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
Most people consider bacteria dangerous. After all, these microorganisms cause a host of serious human diseases, including tuber
Most people consider bacteria dangerous. After all, these microorganisms cause a host of serious human diseases, including tuber
admin
2016-01-14
67
问题
Most people consider bacteria dangerous. After all, these microorganisms cause a host of serious human diseases, including tuberculosis, typhoid fever, pneumonia, and food poisoning. In fact, however, only a small percentage of bacteria cause diseases, while many bacteria are actually beneficial to humans. For example, doctors use bacteria to produce vaccines and other medicines.
Bacteria are also critical to many industrial processes, from fermenting wine to recycling wastes, and scientists use bacteria to study many of the biological processes common to all living things.
With such a wide variety of economic and scientific applications, it is no surprise that several laboratories around the United States grow and sell bacteria as a crop. These laboratories use specialized farming techniques to produce one of the nation’ s most valuable biological commodities.
Like plants, bacteria have specific growth requirements. In particular, they need a place to grow and they need a supply of nutrients. Bacteria may be cultivated in containers ranging from small test tubes to giant steel tanks. The organisms are placed in a container along with a nutritionally balanced liquid or jelly, called a culture medium, which provides vitamins, minerals, and fluids to the growing bacteria. The growth container and culture medium must be kept at a constant temperature that is appropriate for the type of bacteria being cultivated. Most bacteria used in medicine and industry grow best between 20℃ and 45℃.
In a closed container, bacteria exhibit a definite growth pattern. The figure shows a typical bacterial growth curve. All bacteria follow this pattern, a fact that is very important to anyone who wants to cultivate them in large numbers.
When bacteria are first placed in a growth container, they must adapt to their new environment, and growth is slow while they are making this adjustment.
This period is called the " start phase" of the bacterial growth cycle. At the end of this phase, as the bacteria become accustomed to their new living conditions, they begin to grow and reproduce rapidly. During the second phase, called the "log phase," a population explosion occurs. In a large tank, millions of new bacteria may be produced every hour during this phase. Eventually, however, the bacterial population reaches the maximum size possible, given the limitations of the growth container. At this point, the bacteria enter the " stationary growth phase," during which they continue to reproduce, but at a slower rate. After a time, the bacteria use up their supply of nutrients and their wastes accumulate in the growth container. The final period in the growth cycle, called the "death phase," occurs when the bacteria begin to die faster than they reproduce.
People who grow bacteria for science and industry take advantage of this unique growth cycle. Bacteria are harvested during the " stationary growth phase," yielding a good crop of usable organisms. By carefully monitoring the growth pattern, bacteria farmers can also decide when to add more nutrients to the culture medium or to transfer the bacteria to new growth containers. In this way, they can prevent large losses during the "death phase. " By applying a knowledge of the growth requirements and patterns of bacteria, these modern-day agriculturalists are able to help everyone derive the maximum benefit from these versatile organisms.
Most people consider bacteria dangerous: actually, most of them are beneficial to humans.
选项
A、TRUE
B、FALSE
答案
A
解析
(文章第一段指出大多数人认为细菌是危险的,但事实上只有一小部分的细菌会致病,而大多数的细菌对人体是有益的。)
转载请注明原文地址:https://kaotiyun.com/show/OSAK777K
本试题收录于:
B类竞赛(英语专业本科专科)题库大学生英语竞赛(NECCS)分类
0
B类竞赛(英语专业本科专科)
大学生英语竞赛(NECCS)
相关试题推荐
Peter,DavidandPaulsaidfollowingsentences:Peter:Davidisaliar,Paulalwaystellsthetruth.David:Peteristruthful.P
Newpeaceproposals______attherecentMiddleEastconference.
Iwishyou’dmetmyUncleBill.Hewasatallman--sotallthathecouldchangethebulbsinlightsocketswhilehardlyreaching
Whatisthenumberofcountriesmentionedinthisnewsreport?
ScientistssaytherehasbeenaseveredecreaseintheamountofwaterinLakeChadinnorthernAfricainthelastthirtyyears.
BywhomhasMichaelMoralesbeensparedthesecondtimeintwenty-fourhours?
Theoutbreakisspreading______usualforwantoftransporttotakevictimstohospital,andbasicmedicinesforthosewhodoman
ThisWednesday,GordonBrownwillreplaceTonyBlairasthenewheadofBritain’sLaborParty.Thislong-servingchancellorisa
中国经济发展潜力大、优势足、空间广,前景光明。【T1】我们有9亿多劳动力,其中1.7亿多受过高等教育或有专业技能。(非限制性定语从句)每年大学毕业生700多万,中职毕业生500多万。【T2】科技人员数量世界第一,研发投入(R&Dinput)世界第
Pattygetsalongwithherfloormatesandtheygoouttopartiestogether.
随机试题
过境货物
中性粒细胞碱性磷酸酶活性明显增高见于
慢性颅内压增高主要临床表现是()
某日,王某和李某串通抢劫路人周某的钱财(价值1万元),二人共同实施抢劫,情节相同。但法院审理此案时,考虑到王某是县政府副秘书长的儿子,因此判王某抢劫罪,执行3年有期徒刑,而判李某抢劫罪,执行5年有期徒刑。该法院的做法违背了下列哪项原则:
我国《环境保护法》规定,每年的环境日是:()
在施工合同中,( )是承包人的义务。
某公安局2008年5月向某汽车贸易公司购买一辆小轿车作办公用,支付含增值税的价款534000元,代收的保险费1000元,送车费500元,上牌办证费20000元,均由某汽车贸易公司开具发票和有关收据。该公安局应纳车辆购置税()元。
下列行为中,符合银行业从业人员遵守业务操作指引要求的是()。
下列不属于秘书机构所管理的事务的是()。
AMessontheLadderofSuccessA)ThroughoutAmericanhistorytherehasalmostalwaysbeenatleastonecentraleconomicnarrati
最新回复
(
0
)