首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
外语
→ Mammals and birds generally maintain body temperature within a narrow range (36-38℃ for most mammals and 39-42℃ for most birds
→ Mammals and birds generally maintain body temperature within a narrow range (36-38℃ for most mammals and 39-42℃ for most birds
admin
2012-01-14
42
问题
→ Mammals and birds generally maintain body temperature within a narrow range (36-38℃ 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.A 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. B Vasodilation and vasoconstriction also regulate heat exchange and may contribute to regional temperature differences within the animal.C For example, heat loss from a human is reduced when arms and legs cool to several degrees below the temperature of the body core, where most vital organs are located. D
→ 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 blood vessels in the outer layer of the skin. In hot climates or when vigorous exercise adds large amounts of metabolic heat to the body, many terrestrial mammals and birds may allow body temperature to rise by several degrees, which enhances heat loss by increasing the temperature gradient between the body and a warm environment.
→ Evaporative cooling often plays a key role in dissipating the body heat. If environmental temperature is above body temperature, animals gain heat from the environment as well as from metabolism, and evaporation is the only way to keep body temperature from rising rapidly. Panting is important in birds and many mammals. Some birds have a pouch richly supplied with blood vessels in the floor of the mouth; fluttering the pouch increases evaporation. Pigeons can use evaporative cooling to keep body temperature close to 40℃ in air temperatures as high as 60℃, as long as they have sufficient water. Many terrestrial mammals have sweat glands controlled by the nervous system. Other mechanisms that promote evaporative cooling include spreading saliva on body surfaces, an adaptation of some kangaroos and rodents for combating severe heat stress. Some bats use both saliva and urine to
enhance
evaporative cooling.
Glossary
ATP: energy that drives certain reactions in cells
mitochondria: a membrane of ATP
Look at the four squares [■] that show where the following sentence could be inserted in the passage. The insulating power of a layer of fur or feathers mainly depends on how much still air the layer traps. Where could the sentence best be added? Click on a square [■] to insert the sentence in the passage.
选项
A、Square A.
B、Square B.
C、Square C.
D、Square D.
答案
A
解析
Reference is a transitional device that connects the insert sentence with the previous sentence. "... a layer of fur or feathers" and "how much still air the layer [of fur or feathers] traps" in the insert sentence refers to "... fur or feathers" and "a thicker layer of air" in the previous sentence.
转载请注明原文地址:https://jikaoti.com/ti/SKlYFFFM
0
托福(TOEFL)
相关试题推荐
Completeeachsentencewiththecorrectending,A-G,below.Writethecorrectletter,A-G,inboxes37-40onyouranswersheet
Labelthediagrambelow.ChooseNOMORETHANONEWORDfromthepassageforeachanswer.Writeyouranswersinboxes7-9onyour
writtenresponses
HowlikelyareThomasandNadiatovisitthefollowingattractions?Writethecorrectletter,A,BorCnexttoquestions6-1
A、collatetheanswers.B、ranktheanswers.C、knowalotabouttheanswers.B
ChooseTHREEletters,A-G.WhichTHREEfactorsshouldthestudentconsiderwhileselectingcourses?AclasstimeBcoursetopic
Whichattitudeisassociatedwiththefollowingpeopleduringtheconversation?ChooseSIXanswersfromtheboxandwritetheco
Whatdoesthepoliticiansaythegovernmentwilldointhefollowingareas?AincreaseexpenditureBmaintainthesamelevelof
temperature录音提到热饮让人觉得甜得发腻(toosweett0berefreshing)。饮料冷冻后的甜味就没那么明显。由此可知影响甜味的是温度,故填入temperature。
随机试题
A、Heisproficientindriving.B、Heiskindandlearned.C、Heknowsashortcuttothemuseum.D、Heisaninexperiencedtaxidriv
患儿女性,3岁,因“肺炎,脓毒性休克”收住儿科重症监护室(PICU)。入院第3天,休克已经纠正,呼吸机治疗,腹胀,无肠鸣音,胃管内引流出咖啡样胃液。此时静脉营养成分的选择是
生物转化中甲基可来自生物转化中乙酰基可来自
男性,10岁。突发剑突下阵发性剧烈绞痛3小时,发作时辗转不安,呻吟痛苦,伴恶心呕吐,发作过后如常人。检查无发热无黄疸,腹平软无明显压痛,白细胞计数正常。应诊断为何病
利用中药中各成分沸点的差别进行提取分离的方法是
河流充分混合段是指污染物浓度在断面上均匀分布的河流。当()时,可以认为达到均匀分布。
甲公司严重资不抵债。因不能清偿到期债务向法院申请破产。下列财产属于债务人财产的是()。
个体在解决问题过程中,思维沿着许多不同的方向扩展,使观念发散到各个有关方面,最终产生多种可能的答案的认知方式称为()。
配置路由器时,PC机的串行口与路由器的(59)相连,路由器与PC机串行口通信的默认数据速率为(60)。(59)
AsmanyasoneinfourU.S.workersmaybechronicallyangryonthejob,withangryemployeesalsomorelikelytobebored,hav
最新回复
(
0
)