单选题
Listening 5 "Biology Class"
单选题
What aspect of bacteria is this lecture mainly about?
A. How microscopic organisms are measured
B. The use of bacteria for research in genetics
C. Diseases caused by bacterial infections
D. The three major types of bacteria
A. How microscopic organisms are measured
B. The use of bacteria for research in genetics
C. Diseases caused by bacterial infections
D. The three major types of bacteria
【正确答案】
D
【答案解析】[解析] 23-28
[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.
[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.
单选题
Which of the following slides contain cocci bacteria?
Click on the correct diagram.
Click on the correct diagram.
【正确答案】
B
【答案解析】[解析]
Which of the following slides contain cocci bacteria?
The cocci bacteria are shown in this slide.
Which of the following slides contain cocci bacteria?
The cocci bacteria are shown in this slide.
多选题
Which two characteristics are common in bacteria?
Click on 2 answer choices.
A. They have one cell.
B. They are harmful to humans.
C. They reproduce quickly.
D. They die when exposed to air.
Click on 2 answer choices.
A. They have one cell.
B. They are harmful to humans.
C. They reproduce quickly.
D. They die when exposed to air.
【正确答案】
【答案解析】[解析]
Which two characteristics are common in bacteria?
They have one cell.
They reproduce quickly.
Which two characteristics are common in bacteria?
They have one cell.
They reproduce quickly.
单选题
Why are bacteria being used in the research study at the university?
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.
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.
【正确答案】
C
【答案解析】[解析]
Why are bacteria being used in the research study at the university?
Bacteria are similar to other life forms.
Why are bacteria being used in the research study at the university?
Bacteria are similar to other life forms.
单选题
How does the professor help the students to remember the types of bacteria?
A. He shows them many examples of slides.
B. He tells them to look at specimens in the lab.
C. He uses the first letter to represent the shape.
D. He explains the various DNA structures.
A. He shows them many examples of slides.
B. He tells them to look at specimens in the lab.
C. He uses the first letter to represent the shape.
D. He explains the various DNA structures.
【正确答案】
C
【答案解析】[解析]
How does the professor help the students to remember the types of bacteria?
He uses the first letter to represent the shape.
How does the professor help the students to remember the types of bacteria?
He uses the first letter to represent the shape.
单选题
Why does the professor say this:
A. He is showing the students some slides.
B. He does not want the students to ask questions.
C. He wants the students to pay attention.
D. He thinks that the information is very clear.
A. He is showing the students some slides.
B. He does not want the students to ask questions.
C. He wants the students to pay attention.
D. He thinks that the information is very clear.
【正确答案】
D
【答案解析】[解析]
Listen again to part of the lecture and then answer the following question.
"Because, you see, bacteria 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 ."
Why does the professor say this:
"I think you get the picture."
To "get the picture" means "to understand." He thinks that the information is very clear.
Listen again to part of the lecture and then answer the following question.
"Because, you see, bacteria 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 ."
Why does the professor say this:
"I think you get the picture."
To "get the picture" means "to understand." He thinks that the information is very clear.