『新东方在线托福听力』为托福考生准备了ETS托福TPO/Official 35 Passage 3阅读练习，TPO/Official 35 Passage 3原文答案解析，TPO/Official 35 Passage 3阅读原文练习音频翻译。

托福TPO/Official 35 Passage 3阅读原文题目答案及解析-新东方托福官方网校手机版

浮游植物是微小的能够自由浮动的水生植物。

Phytoplankton are minute, free-floating aquatic plants.

在一年的过程中，浮游植物除了在数量上可以观察到有显著的变化外，在物种组成上也有明显的改变。

In addition to the marked changes in abundance observed in phytoplankton over the course of a year, there is also a marked change in species composition.

优势物种在季节上的变化被称为季节演替，它会在很多地点发生。

This change in the dominant species from season to season is called seasonal succession, and it occurs in a wide variety of locations.

在此过程中，一种或多种物种会在浮游植物中占主导地位，时间或长或短，之后会被其他物种的组合所替代。

Under seasonal succession, one or more species dominate the phytoplankton for a shorter or longer period of time and then are replaced by another set of species.

这种演替不同于典型的陆地生态演替，在后者中不同植物彼此替代，直到最后发展成为所谓的顶级群落并持续多年。

This succession is different from typical terrestrial ecological succession in which various plants replace one another until finally a so-called climax community develops, which persists for many years.

有哪些因素导致了这一现象呢？

What are the factors causing this phenomenon?

鉴于季节演替在（海水温度全年有显著变化的）温带海洋中最常见且最清楚地被观察到，因此温度被认为是一个原因。

Considering that seasonal succession is most often and clearly seen in temperate seas, which have a marked change in temperature during a year, temperature has been suggested as a cause.

这可能是一个原因，但这不可能是唯一的原因，因为有些物种能够在不同的温度下成为优势物种。

This may be one of the factors, but it is unlikely to be the sole cause because there are species that become dominant species at various temperatures.

此外，温度在海水中的变化相当慢，而优势物种的更替速度通常却快得多。

Furthermore, temperature changes rather slowly in seawater, and the replacement of dominant species often is much more rapid.

另一种被提出的原因是一年内海水中营养水平的变化，营养物质浓度的不同有利于不同浮游植物物种的生长。

Another suggested reason is the change in nutrient level over the year, with differing concentrations favoring different phytoplankton species.

这一因素可能也是原因之一，有观察表明不同浮游植物数量的起伏要远远快于营养物质浓度的变化。

While this factor may also contribute, observations suggest that phytoplankton populations rise and fall much more quickly than nutrient concentrations change.

然而，另一种解释是生活在海水里的浮游植物对海水所带来的变化导致了物种演替。

Yet another explanation is that species succession is a consequence of changes in seawater brought about by the phytoplankton living in it.

每一种浮游植物物种都会向海水分泌或排泄有机分子。

Each species of phytoplankton secretes or excretes organic molecules into the seawater.

这些代谢物会对生活在海水中的生物体造成影响，抑制或促进它们的生长。

These metabolites can have an effect on the organisms living in the seawater, either inhibiting or promoting their growth.

对于任何个体生物来说，所分泌的代谢物的量是很少的。

For any individual organism, the amount of metabolite secreted is small.

但在优势物种中所有个体分泌物量的影响对其自身和其他物种来说都是巨大的。

But the effect of secretions by all the individuals of the dominant species can be significant both for themselves and for other species.

这些有机代谢物能够、并且很可能的确包含多种不同的有机化合物。

These organic metabolites could, and probably do, include a number of different classes of organic compounds.

有些很可能是毒素，例如腰鞭毛虫（一种浮游植物）在赤潮期间所释放的物质会抑制其他光合生物的生长。

Some are likely toxins, such as those released by the dinoflagellates (a species of plankton) during red tides, which inhibit growth of other photosynthetic organisms.

在这种情况下，数量激增并达到数以十亿计的腰鞭毛虫会导致海水变成与其细胞一样的棕红色。

In such cases, the population explosion of dinoflagellates is so great that the water becomes brownish red in color from the billions of dinoflagellate cells.

虽然每个细胞只分泌微量的毒素，但大量腰鞭毛虫所产生毒素的浓度足以杀死很多生物。

Although each cell secretes a minute amount of toxin, the massive dinoflagellate numbers cause the toxin to reach concentrations that kill many creatures.

这种毒素会在例如蛤蜊和蚌类等滤食性生物体内聚集，从而导致人类中毒。

This toxin can be concentrated in such filter-feeding organisms as clams and mussels, rendering them toxic to humans.

Another class of metabolite is the vitamins.

众所周知，特定的浮游植物物种需要特定的维生素，同时不同浮游植物物种对维生素的需求存在很大差异。

It is now known that certain phytoplankton species have requirements for certain vitamins, and that there are considerable differences among species as to requirements.

B族维生素，尤其是维生素B12，硫胺素以及生物素通常是最为必备的维生素。

The B vitamins, specially vitamin B12, thiamine, and biotin, seem to be the most generally required.

如果水中缺少某一特定维生素或者某些维生素时，有些物种就无法生存。

Some species may be unable to thrive until a particular vitamin, or group of vitamins, is present in the water.

这些维生素只能由其他物种所生产；因此，当生产某种维生素的物种首先出现，需要该维生素的物种就会随之出现，物种更替就能够发生。

These vitamins are produced only by another species; hence, a succession of species could occur whereby first the vitamin-producing species is present and then the vitamin-requiring species follows.

其他能够抑制或促进不同物种生存的有机化合物包括氨基酸、碳水化合物和脂肪酸。

Other organic compounds that may inhibit or promote various species include amino acids, carbohydrates, and fatty acids.

