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
52
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.
Most people consider bacteria dangerous, actually, most of them are______.
选项
答案
beneficial to humans
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/3NAK777K
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
Changesinthewaypeoplelivebringaboutchangesinthejobsthattheydo.Moreandmorepeopleliveintownsandcitiesinste
"Home,sweethome"isaphrasethatexpressesanessentialattitudeintheUnitedStates.Whethertherealityoflifeinthefa
Whendifficultpeopleexpressthemselvesorally,theygenerallywantatleasttwothings:they’vebeenheardandthey’vebeen
FireswerecommoninLondoninthe17thcentury.Mostbuildingsweremadefromwood【M1】_______andwereveryclosetogether,so
Doyouthinkyou’reagoodlistener?Chancesareyoudo.Butstudiesshowthatmostpeopleseriouslyoverestimatetheirability
MartinsaidbananaswereintroduceddirectlyintoAustraliafromChina.
Todaymenarefacingnewexpectationsandnewchoicesabouttheircommitmentstosociety,familyandwork.Nolongercertainwha
Iwasaskedtheotherdaywhetherhighandlowpressuresystemswere______thecentralpressure.
TheUnitedKingdomBritain(orGreatBritain)isanislandthatliesoffthenorth-westcoastofEurope.Thenearestcountr
YYZZZYZZYisto221112112asYYZZYZZYisto______.
随机试题
A.中性粒细胞B.NK细胞C.Th细胞D.CTLE.浆细胞辅助免疫应答的细胞是
A.变质性炎症B.浆液性炎症C.增生性炎症D.化脓性炎症E.出血性炎症流行性脑脊髓膜炎属于
治疗脑水肿的首选药是
过期妊娠是指孕妇妊娠达到或超过()。
在可行性研究阶段的建筑工程费用估算中,单位建筑工程投资估算法可以进一步分为()。
劳务派遣单位和用工单位不得向被派遣劳动者收取费用。()
导游人员在接受散客接待任务后,应详细阅读接待计划,明确()。
从妇女性腺功能开始衰退到完全消失的时期,亦即绝经前后的一段时期,是()。
Howstupiddoesoneneedtobetogetajobreadingthetelevisionnews?IsitactuallybeneficialforTVnewsreaderstohave,i
Thebank【56】borrowersenoughinteresttopaytheexpenseofthebankandhavesomethingleftoverfor【57】Theinterestcannotbe
最新回复
(
0
)