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
2013-01-10
33
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 organ-isms. 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.
Large losses of bacteria in the______phase can be avoided artificially.
选项
答案
death
解析
(文章最后一段提到By carefully monitoring the growth pattern....can prevent large losses during the“death phase.”由此可知通过人工的方法可以阻止细菌在“death phase”的死亡。)
转载请注明原文地址:https://kaotiyun.com/show/DNAK777K
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
Whenyourphoneisinyourpocket,therearetwopossiblestates:itiseithervibrating【D1】________.Meanwhile,youals
Writeanessayofatleast120wordsinwhichyoustateyourpersonalviewsonthesubject.Writethepassageontheanswershee
Inalittle-knownpartofthecounter-terrorismworld,oneofthemosteffectivedetectionsystemsisa600-poundanimal【C1】____
WhatwilltheathletesbeaskedtododuringtheTokyoOlympicsandParalympics?
Peopleshouldstopeatingseafoodsotheocean’secosystemcanberestored.
Eachgenerationhasitsownsetofvaluesandcharacteristics.Butonethingcommontoallgenerationsisthattheyaresufferin
Themostinterestingarchitecturalphenomenonofthe1970swastheenthusiasmforrefurbishingoldbuildings.Obviously,thiswa
Merv:Aretheseyoursons,Jean?Ihaven’tseenthemforages.Jean:Yes,thatphotowastakenafewmonthsago.Merv:Johnhasn
Garethiscertainlykeenonhisjobanddespitenever______,heobviouslyenjoyseveryminuteofhiswork.
现在是一个极具变革的年代,你们为迎接新的挑战已经做好了准备。(81)是你们使我们的社会更加强大,我们的家庭更加健康和安全,我们的人民更加富裕。同胞们,我们已经进入了全球信息化时代,这是美国复兴的伟大时代。(82)作为总统,我所做的一切—
随机试题
下列说法不正确的是()
A,胸外心脏挤压B,胸内心脏挤压C,两者均可D,两者均不可易并发肋骨骨折的是
有关滤线栅的叙述,错误的是
若∫f(x)dx=x3+C,则∫f(cosx)sinxdx等于()(式中C为任意常数)。
背景材料:某高速公路第五施工合同段地处城郊,主要工程为路基填筑施工。其中K48+010~K48+328段原为路基土方填筑,因当地经济发展和交通规划需要,经各方协商,决定将该段路基填筑变更为(5×20+3×36+5×20m)预应力钢筋混凝土箱梁桥,
()不属于企业存货。
下列选项对烹饪方式的解释表述正确的是:
设f(x)连续,证明:∫0x[∫0tf(u)du]dt=∫0xf(x)(x—t)dt.
数字视频的数据量极大,对存储和传输都是极大的负担,为此必须进行数据压缩。目前DVD影视光盘上存储的数字视频采用的压缩编码标准是【】。
请在【答题】菜单下选择【进入考生文件夹】命令,并按照题目要求完成下面的操作。注意:以下的文件必须保存在考生文件夹下。文涵是大地公司的销售部助理。负责对全公司的销售情况进行统计分析,并将结果提交给销售部经理。年底,她根据各门店提交的销售报
最新回复
(
0
)