GreatBarrier Reef
The GreatBarrier 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 GreatBarrier 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 GreatBarrier 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 ol
D、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 GreatBarrier Reef is also of great scientific interest because of the diversity of marine life that lives in its vicinity.
As stated above, the GreatBarrier 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 GreatBarrier 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 Reef’s fish species have been documente
D、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 battleAIDS and various cancers.
Coral reefs in general, and the GreatBarrier 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 affecte
D、
The future of the GreatBarrier 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 fue

Thermoregulation
Mammals and birds generally maintain body temperature within a narrow range (36-38~C、for most mammals and 39-42℃ for most birds) that is usually considerably warmer than the environment.Because heat always flows from a warm object to cooler surroundings, birds and mammals must counteract the constant heat loss. This maintenance of warm body temperature depends on several key adaptations. The most basic mechanism is the high metabolic rate of endothermy itself.Endotherms can produce large amounts of metabolic heat that replace the flow of heat to the environment, and they can vary heat production to match changing rates of heat loss. Heat production is increased by such muscle activity as moving or shivering. In some mammals, certain hormones can cause mitochondria to increase their metabolic activity and produce heat instead of ATP. This nonshivering thermogenesis (NST) takes place throughout the body, but some mammals also have a tissue called brown fat in the neck and between the shoulders that is specialized for rapid heat production. Through shivering and NST, mammals and birds in cold environments can increase their metabolic heat production by as much as 5 to 10 times above the minimal levels that occur in warm conditions.
Another major thermoregulatory adaptation that evolved in mammals and birds is insulation (hair, feathers, and fat layers), which reduces the flow of heat and lowers the energy cost of keeping warm. Most land mammals and birds react to cold by raising their fur or feathers, thereby trapping a thicker layer of air.
Humans rely more on a layer of fat just beneath the skin as insulation; goose bumps are a vestige of hair-raising left over from our furry ancestors.
Vasodilation and vasoconstriction also regulate heat exchange and may contribute to regional temperature differences within the animal.
For example, heat loss from a human is reduced when arms and legs coo] to several degrees below the temperature of the body core, where most vital organs are locateD、

Hair loses most of its insulating power when wet. Marine mammals such as whales and seals have a very thick layer of insulation fat called blubber, just under the skin. Marine mammals swim in water colder than their body core temperature, and many species spend at least part of the year in nearly freezing polar seas. The loss of heat to water occurs 50 to 100 times more rapidly than heat loss to air, and the skin temperature of a marine mammal is close to water temperature.Even so, the blubber insulation is so effective that marine mammals maintain body core temperatures of about 36-38℃ with metabolic rates about the same as those of land mammals of similar size. The flippers or tail of a whale or seal lack insulating blubber, but countercurrent heat exchangers greatly reduce heat loss in these extremities, as they do in the legs of many birds.
Through metabolic heat production, insulation, and vascular adjustments, birds and mammals are capable of astonishing feats of thermoregulation. For example, small birds called chickadees, which weigh only 20 grams, can remain active and hold body temperature nearly constant at 40℃ in environmental temperatures as low as -40℃--as long as they have enough food to supply the large amount of energy necessary for heat production.
Many mammals and birds live in places where thermoregulation requires cooling off as well as warming. For example, when a marine mammal moves into warm seas, as many whales do when they reproduce, excess metabolic heat is removed by vasodilation of numerous bl

Energy from Natural Gas
1. Much of the world gets its energy from fossil fuel sources, including coal, oil, and natural gas, all of which were created millions of years ago.The process began with dead plant and animal matter that collected and over time was buried deep within the earth. There, exposed to extreme pressure and temperatures, the carbon-based material underwent various chemical and physical changes. Some of it became coal, some oil, and some natural gas, depending on the exact conditions it was subjected to.
2. Natural gas is both invisible and odorless.During the first century of the fossil fuel era, it was disregarded as a worthless byproduct of coal and oil. However, people later discovered that it could also be a useful source of energy, and they set about trying to realize its potential. Its use began to grow in the twentieth century and has increased rapidly within the last 40 years. Nowadays, natural gas is employed all over the world to heat homes, generate electricity, power factories, and even fuel vehicles.
3.Because it was created through the same process as other fossil fuels, natural gas can often be retrieved from oil fields, something known as an associated source.Coal beds have similarly been known to yield natural gas. In addition, there are isolated deposits containing only gas that are referred to as non-associated sources. To access a subterranean natural gas pocket, a hole is drilled down into it, just as in oil extraction. However, due to the gas’s lightness, it will rise to the surface on its own instead of having to be pumped out.
4. The compound we know as natural gas is actually a composite of several different substances, the primary one being methane gas.Each deposit has a unique makeup, but other common components of natural gas include propane, butane, and sulfur.Borrowing terms used in the description of oil, natural gas with a high sulfur content is called "sour" while that with a low content is referred to as "sweet" Regardless of the exact composition, natural gas must be refined to remove its impurities; when ready for use, it is nearly pure methane.
5. Natural gas offers many advantages as a fuel source, the first and most important being that it is extremely clean burning. While oil and coal both have complex molecular structures, methane’s is simple: one carbon atom surrounded by four atoms of hydrogen. The lack of excess particles translates into fewer waste byproducts during combustion. For example, all fossil fuels produce carbon dioxide when burned, but natural gas releases substantially less carbon dioxide than other fuels. Given the major role of carbon dioxide in the acceleration of global warming, this is an important attribute. In addition, natural gas emits far less nitrogen and sulfur, which are key contributors to the smog that pollutes the air in metropolitan areas, as well as acid rain.
6. The benefits of natural gas extend far beyond its cleanliness. Since it contains fewer waste particles, its energy can be acquired with much more efficiency than that of the other fossil fuels, meaning a lower overall cost for the consumer.
Another advantage is that natural gas is transported via underground pipelines instead of by ships and trucks.
Finally, natural gas is relatively plentiful and widespreaD、
Geologists have identified extensive stores inCanada, the United States, Russia, the MiddleEast, andAustralia, among other locations.
With the world’s oil supplies quickly dwindling, it is becoming more important than ever to utilize alternative energy resources such as natural gas.
7. Of

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