尽管有怀疑认为这些有机代谢物或许在物种演替中起到重要作用，而且有实验证明不同种类的浮游植物在生产所需维生素的能力以及为了生长对维生素的需求是不同的，但是它们在海里所发挥的真正作用依旧缺乏足够的证据。

Although it is suspected that these organic metabolites may have an important role in species succession and it has been demonstrated in the laboratory that phytoplankton species vary both in their ability to produce necessary vitamins and in their requirements for such in order to grow, evidence is still inadequate as to their real role in the sea.

也有证据表明食草动物（以植物为食的动物或静态动物），尤其是较为挑剔的食草动物会影响到浮游植物的物种组成。

There is also evidence to suggest that grazers (animals that feed on plants or stationary animals),particularly selective grazers, can influence the phytoplankton species composition.

很多桡足动物（小型食草类甲壳纲动物）和无脊椎动物的幼体会从混合的种群中挑出特定的浮游植物物种，从而改变物种组成。

Many copepods (small, herbivorous crustaceans) and invertebrate larvae pick out selected phytoplankton species from mixed groups, changing the species composition.

有越来越多的证据表明，这里所涉及到的所有因素会同时产生作用来引发物种演替。

A growing body of evidence now suggests that all of the factors considered here are operating simultaneously to produce species succession.

任何一种因素的重要性都会随着特定浮游植物种类和环境条件而发生改变。

The importance of any factor will vary with the particular phytoplankton species and the environmental conditions.

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

According to paragraph 2, one reason temperature is not likely to be the sole cause of seasonal succession in phytoplankton is

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

Why does the author provide the information that “phytoplankton populations rise and fall much more quickly than nutrient concentrations change”?

According to paragraph 4, all of the following are true about metabolites secreted by phytoplankton EXCEPT:

According to paragraph 5, all of the following statements are true about dinoflagellates EXCEPT:

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

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

Paragraph 6 supports which of the following statements about a phytoplankton species that cannot produce thiamine?

The copepods mentioned in paragraph 8 are

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

Which of the following statements best describes how the passage is organized?

Look at the four squares  that indicate where the following sentence could be added to the passage. In fact, seasonal succession has been observed all over the globe, from the Arctic to the Tropics.  Where would the sentence best fit? Click on a square  to add the sentence to the passage.

Directions: An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. Some sentences do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points.

Seasonal Succession in Phytoplankton Phytoplankton are minute, free-floating aquatic plants. In addition to the marked changes in abundance observed in phytoplankton over the course of a year, there is also a marked change in species composition.  This change in the dominant species from season to season is called seasonal succession, and it occurs in a wide variety of locations.  Under seasonal succession, one or more species dominate the phytoplankton for a shorter or longer period of time and then are replaced by another set of species.  This pattern is repeated yearly.  This succession is different from typical terrestrial ecological succession in which various plants replace one another until finally a so-called climax community develops, which persists for many years. What are the factors causing this phenomenon? Considering that seasonal succession is most often and clearly seen in temperate seas, which have a marked change in temperature during a year, temperature has been suggested as a cause. This may be one of the factors, but it is unlikely to be the sole cause because there are species that become dominant species at various temperatures. Furthermore, temperature changes rather slowly in seawater, and the replacement of dominant species often is much more rapid. Another suggested reason is the change in nutrient level over the year, with differing concentrations favoring different phytoplankton species. While this factor may also contribute, observations suggest that phytoplankton populations rise and fall much more quickly than nutrient concentrations change. Yet another explanation is that species succession is a consequence of changes in seawater brought about by the phytoplankton living in it. Each species of phytoplankton secretes or excretes organic molecules into the seawater. These metabolites can have an effect on the organisms living in the seawater, either inhibiting or promoting their growth. For any individual organism, the amount of metabolite secreted is small. But the effect of secretions by all the individuals of the dominant species can be significant both for themselves and for other species. These organic metabolites could, and probably do, include a number of different classes of organic compounds. Some are likely toxins, such as those released by the dinoflagellates (a species of plankton) during red tides, which inhibit growth of other photosynthetic organisms. In such cases, the population explosion of dinoflagellates is so great that the water becomes brownish red in color from the billions of dinoflagellate cells. Although each cell secretes a minute amount of toxin, the massive dinoflagellate numbers cause the toxin to reach concentrations that kill many creatures. This toxin can be concentrated in such filter-feeding organisms as clams and mussels, rendering them toxic to humans. Another class of metabolite is the vitamins. It is now known that certain phytoplankton species have requirements for certain vitamins, and that there are considerable differences among species as to requirements. The B vitamins, specially vitamin B12, thiamine, and biotin, seem to be the most generally required. Some species may be unable to thrive until a particular vitamin, or group of vitamins, is present in the water. These vitamins are produced only by another species; hence, a succession of species could occur whereby first the vitamin-producing species is present and then the vitamin-requiring species follows. Other organic compounds that may inhibit or promote various species include amino acids, carbohydrates, and fatty acids. Although it is suspected that these organic metabolites may have an important role in species succession and it has been demonstrated in the laboratory that phytoplankton species vary both in their ability to produce necessary vitamins and in their requirements for such in order to grow, evidence is still inadequate as to their real role in the sea. There is also evidence to suggest that grazers (animals that feed on plants or stationary animals), particularly selective grazers, can influence the phytoplankton species composition. Many copepods (small, herbivorous crustaceans) and invertebrate larvae pick out selected phytoplankton species from mixed groups, changing the species composition. A growing body of evidence now suggests that all of the factors considered here are operating simultaneously to produce species succession. The importance of any factor will vary with the particular phytoplankton species and the environmental conditions.