大学英语六级考试阅读：背诵美文(4)
<p> <span word="Salt">Salt</span> <span word="and">and</span> <span word="Metabolism">Metabolism</span></p><p> <span word="Just">Just</span> <span word="how">how</span> <span word="salt">salt</span> <span word="became">became</span> <span word="so">so</span> <span word="crucial">crucial</span> <span word="to">to</span> <span word="our">our</span> <span word="metabolism">metabolism</span> <span word="is">is</span> <span word="a">a</span> <span word="mystery">mystery</span>; <span word="one">one</span> <span word="appealing">appealing</span> <span word="theory">theory</span> <span word="traces">traces</span> <span word="our">our</span> <span word="dependence">dependence</span> <span word="on">on</span> <span word="it">it</span> <span word="to">to</span> <span word="the">the</span> <span word="chemist">chemist</span> <span word="ry">ry</span> <span word="of">of</span> <span word="the">the</span> <span word="late">late</span> <span word="Cambrian">Cambrian</span> <span word="seas">seas</span>. <span word="It">It</span> <span word="was">was</span> <span word="there">there</span>, <span word="a">a</span> <span word="half">half</span> <span word="billion">billion</span> <span word="years">years</span> <span word="ago">ago</span>, <span word="that">that</span> <span word="tiny">tiny</span> <span word="metazoan">metazoan</span> <span word="organisms">organisms</span> <span word="first">first</span> <span word="evolved">evolved</span> <span word="systems">systems</span> <span word="for">for</span> <span word="sequestering">sequestering</span> <span word="and">and</span> <span word="circulating">circulating</span> <span word="fluids">fluids</span>. <span word="The">The</span> <span word="water">water</span> <span word="of">of</span> <span word="the">the</span> <span word="early">early</span> <span word="oceans">oceans</span> <span word="might">might</span> <span word="thus">thus</span> <span word="have">have</span> <span word="become">become</span> <span word="the">the</span> <span word="chemical">chemical</span> <span word="prototype">prototype</span> <span word="for">for</span> <span word="the">the</span> <span word="fluids">fluids</span> <span word="of">of</span> <span word="all">all</span> <span word="animal">animal</span> <span word="life">life</span> - <span word="the">the</span> <span word="medium">medium</span> <span word="in">in</span> <span word="which">which</span> <span word="cellular">cellular</span> <span word="operations">operations</span> <span word="could">could</span> <span word="continue">continue</span> <span word="no">no</span> <span word="matter">matter</span> <span word="how">how</span> <span word="the">the</span> <span word="external">external</span> <span word="environment">environment</span> <span word="changed">changed</span>. <span word="This">This</span> <span word="speculation">speculation</span> <span word="is">is</span> <span word="based">based</span> <span word="on">on</span> <span word="the">the</span> <span word="fact">fact</span> <span word="that">that</span>, <span word="even">even</span> <span word="today">today</span>, <span word="the">the</span> <span word="blood">blood</span> <span word="serums">serums</span> <span word="of">of</span> <span word="radically">radically</span> <span word="divergent">divergent</span> <span word="species">species</span> <span word="are">are</span> <span word="remarkably">remarkably</span> <span word="similar">similar</span>. <span word="Lizards">Lizards</span>, <span word="platypuses">platypuses</span>, <span word="sheep">sheep</span>, <span word="and">and</span> <span word="humans">humans</span> <span word="could">could</span> <span word="hardly">hardly</span> <span word="be">be</span> <span word="more">more</span> <span word="different">different</span> <span word="in">in</span> <span word="anatomy">anatomy</span> <span word="or">or</span> <span word="eating">eating</span> <span word="habits">habits</span>, <span word="yet">yet</span> <span word="the">the</span> <span word="salt">salt</span> <span word="content">content</span> <span word="in">in</span> <span word="the">the</span> <span word="fluid">fluid</span> <span word="surrounding">surrounding</span> <span word="their">their</span> <span word="blood">blood</span> <span word="cells">cells</span> <span word="is">is</span> <span word="virtually">virtually</span> <span word="identical">identical</span>. <span word="As">As</span> <span word="early">early</span> <span word="marine">marine</span> <span word="specics">specics</span> <span word="made">made</span> <span word="their">their</span> <span word="way">way</span> <span word="to">to</span> <span word="fresh">fresh</span> <span word="water">water</span> <span word="and">and</span> <span word="eventually">eventually</span> <span word="to">to</span> <span word="dry">dry</span> <span word="land">land</span>, <span word="sodium">sodium</span> <span word="remained">remained</span> <span word="a">a</span> <span word="key">key</span> <span word="ingredient">ingredient</span> <span word="of">of</span> <span word="their">their</span> <span word="interior">interior</span>, <span word="if">if</span> <span word="not">not</span> <span word="their">their</span> <span word="exterior">exterior</span>, <span word="milieu">milieu</span>. <span word="The">The</span> <span word="most">most</span> <span word="successful">successful</span> <span word="mammalian">mammalian</span> <span word="species">species</span> <span word="would">would</span> <span word="have">have</span> <span word="been">been</span> <span word="those">those</span> <span word="that">that</span> <span word="developed">developed</span> <span word="efficient">efficient</span> <span word="hormonal">hormonal</span> <span word="systems">systems</span> <span word="for">for</span> <span word="maintaining">maintaining</span> <span word="the">the</span> <span word="needed">needed</span> <span word="sodium">sodium</span> <span word="concentrations">concentrations</span>. <span word="The">The</span> <span word="human">human</span> <span word="body">body</span>, <span word="for">for</span> <span word="example">example</span>, <span word="uses">uses</span> <span word="the">the</span> <span word="hormones">hormones</span> <span word="renin">renin</span>, <span word="angiotensin">angiotensin</span>, <span word="and">and</span> <span word="aldosterone">aldosterone</span> <span word="to">to</span> <span word="retain">retain</span> <span word="or">or</span> <span word="release">release</span> <span word="tissue">tissue</span> <span word="fluids">fluids</span> <span word="and">and</span> <span word="blood">blood</span> <span word="plasma">plasma</span>. <span word="The">The</span> <span word="result">result</span>, <span word="under">under</span> <span word="favorable">favorable</span> <span word="conditions">conditions</span>, <span word="is">is</span> <span word="a">a</span> <span word="dynamic">dynamic</span> <span word="equilibrium">equilibrium</span> <span word="in">in</span> <span word="which">which</span> <span word="neither">neither</span> <span word="fluid">fluid</span> <span word="volume">volume</span> <span word="nor">nor</span> <span word="sodium">sodium</span> <span word="concentration">concentration</span> <span word="fluctuates">fluctuates</span> <span word="too">too</span> <span word="dramatically">dramatically</span>. <span word="But">But</span> <span word="if">if</span> <span word="the">the</span> <span word="body">body</span> <span word="is">is</span> <span word="deprived">deprived</span> <span word="of">of</span> <span word="salt">salt</span>, <span word="the">the</span> <span word="effects">effects</span> <span word="soon">soon</span> <span word="become">become</span> <span word="dangerous">dangerous</span>, <span word="despite">despite</span> <span word="compensatory">compensatory</span> <span word="mechanisms">mechanisms</span>.</p>
页:
[1]