托福閱讀真題Official 44 Passage 3（五）

托福閱讀真題Official 44 Passage 3（五）

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 9 of 14

In paragraph 4,why does the author mention that eelgrass thrives in both the Arctic and in the northeastern United States?

A.To show that environments with extreme temperatures rarely have any effect on eelgrass

B.To identify the northern and southern limits of the range where eelgrass is found

C.To support the author’s statement that eelgrass is a particularly widespread kind of seagrass

D.To cite evidence tending to disprove one view about the importance of temperature to the growth of eelgrass

正確答案：D

題目詳解

題型分類：修辭目的題

題干分析：定位詞：eelgrass thrives in both the Arctic and in the northeastern United States。利用定位詞定位到第四段的第三句。分析該句：邏輯上前后為轉(zhuǎn)折關(guān)系，具體內(nèi)容是說盡管溫度對(duì)于eelgrass的生長(zhǎng)至關(guān)重要，但是在一些溫度（或高或低）的地方還是發(fā)現(xiàn)eelgrass都可以廣泛生長(zhǎng)，也就是證明溫度的影響不是唯一的或絕對(duì)的。該題為句間關(guān)系的修辭目的題。

選項(xiàng)分析：

D選項(xiàng)說disprove one view about the importance of temperature to the growth of eelgrass，與定位句的邏輯和內(nèi)容相符。

A選項(xiàng)說極端溫度的環(huán)境對(duì)eelgrass很少起作用。不符合定位句的前半部分temperature was critical to the growth and reproduction of eelgrass。與原文描述不符。

B選項(xiàng)說確定eelgrass生長(zhǎng)的南北范圍界限。但定位句說的是溫度的影響。無中生有。

C選項(xiàng)說支持eelgrass是一種特別廣泛的海草類型這一觀點(diǎn)，與定位句內(nèi)容不符。

Question 10 of 14

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

A.harmful

B.significant

C.unexpected

D.distinct

正確答案：A

題目詳解

題型分類：詞匯題

題干分析：詞匯所在句子Still,extreme temperatures,in combination with other factors,may have dramatic detrimental effects譯為“當(dāng)然，極端溫度及其他因素可能會(huì)一起產(chǎn)生巨大的不良影響”，detrimental不良的。另外根據(jù)下文的舉例，提到scouring the bottom and uprooting the eelgrass以及cause excessive mortality等，我們也可以得到線索detrimental是表示消極意義的詞匯。

選項(xiàng)分析：

A選項(xiàng)harmful有害的。

B選項(xiàng)significant重要的。

C選項(xiàng)unexpected意料之外的。

D選項(xiàng)distinct獨(dú)特。

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