This section measures your ability to understand academic passages in English. The Reading section of TOEFL iBT is divided into 2 or 3 separately timed, parts. Most questions in the Reading section are worth 1 point, but the last question for each passage is worth more than 1 point. The directions for the last question include the point value of the question. Some passages will include a word or phrase that is underlined in blue. Click on the word or phrase to see its definition or an explanation. Within each part, you can go on to the next question by clicking the Next icon. You may skip questions and go back to them later. If you want to go back to previous questions, click the Back icon. You may click the Review icon at any time and the review screen will show you which questions you have answered and which you have not. From the review screen, you can go directly to any question you have already seen in the Reading section. You will now begin the Reading section. There is 1 passage for this part of the section, and you will have 20 minutes to read the passage and answer the questions. Click Continue to go on. Great Barrier Reef The Great Barrier Reef is made of coral, a colorful rock-like substance actually composed of many small marine animals, each one less than half a centimeter in size. Coral grows in colonies that can reach over a meter and a half in height, and several of these colonies grow in close proximity to each other, eventually joining up to form. an underwater chain or reef. The Great Barrier Reef refers to a series of almost three thousand coral reefs that stretch across the ocean floor in a twelve hundred mile chain, which makes it so long that it can actually be seen from space. Apart from its size, the Great Barrier Reef is also renowned for its age. The living part of the reef itself is around 8,000 years old, but sits atop the remains of dead coral that is much older, in some places almost half a million years old. A system of living organisms so anc ient and so large would be fascinating to scientists by the simple fact of its existence alone, but the Great Barrier Reef is also of great scientific interest because of the diversity of marine life that lives in its vicinity. As stated above, the Great Barrier Reef is made of coral, but just as there are many different varieties of dogs, cats, and finches, there are many varieties of coral, over 500 of which are found in the Great Barrier Reef. The rocky formations of the reefs also provide shelter for a variety of smaller marine fish, and these in turn provide food for larger, more predatory fish. As a result, some scientists believe that the Reef is home to up to twenty-five percent of all marine fish species. However, this is only a rough estimate since so few of the Reefs fish species have been documented. In addition, the Reef hosts a variety of sponges, anemones, sea turtles, sea snakes, sea birds, and whales. Marine biologists, therefore, value the Reef for what it can teach them about ocean ecology, while other scientists are eagerly investigating the practical applications of chemical compounds produced by the creatures of the Reef. Indeed, chemicals initially discovered in Reef organisms are already the basis for many potent new medicines, including some that help battle AIDS and various cancers. Coral reefs in general, and the Great Barrier Reef in particular, have been considered so environmentally important that the governments that control the waters where they exist have designated vast tracts of ocean as environmentally protected areas. Nevertheless, the reefs form. one giant, interconnected ecosystem, and human activities in unprotected areas of the reefs can affect the entire system. One such human activity is fishing. (A) The rich biodiversity of the reefs attracts many predatory fish that in turn draw large numbers of fishing vessels. (B) Unfortunately, many modern fishing techniques employ nets that catch not only the target species, but all fish too big to slip through the holes in the net. (C) Besides fishing, the reefs face pressure from shipping and oil spills. (D) Shipping can become a problem when freighters make mistakes in navigation and run into the reef, shattering segments of it that have taken decades or even centuries to grow. Oil spills-- always damaging to the environment--have an especially devastating effect when they occur near the reefs because so many endangered species are affected. The future of the Great Barrier Reef is uncertain. In addition to the environmental hazards outlined above, the Reef is under threat of global warming. Although coral consists of tiny, carnivorous animals, those animals do not get most of their nutrients from the organisms they catch. Instead, they enjoy a symbiotic relationship with a form. of algae called zooxanthellae. These algae live off the nitrogen emitted by the coral. Like many other types of algae, zooxanthellae undergo photosynthesis, using energy from sunlight to create sugars that they can use for fuel. Some of those sugars are also absorbed by the coral that shelter the algae, providing the coral with the fuel it needs to live. However, these particular algae can only perform. photosynthesis if the water around them is within a very narrow temperature range. If the temperature of the water in the ocean increases by too much, the algae cease to be able to carry out photosynthesis and are expelled by the coral, which then begins to starve to death. Because it is the presence of zooxanthellae that normally gives coral its rich color, coral that has expelled the algae becomes white, leading scientists to term this process 'coral bleaching.' According to paragraph 1, what is coral made of?