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TOEFL COURSES --> Mastering iBT TOEFL -->Writing Section
Integrated Writing

For this task, you will read a passage about an academic topic and you will listen to a lecture about the same topic. You may take notes while you read and listen.
Then you will write a response to a question that asks you about the relationship be-tween the lecture you heard and the reading passage. Try to answer the question as completely as possible using information from the reading passage and the lecture.
The question does not ask you to express your personal opinion. You may refer to the reading passage again when you write. You may use your notes to help you answer the question.
Typically, an effective response will be 150 to 225 words. Your response will be judged on the quality of your writing and on the completeness and accuracy of the content.
You should allow 3 minutes to read the passage. Then listen to the lecture. Then allow 20 minutes to plan and write your response.
The ability of tree frogs to climb hazardously slippery slopes and to cling upside down has long fascinated scientists. Tree frogs inhabit trees, as their name implies, and most species have adhesive pads on their toes. The toe pads of the White's tree frog secrete mucus. Scientists believe it is this fluid that acts as an adhesive to help the frog climb trees and cling to the underside of branches. The toe pads are made up of hexagonal—six-sided—cells, separated by small channels through which the mucus drains. Furthermore, each hexagonal cell is divided into microscopic pegs, and it is believed that the pad design works with the mucus to keep the pads permanently wet, enabling the frog to grip. Evidence points to viscosity and surface tension as the keys to how the mucus helps the tree frog stick to surfaces.
Viscosity is a property of liquids that determines the speed at which the liquid will flow over a solid surface or other layers of fluid. In general, the higher the viscosity, the more slowly the - fluid flows over a surface. The apparently high viscosity of the mucus of the White's tree frog ensures that the pad is continually covered with the adhesive liquid. For its part, the surface tension of the mucous determines the force with which the toe pads cling to surfaces. Again, the more surface tension, the greater the force, the better the ability to cling. Scientists believe that the properties of the mucus combine with the toe pad design to give the White's tree frog its incredible capacity to climb and grip.

Question: Summarize the points made in the lecture, explaining how they cast doubt on points made in the reading passage.
Count: 0 word(s)


Now listen to part of a lecture on the topic you just read about.
M: For quite a long time now, scientists have believed that the mucus of the White's tree frog—mucus, that's a thick liquid—the mucus and the pads on its toes hold the key to the tree frog's ability—its ability to climb slippery trees and other surfaces and to perch upside down on branches. Of course, these are essential abilities for any amphibian that's gonna make its home in a tree! Scientists hypothesized that a combination of the viscosity ---you know, how fast or slow a liquid runs--- helps keep the pads covered with the liquid. It doesn't drain away fast. And the surface tension of the mucus helps increase its adhesive power. So scientists have been putting their theories to the test. Recently, some researchers in England came up with some fascinating--and rather unexpected, I must add---results. What got them thinking about this line of research in the first place was an observation of some tree frogs climbing on rocks, on rocks over which water was flowing. How would this mucus be working through the flowing water? Well, the scientists did some studies and discovered a couple of important things. First, they discovered that the mucus layer between the toe pad of the frog and whatever it was standing on, that mucus layer was so thin—we're talking a millionth of a millimeter here, infinitesimal—that the thickness was, to quote them, "indistinguishable from zero." Basically, there was no mucus layer between the frog's toe pads and the surface. They were in direct, dry contact with whatever the frog was standing on. All the mucus was squeezed out through the channels that surround the pad's cells.
The second thing they discovered was that the viscosity of the tree frog's mucus was nowhere near as high as they expected: only half again as viscous as water. The scientists concluded from this that actually that design of the toe pads--- those hexagonal cells and little pegs and channels ---that design likely evolved to rapidly drain away the mucus from the toe pads, rather than to keep it there. That is, to drain it away so that the toe pads could grip.
One final thing—they looked at the force with which the tree frog's toe pads cling to the surface. What did they find? Well, the toe pads held their strength to cling for two minutes at least—and two minutes was long past the point when the mucus would have all drained away, based on its viscosity level. Again, it wasn't the mucus that was enabling the tree frogs to cling and climb on those slippery surfaces.
Back to the drawing board. Because clearly there is something in the White's tree frog's toes that is giving it this extraordinary clinging and climbing ability. What's holding them to the surfaces? Oh, and by the way, now there's another question. If all the mucus White's tree frogs produce isn't used for glue, to help the frogs stick to surfaces, well, then, what is it used for?
Sample answer:
The lecture made three points about recent discoveries made by researchers in England regarding how the White's tree frog manages to climb slippery surfaces and perch upside down. The reading passage stated that scientists believed two things helped the tree frog do this. One was the mucus that the tree frog secretes onto its toe pads, and the other was the design of the toe pads themselves. Scientists presumed that the mucus had a viscosity and surface tension that helped it to stay on the pads and be sufficiently sticky to adhere to surfaces. The tiny channels of the pads would help spread the mucus all over the pad.
In fact, what scientists have recently discovered, according to the lecture, is that the mucus on the toe pad is so incredibly thin that it might as well not be there. It can't be having any effect. When a tree frog stands somewhere, its toes are, for all intents and purposes, making direct and dry contact with the surface. So what happens to the mucus? It's squeezed out. It seems that those channels, instead of being there to carry the mucus all over the pad, are actually there to quickly drain the mucus away from the pad. In fact, the viscosity of the mucus is much lower than expected, only one and a half times the viscosity of water, which means the mucus flows more quickly than scientists had expected it to. The other discovery that puts into question the theories described in the reading passage is that the toe pads of the tree frog maintain the force with which they cling to the surface for at least a good two minutes. The mucus would be long gone by then, because of its viscosity. So the mucus is clearly not the secret ingredient that accounts for the adhesiveness of the tree frog's toe pads. There must be something else happening, although scientists aren't sure what. Also, scientists are back to the beginning when it comes to understanding what function all that mucus might actually perform for the tree frog.

Total: 2 page(s)
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