文勇的新托福黄金&ccedil

because they were becoming extinct the

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Unformatted text preview: short and slender, and anthocyanin discoloration occurs on stems, petioles, and lower leaf surfaces. Phosphorus­deficient plants are often stunted, with leaves turning a characteristic 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. 2. The word exhibit in the passage is closest in meaning to fight off show cause spread 3. According to Paragraph2, which of the following symptoms occurs in phosphorus­deficient plants but not in plants deficient in nitrogen or iron? Chlorosis on leaves Change in leaf pigmentation to a dark shade of green Short, stunted appearance of stems Reddish pigmentation on the leaves or stem 4. According to Paragraph2, a symptom of iron deficiency is the presence in young leaves of Deep red discoloration between the veins. 182 Mail@liuwenyong.com 在在在在在在 www.liuwenyong.com 在在在在在在在在在在在在在在在,在在在在在在在在在在 White or yellow tissue between the veins. Dead spots between the veins. Characteristic dark green veins. Paragraph3: Much of the research on nutrient deficiencies is based on growing 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 growing of greenhouse vegetables during winter. Acroponics, a technique in which plants are suspended and the roots misted with a nutrient solution, is another method for growing plants without soil. 5. The word facilitates in the passage is closest in meaning to slows down affects makes easier focuses on 6. According to Paragraph3, what is the advantage of hydroponics for research on nutrient deficiencies in plants? It allows researchers to control what nutrients a plant receives. It allows researchers to observe the growth of a large number of plants simultaneously. It is possible to directly observe the roots of plants. It is unnecessary to keep misting plants with nutrient solutions. 7. The word suspended in the passage is closest in meaning to grown protected spread out hung Paragraph5: Scientists have known for some time that certain plants, called hyper accumulators, can concentrate minerals at levels a hundredfold or greater than normal. A survey of known hyper accumulators identified that 75 percent of them amassed nickel, cobalt, copper, zinc, manganese, lead, and cadmium are other minerals of choice. Hyper accumulators 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 hyper accumulators. Many are found in tropical and subtropical areas of the world, where accumulation of high concentrations of metals may afford some protec...
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