托福TPO5阅读Passage1原文文本+题目+答案解析.pdf
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1、 为了帮助大家高效备考托福,为大家带来托福 TPO5 阅读 Passage1 原文文本+题目+答案 解析,希望对大家备考有所帮助。 托福 TPO5 阅读 Passage1 原文文本: Minerals and Plants Research has shown that certain minerals are required by plants for normal growth and development. The soil is the source of these minerals, which are absorbed by the plant with the water
2、from the soil. Even nitrogen, which is a gas in its elemental state, is normally absorbed from the soil as nitrate ions. Some soils are notoriously deficient in micro nutrients and are therefore unable to support most plant life. So-called serpentine soils, for example, are deficient in calcium, and
3、 only plants able to tolerate low levels of this mineral can survive. In modern agriculture, mineral depletion of soils is a major concern, since harvesting crops interrupts the recycling of nutrients back to the soil. Mineral deficiencies can often be detected by specific symptoms such as chlorosis
4、 (loss of chlorophyll resulting in yellow or white leaf tissue), necrosis (isolated dead patches), anthocyanin formation (development of deep red pigmentation of leaves or stem), stunted growth, and development of woody tissue in an herbaceous plant. Soils are most commonly deficient in nitrogen and
5、 phosphorus. Nitrogen-deficient plants exhibit many of the symptoms just described. Leaves develop chlorosis; stems are short and slender, and anthocyanin discoloration occurs on stems, petioles, and lower leaf surfaces. Phosphorus-deficient plants are often stunted, with leaves turning a characteri
6、stic dark green, often with the accumulation of anthocyanin. Typically, older leaves are affected first as the phosphorus is mobilized to young growing tissue. Iron deficiency is characterized by chlorosis between veins in young leaves. Much of the research on nutrient deficiencies is based on growi
7、ng plants hydroponically, that is, in soilless liquid nutrient solutions. This technique allows researchers to create solutions that selectively omit certain nutrients and then observe the resulting effects on the plants. Hydroponics has applications beyond basic research, since it facilitates the g
8、rowing of greenhouse vegetables during winter. Aeroponics, a technique in which plants are suspended and the roots misted with a nutrient solution, is another method for growing plants without soil. While mineral deficiencies can limit the growth of plants, an overabundance of certain minerals can b
9、e toxic and can also limit growth. Saline soils, which have high concentrations of sodium chloride and other salts, limit plant growth, and research continues to focus on developing salt-tolerant varieties of agricultural crops. Research has focused on the toxic effects of heavy metals such as lead,
10、 cadmium, mercury, and aluminum; however, even copper and zinc, which are essential elements, can become toxic in high concentrations. Although most plants cannot survive in these soils, certain plants have the ability to tolerate high levels of these minerals. Scientists have known for some time th
11、at certain plants, called hyperaccumulators, can concentrate minerals at levels a hundredfold or greater than normal. A survey of known hyperaccumulators identified that 75 percent of them amassed nickel, cobalt, copper, zinc, manganese, lead, and cadmium are other minerals of choice. Hyperaccumulat
12、ors run the entire range of the plant world. They may be herbs, shrubs, or trees. Many members of the mustard family, spurge family, legume family, and grass family are top hyperaccumulators. Many are found in tropical and subtropical areas of the world, where accumulation of high concentrations of
13、metals may afford some protection against plant-eating insects and microbial pathogens. Only recently have investigators considered using these plants to clean up soil and waste sites that have been contaminated by toxic levels of heavy metalsan environmentally friendly approach known as phytoremedi
14、ation. This scenario begins with the planting of hyperaccumulating species in the target area, such as an abandoned mine or an irrigation pond contaminated by runoff. Toxic minerals would first be absorbed by roots but later relocated to the stem and leaves. A harvest of the shoots would remove the
15、toxic compounds off site to be burned or composted to recover the metal for industrial uses. After several years of cultivation and harvest, the site would be restored at a cost much lower than the price of excavation and reburial, the standard practice for remediation of contaminated soils. For exa
16、mples, in field trials, the plant alpine pennycress removed zinc and cadmium from soils near a zinc smelter, and Indian mustard, native to Pakistan and India, has been effective in reducing levels of selenium salts by 50 percent in contaminated soils. 托福 TPO5 阅读 Passage1 题目: Question 1 of 14 Accordi
17、ng to paragraph 1, what is true of plants that can grow in serpentine soil? A. They absorb micronutrients unusually well. B. They require far less calcium than most plants do. C. They are able to absorb nitrogen in its elemental state. D. They are typically crops raised for food. Question 2 of 14 Th
18、e word “exhibit ” in the passage is closest in meaning toA. fight offB. showC. causeD. spread Question 3 of 14 According to paragraph 2, which of the following symptoms occurs in phosphorus- deficient plants but not in plants deficient in nitrogen or iron? A. Chlorosis on leaves B. Change in leaf pi
19、gmentation to a dark shade of green C. Short, stunted appearance of stems D. Reddish pigmentation on the leaves or stem Question 4 of 14 According to paragraph 2, a symptom of iron deficiency is the presence in young leaves of A. deep red discoloration between the veins B. white or yellow tissue bet
20、ween the veins C. dead spots between the veins D. characteristic dark green veins Question 5 of 14 The word “facilitates ” in the passage is closest in meaning to A. slows down B. affects C. makes easier D. focuses on Question 6 of 14 According to paragraph 3, what is the advantage of hydroponics fo
21、r research on nutrient deficiencies in plants? A. It allows researchers to control what nutrients a plant receives. B. It allows researchers to observe the growth of a large number of plants simultaneously. C. It is possible to directly observe the roots of plants. D. It is unnecessary to keep misti
22、ng plants with nutrient solutions. Question 7 of 14 The word “suspended ” in the passage is closest in meaning to A. grown B. protected C. spread out D. hung Question 8 of 14 Why does the author mention “herbs”, “shrubs”, and “trees”? A. To provide examples of plant types that cannot tolerate high l
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