1、D1 水的 特性要 点水的 化学特性 水是 所有有机体普遍的内部介质，构成 90%以上的生命物质。水分子是由具有 105角的氢 -氧 -氢组成，其形状导致有氢的一边显正电荷（正电性的），而另一边显负电荷（负电性的）。这解释了与物理和化学反应有关的水的许多特性。它也解释了为什么水被吸附到带电的离子上。光线穿透水 可见光穿过水体遵循一个称为 “比尔定律 ”（ Beers law） 的负指数关系。由于水激烈地吸收了红外线的辐射，太阳光谱的红外线部分随水深增加而急剧耗竭。因此，由于县浮的固体（泥沙）引起的混浊，将急剧地使可见光衰竭。合理利用水资源从水下拍摄的天空 Water is the univer
2、sal internal medium of all organisms, comprising more than 90% of living matter. The shape of the water molecule, with an HOH angle of 105。 Results in the side with the hydrogen being positively charged (electropositive) whereas the other side is negatively charged (electronegative). This explains m
3、any of waters properties relative to physical and chemical reactions. It also explains why water is attracted to charged ions.Key NotesThe penetration of visible light through water bodies follows a negative exponential relationship calledBeers law. Since water strongly absorbs infrared radiation,th
4、at portion of the solar spectrum will be sharply depleted as water depth increases. Furthermore, turbidity due to suspended solids (silt) will strongly deplete visible light.D1 THE PROPERTIES OF WATERChemical properties of waterPenetration of light through water水和 温度 水的两个 特性使它特别适合于作为许多生物栖息的一种介质。（ i）
5、 水有高的热容量，（ ii） 4 时水的密度最大。高热容量意味着它能吸收热能，而只增加很少的温度。其结果使水生生物减少了受温度波动的影响。在较低温度时，水的密度增加，因而也更重，最大的密度发生在 4 。 因此，冰浮在水上，水体从上向下冻结。这种现象保护了水生生物，因为冰作为一种绝热体，阻止下层水的温度进一步降低。Two features of water make it particularly suitable as a medium for life-forms to inhabit. Water has (i) a high heat capacity and (ii) maximal
6、density at . A high heat capacity means that it can absorb heat energy with only a small increase in temperature. As a result,aquatic life forms are buffered from temperature fluctuations. Water becomes increasingly dense and therefore heavier at lower temperatures,with the maximum density occurring
7、 at . Thus,ice floats on water and a body of water freezes from the top down. This phenomenon protects aquatic organisms because ice acts as an insulator to prevent further decreases in temperature in the underlying water. Water and temperature相关主题 植物与水（ D2） 动物与水（ D3）能量转换和水相在 陆地温度中，水很容易从蒸汽转化成液相和固相，同
8、时释放或吸收大量的热。例如， 1g水蒸发，大约需要 2430J的热量，即汽化潜在热。水蒸气进入空气中直到冷凝，释放出热量 2430J/g。 当水结冰时，大约 335J/g被释放作为熔合热，而雪融化时也需要相同数量的能量。因此，在水的相变化中这些能量的消耗和释放过程，提供了从地球表面和到地球表面的大量热的转化机制。At terrestrial temperatures, water passes easily from vapor to liquid and solid phases with a large release or absorption of heat. For example,
9、the evaporation of 1 g of water requires about 2430 J of heat, the latent heat of vaporization. The vapor is carried in air until the water condenses, releasing 2430 J g-1. When water freezes, about 335 J g-1 is released as the heat of fusion and the same amount of energy is required to melt the sno
10、w. Thus, these energy-consuming and releasing processes in water phase changes provide the mechanisms for the transportation of large quantities of heat to and from the surface of the earth.Related topics Plants and water (D2) Animals and water (D3)Energy transfer and water phases D2 植物与水要 点土 壤 水 对于陆地植物，水的主要来源是土壤，它起了蓄水池的作用。当下雨或雪融化时，水进入蓄水池，并流进孔隙。土壤的水容量上限称为田间持水量（ field cap-acity）。 这是土壤孔隙抗地心引力所储蓄的水量。植物不能吸取土壤中储蓄的全部水，因为它们不能产生足够的吸力从更细的土壤孔隙中吸水。因此可利用水的下限是由植物物种的生理特性所决定的，被称为 永久萎蔫点 （ permanent wilting point） 土壤水（ soil water） 含量在这个点上，植物枯死，不能恢复。
