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315 READING TOEFL iBT® Practice Test 2 This section measures your ability to understand academic passages in English. You will have 54 minutes to read and answer questions about 3 passages. A clock at the top of the screen will display the starting time as 00 : 54 : 00 and show you how much time is remaining. Most questions are worth 1 point, but the last question for each passage is worth more than 1 point. The directions for the last question indicate how many points you may receive. Some passages in the computer-based test include a word or phrase that is underlined in blue. When you click on the word or phrase underlined in blue, you will see a verbal or visual definition of the word or term. In this book, those definitions are provided as endnotes below the reading passage. Within this section, you can move to the next question by clicking on Next. You can skip questions and go back to them later as long as there is time remaining. If you want to return to previous questions, click on Back. You can click on Review at any time and the review screen will show you which questions you have answered and which you have not answered. From this review screen, you may go directly to any question you have already seen in the Reading section. During this practice test, you may click the Pause icon at any time. This will stop the test until you decide to continue. You may continue the test in a few minutes or at any time during the period that your test is activated. You will now begin the Reading section. Again, in an actual test you will have 54 minutes to read the 3 passages and answer the questions. NOTE: In an actual test, some test takers might receive 4 passages; those test takers will have 72 minutes (1 hour and 12 minutes) to answer the questions. Turn the page to begin the Reading section.
TOEFL iBT ® Practice Test 2 FEEDING HABITS OF EAST AFRICAN HERBIVORES Buffalo, zebras, wildebeests, topi, and Thomson’s gazelles live in huge groups that together make up some 90 percent of the total weight of mammals living on the Serengeti Plain of East Africa. They are all herbivores (plant-eating animals), and they all appear to be living on the same diet of grasses, herbs, and small bushes. This appearance, however, is illusory. When biologist Richard Bell and his colleagues analyzed the stomach contents of four of the five species (they did not study buffalo), they found that each species was living on a different part of the vegetation. The different vegetational parts differ in their food quali- ties: lower down, there are succulent, nutritious leaves; higher up are the harder stems. There are also sparsely distributed, highly nutritious fruits, and Bell found that only the Thomson’s gazelles eat much of these. The other three species differ in the proportion of lower leaves and higher stems that they eat: zebras eat the most stem matter, wildebeests eat the most leaves, and topi are intermediate. How are we to understand their different feeding preferences? The answer lies in two associated differences among the species, in their digestive systems and body sizes. According to their digestive systems, these herbivores can be divided into two categories: the nonruminants (such as the zebra, which has a digestive system like a horse) and the ruminants (such as the wildebeest, topi, and gazelle, which are like the cow). Nonrumi- nants cannot extract much energy from the hard parts of a plant; however, this is more than made up for by the fast speed at which food passes through their guts. Thus, when there is only a short supply of poor-quality food, the wildebeest, topi, and gazelle enjoy an advantage. They are ruminants and have a special structure (the rumen) in their stom- achs, which contains microorganisms that can break down the hard parts of plants. Food passes only slowly through the ruminant’s gut because ruminating—digesting the hard parts—takes time. The ruminant continually regurgitates food from its stomach back to its mouth to chew it up further (that is what a cow is doing when “chewing cud”). Only when it has been chewed up and digested almost to a liquid can the food pass through the rumen and on through the gut. Larger particles cannot pass through until they have been chewed down to size. Therefore, when food is in short supply, a ruminant can last longer than a nonruminant because it can derive more energy out of the same food. The difference can partially explain the eating habits of the Serengeti herbivores. The zebra chooses areas where there is more low-quality food. It migrates first to unexploited areas and chomps the abundant low-quality stems before moving on. It is a fast-in/fast-out feeder, relying on a high output of incompletely digested food. By the time the wildebeests (and other ruminants) arrive, the grazing and trampling of the zebras will have worn the vegetation down. As the ruminants then set to work, they eat down to the lower, leafier parts of the vegetation. All of this fits in with the differences in stomach contents with which we began. The other part of the explanation is body size. Larger animals require more food than smaller animals, but smaller animals have a higher metabolic rate. Smaller animals can therefore live where there is less food, provided that such food is of high energy content. That is why the smallest of the herbivores, Thomson’s gazelle, lives on fruit that is very nu- tritious but too thin on the ground to support a larger animal. By contrast, the large zebra lives on the masses of low-quality stem material. The differences in feeding preferences lead, in turn, to differences in migra- tory habits. The wildebeests follow, in their migration, the pattern of local rainfall. The other species do likewise. But when a new area is fueled by rain, the mammals 316