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Chapter 37

Ch.37 Water and sugar transport in plants

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University of Toronto Mississauga
Ingo Ensminger

Water and sugar transport in Plants October-15-11 5:41 PM • Water loss is a side effect of photosynthesis ○ Beneficial: cools the plants 10-15 degrees 37.1 Water potential and water movement • Transpiration ○ Stomata open (day) ○ Air in surrounding dryer than leaf (>100 humidity) • Water moves passively, differences in potential energy of water (stored energy) • Water potential - potential energy of water compared to pure water at room temp. • High water potential -> low potential ○ High in roots, low in leaves (water potential gradient) What factors Affect water potential? • Isotonic - solute concentrations in cell and surrounding are the same ○ Hypotonic - relatively less solutes • Osmosis- water moves by water potential • Solute potential /osmotic potential - water moves from low solutes concentration to high solutes concentration • Wall pressure - when plant cell walls prevent cells from bursting by osmosis of water in • Turgor pressure/turgid - pressure from the inside pushing out (ie. Water) • Pressure potential -any physical pressure on water • Water moves: ○ Difference in concentrations of solutes ○ Pressure Calculating Water Potential • Water moves from high solute to low solute potential when permeable membranes are present • Water moves from high pressure to low pressure when no membrane are present • Pressure potential + solute potential = potential energy of water at position (megapascals) • Solute potentials are almost always negative in cells (pure = 0) (high -> low) • Pressure potential is positive in cells (turgor pressure) (can sometimes be negative) • Flaccid - no turgor pressure(pressure potential = 0) • When pressure potential + solutes potential = 0MPa (pure water) it reaches equilibrium Water Potentials in Soils, Plants, and the Atmosphere • In atmosphere water vapour has solute potential of 0 , water potential is low in atmosphere than leaf • Soil have few solutes and not under much pressure, water potential tend water moves from soil to root to leaf to to be higher than roots • ^^ can change du
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