LISTENING 5 : “BIOLOGY CLASS”
Narrator Listen to part of a lecture in a biology class. The professor is discussing blood types.
Before we begin our discussion of blood types, let’s review what we know about blood. According to the textbooks, about half of the volume of blood is made up of blood cells that begin as stem cells in bone marrow. And these stem cells can develop into any of the other kinds of cells found in blood, including red cells, white cells, and platelets. So … some stem cells become white cells or leukocytes and these are essential to the immune system. And when bacteria or germs invade the body, some of the white cells form antibodies to resist the infection directly while other white cells begin to work on the chemistry of the foreign substance itself… to fight the infection. Now, compared with red blood cells, there are relatively few white blood cells . .. only about one for every seven hundred red cells. And the smallest of the blood cells are called platelets, but what they don’t have in size they make up for in numbers. Well, most of us have about two trillion of them and they work to help the Wood to dot and . .., uh, repair holes in the walls of blood vessels. But we need a way to transport the blood, right? Plasma is the liquid substance in blood that transports most of the chemicals .. . vitamins, minerals . . . hormones and enzymes.
But most stem cells become red blood cells, or erythocytes. They’re the most numerous. As I mentioned before, there are about seven hundred to every one white blood cell. So the red cells give blood the color red. and they’re important for what we call blood typing. And blood typing is what I want to get going on today.
Now blood types are a classification of red blood cells according to the presence of specific sub-stances … antigenic proteins and carbohydrates … and you can see them under the microscope on the surface of the cells. The four blood types are identified by letters … A, B, AB, and O. Blood type A contains red blood cells with the antigen A Blood type B contains red blood cells with the antigen B. The AB blood type contains both antigens, and the O blood type contains no antigens, but the individual with this type can form antibodies containing either A or B antigens.
Excuse me. Is that why the O blood type is considered a universal blood type? Because it can form anti-bodies with either A or B antigens?
Right you are. But, in typing the blood, the antigens are really much more complex than Ibis explanation might suggest. There are at least 300 different antigens. In fact, there are so many potential combina-tions that an irxfividual’s blood type is almost as unique as a fingerprint. But anyway, these basic types are used for determining compatibilities for blood transfusions. Before a transfusion is approved, hospi-tals always perform a procedure called a cross match which involves taking a sample of the donor’s red blood cells and mixing them with a sample of the patient’s plasma. You see, in almost every individual, the plasma contains antibodies that will react to antigens that aren’t found on their own red blood cells. So during a transfusion, antibodies in the patient’s plasma can bind to antigens on the donor’s red blood cells when the donor’s blood isn’t similar to that of the patient Well, many minor reactions can occur like fever or chills, but some reactions are so severe that they lead to a… a spontaneous destruction of the red blood cells from the donor and that can result in shock or even death. So you can understand why blood typing is so important. Cross matching lowers the risk of a serious reaction.
Okay. In cross matching, we take red cells from one person and plasma from the other person, and we watch to see whether there’s a negative response. Take a look at this diagram. Ifs on page 112 in your textbook. Here’s what you would be looking at with a reaction caused by incompatible blood. See how the cells dump together?
The reason that this is happening is because there’s a chemical reaction between the protein molecules in the red cells of one person and the plasma of the other. Now look at this slide. This diagram is on the next page in your text and this shows a compatible match with no dumping.
See how the cells are evenly spaced?
Well, of course, doctors prefer to use the same type as that of the patient, but compromises have to be made in emergencies. Type A patients can’t receive type B blood, and type B patients can’t receive type A blood, but back to your question; since an O donor has blood that’s compatible with both A and B antigens, ifs the ideal, or as you said, the universal donor. In an emergency, type O blood can be used for patients of all blood types. And fortunately, worldwide, type O is the most common, followed by type A. Relatively few people have type B blood, and the fewest have type AB.
Student 2: Professor Stephens, can you tell us anything about artifkaal blood?
Well actually, sdentists have developed artificial blood that’s been used successfully in blood transfu-sions with human patients. Ifs a white fluid, chemically similar to Teflon, the material that coats cook-ware and prevents material from adhering to it The fluid can be used as a match with all blood types, and so, the cross matching step in transfusions . . . that can be eliminated. So far, artificial blood has done a good job of replacing the red cells by carrying oxygen through the body and eliminating carbon dioxide, but there are no white cells present, no antibodies, no platelets. So, it doesn’t dot and it doesn’t remain in the body very long. Still, continuing research along these lines should probably be encouraged. Um, even with cross matching and other precautions, transfusions with human blood involve risks.
LISTENING 6 “ORIENTATION SESSION”
Narrator Listen to part of a discussion in an orientation dass.
