托福阅读真题Official 45 Passage 3（六）

托福阅读真题Official 45 Passage 3（六）

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 11 of 14

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

A.huge

B.adaptable

C.powerful

D.precise

正确答案：B

题目详解

题型分类：词汇题

选项分析：

词汇所在句“这些动物不仅是牙齿变得很大和/或下巴变长，而且它们的下颌关节非常flexible甚至可以有效地脱臼，所以嘴巴能够张得很大”。下颌可以有效地脱臼，所以猜测flexible意为“灵活的”。即B选项adaptable有适应能力的。

A选项huge巨大的。

C选项powerful强有力的。

D选项precise精确的。

因此，选项B符合题干词意。

Question 12 of 14

According to paragraph 5,why do some fish swallow their prey whole?

A.Their teeth are too large to allow for cutting prey.

B.They have no jaw muscles to allow chewing.

C.Swallowing prey whole results in a higher net energy gain.

D.Chewing can cause their jaws to dislocate.

正确答案：A

题目详解

题型分类：事实信息题

原文定位：根据their prey whole定位到第五段最后一句

选项分析：

A选项too large to allow for cutting prey对应定位句Very large or long teeth provide almost no room for cutting the prey。

B选项no jaw muscles无中生有。

C选项a higher net energy gain无中生有。

D选项与倒数第二句the jaw articulations so flexible that they can be effectively dislocated矛盾。