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托福阅读TPO5(试题+答案+译文)第1篇:Minerals and Plants
托福阅读原文
Rearch has shown that certain mineralsare required by plants for normal growth and development. The soil is thesource of the minerals, which are absorbed by the plant with the water fromthe soil. Even nitrogen, which is a gas in its elemental state, is normallyabsorbed from the soil as nitrate ions. S
英语好句摘抄大全ome soils are notoriously deficient inmicro nutrients and are therefore unable to support most plant life. So-calledrpentine soils, for example, are deficient in calcium, and only plants ableto tolerate low levels of this mineral can survive. In modern agriculture,mineral depletion of soils is a major concern, since harvesting cropsinterrupts the recycling of nutrients back to the soil.党章考试题
唐朝的故事Mineral deficiencies can often be detectedby specific symptoms such as chlorosis (loss of chlorophyll resulting in yellowor white leaf tissue), necrosis (isolated dead patches), anthocyanin formation(development of deep red pigmentation of leaves or stem), stunted growth, anddevelopment of woody tissue in an herbaceous plant. Soils are most commonlydeficient in nitrogen and phosphorus. Nitrogen-deficient plants exhibit many ofthe symptoms just described. Leaves develop
chlorosis; stems are short andslender, and anthocyanin discoloration occurs on stems, petioles, and lowerleaf surfaces. Phosphorus-deficient plants are often stunted, with leavesturning a characteristic dark green, often with the accumulation ofanthocyanin. Typically, older leaves are affected first as the phosphorus ismobilized to young growing tissue. Iron deficiency is characterized bychlorosis between veins in young leaves.
关联营销
Much of the rearch on nutrientdeficiencies is bad on growing plants hydroponically, that is, in soillessliquid nutrient solutions. This technique allows rearchers to createsolutions that lectively omit certain nutrients and then obrve theresulting effects on the plants. Hydroponics has applications beyond basicrearch, since it facilitates the growing of greenhou vegetables duringwinter. Aeroponics, a technique in which plants are suspended and the rootsmisted with a nutrient solution, is another method for growing plants withoutsoil.
While mineral deficiencies can limit thegrowth of plants, an overabundance of certain minerals can be toxic and canalso limit growth. Saline soils, which have high concentrations of sodiumchloride and other salts, limit plant growth, and rearch continues to focuson developing salt-tolerant varieties of agricultural crops. Rearch hasfocud on the toxic effects of heavy metals such as lead, cadmium, mercury,and
aluminum; however, even copper and zinc, which are esntial elements, canbecome toxic in high concentrations. Although most plants cannot survive inthe soils, certain plants have the ability to tolerate high levels of theminerals.
Scientists have known for some time thatcertain plants, called hyper accumulators, can concentrate
minerals at levels ahundredfold or greater than normal. A survey of known hyper accumulatorsidentified that 75 percent of them amasd nickel, cobalt, copper, zinc,mangane, lead, and cadmium are other minerals of choice. Hyper accumulatorsrun 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 andsubtropical areas of the world, where accumulation of high concentrations ofmetals may afford some protection against plant-eating incts and microbial pathogens.
有寓意的故事Only recently have investigators consideredusing the plants to clean up soil and waste sites that have been contaminatedby toxic levels of heavy metals–an environmentally friendly approach known asphytoremediation. This scenario begins with the planting of hyper accumulatingspecies in the target area, such as an abandoned mine or an irrigation
pondcontaminated by runoff. T oxic minerals would first be absorbed by roots butlater relocated to the stem and leaves. A harvest of the shoots would removethe toxic compounds off site to be burned or composted to recover the metal forindustrial us. After veral years of cultivation and harvest, the site wouldbe restored at a cost much lower than the price of excavation and reburial, thestandard practice for remediation of contaminated soils. For examples, in fieldtrials, the plant alpine pennycres
s removed zinc and cadmium from soils near azinc smelter, and Indian mustard, native to Pakistan and India, has beeneffective in reducing levels of lenium salts by 50 percent in contaminatedsoils.
托福阅读试题
文艺晚会1. According to paragraph 1, what is trueof plants that can grow in rpentine soil?
A.They absorb micronutrients unusuallywell.
B.They require far less calcium than mostplants do.
甘松的功效与作用C.They are able to absorb nitrogen in itlemental state.
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