For the most part, college students don’t read fast enough to keep up with the demands of their reading assignments. Let’s just say that the typical college student reads 150 to 300 words per minute Okay. The professor in the Western Civilization course uses the topics from Chapter 1 of the textbook for three lectures the first week of the semester. Each page has about 500 words on it, and that includes space for pictures and drawings. So, at 150 words per minute… let me see … each page will lake more than three minutes to complete, and … if my figures are right… that’s almost three hours just to read the textbook assignment once through. That doesn’t even count what you need to do to think and connect the lectures with the book, and you can be sure that there will be additional reading or other assignments besides the lectures and the textbook…. Have you heard about the limes two rule?
Isn’t that… doesn’t that mean a student should spend two hours of study time for every hour of class time in every subject?
Exactly. Okay. I think you’ll agree that reading faster is important to success in college. So its only practical to leam to read faster. And, uh. that’s why I’m going to talk with you about the human capacity for reading … and some habits that you may have that could be slowing you down First, I want you to think about reading ike you think about running. The more you run, the faster and farther you can go… and the more you read, the faster you’re going to read. In fact, researchers hypothesize that our physical capacity to read surpasses our ability to turn the pages. In other words, our brains can take in the information faster than our hands can move. So reading 700 to 1000 words a minute should be a reasonable goal for almost everyone That would be quite a time saver, wouldn’t it ?
Student 1: Yeah. It sure would.
Now. let’s talk about why most of us probably aren’t reading at that speed … at 1000 words a minute … why we’re not doing that now. We know that we have the capacity—that our brains can take it in. But there are a few habits that prevent readers from reaching that target speed of 700 to 1000 words. In the first place, some people are auditory readers. That means that they hear every word in their minds. Some people even move their lips so they seem to be speaking while they’re reading. This is a serious problem because we can only speak about 300 words per minute, but, uh, our capacity to read … ifs many times faster. So if you’re hearing the words in your head or moving your lips, you know that you’re preventing your mind from processing as fast as it can. Can any of you relate to that?
Student 2: I can. I hear every word.
A lot of people do. Now, another problem is something called fixations. Fixations are the actual pauses that the eye makes. We can’t see while the eye is moving so we have to stop to take in the text. Everyone has to fixate to see the print, but, uh, some people… they stop their eyes on every single word and that will really slow you down. So if you’re looking at every word or even at every few words, that habit is something to work on. When you’re not reading word by word, your mind has to connect and, uh, build associations and … and patterns. You can do this because so much of a written text is redundant—that means that there’s a lot of repetition, so quite a few words can be skipped without losing the meaning.
Student 3: So you’re saying-we should try to guess the meaning?
I think I would use the term predict rather than guess, but basically the answer to your question is *yes.* Now this may surprise you. Using a dictionary is a good habit. Right? Well, yes, in moderation. But stopping to look up every new word is a bad habit because you don’t need to know every word in order to understand what you’re reading. Remember what I just said about redundancy. So, uh, stopping to use the dictionary too often … that interrupts your train of thought and, uh, prevents you from reaching your potential reading speed.
Student 3: I’ve heard that before and it makes sense but…
Professor. But you’re afraid to try it?
Student 3: That’s probably true.
Well, I’ll come back to that in a minute. First I want to point out one more problem. A lot of readers go back over the words they’ve already read to clarify the meaning. But this is probably the worst habit because, uh, when we’re repeating twice or even more times, that causes our reading speed to drop and it goes to 50 or even 30 percent of our capacity. Did I mention that this is called regression ? Okay, well this regression not only slows us down, it also makes it more difficult to understand the meaning because, uh, the way that we comprehend we understand by connecting with the next phrase, so going back all the time makes us lose the connections.
And this is what’s realty important in all of this—research demonstrates a correlation between speed and comprehension. In an overwhelming number of cases, when students increase their reading speed, they also increase their comprehension of the material. So how can you do this? First break the habits that are causing you to read slowly. Don’t think the words in your head or move your lips to sound out each word. Don’t let your eyes pause on every word. Don’t look up every new word in the dictionary. And try not to go back over paragraphs and, uh, sentences that you’ve already read. But, that’s hard to do if you have these habits, isn’t it? Especially if you’re also trying to read in order to learn a new subject. That’s why you’re afraid to try it… because, uh, you have to leam the content in order to pass the course and … you don’t want to try something new — to take a risk.
Student 3: Yeah. That’s about the size of it.
Well. I understand that But you can take a nsk and try to change some of those habits, but it helps if you do it in a structured environment like the Learning Center. If s free and you’ll more than make up for the time you spend in one of the reading courses they offer when you begin to read all of your assignments at twice the speed you’re reading them now.