(水的理化特性及意义.pptVIP

1．1 水分与植物的生命活动1.1.1 水的某些理化特性 结构：水是极性分子，能形成分子间氢键 2. 水的特性 1) 水的高汽化热 汽化热（Vaporization heat）指在一定温度下，将单位质量的物质由液态转变成气态所需的热量。在25℃时水的汽化热为2.45 kJ·g-1。在已知的所有液体物质中水的汽化热最大（表1.1）。 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. 4.187 J·g-1/0C。(表1。1） 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 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):液相与固相间不同类分子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。 水的内聚力和粘附力，十分有利于水分在植物体内的长距离运输 cohesion, adhesion and surface tension leads to capillarity(内聚力、粘附力和表面张力导致毛细现象) * * 1. 植物的水分代谢 提要? 通过本章的学习要了解植物对水分吸收、运输及蒸腾的方式、途径和机制，认识植物如何维持水分平衡及其重要性，为合理灌溉提供理论依据。 Contents in brief: Absorption of water Transport of water Loss of water(transpiration) Irrigation Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 图1.1 水分子的结构和氢键 Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. Evaluation o