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
2011-02-05
48
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 bacteria used in medicine and industry grow best between the temperature of ______.
选项
答案
20℃and 45℃
解析
(文章第三段最后一句话明确指出Most bacteria used in medicine and industry grow best between 20℃and 45℃。)
转载请注明原文地址:https://kaotiyun.com/show/1JAK777K
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
Summary:DifferentpeoplehavedifferentopinionsaboutLondon’s【51】______theOlympicGamesin2012.EonthinkstheGamesw
Don’tputthe______onme!I’mnotresponsible______yourfinancialproblems.
IftwodaysbeforeyesterdaywasMonday,whatisthethirdletterofthedaywhichcomestwodaysaftertomorrow?
Everybodymakeslanguagemistakes,whetheritisintheirownlanguageoraforeignlanguage.Sometimesinsteadofthewordthat
Whichisthemissingtile?
"Home,sweethome"isaphrasethatexpressesanessentialattitudeintheUnitedStates.Whethertherealityoflifeinthefami
Accordingtothepolls,whatwillhappentogunshopsinBrazil?
Whichnumberismissingfromthethirdcircle?
随机试题
简述能力等级与成熟度等级之间的关系。
无法查明原因的现金溢余经批准处理后记入()
生产性粉尘在空气中的稳定程度主要取决于
各地地下水监测部门,应在不同质量类别的地下水域设立监测点进行水质监测,监测频率不得少于每年()。
合理利用矿产资源,应该坚定不移地实行对外开放政策,在互惠互利的基础上,积极参与矿产资源领域的国际合作,推进国、内外()专门交流。
某工程项目的赢得值曲线如下图,关于项目偏差原因分析与纠偏措施的说法,正确的是()。
甜菜叶
采用保证担保方式的,保证人应与贷款银行签订保证合同,保证人为借款人提供的贷款担保可以为全额连带责任保证,也可以为部分连带责任保证,借款人与保证人之间不得相互提供保证。()
A、 B、 C、 D、 D
TheH5N1virusdoesnotusuallyinfecthumans.In1997,however,thefirstcaseof【S1】______fromabirdtoahumanwasseendu
最新回复
(
0
)