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
2013-11-20
89
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.
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.
选项
答案
细菌置于生长皿中时,它们必须要适应新环境,在这一适应过程中,它们的生长过程缓慢。
解析
(将被动化为主动,在适当的地方增加词语,如growth译为“它们的生长”。)
转载请注明原文地址:https://kaotiyun.com/show/1gAK777K
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
Normallyastudentmustattendacertainnumberofcoursesinordertograduate,andeachcoursewhichheattendsgiveshimacr
Adrian:Boris.TowhatdoIowethishonor?Boris:Justasocialcall,Adrian.Goodtofindyouallathome.Adrian:I’dlikeyo
somepeoplepreferworkoractivitiesthatmainlyinvolveworkingwithpeople.Otherschooseworkoractivitiesthatmainlyinvo
Whichofthebottomwatchescompletesthesequence?
Makingagoodfirstimpressionisimportantforbuildingrelationshipswithotherpeople.Inbusinessnetworking,apositivefir
8195+1921Ifthesetwonumberstotal6879,whatdothetwonumbersbelowtotal?8216+1909
Onetheoryabouttheuniversesaysthatithasnoboundary,noedge.ThistheorywasproposedbyStephenHawkingandJimHartle.
如果你是一个中等水平的读者,你能够以每分钟300字的速度阅读一本中等水平的书。不过,你必须每天这样坚持下去,否则就无法保持这种水平。【T1】你也不可能以这个速度阅读科学、数学、农业、商业方面的书,或是对你来说内容生疏的书。(Nor…or…)你绝不会以这种速
【T1】人民很容易陷入这样的思维,觉得一旦把东西扔掉,他就消失了。(getstuckin)针对这样的想法,某机构固体废弃物及再循环部门经理表示:“什么都没有消失"。刚刚扔进垃圾桶的塑料瓶也许离开了我们的视线,但并不意味着它们就消失了。我们往往认为:眼不
YYZZZYZZYisto221112112asYYZZYZZYisto______.
随机试题
不属于汉语特点的是()
心脏按压的方法不正确的是
女性,35岁,劳累时心悸、气短,休息后可缓解,反复双下肢轻度水肿一年。半月前因受凉后咳嗽,咳白色泡沫痰及少许黏痰,同时伴心悸、气短、不能平卧来急诊。体检:呼吸22次/分,口唇发绀,心率120次/分,心律绝对不规则,心尖区闻及SM3/6级杂音和DM,双肺对称
对于股骨头骨软骨病病理变化叙述正确的是
利用施工图改绘竣工图,必须标明变更依据;凡施工图结构、工艺、平面布置等有重大改变,或变更部分超过图面( )的,应当重新绘制竣工图。
在个人住房贷款中,若保证人向第三方提供超出其自身负担能力的担保的,银行应限期要求借款人更换贷款银行认可的新的担保。()
教育是培养人的社会实践活动,这一本质决定了教育既是一个相对独立的系统,又是一个复杂开放的系统。()
放弃可能明显导致亏损的投资项目属于风险对策中的()。
Panel和Applet的默认布局管理器是
Peoplewhodon’tunderstandwhattheiremployersexpectthemtodomaybeheadedforoneofthemostcommonandyetmostavoidab
最新回复
(
0
)