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Biological Sciences

Plant Physiology BGYB31 Midterm Notes 1PART 2 Water Relations at the Cell Plant and Environmental LevelsWatery 8095 of plant fresh weight seeds are an exception with only 515 when dormant but this rises when the seed is make active y solvent of life and a major limiting resource in plant productivity it is the main growth driving factor y provides turgor pressure outward pressure on cell wall required for structural rigidity Transpiration water loss from leaf surfaces 97 of all water uptake y a necessary consequence of photosynthesis used to take in CO 2y important in heat dissipation y means to bring minerals to root surface and upward y its important for a plant to regulate rate of transpiration and water uptake Properties of water y O is more EN then H so O is partiallyand Hallowing for Hbond fromation y Hbonds hold water in organized structure at any given time water in a cup will have some highly organized and disorganized water molecules y Partial charges make it anexcellent solventions polar molecules macromolecules y high specific heatbuffer against temp fluctuations y high latent heat of vaporizationcooling effect the molecules that vaporize have higher energy than those left behind thus after they leave they reduce the energy of the liquid water left behind y surface tension energy required to increase surface area of airwater interface y cohesionattraction between water molecules y adhesionattraction of water to solid surface y tensile strengthability to resist pulling breaking force y cavitations expanding of air bubble to the point of breaking the water column air bubble will only grow if the pulling force is greater than the surface tension force y cohesion between water is stronger than adhesion to air so the lowest energy state minimizes surface area to minimize airwater interfaceIn test tubes cohesion causes tensile strength and holds the water together in 1 columnIf you had a sealed syringe so you can create pressure without water being lost with water and air bubbles in it pushing in on the syringe causespressure causing the water to push in on the air shrinking the bubbleThe opposite happens if you pull out the syringe causing negative pressure tension in the water that will expand the air bubble aka cavitationWater Transportation Processes 1 Diffusion random thermal movement causing net movement down a concentration gradientis the driving force st Ficks 1 law of diffusion diffusion ratediffusion coefficient x gradientdistanceRate is related to 1 gradient size2 diffusion coefficient which is a constant that depends on the properties of what diffusing and what its diffusing in 2Thus time of diffusiondistance diffusion coefficientshort distance cellsfastlong distance whole plantextremely slow 2 Bulk flow mass movement usually pressure driven 4 Poiseuilles equation Rater8viscosity X pdistanceThus doubling the radius increases the rate by 16foldHere rate is independent of solutegradient as long as viscosity doesnt change much ex different parts of a plant 3 Osmosis solvent movement across selectively permeable membrane driven by both pressure gradients combination of diffusion and bulk flowFacilitated by integral membrane proteins water selective channels called aquaporins Water potential free energy per unit volume of waterWater moves passively from high free energy water potential to low down the potential gradient AS LONG as water is the only substance being movedWater can move against the potential gradient if its coupled with a solute movement
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