•The high water content of most organisms, which ranges from 50% to 90% reflects life‘s aquatic origins.生物含水量高达50%- 90% 的事实表明生命
起源于水。
•Life on earth originated in salty aquatic(起源于 盐水) environments and is built around biochemistry within an aquatic medium.在水环
显得尤为突出。
Most organisms must expend energy to maintain their internal pool of water.
大多生物必须通过消耗能量以维持体内水分储备.
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1 水分的有效性
Water availability
Water Content of Air
境中构建其生化结构.
•To survive and reproduce, organisms must maintain appropriate internal concentrations of water and dissolved substances.生物的生存和
繁段殖舜山 ，2020必/9/27 须保持体内适当的水分4 和溶解性物质的浓度。
空气含水量
Water Movement in Aquatic Environmer Movement Between Soils and
Plants 段舜山 2020/9/27
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水分向低浓度梯度的运动制约其对生物的有效性
The movement of water down concentration gradients in terrestrial and aquatic environments determines the availability of water to organisms.
The most familiar measure of the water content of air relative to its content at saturation is relative humidity(相对湿度).
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空气中的水分含量以相对湿度表示
How organisms maintain this water balance is called their water relations, which is the subject of chapter 5. 生物体是如何维持体内水分平衡
关系的，这就是第五章所探讨的主题:水关系。
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A parallel challenge faces organisms that live in aquatic environments with a high salinity.高盐度环
境中的水生生物也面临着类似的问题.
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极端环境生物的水关系
In those extreme environments, the water relations of organisms stand out in bold relief.在那些极端环境中，生物的水关系
Water balance 水分平
衡
To maintain these internal concentrations organisms must balance water losses to the environment with water intake.生物体为了维持体
内水分和盐分的适宜浓度，就必须平衡水分的摄入和排出。
第5章
水分关系 Water Relations
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Contents 主要内容
Water availability
用性
水分的可利
Water regulation on land 陆上水分
调节
Water and salt balance in
aquatic environments 水环境中的水
陆生和水生环境中的水分沿浓度梯度的运动制约生物体对水 的有效性.
水环境中也有水分 浓度梯度吗？
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1.1 Water Content of Air
空气水分含量
Measure of water content (空气水分含量的度量): Since air is rarely completely saturated (饱和) with water vapor, we can use its degree of saturation as a relative measure of water content.
分和盐分平衡 段舜山 2020/9/27
2
气温为46℃，高于蝉的 最高致死温度
地面温度高达 70℃,能使
蝉致死 A question
蝉如何在高于致死温度的情 况下保持活跃？
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FIGURE 5.1
An ecological puzzle.
一个生态之谜
3
Water & life on earth are closely linked 地球生 命和水密不可分
5
不同环境下生物面临的水分问题
In some environments, organisms face the problem of water loss. Elsewhere, water streams in from the environment.生物失水和水分过多
The problem of maintaining proper water balance is especially strong for those organisms, such as Diceroprocta, that live in arid terrestrial environments.水平衡对干旱环境中的生物非常重要.