首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
外语
This section measures your ability to understand academic passages in English. There are three passages in the section. Give you
This section measures your ability to understand academic passages in English. There are three passages in the section. Give you
admin
2014-09-29
97
问题
This section measures your ability to understand academic passages in English.
There are three passages in the section. Give yourself 20 minutes to read each passage and answer the questions about it. The entire section will take 60 minutes to complete.
You may look back at a passage when answering the questions. You can skip questions and go back to them later as long as there is time remaining.
Directions: Read the passage. Then answer the questions. Give yourself 20 minutes to complete this practice set.
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 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 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(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 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 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.
Much of the research on nutrient deficiencies is based on growing plants hydro-ponically, 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. 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 be 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, 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 that certain plants, called hyperaccumu-lators, 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. Hyperaccumulators 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 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 metals—an environmentally friendly approach known as phytoremediation. 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 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 example, 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.
Directions: Now answer the questions.
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 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 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.
According to paragraph 1, what is true of plants that can grow in serpentine soils?
选项
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.
答案
B
解析
转载请注明原文地址:https://kaotiyun.com/show/7GfO777K
0
托福(TOEFL)
相关试题推荐
Completethetablebelow.WriteNOMORETHANTHREEWORDSORANUMBERforeachanswer.
Completethenotesbelow.Areasdealtwith:【L1】______northsuburbsRent:from【L2】£______to£______am
Whatinstructionswerethestudentsgivenabouttheirproject?AtheymustdothisBtheycandothisiftheywanttoCtheycan
JacksaysthatinLondonthesedays,manypeople
Whatinformationwasgivenbyeachwriter?ChooseyouranswersfromtheboxandwritethelettersA-FnexttoQuestions24-27.A
Completethenotesbelow.WriteONEWORDONLYforeachanswer.EngineeringforsustainabledevelopmentTheGreenhou
ChooseTWOletters,A-E.InwhichTWOareasdidtheseresearchfindingsdifferfromthoseoftheoriginalstudy?AStudents’int
Completethenotesbelow.WriteNOMORETHANTWOWORDSAND/ORANUMBERforeachanswerENVIRONMENTALCHANGEDISCUSSIONInSouthe
Completethenotesbelow.WriteNOMORETHANTWOWORDSforeachanswer.AdvertisingEffectTheimportantfactortoconsider
NarratorListentoalectureintheliteratureclass.WhydidWilliamFaulknerwriteaboutthesouthernstatesofAmerica?
随机试题
You______herinherofficelastFriday;she’sbeenoutoftownfortwoweeks.
关于细菌芽孢的叙述,下列哪项是错误的
招标代理机构应当具备的条件不包括()。
外国投资者自收到外商投资企业营业执照之日起的一定期间内,到税务、海关、土地管理和外汇管理等有关部门办理登记手续。这个期限是()。
在所有的融资方式中,管理层不需要听取任何企业外部组织或个人意见的融资方式是()。
实际交付的定金数额多于或者少于约定数额的,视为变更定金合同;收受定金一方提出异议并拒绝接受定金的,定金合同不生效。()
注册会计师不能认可管理层通过下列()措施支持其在财务报表中将一项关联方交易认定为公平交易。
什么是“以学论教”?
“男、女,单、双”这类词,可以作定语,不能作谓语,我们称之为“非谓形容词”,也称()。
信息安全就是要防止非法攻击和病毒的传播,保障电子信息的有效性。从具体的意义上来理解,需保证以下哪几个方面的内容?Ⅰ.保密性(Confidentiality)Ⅱ.完整性(Integrity)Ⅲ.可用性(Availability)
最新回复
(
0
)