【词汇】托福同义词串串烧(136) – Soil Formation

TPO-36-1 Soil Formation

Living organisms play an essential role in soil formation. The numerous plants and animals living in the soil release minerals from the parent material from which soil is formed, supply organic matter, aid in the translocation (movement) and aeration of the soil, and help protect the soil from erosion. The types of organisms growing or living in the soil greatly influence the soil’s physical and chemical characteristics. In fact, for mature soils in many parts of the world, the predominant type of natural vegetation is considered the most important direct influence on soil characteristics. For this reason, a soil scientist can tell a great deal about the attributes of the soil in any given area simply form knowing what kind of flora the soil supports. Thus prairies and tundra regions, which have characteristic vegetations, also have characteristic soils.
The quantity and total weight of soil flora generally exceed that of soil fauna. By far the most numerous and smallest of the plants living in soil are bacteria. Under favorable conditions, a million or more of these tiny, single-celled plants can inhabit each cubic centimeter of soil. It is the bacteria, more than any other organisms, that enable rock or other parent material to undergo the gradual transformation to soil. Some bacteria produce organic acids that directly attack parent material, breaking it down and releasing plant nutrients. Others decompose organic litter (debris) to form humus (nutrient-rich organic matter). A third group of bacteria inhabits the root systems of plants called legumes. These include many important agricultural crops, such as alfalfa, clover, soybeans, peas, and peanuts. The bacteria that legumes host within their root nodules (small swellings on the root) change nitrogen gas from the atmosphere into nitrogen compounds that plants are able to metabolize, a process, known as nitrogen fixation, that makes the soil more fertile. Other microscopic plants also are important in soil development. For example, in highly acidic soils where few bacteria can survive, fungi frequently become the chief decomposers of organic matter.

More complex forms of vegetation play several vital roles with respect to the soil. Tress, grass, and other large plants supply the bulk of the soil’s humus. The minerals released as these plants decompose on the surface constitute an important nutrient source for succeeding generations of plants as well as for other soil organisms. In addition, trees can extend their roots deep within the soil and bring up nutrients from far below the surface. These nutrients eventually enrich the surface soil when the tree drops its leaves or when it dies and decomposes. Finally, trees perform the vital function of slowing water runoff and holding the soil in place with their root systems, thus combating erosion. The increased erosion that often accompanies agricultural use of sloping land is principally caused by the removal of its protective cover of natural vegetation.

Animals also influence soil composition. The faunal counterparts of bacteria are protozoa. These single-celled organisms are the most numerous representatives of the animal kingdom, and, like bacteria, a million or more can sometimes inhabit each cubic centimeter of soil. Protozoa feed on organic matter and hasten its decomposition. Among other soil-dwelling animals, the earthworm is probably the most important. Under exceptionally favorable conditions, up to a million earthworms (with a total body weight exceeding 450 kilograms) may inhabit an acre of soil. Earthworms ingest large quantities of soil, chemically alter it, and excrete it as organic matter called casts. The casts form a high-quality natural fertilizer. In addition, earthworms mix of soil both vertically and horizontally, improving aeration and drainage.

Insects such as ants and termites also can be exceedingly numerous under favorable climatic and soil conditions. In addition, mammals such as moles, field mice, gophers, and prairie dogs sometimes are present in sufficient numbers to have significant impact on the soil. These animals primarily work the soil mechanically. As a result, the soil is aerated broken up, fertilized, and brought to the surface, hastening soil development.


题目

【题目】1. The word “attributes” in the passage is closest in meaning to

O properties

O surrounding

O sources

O nutrients

【题目】2. The word “bulk” in the passage is closet in meaning to

O composition

O largest part

O richest part

O quality

【题目】3. The word “hasten” in the passage is closet

O aid

O begin

O accelerate

O ensure

【题目】4. The word “exceedingly” in the passage is closest in meaning to

O surprisingly

O relatively

O reliably

O extremely


单词解释和答案

1、attribute    

英[əˈtrɪbju:t]    美[əˈtrɪbjut]

vt.    认为…是; 把…归于; 把…品质归于某人; 认为某事[物]属于某人[物];

n.    属性; (人或物的) 特征; 价值; [语法学] 定语

【同义词】:  apply / ascribe / assign / characteristic / feature / give / nature / place / quality / trait

【原句】: For this reason, a soil scientist can tell a great deal about the attributes of the soil in any given area simply form knowing what kind of flora the soil supports.

【题目】1. The word “attributes” in the passage is closest in meaning to

O properties★

O surrounding

O sources

O nutrients


2、bulk    

英[bʌlk]    美[bʌlk]

n.    (大) 体积; 大块,大量; 大多数,大部分; 主体;

vt.    变得越来越大(或重要);

vi.    显得庞大; 形成大块; 堆积起来

【同义词】:  lump / majority / mass

【原句】: Tress, grass, and other large plants supply the bulk of the soil’s humus.

【题目】2. The word “bulk” in the passage is closet in meaning to

O composition

O largest part★

O richest part

O quality


3、hasten    

英[ˈheɪsn]    美[ˈhesən]

vt.    加速; 催促; 使加紧; 赶紧,赶快;

vi.    赶快; 急忙

【反义词】:  delay

【原句】: Protozoa feed on organic matter and hasten its decomposition.

【题目】3. The word “hasten” in the passage is closet

O aid

O begin

O accelerate★

O ensure


4、exceedingly    

英[ɪkˈsi:dɪŋli]    美[ɪkˈsidɪŋli]

adv.    非常,极其,特别,十分; 极大地; 过分地; 极度地,极端

【同义词】:  extremely / passing

【原句】: Insects such as ants and termites also can be exceedingly numerous under favorable climatic and soil conditions.

【题目】4. The word “exceedingly” in the passage is closest in meaning to

O surprisingly

O relatively

O reliably

O extremely★

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