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Cells cannot remain alive outside certain limits of temperature and much narrower limits mark the boundaries of effective functioning. Enzyme systems of mammals and birds are most efficient only within a narrow range around 37C a departure of a few degrees from this value seriously impairs their functioning. Even though cells can survive wider fluctuations the integrated actions of bodily systems are impaired. Other animals have a wider tolerance for changes of bodily temperature. For centuries it has been recognized that mammals and birds differ from other animals in the way they regulate body temperature. Ways of characterizing the difference have become more accurate and meaningful over time, but popular terminology still reflects the old division into " warmblooded" and " coldblooded" species warmblooded included mammals and birds whereas all other creatures were considered coldblooded. As more species were studied, it became evident that this classification was inadequate. A fence lizard or a desert iguana each coldbloodedusually has a body temperature only a degree or two below that of humans and so is not cold. Therefore the next distinction was made between animals that maintain a constant body temperature, called home0therms, and those whose body temperature varies with their environments, called poikilotherms. But this classification also proved inadequate, because among mammals there are many that vary their body temperatures during hibernation. Furthermore, many invertebrates that live in the depths of the ocean never experience change in the depths of the ocean never experience change in the chill of the deep water, and their body temperatures remain constant. |
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xì bāo zhǐ néng zài yí dìng de wēn dù fàn wéi nèi cún huó, ér jìn yī bù bǎo zhèng tā men yǒu xiào gōng zuò de wēn dù fàn wéi jiù gèng xiǎo le. bǔ rǔ dòng wù hé niǎo lèi de méi xì tǒng zhǐ néng zài 37 zuǒ yòu de hěn xiǎo fàn wéi nèi cái néng yǒu xiào gōng zuò. yǔ cǐ xiāng chà jǐn jǐ dù de wēn dù dōu huì dà dà xuē ruò tā men de gōng zuò xiào lǜ. jǐn guǎn wēn dù biàn huà gèng dà shí xì bāo réng néng cún huó, dàn jī tǐ xì tǒng de zhěng tǐ yùn xíng néng lì què bèi xuē ruò le. qí tā dòng wù duì tǐ wēn de biàn huà yǒu gèng qiáng de shì yìng xìng. jǐ gè shì jì yǐ lái, rén men jiù rèn shi dào bǔ rǔ dòng wù hé niǎo lèi tiáo jié tǐ wēn de fāng shì yǔ qí tā dòng wù bù tóng. suí zhe shí jiān de tuī yí, rén men duì zhè zhǒng chā yì de miáo shù yuè lái yuè jīng què hé yǒu yì yì, dàn shì" nuǎn xuè dòng wù" hé" lěng xuè dòng wù" zhè yī gǔ lǎo de fēn lèi fāng shì zhì jīn réng zài dà zhòng cí huì zhōng yǒu suǒ fǎn yìng. nuǎn xuè dòng wù bāo kuò bǔ rǔ dòng wù hé niǎo lèi, qí tā dòng wù tǒng tǒng bèi shì wéi lěng xuè dòng wù. dàn shì duì gèng duō wù zhǒng jìn xíng de yán jiū biǎo míng zhè zhǒng fēn lèi xiǎn rán shì bù shì dàng de. měi zhōu yī zhǒng xiǎo xíng xī yì hé shā mò liè xī tóng shǔ lěng xuè dòng wù, dàn shí jì shang tā men de tǐ wēn tōng cháng zhǐ bǐ rén lèi de tǐ wēn dī 1 2 dù, yīn cǐ bìng bú shì zhēn zhèng de lěng xuè. yīn cǐ yòu chū xiàn le héng wēn dòng wù jí bǎo chí héng dìng tǐ wēn de dòng wù hé biàn wēn dòng wù jí tǐ wēn suí wài jiè huán jìng de biàn huà ér gǎi biàn de dòng wù zhè yī qū fēn fāng shì. dàn zhè zhǒng fēn lèi yě bù qià dàng. yīn wèi yǒu bù shǎo bǔ rǔ dòng wù zài dōng mián qī jiān huì gǎi biàn tǐ wēn, ér xǔ duō shēng huó zài shēn hǎi de wú jǐ zhuī dòng wù zài hán lěng de shēn hǎi shuǐ yù zhōng tǐ wēn bìng bù biàn huà, ér shì héng dìng de. |