Chapter 2 Water metabolism
Chapter 2 Water Metabolism
Plant Water Relations For every g of organic matter made by the plant, approximately 500 g of water is transpired by the plant Leaves loose up to x 100%of their water/hr
➢ For every g of organic matter made by the plant, approximately 500 g of water is transpired by the plant. ➢ Leaves loose up to ~ 100% of their water/hr. Plant Water Relations
1500 E 1000 500 Taiz Zeiger 2002. used with ⊥ permission 0.5 10 15 2.0 Annual precipitation(m)
Amounts of water in plants >Living plants=w80 to 95%water >Vegetables=- 85 to 95% water Sapwood =- 35 to 75% water Seeds =s 5 to 15% water
➢Living plants =~ 80 to 95% water. ➢Vegetables =~ 85 to 95% water ➢ Sapwood =~ 35 to 75% water ➢ Seeds =~ 5 to 15% water Amounts of water in plants
Roles of water in plant cells Medium for biochemical reactions Physical support Turgor pressure Thermal requlation Transport of water, nutrients and other molecules
Roles of Water in Plant cells ➢ Medium for biochemical reactions. ➢ Physical support. • Turgor pressure. ➢ Thermal regulation. ➢ Transport of water, nutrients and other molecules
Status of water in plants bound water free water √ Cytoplasm Protein =60% Hydrophilic Hydrophobic OO OD
Status of water in plants ➢ bound water ➢ free water ✓ Cytoplasm Protein = 60% • Hydrophilic • Hydrophobic
How Does water move? Passive processes Diffusion -down a concentration gradient Bulk Flow-down a pressure-driven gradient Osmosis -down both a concentration pressure driven gradient water potential) Across a selectively semi-permeable membrane
How Does Water Move? – Passive Processes ➢ Diffusion - down a concentration gradient. ➢ Bulk Flow - down a pressure-driven gradient. ➢ Osmosis - down both a concentration & pressure driven gradient (= water potential). • Across a selectively semi-permeable membrane
Diffusio Diffusion-directed movement- high to low concentration(higher to lower free energy) Random thermal motion Significant role in short-distance movement
Diffusion ➢ Diffusion - directed movement - high to low concentration (higher to lower free energy). ➢ Random thermal motion. ➢ Significant role in: • short-distance movement
Bulk Flow E Mass Flow The concerted movement of groups of molecules by mass, most often in response to a pressure gradient Examples Water moving through the xylem Ariver flowing, rain falling Controled by Aquaporin(水孔蛋白)
Bulk Flow = Mass Flow ➢ The concerted movement of groups of molecules by mass, most often in response to a pressure gradient. ➢ Examples: • Water moving through the xylem. • A river flowing, rain falling. ➢ Controled by : • Aquaporin (水孔蛋白）
细胞外 水分子 水分子选择性孔 X 膜双分子层 088 细胞质 6882 图3.6水分子可以穿过植物体膜,通过单个水分子的扩散作用穿过 膜双分子层,如左部分所示,微量的水分子流通过由完整膜 蛋白如水孔蛋白形成的水分子选择性孔道进入植物体膜内
