托福閱讀真題Official 45 Passage 3（四）

托福閱讀真題Official 45 Passage 3（四）

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 7 of 14

The word“scarcity”in the passage is closest in meaning to

A.speed

B.variety

C.lack

D.size

正確答案：C

題目詳解

題型分類：詞匯題

選項分析：

scarcity意思為“不足，缺乏”。詞匯所在句“因此，深水中成功的濾食性動物很少，這部分濾食性動物中有一部分有更大的過濾系統(tǒng)來應(yīng)對有機物的scarcity”，scarcity應(yīng)該與前文的fewer successful filter-feeders情感態(tài)度一致，C選項lack意思為“缺乏”，符合語境。

A選項speed速度。

B選項variety多樣性。

D選項size尺寸。

因此，選項C符合題干詞意。

Question 8 of 14

According to paragraph 4,deep-water filter-feeders have adopted all of the following ways to obtain food EXCEPT

A.developing larger filtering systems

B.capturing prey using sticky tentacles

C.swimming up to the surface at feeding time

D.searching in ocean layers that contain a substantial amount of particles

正確答案：C

題目詳解

題型分類：否定事實信息題

原文定位：本段都在講deep-water filter-feeders，根據(jù)選項定位

選項分析：

A選項larger filtering systems對應(yīng)第一句larger filtering systems。

B選項sticky tentacles出自最后一句sticky tentacles。

D選項a substantial amount of particles對應(yīng)第二句where the particles may be more concentrated。

C選項feeding time無中生有。

因此選擇C選項。

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