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
"Biology Class" Why are bacteria being used in the research study at the university?
"Biology Class" Why are bacteria being used in the research study at the university?
admin
2012-01-14
23
问题
"Biology Class"
Why are bacteria being used in the research study at the university?
[Narrator] Listen to part of a lecture in a biology class. The professor is talking about bacteria.
[Professor]
Bacteria is the common name for a very large group of one-celled microscopic organisms that, we
believe, may be the smallest, simplest, and perhaps even the very first forms of cellular life that evolved
on Earth. Because they’re so small, bacteria must be measured in microns, with one micron measuring
about 0.00004 inches long. Most bacteria range from about 0.1 microns to about 4 microns wide and
about 0.2 microns to almost 50 microns long. So how can we observe them? I’ll give you one guess.
Under the microscope, of course. As I said, bacteria are very primitive and simple. In fact, they’re unicellular, Q25
which means that they’re made up of a single cell. We think they probably evolved about three
and a half billion years ago. Some of the oldest fossils are bacterial organisms. They’ve been found
almost everywhere on Earth, including all the continents, seas, and fresh water habitats, and in the tissues
of both plants and animals.
Well, since they’re so prevalent, you might ask, how do they reproduce? Okay, they grow in Q25
Colonies and can reproduce, quite rapidly, in fact, by a process called fission. In fission, the cell, and
remember, there’s only one in bacteria, one cell. So the cell increases in size and then splits in two
parts. Fission is also referred to in your text as asexual budding. Now you’ll also read about conjugation,
and that’s when two separate bacteria exchange pieces of DNA, so there are two ways that reproduction
can occur, but we think that fission is more common.
Okay. Bacteria were virtually unknown until about 1600 when microscopes were introduced, and at
that time, bacteria were observed and classified into three main types according to their shapes, and
that classification hasn’t really changed that much over the years. So that’s what I want to talk about Q23
today—the main types of bacteria. The slides that I’m going to show you are enlargements of bacteria
that I observed under the microscope in the lab earlier today. Now, this first slide is an example of bacilli.
The bacilli are a group of bacteria that occur in the soil and air. As you can see, they’re shaped like
rods, and if you were to see them in motion, they’d be rolling or tumbling under the microscope. Of
course, you can’t see that because this is a still visual, but later, when you go into the lab, you’ll see that
rolling motion in examples of bacilli. These are kind of a greenish blue, but some are yellow. So don’t try
to identify them by their color. Look at the shape. These bacilli are largely responsible for food spoilage.
Okay, the next slide is a very different shape of bacteria. Its referred to as the cocci group, and it Q24
tends to grow in clusters or chains, like this example. This specimen is one of the common streptococci
bacteria that cause strep throat.
Finally, let’s look at the spiral-shaped bacteria called the spirilla.
This is the spirilla. They look a little like corkscrews, and they’re responsible for a number of diseases
in humans. But I don’t want you to get the wrong idea. It’s true that some species of bacteria do
cause diseases, but for the most part, bacteria are benign.
There’s a lot of bacteria in this room in fact. We all have it on us. They live harmlessly on the skin,
in the mouth, and in the intestines. In fact, bacteria are very helpful to researchers because bacterial Q26
cells resemble the cells of other life forms in many ways. and may be studied to give us insights. For
example, we have a major research project in genetics here at the university. Since bacteria reproduce
very rapidly, we’re using them to determine how certain characteristics are inherited.
Okay, now, let me review these three types with you... cocci are spheres, bacilli are rods, and spirilli
are spirals. One of my students came up with a way to remember them. Just try to visualize the first Q27
letter in the name of each of the different types: Cocci starts with C like the shape of half a sphere. Bacilli
starts with a Straight line on the B, and a rod is straight. Spirilla starts with S. and that’s a spiral shape.
If it helps you, use it.
In any case, although I want you to know the three major classifications, within these basic groups
there are virtually hundreds of variations that make them somewhat more difficult to identify and classify
than the rather straightforward specimens that I showed you a minute ago. Because, you see, bacteria Q28
can join in chains, clusters, pairs. And sometimes, more than one type of bacteria may be found
together in a specimen. I think you get the picture.
Okay then, in addition to identifying bacteria by their shape, which we now know isn’t really a very
good method for distinguishing them easily, if we really want to identify what type of bacteria we’re dealing
with, it’s better to study the biochemistry or genetic structure of the specimen. They have one chromosome
of double-stranded DNA in a ring, which we can analyze fairly easily.
选项
A、Bacteria have unusual cell formations.
B、Bacteria live harmlessly on the skin.
C、Bacteria are similar to other life forms.
D、Bacteria cause many diseases in humans.
答案
C
解析
Bacteria are similar to other life forms.
转载请注明原文地址:https://jikaoti.com/ti/MIlYFFFM
0
托福(TOEFL)
相关试题推荐
Youshouldspendabout20minutesonQuestions1-13,whicharebasedonReadingPassage1below.Seedvault
REVIEWOFRESEARCHONTHEEFFECTSOFFOODPROMOTIONTOCHILDRENThisreviewwascommissionedbytheFoodStandardsAgencytoex
Inthelastdecadearevolutionhasoccurredinthewaythatscientiststhinkaboutthebrain.Wenowknowthatthedecisionshu
Inthelastdecadearevolutionhasoccurredinthewaythatscientiststhinkaboutthebrain.Wenowknowthatthedecisionshu
AncientPeopleinSaharaOnOct.13,2000,PaulSereno,aprofessorfromtheUniversityofChicago,guidedateamofpalaeon
Lookatthefollowingopinionsordeedsandthelistofpeoplebelow.Matcheachopinionordeedwiththecorrectperson,A,
Tiktaalikrosaeisconsideredtobeanevolutionary______.TheremainsoftheTiktaalikrosaewerefound600milesfromthe_
Howdidthestudentgettheuniversityprospectus?scholarships
Thestudentsayssheis______whensheisstudyingathome.Theadvisersuggests______withanotherstudentafterlectureso
Choosethecorrectletter,A,BorC.PlanningapresentationonnanotechnologyRusssaysthathisdifficultyinplanningthep
随机试题
论想象力在意象生成过程中的作用,并举例说明
(2009年10月)商品的二因素是指_______。
平衡是指
下列有关防止采血过程中发生溶血的措施,错误的是
根据我国《合同法》的规定,在使用格式条款合同时,由提供格式条款合同的一方当事人在合同中设定、但不具备法律效力的条款有()的条款。
估计线性回归方程=β0+β1x中的回归参数β0、β1时,普遍采用的估计准则是最小二乘准则。()
下列关于工程承包合同的说法中,正确的是()。[2008年真题]
林先生要将从故乡带回的一包泥土分成小包装送给占其朋友总数30%的老年朋友。在分包装过程中发现,如果每包200克,则缺少500克,如果每包150克,则多余250克。那么,林先生的朋友共有多少人?
甲从1998年2月至1999年7月,先后拐卖妇女10余人,在拐卖的过程中,还强行奸淫被拐卖的妇女3名,强迫2名被拐卖的妇女卖淫,1名被拐妇女因不堪折磨而逃跑未成,甲为灭口而将其杀害。对甲应以哪些罪名追究刑事责任?()
字符串长度函数LEN(SPACE(3)-SPACE(2))的值是
最新回复
(
0
)