托福閱讀真題Official 44 Passage 3（二）

托福閱讀真題Official 44 Passage 3（二）

Seagrasses

Many areas of the shallow sea bottom are covered with a lush growth of aquatic flowering plants adapted to live submerged in seawater.These plants are collectively called seagrasses.Seagrass beds are strongly influenced by several physical factors.The most significant is water motion:currents and waves.Since seagrass systems exist in both sheltered and relatively open areas,they are subject to differing amounts of water motion.For any given seagrass system,however,the water motion is relatively constant.Seagrass meadows in relatively turbulent waters tend to form a mosaic of individual mounds,whereas meadows in relatively calm waters tend to form flat,extensive carpets.The seagrass beds,in turn,dampen wave action,particularly if the blades reach the water surface.This damping effect can be significant to the point where just one meter into a seagrass bed the wave motion can be reduced to zero.Currents are also slowed as they move into the bed.

The slowing of wave action and currents means that seagrass beds tend to accumulate sediment.However,this is not universal and depends on the currents under which the bed exists.Seagrass beds under the influence of strong currents tend to have many of the lighter particles,including seagrass debris,moved out,whereas beds in weak current areas accumulate lighter detrital material.It is interesting that temperate seagrass beds accumulate sediments from sources outside the beds,whereas tropical seagrass beds derive most of their sediments from within.

Since most seagrass systems are depositional environments,they eventually accumulate organic material that leads to the creation of fine-grained sediments with a much higher organic content than that of the surrounding unvegetated areas.This accumulation,in turn,reduces the water movement and the oxygen supply.The high rate of metabolism(the processing of energy for survival)of the microorganisms in the sediments causes sediments to be anaerobic(without oxygen)below the first few millimeters.According to ecologist J.W.Kenworthy,anaerobic processes of the microorganisms in the sediment are an important mechanism for regenerating and recycling nutrients and carbon,ensuring the high rates of productivity—that is,the amount of organic material produced—that are measured in those beds.In contrast to other productivity in the ocean,which is confined to various species of algae and bacteria dependent on nutrient concentrations in the water column,seagrasses are rooted plants that absorb nutrients from the sediment or substrate.They are,therefore,capable of recycling nutrients into the ecosystem that would otherwise be trapped in the bottom and rendered unavailable.

Other physical factors that have an effect on seagrass beds include light,temperature,and desiccation(drying out).For example,water depth and turbidity(density of particles in the water)together or separately control the amount of light available to the plants and the depth to which the seagrasses may extend.Although marine botanist W.A.Setchell suggested early on that temperature was critical to the growth and reproduction of eelgrass,it has since been shown that this particularly widespread seagrass grows and reproduces at temperatures between 2 and 4 degrees Celsius in the Arctic and at temperatures up to 28 degrees Celsius on the northeastern coast of the United States.Still,extreme temperatures,in combination with other factors,may have dramatic detrimental effects.For example,in areas of the cold North Atlantic,ice may form in winter.Researchers Robertson and Mann note that when the ice begins to break up,the wind and tides may move the ice around,scouring the bottom and uprooting the eelgrass.In contrast,at the southern end of the eelgrass range,on the southeastern coast of the United States,temperatures over 30 degrees Celsius in summer cause excessive mortality.Seagrass beds also decline if they are subjected to too much exposure to the air.The effect of desiccation is often difficult to separate from the effect of temperature.Most seagrass beds seem tolerant of considerable changes in salinity(salt levels)and can be found in brackish(somewhat salty)waters as well as in full-strength seawater

Question 3 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.Light particles and debris collect in some seagrass beds,but are washed out of those affected by strong currents.

B.Seagrass beds under the influence of strong currents tend to accumulate many of the lighter particles from other beds.

C.The strength of the currents determines how quickly accumulated seagrass debris is moved out of the beds.

D.Seagrass debris and other light particles are often moved from areas of strong currents to areas of weak currents.

正確答案：A

題目詳解

題型分類：簡化句子題

原文分析：該題型我們從邏輯和主干信息上進行分析處理。首先句中whereas表示前后兩部分為對比；其次我們分別處理兩個部分的主干信息。前半部分的主干信息是在強水流的影響下海草床中的一些較輕的顆粒會被帶走；后半部分對比在較弱的水流中，這些碎屑物質(zhì)則會沉積下來。

選項分析：

A選項中的but對應原句的whereas，表達兩種不同情況，邏輯正確；collect對應accumulate；washed out對應moved out，并且說明是by strong currents。內(nèi)容正確。

B選項說海草床在strong currents中會accumulate，與原句意思相反，內(nèi)容錯誤。

C選項說determines how quickly，原句中沒有提及速度這方面的信息，無中生有。

D選項說moved from areas of strong currents to areas of weak currents，原句沒說是從strong currents移到weak currents，與原句描述不符。

Question 4 of 14

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

A.maintain

B.expel

C.obtain

D.enrich

正確答案：C

題目詳解

題型分類：詞匯題

題干分析：詞匯所在句子It is interesting that temperate seagrass beds accumulate sediments from sources outside the beds,whereas tropical seagrass beds derive most of their sediments from within譯為“有趣的是，溫帶海草床會沉積外來的物質(zhì)，而熱帶海草床則是從內(nèi)部獲得沉積物”，derive獲得，得到。

選項分析：

C選項obtain獲得，得到。

A選項maintain維持。

B選項expel逐出。

D選項enrich使豐富。

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