all of the following are true about the experiment involving African mammalian herbivores EXCEPT:

  • It included a variety of plant species.
  • It involved removing the thorns from half the branches in the sample.
  • It required researchers to accurately count the number of leaves lost from each branch.
  • It involved a two-month waiting period.

• 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.

  • The ungulates favored leaves rich in protein regardless of whether the leaves grew on thorny plants or on plants without thorns.
  • The ungulates consumed thorny plants high in protein and thorn-free plants with less protein at about the same rate.
  • The ungulates fed on most of the thorny plants the researchers had selected for the purpose of the experiment.
  • The more a thorny plant resembled one that did not have thorns, the more likely the ungulates were to feed on it.

• Which of the following best describes the organization of the passage?

  • The energy costs of plant defense structures are investigated and their significance for plants is illustrated.
  • The findings of one study on plant defense structures are contrasted with the findings of earlier research.
  • A number of features of large African herbivores are described with particular emphasis on their eating habits.
  • The characteristics of some physical defense mechanisms in plants are stated and their impact on predators evaluated.

• Look at the four squares[█]that indicate where the following sentence can be added to the passage.Where would the sentence best fit?Click on a square[█] to insert the sentence in the passage
  Such defensive structures certainly slow feeding time.

• 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 answer choices 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 questions is worth 2 points.
  A long-held assumption in plant biology is that certain features of plants provide protection from predatory attacks

  • Structural features that may fulfill a defensive role include tough leaves, spines and thorns, epidermal hairs, and seeds with hard coats.
  • The focus of one study has been the extent to which thorns and spines impact what and how African herbivores eat.
  • Plants with thorns generally have less protein than plants without, and this may explain why they make up only a small part of the diet of most herbivores.
  • Over the years, a large body of data has been amassed, demonstrating that structural plant defenses are very effective at preventing predation.
  • Analysis of the eating habits of herbivores revealed that the kudu was the only species affected by thorns and spines.
  • Research has shown that plant spinescence may cause an animal to slow down its eating rate, reduce its food intake per bite, and injure itself.

The earliest-known horse fossils come from the Eocene epoch (from 57 to 34 million years ago), and they are so different from the modern version that it was not initially realized that there was any relation. Dawn horse, or Eohippus, as this animal has been called, has been found in both Europe and North America. Eohippus was tiny, about the size of a small dog, and apparently lived in wooded areas. These animals had hooves but, in contrast to modern horses, they had four hoofed toes on the front feet, three on the rear, and the hooves were padded. Eohippus was also pug-nosed by comparison to modern horses, and its teeth reveal that it was a browser that fed on a variety of plants. In fact, although it was completely herbivorous (plant eating), this little horse had canine teeth—a reminder that many of its predecessors were carnivores (meat eaters).

Throughout the Eocene and Oligocene epochs (from 57 to 23 million years ago), the descendants of Eohippus evolved in a fairly straightforward way that is well documented by their fossils. They became gradually larger; the middle toe, eventually to become the single hoof of the modern horses, became stronger and more prominent, and the grinding surfaces of the teeth became larger, with complex, resistant ridges. But the resemblance to Eohippus remained clear. It was only in the Miocene (from 23 to 5 million years ago), coincident with the spread of grassy prairies, that abrupt changes took place, resulting in several different lineages of horse evolution, only one of which is still extant: the modern horse.

Several of the physical characteristics of today’s animals are ultimately linked to their diet of grasses. [█] Foremost among the Miocene modifications that led toward present-day horses were changes in the teeth and the shape of the head. [█] Compared to the succulent leaves of tropical trees that were the fodder for some of the horse’s ancestors, grasses are abrasive and much more difficult to chew and grind. [√] The response of the Miocene horses was to develop teeth with much more elaborate and resistant grinding surfaces and with much larger crowns, at least part of which could grow out of the gums as they were worn down. [█] These changes meant that the head had to be much deeper, and the muzzle longer, to make room for the long rows of grinding teeth along the horse’s cheeks. At about the same time, the legs and feet of the ancestors of today’s horses became better adapted to rapid running across the spreading grasslands. This occurred through fusion of several of the independent bones in the lower parts of the legs, making them stiffer, and through further emphasis of the central hoofed toe, which by now bore the entire weight of the animal. In place of a foot, the horse has a single toe at the end of its leg.

