TOEFL READING 1994/01(4)
Just how salt became so crucial to our metabolism is a mystery;one
appealing theory traces our dependence on it to the chemistry of the late
Cambrian seas. It was there , a half-billion years ago, that tiny metazoan
organisms first evolved systems for sequestering and circulating fluids. The
water of the early oceans might thus have become the chemical prototype for the
fluids of all animal life - the medium in which cellular operations could
continue no matter how the external environment changed. This speculation is
based on the fact that , even today, the blood serums of radically divergent
species are remarkably similar . Lizards , platypuses, sheep , and humans could
hardly be more different in anatomy of eating habits , yet the salt content in
the fluid surrounding their blood cells is virtually identical.
As early marine species made their way to freshwater and eventually to
dry land , sodium remained a key ingredient of their interior , if not their
exterior , milieu. The most successful mammalian species would have been those
that developed efficient hormonal systems for maintaining the needed sodium
concentrations. The human body , for example , uses the hormones renin ,
angiotensin , and aldosterone to retain or release tissue fluids and blood
plasma. The result , under favorable conditions , is a dynamic equilibrium in
which neither fluid volume nor sodium concentration fluctuates too dramatically.
But if the body is deprived of salt , the effects soon become dangerous ,
despite compensatory mechanisms.
重点单词：
crucial : a. 决定性的,重要的,严厉的
metabolism : n. 新陈代谢,变形
mystery : n. 秘密,神秘,奇谈
appealing : a. 引起兴趣的,动人的,恳求的 appeal : n. 恳求,上诉,吸引力,要求;vi.
求助,诉请,要求;vt. 控诉
theory : n. 理论,学说,原理,意见,推测
trace : n. 痕迹,踪迹,微量,迹线,缰绳;vt. 追踪,回溯,描绘;vi.
上溯,沿路走
chemistry : n. 化学,化学作用
tiny : a. 很少的,微小的
metazoan : n. 后生动物;a. 后生动物的
organism : n. 生物,有机体,社会组织
evolve : vi. 进展,进化,展开;vt. 使发展,推论,使进化
sequester : vt. 使隐退,使隔绝,扣押,没收
circulating : a. 循环,流通
fluid : n. 液体,分泌液,流体;a. 流动的,可改变的,不安定的
chemical : n. 化学药品;a. 化学的,化学用的
prototype : n. 原型
medium : n. 媒体,方法,媒介;a. 半生熟的,中的
cellular : a. 细胞的
external : n. 外部,外面;a. 外部的,客观的,表面的
environment : n. 环境,外界,围绕
speculation : n. 沉思,推测,投机
serum : n. 浆液,血清,乳浆
radically : ad. 根本地,完全地
divergent : a. 分歧的
remarkably : ad. 显著地,引人注目地,非常地
similar : a. 相似的,类似的;n. 相似的东西
lizard : n. 蜥蜴
platypus : 鸭嘴兽
sheep : n. 羊,懦怯之人,信徒
anatomy : n. 剖析,解剖学,骨骼
habit : n. 习惯,嗜好,习性;vt. 使穿衣
content : n. 内容,满足,意义,要旨;a. 满足的,满意的,意义的;vt.
使...满足,使...安心
virtually : ad. 事实上
identical : a. 同一的,恒等的,完全相同的
marine : n. 舰队,水兵,海运业;a. 海的,海产的,海底的,船舶的,海运的
make one's way to : 去, 前往
freshwater : 淡水
eventually : ad. 最后,终于
sodium : n. 钠
remain : vi. 保持,逗留,剩余
ingredient : n. 成分,因素
milieu : n. 周围环境
mammalian : n. 哺乳动物;a. 哺乳动物的
efficient : a. 有效率的,能干的
hormonal : a. 荷尔蒙的
maintain : vt. 维持,维修,保持,坚持,供养,主张
concentration : n. 集中,集合,专心
renin : 肾素
angiotensin : 血管收缩素
aldosterone : n. 醛固酮
retain : vt. 保持,保有,留住,记得,聘请
release : n. 释放,让渡,豁免,发行的书,释放证书;vt. 释放,解放,放松,放弃,让与,免除,发表,豁免;n.版本,发布
plasma : n. 等离子体
favorable : a. 有利的,赞许的,良好的
dynamic : a. 动态的,有动力的,有力的,动力的;n. 动力,动态
equilibrium : n. 平衡,平静,均衡
volume : n. 体积,大小,册,许多,大量,份量,卷,容量,音量;vi.
成团卷起;vt. 收集成卷;a. 大量的
fluctuate : vi. 变动,上下,动摇;vt. 使动摇
dramatically : ad. 戏剧地,引人注目地
deprive : vt. 剥夺,使丧失
effect : n. 结果,影响,效果,印象;vt. 招致,引起,完成
dangerous : a. 危险的 danger : n. 危险,威胁
compensatory : a. 赔偿的,补偿的,补充的
mechanism : n. 机械,机构,结构,机理,技巧
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