有关托福阅读背景材料的积累，不是一天两天就可以解决的，需要长期的坚持。北京新航道小编搜集了一些有关材料，供大家参考学习。

　　【过往机经】骆驼，为什么可以在沙漠生存，和他的skin，fat，hump 等等有关，我觉得这篇不是太难，但是细节挺多的

　　【重点词汇解析】 　　Camel 骆驼 　　Hump驼峰 　　Skin 皮肤 　　Fat 脂肪 　　Dehydration 缺水 　　Store water 储水 　　Drought enduring 耐旱 　　Heat resisting 耐热

　　【机经解析】 　　骆驼的抗旱储水能力 　　Camel Eco-behavioral adaptations 　　Camels do not directly store water in their humps as was once commonly believed. The humps are actually reservoirs of fatty tissue: concentrating body fat in their humps minimizes the insulating effect fat would have if distributed over the rest of their bodies, helping camels survive in hot climates. When this tissue is metabolized, it yields more than one gram of water for every gram of fat processed. This fat metabolization, while releasing energy, causes water to evaporate from the lungs during respiration (as oxygen is required for the metabolic process)： overall, there is a net decrease in water. 　　A camel's thick coat is one of their many adaptations that aid them in desert-like conditions. 　　The Horn of Africa has the world's largest population of camels. 　　Camels have a series of physiological adaptations that allow them to withstand long periods of time without any external source of water. Unlike other mammals, their red blood cells are oval rather than circular in shape. This facilitates the flow of red blood cells during dehydration and makes them better at withstanding high osmotic variation without rupturing when drinking large amounts of water: a 600 kg (1,300 lb) camel can drink 200 L (53 US gal) of water in three minutes. 　　Camels are able to withstand changes in body temperature and water consumption that would kill most other animals. Their temperature ranges from 34 °C (93 °F) at dawn and steadily increases to40 °C (104 °F) by sunset, before they cool off at night again. Camels rarely sweat, even when ambient temperatures reach 49 °C (120 °F). Any sweat that does occur evaporates at the skin level rather than at the surface of their coat; the heat of vaporization therefore comes from body heat rather than ambient heat. Camels can withstand losing 25% of their body weight to sweating, whereas most other mammals can withstand only about 12-14% dehydration before cardiac failure results from circulatory disturbance. 　　When the camel exhales, water vapor becomes trapped in their nostrils and is reabsorbed into the body as a means to conserve water. Camels eating green herbage can ingest sufficient moisture in milder conditions to maintain their bodies' hydrated state without the need for drinking. 　　Camels are used as draft animals inPakistan. 　　The camels' thick coats insulate them from the intense heat radiated from desert sand, and a shorn camel has to sweat 50% more to avoid overheating. During the summer the coat becomes lighter in color, reflecting light as well as helping avoid sunburn. Its long legs help by keeping them farther from the hot ground, which can heat up to 70 °C (158 °F). 　　Camels' mouths have a thick leathery lining, allowing them to chew thorny desert plants. Long eyelashes and ear hairs, together with nostrils that can close, form a barrier against sand. If sand gets lodged in their eyes, they can dislodge it using their transparent third eyelid. The camels' gait and widened feet help them move without sinking into the sand. 　　The kidneys and intestines of a camel are very efficient at reabsorbing water. Camel urine comes out as a thick syrup, and camel feces are so dry, the Bedouins use it to fuel fires. 　　Camels' immune system differs from those of other mammals. Normally, the Y-shaped antibody molecules consist of two heavy (or long) chains along the length of the Y, and two light (or short) chains at each tip of the Y. Camels, in addition to these, also have antibodies made of only two heavy chains, a trait that makes them smaller and more durable. These "heavy-chain-only" antibodies, discovered in 1993, are thought to have developed 50 million years ago, after camelids split from ruminants and pigs。

　　希望上面的托福阅读背景材料可以帮助同学们在备考中积累知识，获得的素材。北京新航道小编预祝各位考试顺利，早日结束考试。

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