水的特性与生物学意义分析.ppt

Chapter 1 Plant Water Metabolism Contents in brief: Absorption of water Transport of water Loss of water(transpiration) Irrigation §1 水的结构与特性 结构：水是极性分子，能形成分子间氢键 2. 水的特性 1) High boiling point(高沸点) Compare: CH4 16 CH3CH3 30 CH3CH2CH3 44 CH3CH2CH2CH3 58 CH3(CH2)3CH3 72 boiling point 36℃ but : water 18 boiling point 100℃ reason: n H2O≒(H2O) n +heat 2)Water has high specific heat(高比热) The polarity of water and the resulting hydrogen bonding among water molecules means that it takes much heat (one calorie) to raise the temperature of 1 mL of water just 1°C. The hydrogen bonding has to be given a lot of energy to get them to vibrate and generate the temperature change. This property of water is called specific heat. It means that this liquid can absorb much heat from the various chemical reactions occurring in cells without temperature change; it is a heat buffer. It helps maintain an even body temperature. 3) Water has a high latent heat of vaporization(高汽化热) Among liquids, water has the highest latent heat of vaporization (44 kJ·mol-1). This means that when water goes from liquid to gas it takes a lot of energy. This property can obviously be traced directly to hydrogen bonding again. As the highest energy molecules in the liquid achieve what it takes to move away as a gas, their energy is removed from the liquid and it gets cooler. We sometimes refer to this as evaporative cooling. This is a critical property in maintaining the temperature of dark green leaves essentially parked in sunshine. 3) Water demonstrates cohesion and adhesion(内聚力和粘附力) 内聚力(Cohesion):液体状况下同类分子间的吸引力叫内聚力 ，水的内聚力可达30MPa. 粘附力(adhesion):液相与固相间的吸引力叫粘附力或附着力 原因：水是极性分子，与其它极性分子形成氢鍵。 若水与某物质的粘附力大于水的内聚力，则水可吸附在该物质上，该物质即为可湿的，或可浸润的；反之则不可湿或不可浸润。如水可浸润土壤(SiO32-)、滤纸、CO32-，