内容文本植物生理学chapter01water relationship.pptx

Chapter 1 Water Relationship in Plant 植物水分的吸收、体内运输分配以及排出的过程——水分代谢。“有收无收在于水，多收少收在于肥”。 No water, no life.Plant cells have cell walls while animal cells do not have.Cell walls allow plant cells build up large hydrostatic pressure- turgor pressureTurgor pressure is essential for many physiological processes: cell enlargement,stomatal opening,transport in the pholem,and various transport processes across membranes, the rigidity and mechanical stability of nonlignified plant tissues.Water is frequently a limiting resources, but much less so for animals.Plants use water in huge amounts, and most (about 97%) of the water absorbed by plant roots is carried through the plant and evaporates from leaf surfaces (transpiration).The uptake of CO2 is coupled to the loss of water through a common diffusional pathway: as CO2 diffuse into leaves,water vapor diffuse out.The driving force for water vapor is much larger for CO2 uptake,as many as 400 water molecules are lost for every CO2 molecul gained.To prevent leaf desiccation,water must be absorbed by the roots and transported through plant body.Even slight imbalance between the uptake and transport and the water loss can cause water deficits and severe malfunctioning of many cellular processes.Section1 Role of water in plant life1.1.Structure and physi-chemical characters of water OOOHHHHHHHδ-104.9oδ+HHhydrogen bondδ+A.Water is a polar molecule with hydrogen bond between themB. High specific heat and latent heat of evaporation(高比热和高气化热) 水的比热容为4.187J·g-1·℃-1，除液态氨外，在其它的液态和固态物质中，水的比热容最大。 水对气温、地温及植物体温有巨大的调节作用，从而有利于植物适应冷热多变的环境。在正常气压(1atm)下水的沸点为100℃,此时水的气化热为2.257kJ·g-1, 在 25℃时为2.45 kJ·g-1。在所有液体中水的气化热是最大的。水的气化热高，有利于植物通过蒸腾作用有效地降低体温。C. Great surface tension(大的表面张力) and cohesion(内聚力）同类分子间具有的分子间引力叫做内聚力(cohesion)。由于水中存在大量的氢键，水的内聚力很大。液相与固相间的相互引力叫做粘附力(adhesion)。由于水是极性分子,它可以与其他极性物质形成氢键,因此水与极性物质间有较强的粘附力。如果水与某物质间的粘附力大于水的内聚力，则此物质为可湿性的。处于界面的水分子均受着垂直向内的拉力，这种作用于单位长度表面上的力，称为表面张力(surface tension)。表面张力趋于使表面积缩小，减少界面高能分子。The tensile strength of waterIf we