托福閱讀真題Official 45 Passage 3（三）

托福閱讀真題Official 45 Passage 3（三）

Feeding Strategies in the Ocean

In the open sea,animals can often find food reliably available in particular regions or seasons(e.g.,in coastal areas in springtime).In these circumstances,animals are neither constrained to get the last calorie out of their diet nor is energy conservation a high priority.In contrast,the food levels in the deeper layers of the ocean are greatly reduced,and the energy constraints on the animals are much more severe.To survive at those levels,animals must maximize their energy input,finding and eating whatever potential food source may be present.

In the near-surface layers,there are many large,fast carnivores as well as an immense variety of planktonic animals,which feed on plankton(small,free-floating plants or animals)by filtering them from currents of water that pass through a specialized anatomical structure.These filter-feeders thrive in the well-illuminated surface waters because oceans have so many very small organisms,from bacteria to large algae to larval crustaceans.Even fishes can become successful filter-feeders in some circumstances.Although the vast majority of marine fishes are carnivores,in near-surface regions of high productivity the concentrations of larger phytoplankton(the plant component of plankton)are sufficient to support huge populations of filter-feeding sardines and anchovies.These small fishes use their gill filaments to strain out the algae that dominate such areas.Sardines and anchovies provide the basis for huge commercial fisheries as well as a food resource for large numbers of local carnivores,particularly seabirds.At a much larger scale,baleen whales and whale sharks are also efficient filter-feeders in productive coastal or polar waters,although their filtered particles comprise small animals such as copepods and krill rather than phytoplankton.

Filtering seawater for its particulate nutritional content can be an energetically demanding method of feeding,particularly when the current of water to be filtered has to be generated by the organism itself,as is the case for all planktonic animals.Particulate organic matter of at least 2.5 micrograms per cubic liter is required to provide a filter-feeding planktonic organism with a net energy gain.This value is easily exceeded in most coastal waters,but in the deep sea,the levels of organic matter range from next to nothing to around 7 micrograms per cubic liter.Even though mean levels may mask much higher local concentrations,it is still the case that many deep-sea animals are exposed to conditions in which a normal filter-feeder would starve.

There are,therefore,fewer successful filter-feeders in deep water,and some of those that are there have larger filtering systems to cope with the scarcity of particles.Another solution for such animals is to forage in particular layers of water where the particles may be more concentrated.Many of the groups of animals that typify the filter-feeding lifestyle in shallow water have deep-sea representatives that have become predatory.Their filtering systems,which reach such a high degree of development in shallow-water species,are greatly reduced.Alternative methods of active or passive prey capture have been evolved,including trapping and seizing prey,entangling prey,and sticky tentacles.

In the deeper waters of the oceans,there is a much greater tendency for animals to await the arrival of food particles or prey rather than to search them out actively(thus minimizing energy expenditure).This has resulted in a more stealthy style of feeding,with the consequent emphasis on lures and/or the evolution of elongated appendages that increase the active volume of water controlled or monitored by the animal.Another consequence of the limited availability of prey is that many animals have developed ways of coping with much larger food particles,relative to their own body size,than the equivalent shallower species can process.Among the fishes there is a tendency for the teeth and jaws to become appreciably enlarged.In such creatures,not only are the teeth hugely enlarged and/or the jaws elongated but the size of the mouth opening may be greatly increased by making the jaw articulations so flexible that they can be effectively dislocated.Very large or long teeth provide almost no room for cutting the prey into a convenient size for swallowing;the fish must gulp the prey down whole.

Question 5 of 14

According to paragraph 2,in which of the following ways are baleen whales and whale sharks different from smaller filter-feeders like sardines and anchovies?

A.They are not found in coastal waters.

B.They are caught by commercial fisheries.

C.They filter small animals instead of phytoplankton.

D.They are not carnivores.

正確答案：C

題目詳解

題型分類：事實信息題

原文定位：根據(jù)baleen whales,whale sharks定位到第二段最后一句，先說baleen whales,whale sharks很大程度上是filter-feeders，后用although說他們之間的不同點。

選項分析：

C選項small animals對應(yīng)定位句small animals such as copepods and krill，C選項正確。

A選項與定位句in productive coastal or polar waters矛盾。

B選項caught無中生有。

D選項not carnivores與定位句filtered particles comprise small animals矛盾。

Question 6 of 14

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.An organism may obtain food particles from seawater when currents generated by the organism cause water to pass through its filter.

B.The nutritional content of the food particles in seawater is sufficient to meet the energy demands of most planktonic animals.

C.As planktonic animals require a lot of energy,they have to generate a current strong enough to bring them sufficient particles of food.

D.Organisms that filter seawater to meet their nutritional needs expend a lot of energy,especially those organisms that have to create their own currents.

正確答案：D

題目詳解

題型分類：簡化句子題

原文分析：考察識別主干內(nèi)容和核心邏輯的能力，原句主干為：過濾海水的顆粒物營養(yǎng)成分可以是一種需要很多能量的進(jìn)食方法，特別是當(dāng)過濾的水流必須由生物體自身產(chǎn)生時，就像所有浮游動物一樣。這句話有兩個內(nèi)容：1.過濾需要很大能量；2.尤其當(dāng)水流需要生物自己去產(chǎn)生。

選項分析：

D選項包含了原句的兩個內(nèi)容，expend a lot of energy對應(yīng)原句an energetically demanding method，create their own currents對應(yīng)原句the current...generated by the organism itself。所以選擇D選項。

A選項邏輯關(guān)系錯誤，原句第二個內(nèi)容是第一個內(nèi)容的特別情況，而不是第一個內(nèi)容的條件。

B選項，sufficient to meet the energy demands原句沒有討論。

C選項邏輯關(guān)系錯誤，浮游生物需要能量不是后者的原因。原句中的as也不是因果關(guān)系，而是定語從句的關(guān)系詞。

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