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
31
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
WhichholidayinspiredMr.Botellotobegindesigningclothing?
中国是世界上种茶最早、制茶最精、饮茶最多的国家,是茶的故乡。最初,茶只是被作为一种药材而非饮品。【T1】后来,古人逐渐将茶从材中分离出来称为一种清热的饮料。(定语从句)在那之后,中国的茶文化逐渐形成。【T2】据史料记载,西汉时期已经有了饮茶的习
【B1】________Oneofthemostimportantaspectsofdoingbusinessinternationallyisbeingabletospeakotherlanguages.For
Thereisdistinctionbetweenreadingforinformationandreadingforunderstanding.【B1】________Thefirstsenseistheone
Inalittle-knownpartofthecounter-terrorismworld,oneofthemosteffectivedetectionsystemsisa600-poundanimal【C1】____
ThecombinedagesofFrasierandNilesis88years.ThecombinedagesofNilesandDaphneis76years.ThecombinedagesofFras
Whenwasthelasttimeyousawafrog?Chancesare,ifyouliveinacity,youhavenotseenoneforsometime.Eveninwetarea
Nobodyknowsforcertainwhattheoriginsofmusicwere.Musiciscertainlyolderthanpoetryandpaintingbutasearlymanhad
Writeaboutthefollowingtopic.Inmanycountries,increasingnumbersofyoungpeoplearegraduatingfromuniversity,butareu
Iftwotypistscantypetwopagesintwominutes,howmanytypistswillittaketotype18pagesinsixminutes?
随机试题
在作业环境中,天然气和油田伴生气的含量(体积分数)达()以上时,作业工人就可能出现缺氧症状。
女,18岁,皮肤反复紫瘢和瘀斑,月经量多2年。既往经常关节疼痛,10岁起经常刷牙出血。
A.肝B.心C.脾D.肺E.肾
甲公司签发金额为1000万元、到期日为2006年5月30日、付款人为大满公司的汇票一张,向乙公司购买A楼房。甲乙双方同时约定:汇票承兑前,A楼房不过户。其后,甲公司以A楼房作价1000万元、丙公司以现金1000万元出资共同设立丁有限公司。某会计师事务
下列关于公司减少注册资本的表述中,不符合公司法律制度规定的是()。(2012年)
某公司技术人员为了搞技术革新,废寝忘食,夜以继日,积劳成疾,虽然技术革新取得了一定进展,但由于公司业务拓展过大导致后续资金投入不足,继而导致技术革新半途而废。假如你就是那位技术人员,你会()。
公安工作的特点有()。
盈利能力强的公司应具有更高的负债率,这一表述比较符合下述何种理论的预期()。
Psychologiststakecontrastiveviewsofhowexternalrewards,from【31】______praisetocoldcash,affectmotivationandcreativit
"MigrationfromAsia"TheAsianmigrationhypothesisistodaysupportedbymostofthescientificevidence.Thefirst"hard"
最新回复
(
0
)