水的特性

植物与水（D2）
动物与水（D3）
Energy transfer and water phases
At terrestrial temperatures, water passes easily from vapor to liquid and solid phases with a large release or absorption of heat. For example,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 snow. Thus, these energyconsuming 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.
Roots can cap capture water from the soil in two ways: either water may move through the soil towards a root or the root may grow through the soil towards the water. As a root withdraws water from the soil capillary pores at its surface, it creates water depletion zones around it. If a root draws water from the soil very rapidly, the resource depletion zone (EDZ) will receive water from the surrounding soil at a slow rate, restricting water availability, so plants may wilt even in soil containing abundant 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）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。
D1 水的特性
要点
水的化学特性 光线穿透水
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。
Key Notes
Chemical properties of water
Water is the universal 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 many of water’s properties relative to physical and chemical reactions. It also explains why water is attracted to charged ions.
Aquatic plants and water
Water is apparently available in aquatic environments. However, the osmotic regulation of internal fluids can be energetically expensive, especially in saline environments. The salinity of an aquatic environment and of terrestrial habitats bordering the sea has an important influence on plant distribution and abundance. Plants which grow in high salinity, halophytes, accumulate electrolytes in their vacuoles, but the concentration in the cytoplasm and organelles is kept low.
可见光穿过水体遵循一个称为“比尔定律”（Beer’s 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
D1 THE PROPERTIES OF WATER
D2 PLANTS AND WATER
Key Notes
Soil water
For terrestrial plants the main source of water is the soil, which serves as a reservoir., water enters the reservoir as rain or melting snow and passes into the soil pores. The upper limit of the waterholding capacity of a soil is called the field capacity. This is the amount of water which can be held by soil pores against the force of gravity. Plants cannot extract all the water held in the soil, as they cannot exert sufficient suction force to extract water from the narrower soil pores. The lower limit of water availability is thus determined by the physiology of the plant species and is known as the permanent wilting point – the soil water content at which plants wilt and are unable to recover.
能量转换和 水相
相关主题
在陆地温度中，水很容易从蒸汽转化成液相和固相， 同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/Baidu Nhomakorabea。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。
根对水的吸收 水生植物和水
根以两种方式从土壤中捕获水：要么水穿过土壤向根 移动，要么根生长穿过土壤向水移动。当根以它的表 面从土壤毛细管孔隙吸水时，在根的周围产生了水耗 竭区。如果根从土壤中吸水很快，资源耗竭区（RDZ） 将以一个低速率从周围土壤中接收水，从而限制了水 的可利用性，使植物即使在含水丰富的土壤中也可能 枯萎。
Penetration of light through water
The penetration of visible light through water bodies follows a negative exponential relationship called’Beer’s law’. Since water strongly absorbs infrared radiation,that 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.
在水环境中，水显然是随意可利用的。然而，内部体 液的渗透压调节可能消耗能量，特别是在盐水环境中。 水环境的盐度与沿海陆地栖息地的盐度，对植物分布 移度有重要的影响。生长在高盐度中的植物，即盐生 植物，它们的液泡中累积了电解质，但在细胞质和细 胞器官中保持着低浓度。
根的向水生长
宁波莲苑
The uptake of water by roots
Water and temperature
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 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 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.
Related topics
Plants and water (D2) Animals and water (D3)
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 capacity）。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。