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
43
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.
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/nJAK777K
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
WhendidDr.EvansstarttowriteherbookAngerManagement?
Whichisthemissingtile?
Foundedin1831,NewYorkUniversityisnowoneofthelargestprivateuniversitiesintheUnitedStates.Atthattime,moststud
Outsideoftheirrespectivesizes,gorillasandchimpanzeesareverysimilarphysically,butwhataboutsocially?Infact,there
Accordingtothepolls,whatwillhappentogunshopsinBrazil?
Accordingtothepolls,whatwillhappentogunshopsinBrazil?
Sincewearesocialbeings,thequalityofourlivesdependsinlargemeasureonourinterpersonalrelationships.Onestrengtho
Eachnumbershownbelowfollowsacertainrule.Figureouttheruleandworkoutthemissingnumber:
Howmanycirclescontainablackdot?
Eachnumbershownbelowfollowsacertainrule.Figureouttheruleandworkoutthemissingnumber:
随机试题
房地产转让的合法方式有()。
我国社会主义经济体制改革与政治体制改革的关系表现为()
下列哪项是数字扫描变换器(DSC)的功能
护理伦理基本原则中的自主原则要求护理人员
72岁,女性,原无恙,近消瘦,嗜睡,神态淡漠。胃镜,肠镜检查无阳性,肝/肾功能正常,心电图示房颤,该患者诊断最大可能是
关于犯罪中止,下列哪些说法正确?
《中华人民共和国城乡规划法》第二条规定,本法所称的城乡规划包括()。
一般保证最重要的特点就是保证人享有先诉抗辩权。先诉抗辩权的存在使一般保证中的保证人所承担的责任成为一种纯粹的()。
下列所得中,属于“劳务报酬所得”的是()。
所有物质实体都是可见的,而任何可见的东西都没有神秘感。因此,精神世界不是物质实体。以下哪项最可能是上述论证所假设的?
最新回复
(
0
)