By the middle or late Miocene, many of the extant horses were at least superficially similar to modern horses. Based on the fossil record, much of their development seems to have occurred in North America, but by the Pleistocene epoch (from 1.6 million to 10,000 years ago), the modern horse genus, Equus, had spread over much of the world. Then, inexplicably, only 8,000 to 10,000 years ago, horses disappeared from North America. The reason for this extinction is unknown. Whatever the cause, it is a fact that the plains of North America were without these animals for thousands of years, until horses brought from Europe by the early Spanish explorers escaped and began to repopulate the vast grasslands.

It is clear that many of the familiar features of the modern horse are directly or indirectly related to its diet and its preferred environment, grasslands. But how and why did the grasslands develop when they did? There are competing theories on this question, but only a few are consistent with the evidence. Most of these invoke a change in global climate as an important factor, perhaps the overriding factor. In particular, grasslands expanded rapidly as the climate in continental interiors became cooler and drier.

• In paragraph 1, why does the author mention that Eohippus had canine teeth?

  • To make the point that Eohippus evolved from ancestors with a diet different from that of Eohippus
  • To explain why Eohippus’ teeth were so similar to those of its predecessors
  • To show why scientists believe that Eohippus was exclusively herbivorous
  • To argue that physical features that originally evolved to serve one purpose can later serve a different purpose

• Paragraph 2 supports which of the following claims about the evolution of the horse?

  • The ancestors of the modern horse changed more dramatically in the Miocene than in the earlier Eocene and Oligocene epochs.
  • Most lineages of the modern horse that survived the Eocene and Oligocene epochs became extinct during the Miocene epoch.
  • During the Eocene and Oligocene epochs, the horse lost all but the middle toe on each foot.
  • There is little fossil evidence of how horses evolved during the Miocene epoch.

• The phrase “more elaborate” in the passage is closest in meaning to

  • harder
  • stronger
  • more complex
  • more effective

• According to paragraph 3, the shape of the horse’s head changed in response to the

  • increased difficulty of reaching the leaves of tropical trees
  • horse’s need to become better adapted to running across grasslands
  • larger overall size of the horse’s body
  • changes in the teeth required by the horse’s diet

• All of the following are mentioned in paragraph 3 as changes that appeared in horses’ legs in the Miocene EXCEPT:

  • Some independent leg bones fused together.
  • The upper parts of the legs became strong enough to support the entire body weight.
  • The lower legs became more rigid.
  • More stress was placed on the central hoofed toe.

• 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.
  Whatever the cause, it is a fact that the plains of North America were without these animals for thousands of years, until horses brought from Europe by the early Spanish explorers escaped and began to repopulate the vast grasslands.

  • Early Spanish explorers captured horses from the plains of North America and brought them to grasslands in order to repopulate those areas.
  • Horses did not populate the plains of North America until Spanish explorers planted grassland to ensure survival of these animals.
  • Until the horses brought by Spanish explorers escaped, the North American plains did not have horses for thousands of years.
  • It is a fact that Spanish explorers did not intend their horses to escape and repopulate the grasslands of North America.

• The word “overriding” in the passage is closest in meaning to

  • most reliable
  • dominant
  • most interesting
  • sole

• According to paragraph 5, why are many theories about the development of grasslands not likely to be true?

  • They assume that there was a change in global climate.
  • They cannot explain how a region can become cooler and drier at the same time.
  • They conflict with some established facts.
  • They ignore competing theories.

• Look at the four squares[█] that indicate where the following sentence can be added to the passage.Where would the sentence best fit?Click on a square[█] to insert the sentence in the passage
  Thus the teeth that had evolved in Eocene and Oligocene epochs were not suited for life on the prairies of the Miocene.

• 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 answer choices 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 questions is worth 2 points.
  The fossil record suggests the complexity of the horse’s evolution.

  • Eohippus began to be called dawn horse, after its relationship to the modern horse was established through fossil evidence.
  • During the Eocene and Oligocene epochs, the descendants of the Eohippus began to develop some of the characteristics associated with the modern horse.
  • By the end of the Pleistocene, the modern horse, Equus, had spread over much of the world but for reasons that are unclear, it disappeared from the plains of North America for thousands of years.
  • By the end of the Eocene epoch, Eohippus’ nose had slowly developed into a long muzzle, and the four toes on its front feet had disappeared.
  • As grasslands expanded in the Miocene, horses changed abruptly in ways that made their relationship to modern horses more apparent and developed several lineages.
  • Several theories about the development of grasslands have answered most questions about the evolution of Eohippus and its descendants.